Transcript Ch 14

Chapter 14
Part 1
The Brain and Cranial Nerves
Lecture Outline
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INTRODUCTION
• The brain is the center for registering sensations, correlating
them with one another and with stored information, making
decisions, and taking action.
• It is also the center for intellect, emotions, behavior, and
memory.
• It also directs our behavior towards others.
• In this chapter we will consider the principal parts of the
brain, how the brain is protected and nourished, and how it
is related to the spinal cord and to the 12 pairs of cranial
nerves.
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Chapter 14
The Brain and Cranial
Nerves
• Largest organ in the body at almost 3 lb.
• Brain functions in sensations, memory, emotions, decision making,
behavior
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OVERVIEW OF BRAIN ORGANIZATION AND
BLOOD SUPPLY
• The major parts of the brain are the brain stem,
diencephalon, cerebrum, and cerebellum (Figure 14.1).
• The CNS develops from an ectodermal neural tube
– Three primary vesicles: prosencephalon,
mesencephalon, and rhombencephalon develop from the
neural tube. (Figure 14.29)
• The embryologic development of the CNS is summarized in
table 14.1
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Principal Parts of
the Brain
• Cerebrum
• Diencephalon
– thalamus & hypothalamus
• Cerebellum
• Brainstem
– medulla, pons & midbrain
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Blood Supply to Brain
• Arterial blood supply is branches from circle of Willis on base of brain
• Vessels on surface of brain----penetrate tissue
• Uses 20% of our bodies oxygen & glucose needs
– blood flow to an area increases with activity in that area
– deprivation of O2 for 4 min does permanent injury
• at that time, lysosome release enzymes
• Blood-brain barrier (BBB)
– protects cells from some toxins and pathogens
• proteins & antibiotics can not pass but alcohol & anesthetics do
– tight junctions seal together epithelial cells, continuous basement
membrane, astrocyte processes covering capillaries
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Blood Flow and the Blood-Brain Barrier
• An interruption of blood flow for 1 or 2 minutes impairs
neuronal function.
– A total deprivation of oxygen for 4 minutes causes
permanent injury.
• Because carbohydrate storage in the brain is limited, the
supply of glucose to the brain must be continuous.
– Glucose deficiency may produce mental confusion,
dizziness, convulsions, and unconsciousness.
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BBB
• A blood-brain barrier (BBB) protects brain cells from harmful
substances and pathogens by serving as a selective barrier
to prevent passage of many substances from the blood to
the brain.
• An injury to the brain due to trauma, inflammation, or toxins
causes a breakdown of the BBB, permitting the passage of
normally restricted substances into brain tissue.
• The BBB may also prevent entry of drugs that could be
used as therapy for brain cancer or other CNS disorders, so
research is exploring ways to transport drugs past the BBB.
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Protective Covering of the Brain
• The brain is protected by the cranial bones (Figure 7.4) and
the cranial meninges (Figure 14.2).
– The cranial meninges are continuous with the spinal
meninges and are named dura mater, arachnoid, and pia
mater.
– Three extensions of the dura mater separate parts of the
brain: the falx cerebri, falx cerebelli, and the tentorium
cerebelli.
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Protective Coverings of the Brain
• Bone, meninges & fluid
• Meninges same as around the
spinal cord
– dura mater
– arachnoid mater
– pia mater
• Dura mater extensions
– falx cerebri
– tentorium cerebelli
– falx cerebelli
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CEREBROSPINAL FLUID
• Cerebrospinal fluid (CSF) is a clear, colorless liquid that
protects the brain and spinal cord against chemical and
physical injuries.
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Cerebrospinal Fluid (CSF)
• 80-150 ml (3-5oz)
• Clear liquid containing glucose, proteins, & ions
• Functions
– mechanical protection
• floats brain & softens impact with bony walls
– chemical protection
• optimal ionic concentrations for action
potentials
– circulation
• nutrients and waste products to and from
bloodstream
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Ventricles
• There are four CSF filled cavities within the brain called
ventricles (Figure 14.3).
– A lateral ventricle is located in each hemisphere of the
cerebrum. The lateral ventricles are separated by the
septum pellucidum.
– The third ventricle is a narrow cavity along the midline
superior to the hypothalamus and between the right and
left halves of the thalamus.
– The fourth ventricle is between the brain stem and the
cerebellum.
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Origin of CSF
• Choroid plexus = capillaries covered by ependymal cells
– 2 lateral ventricles, one within each cerebral hemisphere
– roof of 3rd ventricle
– fourth ventricle
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Drainage of CSF from Ventricles
• One median aperture & two lateral apertures allow CSF to exit from the
interior of the brain
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Flow of Cerebrospinal Fluid
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Reabsorption of CSF
•
•
Reabsorbed through arachnoid villi
– grapelike clusters of arachnoid penetrate dural venous sinus
20 ml/hour reabsorption rate = same as production rate
• Reabsorption of CSF
– Reabsorbed through arachnoid villi
» grapelike clusters of arachnoid penetrate dural venous sinus
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Hydrocephalus
• Blockage of drainage of CSF (tumor, inflammation,
developmental malformation, meningitis, hemorrhage
or injury)
– Continued production cause an increase in
pressure --- hydrocephalus
– In newborn or fetus, the fontanels allow this
internal pressure to cause expansion of the skull
and damage to the brain tissue
• Neurosurgeon implants a drain shunting the CSF to
the veins of the neck or the abdomen
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THE BRAIN STEM
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Medulla Oblongata
•
•
•
•
•
Continuation of spinal cord
Ascending sensory tracts
Descending motor tracts
Nuclei of 5 cranial nerves
Cardiovascular center
– force & rate of heart beat
– diameter of blood vessels
• Respiratory center
– medullary rhythmicity area sets basic rhythm of breathing
• Information in & out of cerebellum
• Reflex centers for coughing, sneezing, swallowing etc.
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Ventral Surface of Medulla Oblongata
• Ventral surface bulge
– pyramids
– large motor tract
– decussation of most fibers
• left cortex controls right
muscles
• Olive = olivary nucleus
– neurons send input to cerebellum
– proprioceptive signals
– gives precision to movements
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Dorsal Surface of Medulla
Oblongata
• Nucleus gracilis & nucleus cuneatus = sensory neurons
– relay information to thalamus on opposite side of brain
• 5 cranial nerves arise from medulla -- 8 thru 12
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XII = Hypoglossal Nerve
• Controls muscles of tongue
during speech and
swallowing
• Injury deviates tongue to
injured side when protruded
• Mixed, primarily motor
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XI = Spinal Accessory Nerve
• Cranial portion
– arises medulla
– skeletal mm of throat & soft
palate
• Spinal portion
– arises cervical spinal cord
– sternocleidomastoid and
trapezius mm.
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X = Vagus Nerve
• Receives sensations from
viscera
• Controls cardiac muscle and
smooth muscle of the viscera
• Controls secretion of digestive
fluids
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IX = Glossopharyngeal Nerve
• Stylopharyngeus m. (lifts
throat during swallowing)
• Secretions of parotid gland
• Somatic sensations & taste
on posterior 1/3 of tongue
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VIII = Vestibulocochlear Nerve
• Cochlear branch begins in medulla
– receptors in cochlea
– hearing
– if damaged deafness or tinnitus
(ringing) is produced
• Vestibular branch begins in pons
– receptors in vestibular
apparatus
– sense of balance
– vertigo (feeling of rotation)
– ataxia (lack of coordination)
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Injury to the Medulla
• Hard blow to the back of the head may be fatal
• Cranial nerve malfunctions on same side as injury;
loss of sensation or paralysis of throat or tongue;
irregularities in breathing and heart rhythm
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Pons
• The pons is located superior to the medulla. It connects the
spinal cord with the brain and links parts of the brain with
one another by way of tracts (Figures 14.1, 14.5).
– relays nerve impulses related to voluntary skeletal
movements from the cerebral cortex to the cerebellum.
– contains the pneumotaxic and apneustic areas, which
help control respiration along with the respiratory center
in the medulla (Figure 23.24).
– contains nuclei for cranial nerves V trigeminal, VI
abducens, VII facial, and VIII vestibulocochlear
(vestibular branch only).(Figure 14.5).
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Pons
• One inch long
• White fiber tracts
ascend and descend
• Pneumotaxic &
apneustic areas help
control breathing
• Middle cerebellar
peduncles carry
sensory info to the
cerebellum
• Cranial nerves 5
through 7
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VII = Facial Nerve
• Motor portion
– facial muscles
– salivary & nasal and oral
mucous glands & tears
• Sensory portion
– taste buds on anterior
2/3’s of tongue
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VI = Abducens Nerve
• Lateral rectus eye muscle
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V = Trigeminal Nerve
• Motor portion
– muscles of mastication
• Sensory portion
– touch, pain, &
temperature receptors
of the face
• ophthalmic branch
• maxillary branch
• mandibular branch
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Midbrain
• One inch in length
• Extends from pons
to diencephalon
• Cerebral aqueduct
connects 3rd
ventricle above to
4th ventricle below
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Midbrain in Section
• Cerebral peduncles---clusters of motor & sensory fibers
• Substantia nigra---helps controls subconscious muscle activity
• Red nucleus-- rich blood supply & iron-containing pigment
– cortex & cerebellum coordinate muscular movements by sending
information here from the cortex and cerebellum
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Dorsal Surface of Midbrain
• Corpora quadrigemina = superior & inferior colliculi
– coordinate eye movements with visual stimuli
– coordinate head movements with auditory stimuli
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IV = Trochlear Nerve
• Superior oblique eye muscle
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III = Oculomotor Nerve
• Levator palpebrae raises
eyelid (ptosis)
• 4 extrinsic eye muscles
• 2 intrinsic eye muscles
– accomodation for near
vision (changing shape of
lens during reading)
– constriction of pupil
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Reticular Formation
• Scattered nuclei in medulla, pons & midbrain
• Reticular activating system
– alerts cerebral cortex to sensory signals (sound of
alarm, flash light, smoke or intruder) to awaken from
sleep
– maintains consciousness & helps keep you awake
with stimuli from ears, eyes, skin and muscles
• Motor function is involvement with maintaining muscle
tone
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Cerebellum
• 2 cerebellar hemispheres and vermis (central area)
• Function
– correct voluntary muscle contraction and posture based on sensory
data from body about actual movements
– sense of equilibrium
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Cerebellum
• Transverse fissure between cerebellum & cerebrum
• Cerebellar cortex (folia) & central nuclei are grey matter
• Arbor vitae = tree of life = white matter
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Cerebellar Peduncles
• Superior, middle & inferior peduncles attach to brainstem
– inferior carries sensory information from spinal cord
– middle carries sensory fibers from cerebral cortex & basal
ganglia
– superior carries motor fibers that extend to motor control
areas
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THE DIENCEPHALON
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Diencephalon Surrounds 3rd Ventricle
• Surrounds 3rd ventricle
• Superior part of walls is thalamus
• Inferior part of walls & floor is hypothalamus
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Thalamus
• The thalamus is located superior to the midbrain and
contains nuclei that serve as relay stations for all sensory
impulses, except smell, to the cerebral cortex (Figure 14.9).
– seven major groups of thalamic nuclei on each side
(Figure 14.9 c and d).
– They are the Anterior nucleus, medial nuclei, lateral
group, ventral group, intralaminar nuclei, midline nucleus,
and the reticular nucleus.
• It also registers conscious recognition of pain and
temperature and some awareness of light touch and
pressure.
• It plays an essential role in awareness and the acquisition of
knowledge (cognition.)
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Thalamus
• 1 inch long mass of gray mater in each half of brain
(connected across the 3rd ventricle by intermediate mass)
• Relay station for sensory information on way to cortex
• Crude perception of some sensations
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Thalamic Nuclei
• Nuclei have different roles
– relays auditory and visual impulses, taste and
somatic sensations
– receives impulses from cerebellum or basal
ganglia
– anterior nucleus concerned with emotions,
memory and acquisition of knowledge (cognition)
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Hypothalamus
• The hypothalamus
– inferior to the thalamus, has four major regions
(mammillary, tuberal, supraoptic, and preoptic)
– controls many body activities, and is one of the major
regulators of homeostasis (Figure 14.10).
• The hypothalamus has a great number of functions.
–
–
–
–
It controls the ANS.
It produces hormones.
It functions in regulation of emotional and behavioral patterns.
It regulates eating and drinking through the feeding center, satiety
center, and thirst center.
– It aids in controlling body temperature.
– It regulates circadian rhythms and states of consciousness.
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Hypothalamus
• Dozen or so nuclei in 4 major regions
– mammillary bodies are relay station for olfactory reflexes;
infundibulum suspends the pituitary gland
• Major regulator of homeostasis
– receives somatic and visceral input, taste, smell & hearing information;
monitors osmotic pressure, temperature of blood
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Epithalamus
• The epithalamus lies superior and posterior to the thalamus
and contains the pineal gland and the habenular nuclei
(Figure 14.7).
– The pineal gland secretes melatonin to influence diurnal
cycles in conjunction with the hypothalamus.
– The habenular nuclei (Figure 14.7a) are involved in
olfaction, especially emotional responses to odors.
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Epithalamus
• Pineal gland
– endocrine gland
the size of small
pea
– secretes melatonin
during darkness
– promotes
sleepiness & sets
biological clock
• Habenular nuclei
– emotional
responses to odors
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Subthalamus
• The subthalamus lies immediately inferior to the thalamus
and includes tracts and the paired subthalamic nuclei, which
connect to motor areas of the cerebrum.
– The subthalamic nuclei and red nucleus and substantia
nigra of the midbrain work together with the basal
ganglia, cerebellum, and cerebrum in control of body
movements.
• Table 14.2 summarizes the functions of the parts of the
diencephalon.
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Circumventricular Organs
• Parts of the diencephalon, called circumventricular organs
(CVOs), can monitor chemical changes in the blood
because they lack a blood-brain barrier.
• CVOs include
– part of the hypothalamus,
– the pineal gland,
– the pituitary gland, and a few other nearby structures.
• They function to coordinate homeostatic activities of the
endocrine and nervous systems.
• They are also thought to be the site of entry into the brain of
HIV.
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THE CEREBRUM
• The cerebrum is the largest part of the brain .
– The surface layer, the cerebral cortex, is 2-4 mm thick
and is composed of gray matter. The cortex contains
billions of neurons.
– The cortex contains gyri (convolutions), deep grooves
called fissures, and shallower sulci. (Figure 14.11a)
• Beneath the cortex lies the cerebral white matter, tracts that
connect parts of the brain with itself and other parts of the
nervous system.
• The cerebrum is nearly separated into right and left halves,
called hemispheres, by the longitudinal fissure.
– Internally it remains connected by the corpus callosum, a
bundle of transverse white fibers. Figure 14.12)
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Chapter 14
Part 2
The Brain and Cranial Nerves
Lecture Outline
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Cerebrum
(Cerebral Hemispheres)
• Cerebral cortex is gray matter
overlying white matter
– 2-4 mm thick containing
billions of cells
– grew quickly; formed folds
(gyri) and grooves (sulci or
fissures)
• Longitudinal fissure separates
left & right cerebral hemispheres
– Corpus callosum is a
commisure (band of white
matter) connecting left and
right cerebral hemispheres
• Each hemisphere is subdivided
into 4 lobes
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Lobes
• Each cerebral hemisphere is further subdivided into four
lobes by sulci or fissures (Figure 14.11 a,b)
– frontal, parietal, temporal, and occipital.
• A fifth part of the cerebrum, the insula, lies deep to the
parietal, frontal, and temporal lobes and cannot be seen in
an external view of the brain.
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Lobes and Fissures
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• Longitudinal fissure
(green)
• Frontal lobe
• Central sulcus
(yellow)
– precentral &
postcentral gyrus
• Parietal lobe
• Parieto-occipital
sulcus
• Occipital lobe
• Lateral sulcus (blue)
• Temporal lobe
• Insula
59
Insula within Lateral Fissure
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White Matter
• The white matter is under the cortex and consists of
myelinated axons running in three principal directions
(Figure 14.12).
– Association fibers connect and transmit nerve impulses
between gyri in the same hemisphere.
– Commissural fibers connect gyri in one cerebral
hemisphere to the corresponding gyri in the opposite
hemisphere.
– Projection fibers form ascending and descending tracts
that transmit impulses from the cerebrum to other parts of
the brain and spinal cord.
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Cerebral White Matter
• Association fibers between gyri in same hemisphere
• Commissural fibers from one hemisphere to other
• Projection fibers form descending & ascending tracts
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Basal Ganglia
The basal ganglia are paired masses of gray matter in
each cerebral hemisphere (Figure 14.13).
• Connections to red nucleus, substantia nigra &
subthalamus
• Input & output with cerebral cortex, thalamus &
hypothalamus
• Control large automatic movements of skeletal
muscles
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Caudate nucleus
• Lentiform and caudate nuclei are known as the corpus
striatum.
– Nearby structures functionally linked to the basal ganglia
are the substantia nigra and the subthalamic nuclei.
– They are responsible for helping to control muscular
movements.
• Damage to the basal ganglis results in tremor, rigidity, and involuntary
muscle movements. In Parkinson’s disease neurons from the substantia
nigra to the putamen and cuadate nucleus degenerate.
• Basal ganglia also help initiate and terminate some cognitive
processes. Obsessive compulsive disorder, schizophrenia, chronic
anxiety are thought to involve dysfunction of the circuits between the
basal ganglis and limbic system
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Limbic System
• The limbic system is found in the cerebral hemispheres and
diencephalon (Figure 14.14).
– limbic lobe
– dentate gyrus
– amygdala
– septal nuclei
– mammilary bodies, mammilothalmic tract
– anterior and medial nuclei of the thalamus,
– olfactory bulbs
– fornix, stria terminalis, stria medulllaris,
– medial forebrain bundle
• It functions in emotional aspects of behavior and memory,
and is associated with pleasure and pain.
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Limbic System
• Emotional brain--intense pleasure & intense pain
• Strong emotions increase efficiency of memory
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Brain Injuries
• Brain injuries are commonly associated with head injuries
and result, in part, from displacement and distortion of
neuronal tissue at the moment of impact and in part from the
release of disruptive chemicals from injured brain cells.
• Various degrees of brain injury are described by the terms
– concussion, contusion, and laceration.
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Brain Injuries
• Causes of damage
– displacement or distortion of tissue at impact
– increased intracranial pressure
– infections
– free radical damage after ischemia
• Concussion---temporary loss of consciousness
– headache, drowsiness, confusion, lack of concentration
• Contusion--bruising of brain (less than 5 min
unconsciousness but blood in CSF)
• Laceration--tearing of brain (fracture or bullet)
– increased intracranial pressure from hematoma
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Sensory Areas
• The sensory areas of the cerebral cortex are concerned with
the reception and interpretation of sensory impulses.
• Some important sensory areas include
– primary somatosensory area,
– primary visual area,
– primary auditory area, and
– primary gustatory area
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Sensory Areas of Cerebral Cortex
Receive sensory information from the thalamus
Primary somatosensory area = postcentral gyrus = 1,2,3
Primary visual area = 17
Primary auditory area = 41 & 42
Primary gustatory area = 43
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Motor Areas
• The motor areas are the regions that govern muscular
movement.
• Two important motor areas are
– primary motor area and
– Broca’s speech area. (Figure 14.15)
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Motor Areas of Cerebral Cortex
• Voluntary motor initiation
– Primary motor area = 4 = precentral gyrus
• controls voluntary contractions of skeletal muscles on other side
– Motor speech area = 44 = Broca’s area
• production of speech -- control of tongue & airway
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Association Areas of Cerebral Cortex
•
•
•
•
•
•
Somatosensory area = 5 & 7 (integrate & interpret)
Visual association area = 18 & 19 (recognize & evaluate)
Auditory association area(Wernicke’s) = 22(words become speech)
Gnostic area = 5,7,39 & 40 (integrate all senses & respond)
Premotor area = 6 (learned skilled movements such as typing)
Frontal eye field =8 (scanning eye movements such as phone book)
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Association Areas
• The association areas are concerned with complex
integrative functions such as memory, emotions, reasoning,
will, judgment, personality traits, and intelligence. (Figure
14.15)
– Injury to the association or motor speech areas results in
aphasia, an inability to use or comprehend words.
(Clinical Application)
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Aphasia
Language areas are located in the left cerebral hemisphere of most
people
Inability to use or comprehend words = aphasia
• nonfluent aphasia = inability to properly form words
– know what want to say but can not speak
– damage to Broca’s speech area
• fluent aphasia = faulty understanding of spoken or written words
– faulty understanding of spoken or written words
• word deafness = an inability to understand spoken words
• word blindness = an inability to understand written words
– damage to common integrative area or auditory association
area
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Hemispheric Lateralization
• Although the two cerebral hemispheres share many
functions, each hemisphere also performs unique functions.
• hemispheric lateralization (Figure 14.16).
– The left hemisphere is more important for right-handed
control, spoken and written language, and numerical and
scientific skills.
– The right hemisphere is more important for left-handed
control, musical and artistic awareness, space and
pattern perception, insight, imagination, and generating
mental images of sight, sound, touch, taste, and smell.
• Table 14.3 summarizes some of the distinctive functions
that are more likely to reside in the left or right hemisphere.
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Hemispheric Lateralization
• Functional specialization
of each hemisphere
more pronounced in men
• Females generally have
larger connections
between 2 sides
• Damage to left side
produces aphasia
• Damage to same area
on right side lead to
speech with little
emotional inflection
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Brain Waves
• An EEG may be used to diagnose epilepsy and other
seizure disorders, infectious diseases, tumors, trauma,
hematomas, metabolic abnormalities, degenerative
diseases, and periods of unconsciousness and confusion; it
may also provide useful information regarding sleep and
wakefulness.
• An EEG may also be one criterion in confirming brain death
(complete absence of brain waves in two EEGs taken 24
hours apart).
• Figure 14.17 shows four kinds of brain waves that can be
recorded from normal individuals.
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Electroencephalogram (EEG)
• Brain waves are millions of
nerve action potentials in
cerebral cortex
– diagnosis of brain
disorders (epilepsy)
– brain death (absence of
activity in 2 EEGs 24
hours apart)
• Alpha -- awake & resting
• Beta -- mental activity
• Theta -- emotional stress
• Delta -- deep sleep
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II -- Optic Nerve
• Connects to retina supplying
vision
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I -- Olfactory Nerve
• Extends from olfactory
mucosa of nasal cavity to
olfactory bulb
• Sense of smell
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Developmental Anatomy of the NS
• Begins in 3rd week
– ectoderm forms thickening (neural
plate)
– plate folds inward to form neural
groove
– edges of folds join to form neural tube
• Neural crest tissue forms:
– spinal & cranial nerves
– dorsal root & cranial nerve ganglia
– adrenal gland medulla
• Layers of neural tube form:
– marginal layer which forms white
matter
– mantle layer forms gray matter
– ependymal layer forms linings of
cavities within NS
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Dorsal View of Neural Groove
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Development of Principal Parts
• By end of 4th week, 3 anterior enlargements occur
– prosencephalon
– mesencephalon
– rhombencephalon
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Development of Principal Parts
• By 5th week, 5 enlarged areas exist
• Prosencephalon
– telencephalon
– diencephalon
• Mesencephalon
• Rhombencephalon
– metencephalon
– myelencephalon
• Neural tube defects
– associated with low levels of folic acid (B vitamins)
– spina bifida is failure to close of vertebrae
– anencephaly is absence of skull & cerebral
hemispheres
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Aging & the Nervous System
• Years 1 to 2
– rapid increase in size due to increase in size of
neurons, growth of neuroglia, myelination &
development of dendritic branches
• Early adulthood until death
– brain weight declines until only 93% by age 80
– number of synaptic contacts declines
– processing of information diminishes
– conduction velocity decreases
– voluntary motor movements slow down
– reflexes slow down
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DISORDERS: HOMEOSTATIC IMBALANCES
• The most common brain disorder is a cerebrovascular
accident (CVA or stroke).
• Third leading cause of death after heart attacks and cancer
• CVAs are classified into two principal types:
– ischemic (the most common type), due to a decreased
blood supply
– hemorrhagic, due to a blood vessel in the brain that
bursts.
• Common causes of CVAs are intracerebral hemorrhage,
emboli, and atherosclerosis.
• Tissue plasminogen activator (t-PA) used within 3 hours of
ischemic CVA onset will decrease permanent disability
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Transient Ischemic Attack (TIA)
• Episode of temporary cerebral dysfunction
• Cause
– impaired blood flow to the brain
• Symptoms
– dizziness, slurred speech, numbness, paralysis on one
side, double vision
– reach maximum intensity almost immediately
– persists for 5-10 minutes & leaves no deficits
• Treatment is aspirin or anticoagulants; artery bypass grafting
or carotid endarterectomy
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Alzheimer Disease (AD)
• Dementia = loss of reasoning, ability to read, write, talk,
eat & walk
• Afflicts 11% of population over 65
• Great loss of neurons in specific regions (e.g.,
hippocampus and cerebral cortex); loss of neurons that
release acetylcholine
• Plaques of abnormal proteins deposited outside neurons
(amyloid plaques).
• Tangled protein filaments within neurons (neurofibrillary
tangles).
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Tumors
• Brain tumor is an abnormal growth of tissue it may be
malignant or benign.
• Attention Deficit Hyperactivity Disorder (ADHD) is a laerning
disorder characterized by poor attention span, hyperactivity
and inappropriate impulsiveness.
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CRANIAL NERVE Review
• Twelve pairs of cranial nerves originate from the brain
(Figure 14.5)
– named primarily on the basis of distribution and
numbered by order of attachment to the brain.
• Some cranial nerves (I, II, and VIII) contain only sensory
fibers and are called sensory nerves. The rest are mixed
nerves because they contain both sensory and motor fibers.
• Figures 14.18 – 14.27 illustrate the distribution of many of
the cranial nerves.
• Table 14.4 presents a summary of cranial nerves, including
clinical applications related to their dysfunction.
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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end
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Chapter 14
Part 2
The Brain and Cranial Nerves
Lecture Outline
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Cerebrum
(Cerebral Hemispheres)
• Cerebral cortex is gray matter
overlying white matter
– 2-4 mm thick containing
billions of cells
– grew quickly; formed folds
(gyri) and grooves (sulci or
fissures)
• Longitudinal fissure separates
left & right cerebral hemispheres
– Corpus callosum is a
commisure (band of white
matter) connecting left and
right cerebral hemispheres
• Each hemisphere is subdivided
into 4 lobes
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Lobes
• Each cerebral hemisphere is further subdivided into four
lobes by sulci or fissures (Figure 14.11 a,b)
– frontal, parietal, temporal, and occipital.
• A fifth part of the cerebrum, the insula, lies deep to the
parietal, frontal, and temporal lobes and cannot be seen in
an external view of the brain.
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Lobes and Fissures
• Longitudinal
fissure (green)
• Frontal lobe
• Central sulcus
(yellow)
– precentral &
postcentral gyrus
• Parietal lobe
• Parieto-occipital
sulcus
• Occipital lobe
• Lateral sulcus
(blue)
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Insula within Lateral Fissure
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White Matter
• The white matter is under the cortex and consists of
myelinated axons running in three principal directions
(Figure 14.12).
– Association fibers connect and transmit nerve impulses
between gyri in the same hemisphere.
– Commissural fibers connect gyri in one cerebral
hemisphere to the corresponding gyri in the opposite
hemisphere.
– Projection fibers form ascending and descending tracts
that transmit impulses from the cerebrum to other parts of
the brain and spinal cord.
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Cerebral White Matter
• Association fibers between gyri in same hemisphere
• Commissural fibers from one hemisphere to other
• Projection fibers form descending & ascending tracts
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Basal Ganglia
The basal ganglia are paired masses of gray matter in
each cerebral hemisphere (Figure 14.13).
• Connections to red nucleus, substantia nigra &
subthalamus
• Input & output with cerebral cortex, thalamus &
hypothalamus
• Control large automatic movements of skeletal
muscles
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Caudate nucleus
• Lentiform and cuadate nuclei are known as the corpus
striatum.
– Nearby structures functionally linked to the basal ganglia
are the substantia nigra and the subthalamic nuclei.
– They are responsible for helping to control muscular
movements.
• Damage to the basal ganglis results in tremor, rigidity, and involuntary
muscle movements. In Parkinson’s disease neurons from the substantia
nigra to the putamen and cuadate nucleus degenerate.
• Basal ganglia also help initiate and terminate some cognitive
processes. Obsessive compulsive disorder, schizophrenia, chronic
anxiety are thought to involve dysfunction of the circuits between the
basal ganglis and limbic system
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Limbic System
• The limbic system is found in the cerebral hemispheres and
diencephalon (Figure 14.14).
– limbic lobe
– dentate gyrus
– amygdala
– septal nuclei
– mammilary bodies, mammilothalmic tract
– anterior and medial nuclei of the thalamus,
– olfactory bulbs
– fornix, stria terminalis, stria medulllaris,
– medial forebrain bundle
• It functions in emotional aspects of behavior and memory,
and is associated with pleasure and pain.
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Limbic System
• Emotional brain--intense pleasure & intense pain
• Strong emotions increase efficiency of memory
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Brain Injuries
• Brain injuries are commonly associated with head injuries
and result, in part, from displacement and distortion of
neuronal tissue at the moment of impact and in part from the
release of disruptive chemicals from injured brain cells.
• Various degrees of brain injury are described by the terms
– concussion, contusion, and laceration.
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Brain Injuries
• Causes of damage
– displacement or distortion of tissue at impact
– increased intracranial pressure
– infections
– free radical damage after ischemia
• Concussion---temporary loss of consciousness
– headache, drowsiness, confusion, lack of concentration
• Contusion--bruising of brain (less than 5 min
unconsciousness but blood in CSF)
• Laceration--tearing of brain (fracture or bullet)
– increased intracranial pressure from hematoma
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Sensory Areas
• The sensory areas of the cerebral cortex are concerned with
the reception and interpretation of sensory impulses.
• Some important sensory areas include
– primary somatosensory area,
– primary visual area,
– primary auditory area, and
– primary gustatory area
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Sensory Areas of Cerebral Cortex
Receive sensory information from the thalamus
Primary somatosensory area = postcentral gyrus = 1,2,3
Primary visual area = 17
Primary auditory area = 41 & 42
Primary gustatory area = 43
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Motor Areas
• The motor areas are the regions that govern muscular
movement.
• Two important motor areas are
– primary motor area and
– Broca’s speech area. (Figure 14.15)
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Motor Areas of Cerebral Cortex
• Voluntary motor initiation
– Primary motor area = 4 = precentral gyrus
• controls voluntary contractions of skeletal muscles on other side
– Motor speech area = 44 = Broca’s area
• production of speech -- control of tongue & airway
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Association Areas of Cerebral Cortex
•
•
•
•
•
•
Somatosensory area = 5 & 7 (integrate & interpret)
Visual association area = 18 & 19 (recognize & evaluate)
Auditory association area(Wernicke’s) = 22(words become speech)
Gnostic area = 5,7,39 & 40 (integrate all senses & respond)
Premotor area = 6 (learned skilled movements such as typing)
Frontal eye field =8 (scanning eye movements such as phone book)
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Association Areas
• The association areas are concerned with complex
integrative functions such as memory, emotions, reasoning,
will, judgment, personality traits, and intelligence. (Figure
14.15)
– Injury to the association or motor speech areas results in
aphasia, an inability to use or comprehend words.
(Clinical Application)
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Aphasia
Language areas are located in the left cerebral hemisphere of most
people
Inability to use or comprehend words = aphasia
• nonfluent aphasia = inability to properly form words
– know what want to say but can not speak
– damage to Broca’s speech area
• fluent aphasia = faulty understanding of spoken or written words
– faulty understanding of spoken or written words
• word deafness = an inability to understand spoken words
• word blindness = an inability to understand written words
– damage to common integrative area or auditory association
area
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Hemispheric Lateralization
• Although the two cerebral hemispheres share many
functions, each hemisphere also performs unique functions.
• hemispheric lateralization (Figure 14.16).
– The left hemisphere is more important for right-handed
control, spoken and written language, and numerical and
scientific skills.
– The right hemisphere is more important for left-handed
control, musical and artistic awareness, space and
pattern perception, insight, imagination, and generating
mental images of sight, sound, touch, taste, and smell.
• Table 14.3 summarizes some of the distinctive functions
that are more likely to reside in the left or right hemisphere.
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Hemispheric Lateralization
• Functional specialization
of each hemisphere
more pronounced in men
• Females generally have
larger connections
between 2 sides
• Damage to left side
produces aphasia
• Damage to same area
on right side lead to
speech with little
emotional inflection
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Brain Waves
• An EEG may be used to diagnose epilepsy and other
seizure disorders, infectious diseases, tumors, trauma,
hematomas, metabolic abnormalities, degenerative
diseases, and periods of unconsciousness and confusion; it
may also provide useful information regarding sleep and
wakefulness.
• An EEG may also be one criterion in confirming brain death
(complete absence of brain waves in two EEGs taken 24
hours apart).
• Figure 14.17 shows four kinds of brain waves that can be
recorded from normal individuals.
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Electroencephalogram (EEG)
• Brain waves are millions of
nerve action potentials in
cerebral cortex
– diagnosis of brain
disorders (epilepsy)
– brain death (absence of
activity in 2 EEGs 24
hours apart)
• Alpha -- awake & resting
• Beta -- mental activity
• Theta -- emotional stress
• Delta -- deep sleep
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II -- Optic Nerve
• Connects to retina supplying
vision
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I -- Olfactory Nerve
• Extends from olfactory
mucosa of nasal cavity to
olfactory bulb
• Sense of smell
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Developmental Anatomy of the NS
• Begins in 3rd week
– ectoderm forms thickening (neural
plate)
– plate folds inward to form neural
groove
– edges of folds join to form neural tube
• Neural crest tissue forms:
– spinal & cranial nerves
– dorsal root & cranial nerve ganglia
– adrenal gland medulla
• Layers of neural tube form:
– marginal layer which forms white
matter
– mantle layer forms gray matter
– ependymal layer forms linings of
cavities within NS
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Dorsal View of Neural Groove
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Development of Principal Parts
• By end of 4th week, 3 anterior enlargements occur
– prosencephalon
– mesencephalon
– rhombencephalon
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Development of Principal Parts
• By 5th week, 5 enlarged areas exist
• Prosencephalon
– telencephalon
– diencephalon
• Mesencephalon
• Rhombencephalon
– metencephalon
– myelencephalon
• Neural tube defects
– associated with low levels of folic acid (B vitamins)
– spina bifida is failure to close of vertebrae
– anencephaly is absence of skull & cerebral
hemispheres
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Aging & the Nervous System
• Years 1 to 2
– rapid increase in size due to increase in size of
neurons, growth of neuroglia, myelination &
development of dendritic branches
• Early adulthood until death
– brain weight declines until only 93% by age 80
– number of synaptic contacts declines
– processing of information diminishes
– conduction velocity decreases
– voluntary motor movements slow down
– reflexes slow down
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DISORDERS: HOMEOSTATIC IMBALANCES
• The most common brain disorder is a cerebrovascular
accident (CVA or stroke).
• Third leading cause of death after heart attacks and cancer
• CVAs are classified into two principal types:
– ischemic (the most common type), due to a decreased
blood supply
– hemorrhagic, due to a blood vessel in the brain that
bursts.
• Common causes of CVAs are intracerebral hemorrhage,
emboli, and atherosclerosis.
• Tissue plasminogen activator (t-PA) used within 3 hours of
ischemic CVA onset will decrease permanent disability
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Transient Ischemic Attack (TIA)
• Episode of temporary cerebral dysfunction
• Cause
– impaired blood flow to the brain
• Symptoms
– dizziness, slurred speech, numbness, paralysis on one
side, double vision
– reach maximum intensity almost immediately
– persists for 5-10 minutes & leaves no deficits
• Treatment is aspirin or anticoagulants; artery bypass grafting
or carotid endarterectomy
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Alzheimer Disease (AD)
• Dementia = loss of reasoning, ability to read, write, talk,
eat & walk
• Afflicts 11% of population over 65
• Great loss of neurons in specific regions (e.g.,
hippocampus and cerebral cortex); loss of neurons that
release acetylcholine
• Plaques of abnormal proteins deposited outside neurons
(amyloid plaques).
• Tangled protein filaments within neurons (neurofibrillary
tangles).
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Tumors
• Brain tumor is an abnormal growth of tissue it may be
malignant or benign.
• Attention Deficit Hyperactivity Disorder (ADHD) is a laerning
disorder characterized by poor attention span, hyperactivity
and inappropriate impulsiveness.
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CRANIAL NERVE Review
• Twelve pairs of cranial nerves originate from the brain
(Figure 14.5)
– named primarily on the basis of distribution and
numbered by order of attachment to the brain.
• Some cranial nerves (I, II, and VIII) contain only sensory
fibers and are called sensory nerves. The rest are mixed
nerves because they contain both sensory and motor fibers.
• Figures 14.18 – 14.27 illustrate the distribution of many of
the cranial nerves.
• Table 14.4 presents a summary of cranial nerves, including
clinical applications related to their dysfunction.
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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Cranial Nerve Review
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end
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Chapter 15
The Autonomic Nervous System
Lecture Outline
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INTRODUCTION
• The autonomic nervous system (ANS) operates via reflex
arcs.
• Operation of the ANS to maintain homeostasis, however,
depends on a continual flow of sensory afferent input, from
receptors in organs, and efferent motor output to the same
effector organs.
• Structurally, the ANS includes autonomic sensory neurons,
integrating centers in the CNS, and autonomic motor
neurons.
• Functionally, the ANS usually operates without conscious
control.
• The ANS is regulated by the hypothalamus and brain stem.
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Chapter 15
The Autonomic Nervous System
• Regulate activity of smooth muscle, cardiac muscle &
certain glands
• Structures involved
– general visceral afferent neurons
– general visceral efferent neurons
– integration center within the brain
• Receives input from limbic system and other regions of
the cerebrum
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SOMATIC AND AUTONOMIC NERVOUS SYSTEMS
• The somatic nervous system contains both sensory and
motor neurons.
• The somatic sensory neurons receive input from receptors
of the special and somatic senses.
• These sensations are consciously perceived.
• Somatic motor neurons innervate skeletal muscle to
produce conscious, voluntary movements.
• The effect of a motor neuron is always excitation.
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SOMATIC AND AUTONOMIC NERVOUS SYSTEMS
• The autonomic nervous system contains both autonomic
sensory and motor neurons.
– Autonomic sensory neurons are associated with
interoceptors.
– Autonomic sensory input is not consciously perceived.
• The ANS also receives sensory input from somatic senses
and special sensory neurons.
• The autonomic motor neurons regulate visceral activities by
either increasing (exciting) or decreasing (inhibiting)
ongoing activities of cardiac muscle, smooth muscle, and
glands.
– Most autonomic responses can not be consciously
altered or suppressed.
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SOMATIC vs AUTONOMIC NERVOUS SYSTEMS
• All somatic motor pathways consist of a single motor
neuron
• Autonomic motor pathways consists of two motor neurons
in series
– The first autonomic neuron motor has its cell body in the
CNS and its myelinated axon extends to an autonomic
ganglion.
• It may extend to the adrenal medullae rather than an
autonomic ganglion
– The second autonomic motor neuron has its cell body in
an autonomic ganglion; its nonmyelinated axon extends
to an effector.
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Somatic versus Autonomic NS
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Basic Anatomy of ANS
• Preganglionic neuron
– cell body in brain or spinal cord
– axon is myelinated type B fiber that extends to
autonomic ganglion
• Postganglionic neuron
– cell body lies outside the CNS in an autonomic ganglion
– axon is unmyelinated type C fiber that terminates in a
visceral effector
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Sympathetic vs. Parasympathetic NS
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AUTONOMIC NERVOUS SYSTEM
• The output (efferent) part of the ANS is divided into two
principal parts:
– the sympathetic division
– the parasympathetic division
– Organs that receive impulses from both sympathetic and
parasympathetic fibers are said to have dual innervation.
• Table 15.1 summarizes the similarities and differences
between the somatic and autonomic nervous systems.
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Sympathetic ANS vs. Parasympathetic ANS
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Divisions of the
ANS
• 2 major divisions
– parasympathetic
– sympathetic
• Dual innervation
– one speeds up organ
– one slows down organ
– Sympathetic NS
increases heart rate
– Parasympathetic NS
decreases heart rate
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Divisions of the
ANS
• 2 major divisions
– parasympathetic
– sympathetic
• Dual innervation
– one speeds up organ
– one slows down organ
– Sympathetic NS
increases heart rate
– Parasympathetic NS
decreases heart rate
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Autonomic Ganglia
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Sympathetic Ganglia
• These ganglia include the sympathetic trunk or vertebral
chain or paravertebral ganglia that lie in a vertical row on
either side of the vertebral column (Figures 15.2).
• Other sympathetic ganglia are the prevertebral or collateral
ganglia that lie anterior to the spinal column and close to
large abdominal arteries.
– celiac
– superior mesenteric
– inferior mesenteric ganglia
– (Figures 15.2 and 15.4).
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Parasympathetic Ganglia
• Parasympathetic ganglia are the terminal or intramural
ganglia that are located very close to or actually within the
wall of a visceral organ.
• Examples of terminal ganglia include (Figure 15.3)
– ciliary,
– pterygopalatine,
– submandibular,
– otic ganglia
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Sympathetic ANS vs. Parasympathetic ANS
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Dual Innervation, Autonomic Ganglia
• Sympathetic (thoracolumbar)
division
– preganglionic cell bodies in
thoracic and first 2 lumbar
segments of spinal cord
• Ganglia
– trunk (chain) ganglia near
vertebral bodies
– prevertebral ganglia near
large blood vessel in gut
(celiac, superior mesenteric,
inferior mesenteric)
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• Parasympathetic
(craniosacral) division
– preganglionic cell
bodies in nuclei of 4
cranial nerves and the
sacral spinal cord
• Ganglia
– terminal ganglia in wall
of organ
172
Autonomic Plexuses
• These are tangled networks of sympathetic
and parasympathetic neurons (Figure 15.4)
which lie along major arteries.
• Major autonomic plexuses include
– cardiac,
– pulmonary,
– celiac,
– superior mesenteric,
– inferior mesenteric,
– renal and
– hypogastric
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Autonomic Plexuses
•
•
•
•
•
•
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Cardiac plexus
Pulmonary plexus
Celiac (solar) plexus
Superior mesenteric
Inferior mesenteric
Hypogastric
174
Autonomic Plexuses
•
•
•
•
•
•
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Cardiac plexus
Pulmonary plexus
Celiac (solar) plexus
Superior mesenteric
Inferior mesenteric
Hypogastric
175
Structures of Sympathetic NS
• Preganglionic cell bodies at T1 to L2
• Rami communicantes
– white ramus = myelinated = preganglionic fibers
– gray ramus = unmyelinated = postganglionic fibers
• Postganglionic cell bodies
– sympathetic chain ganglia along the spinal column
– prevertebral ganglia at a distance from spinal cord
• celiac ganglion
• superior mesenteric ganglion
• inferior mesenteric ganglion
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Postganglionic Neurons:
Sympathetic vs. Parasympathetic
• Sympathetic preganglionic neurons pass to the sympathetic
trunk. They may connect to postganglionic neurons in the
following ways. (Figure 17.5).
– May synapse with postganglionic neurons in the ganglion
it first reaches.
– May ascend or descend to a higher of lower ganglion
before synapsing with postganglionic neurons.
– May continue, without synapsing, through the
sympathetic trunk ganglion to a prevertebral ganglion
where it synapses with the postganglionic neuron.
• Parasympathetic preganglionic neurons synapse with
postganglionic neurons in terminal ganglia (Figure 17.3).
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Pathways of Sympathetic Fibers
• Spinal nerve route
– out same level
• Sympathetic chain route
– up chain & out spinal
nerve
• Collateral ganglion route
– out splanchnic nerve to
collateral ganglion
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Organs Innervated by Sympathetic NS
• Structures innervated by each spinal nerve
– sweat glands, arrector pili mm., blood vessels to skin
& skeletal mm.
• Thoracic & cranial plexuses supply:
– heart, lungs, esophagus & thoracic blood vessels
– plexus around carotid artery to head structures
• Splanchnic nerves to prevertebral ganglia supply:
– GI tract from stomach to rectum, urinary &
reproductive organs
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Ganglia & Plexuses of Sympathetic NS
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Circuitry of Sympathetic NS
• Divergence = each preganglionic cell synapses on many
postganglionic cells
• Mass activation due to divergence
– multiple target organs
– fight or flight response explained
• Adrenal gland
– modified cluster of postganglionic cell bodies that
release epinephrine & norepinephrine into blood
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Application
• In Horner’s syndrome, the sympathetic innervation to one
side of the face is lost.
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Structure of the Parasympathetic Division
• The cranial outflow consists of preganglionic axons that
extend from the brain stem in four cranial nerves. (Figure
15.3).
– The cranial outflow consists of four pairs of ganglia and
the plexuses associated with the vagus (X) nerve.
• The sacral parasympathetic outflow consists of
preganglionic axons in the anterior roots of the second
through fourth sacral nerves and they form the pelvic
splanchnic nerve. (Figure15.3)
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Anatomy of Parasympathetic NS
• Preganglionic cell bodies
found in
– 4 cranial nerve nuclei in
brainstem
– S2 to S4 spinal cord
• Postganglionic cell bodies
very near or in the wall of
the target organ in a
terminal ganglia
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Parasympathetic Cranial Nerves
• Oculomotor nerve
– ciliary ganglion in orbit
– ciliary muscle & pupillary constrictor muscle inside eyeball
• Facial nerve
– pterygopalatine and submandibular ganglions
– supply tears, salivary & nasal secretions
• Glossopharyngeal
– otic ganglion supplies parotid salivary gland
• Vagus nerve
– many brs supply heart, pulmonary and GI tract as far as the
midpoint of the colon
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Parasympathetic Sacral Nerve Fibers
• Form pelvic splanchnic
nerves
• Preganglionic fibers end
on terminal ganglia in
walls of target organs
• Innervate smooth muscle
and glands in colon,
ureters, bladder &
reproductive organs
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ANS NEUROTRANSMITTERS AND RECEPTORS
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ANS Neurotransmitters
• Classified as either cholinergic or adrenergic neurons based
upon the neurotransmitter released
• Adrenergic
• Cholinergic
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Cholinergic Neurons and Receptors
• Cholinergic neurons release
acetylcholine
– all preganglionic neurons
– all parasympathetic
postganglionic neurons
– few sympathetic
postganglionic neurons (to
most sweat glands)
• Excitation or inhibition
depending upon receptor
subtype and organ involved.
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Cholinergic Neurons and Receptors
• Cholinergic receptors are integral membrane proteins in the
postsynaptic plasma membrane.
• The two types of cholinergic receptors are nicotinic and
muscarinic receptors (Figure 15.6 a , b).
– Activation of nicotinic receptors causes excitation of the
postsynaptic cell.
• Nicotinic receptors are found on dendrites & cell
bodies of autonomic NS cells (and at NMJ.)
– Activation of muscarinic receptors can cause either
excitation or inhibition depending on the cell that bears
the receptors.
• Muscarinic receptors are found on plasma
membranes of all parasympathetic effectors
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Adrenergic Neurons and Receptors
• Adrenergic neurons release
norepinephrine (NE) )
– from postganglionic
sympathetic neurons only
• Excites or inhibits organs
depending on receptors
• NE lingers at the synapse until
enzymatically inactivated by
monoamine oxidase (MAO) or
catechol-O-methyltransferase
(COMT)
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Adrenergic Neurons and Receptors
• The main types of adrenergic receptors are alpha and beta
receptors. These receptors are further classified into
subtypes.
– Alpha1 and Beta1 receptors produce excitation
– Alpha2 and Beta2 receptors cause inhibition
– Beta3 receptors (brown fat) increase thermogenesis
• Effects triggered by adrenergic neurons typically are longer
lasting than those triggered by cholinergic neurons.
• Table 15.2 describes the location of the subtypes of
cholinergic and adrenergic receptors and summarizes the
responses that occur when each type of receptor is
activated.
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Receptor Agonists and Antagonists
• An agonist is a substance that binds to and activates a
receptor, mimicking the effect of a natural neurotransmitter
or hormone.
• An antagonist is a substance that binds to and blocks a
receptor, preventing a natural neurotransmitter or hormone
from exerting its effect.
• Drugs can serve as agonists or antagonists to selectively
activate or block ANS receptors.
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Physiological Effects of the ANS
• Most body organs receive dual innervation
– innervation by both sympathetic & parasympathetic
• Hypothalamus regulates balance (tone) between
sympathetic and parasympathetic activity levels
• Some organs have only sympathetic innervation
– sweat glands, adrenal medulla, arrector pili mm & many
blood vessels
– controlled by regulation of the “tone” of the sympathetic
system
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Sympathetic Responses
• Dominance by the sympathetic system is caused by physical
or emotional stress -- “E situations”
– emergency, embarrassment, excitement, exercise
• Alarm reaction = flight or fight response
– dilation of pupils
– increase of heart rate, force of contraction & BP
– decrease in blood flow to nonessential organs
– increase in blood flow to skeletal & cardiac muscle
– airways dilate & respiratory rate increases
– blood glucose level increase
• Long lasting due to lingering of NE in synaptic gap and
release of norepinephrine by the adrenal gland
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Parasympathetic Responses
• Enhance “rest-and-digest” activities
• Mechanisms that help conserve and restore body energy
during times of rest
• Normally dominate over sympathetic impulses
• SLUDD type responses = salivation, lacrimation, urination, digestion
& defecation and 3 “decreases”--- decreased HR, diameter of airways and
diameter of pupil
• Paradoxical fear when there is no escape route or no way to win
– causes massive activation of parasympathetic division
– loss of control over urination and defecation
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PHYSIOLOGICAL EFFECTS
OF THE ANS - Summary
• The sympathetic responses prepare the body for emergency
situations (the fight-or-flight responses).
• The parasympathetic division regulates activities that
conserve and restore body energy (energy conservationrestorative system).
• Table 15.4 summarizes the responses of glands, cardiac
muscle, and smooth muscle to stimulation by the ANS.
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INTEGRATION AND CONTROL OF AUTONOMIC
FUNCTIONS
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Autonomic or Visceral Reflexes
• A visceral autonomic reflex adjusts the activity of a
visceral effector, often unconsciously.
– changes in blood pressure, digestive functions etc
– filling & emptying of bladder or defecation
• Autonomic reflexes occur over autonomic reflex arcs.
Components of that reflex arc:
– sensory receptor
– sensory neuron
– integrating center
– pre & postganglionic motor neurons
– visceral effectors
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Control of Autonomic NS
• Not aware of autonomic responses because control
center is in lower regions of the brain
• Hypothalamus is major control center
– input: emotions and visceral sensory information
• smell, taste, temperature, osmolarity of blood, etc
– output: to nuclei in brainstem and spinal cord
– posterior & lateral portions control sympathetic NS
• increase heart rate, inhibition GI tract, increase
temperature
– anterior & medial portions control parasympathetic NS
• decrease in heart rate, lower blood pressure,
increased GI tract secretion and mobility
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Autonomic versus Somatic NS - Review
• Somatic nervous system
– consciously perceived sensations
– excitation of skeletal muscle
– one neuron connects CNS to organ
• Autonomic nervous system
– unconsciously perceived visceral sensations
– involuntary inhibition or excitation of smooth muscle,
cardiac muscle or glandular secretion
– two neurons needed to connect CNS to organ
• preganglionic and postganglionic neurons
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DISORDERS
• Raynaud’s phenomenon is due to excessive sympathetic
stimulation of smooth muscle in the arterioles of the digits as
a result the digits become ischemic after exposure to cold or
with emotional stress.
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Autonomic Dysreflexia
• Exaggerated response of sympathetic NS in cases of spinal
cord injury above T6
• Certain sensory impulses trigger mass stimulation of
sympathetic nerves below the injury
• Result
– vasoconstriction which elevates blood pressure
– parasympathetic NS tries to compensate by slowing heart
rate & dilating blood vessels above the injury
– pounding headaches, sweating warm skin above the injury
and cool dry skin below
– can cause seizures, strokes & heart attacks
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end
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Chapter 16
Sensory, Motor & Integrative Systems
Lecture Outline
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INTRODUCTION
• The components of the brain interact to receive sensory
input, integrate and store the information, and transmit
motor responses.
• To accomplish the primary functions of the nervous system
there are neural pathways to transmit impulses from
receptors to the circuitry of the brain, which manipulates the
circuitry to form directives that are transmitted via neural
pathways to effectors as a response.
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Chapter 16
Sensory, Motor & Integrative Systems
•
•
•
•
Levels and components of sensation
Pathways for sensations from body to brain
Pathways for motor signals from brain to body
Integration Process
– wakefulness and sleep
– learning and memory
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SENSATION
• Sensation is a conscious or unconscious awareness
of external or internal stimuli.
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Is Sensation Different from Perception?
• Perception is the conscious awareness & interpretation of a
sensation.
– precisely localization & identification
– memories of our perceptions are stored in the cortex
• Sensation is any stimuli the body is aware of
– Chemoreceptors, thermoreceptors, nociceptors, baroreceptors
– What are we not aware of?
• X-rays, ultra high frequency sound waves, UV light
– We have no sensory receptors for those stimuli
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Sensory Modalities
• Sensory Modality is the property by which one sensation
is distinguished from another.
• Different types of sensations
– touch, pain, temperature, vibration, hearing, vision
– Generally, each type of sensory neuron can respond
to only one type of stimulus.
• Two classes of sensory modalities
– general senses
– special senses
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Sensory Modalities
• The classes of sensory modalities are general senses and
special senses.
– The general senses include both somatic and visceral
senses, which provide information about conditions
within internal organs.
– The special senses include the modalities of smell, taste,
vision, hearing, and equilibrium.
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Process of Sensation
• Sensory receptors demonstrate selectivity
– respond to only one type of stimuli
• Events occurring within a sensation
– stimulation of the receptor
– transduction (conversion) of stimulus into a graded
potential
• vary in amplitude and are not propagated
– generation of impulses when graded potential
reaches threshold
– integration of sensory input by the CNS
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Sensory Receptors
• Receptor Structure may be simple or complex
– General Sensory Receptors (Somatic Receptors)
• no structural specializations in free nerve endings
that provide us with pain, tickle, itch, temperatures
• some structural specializations in receptors for
touch, pressure & vibration
– Special Sensory Receptors (Special Sense Receptors)
• very complex structures---vision, hearing, taste, &
smell
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Alternate Classifications of Sensory Receptors
•
•
•
•
Structural classification
Type of response to a stimulus
Location of receptors & origin of stimuli
Type of stimuli they detect
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Structural Classification of Receptors
• Free nerve endings
– bare dendrites
– pain, temperature, tickle, itch & light touch
• Encapsulated nerve endings
– dendrites enclosed in connective tissue capsule
– pressure, vibration & deep touch
• Separate sensory cells
– specialized cells that respond to stimuli
– vision, taste, hearing, balance
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Structural Classification
• Compare free nerve ending, encapsulated nerve ending and
sensory receptor cell
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Classification by Stimuli Detected
• Mechanoreceptors
– detect pressure or stretch
– touch, pressure, vibration, hearing, proprioception,
equilibrium & blood pressure
• Thermoreceptors detect temperature
• Nociceptors detect damage to tissues
• Photoreceptors detect light
• Chemoreceptors detect molecules
– taste, smell & changes in body fluid chemistry
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Classification by Response to Stimuli
• Generator potential
– free nerve endings, encapsulated nerve endings &
olfactory receptors produce generator potentials
– when large enough, it generates a nerve impulse in a firstorder neuron
• Receptor potential
– vision, hearing, equilibrium and taste receptors produce
receptor potentials
– receptor cells release neurotransmitter molecules on firstorder neurons producing postsynaptic potentials
– PSP may trigger a nerve impulse
• Amplitude of potentials vary with stimulus intensity
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Classification by Location
• Exteroceptors
– near surface of body
– receive external stimuli
– hearing, vision, smell, taste, touch, pressure, pain,
vibration & temperature
• Interoceptors
– monitors internal environment (BV or viscera)
– not conscious except for pain or pressure
• Proprioceptors
– muscle, tendon, joint & internal ear
– senses body position & movement
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Adaptation in Sensory Receptors
• Most sensory receptors exhibit adaptation – the tendency
for the generator or receptor potential to decrease in
amplitude during a maintained constant stimulus.
• Receptors may be rapidly or slowly adapting.
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Adaptation of Sensory Receptors
• Change in sensitivity to long-lasting stimuli
– decrease in responsiveness of a receptor
• bad smells disappear
• very hot water starts to feel only warm
– potential amplitudes decrease during a maintained,
constant stimulus
• Variability in tendency to adapt:
– Rapidly adapting receptors (smell, pressure, touch)
• specialized for detecting changes
– Slowly adapting receptors (pain, body position)
• nerve impulses continue as long as the stimulus
persists – Pain is not easily ignored.
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SOMATIC SENSATIONS
• Receptors for somatic sensation are summarized in
Table 16.2)
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Tactile Sensations
• Tactile sensations are touch, pressure, and vibration plus
itch and tickle.
• receptors include (Figure 16.2)
– corpuscles of touch (Meissner’s corpuscles),
– hair root plexuses,
– type I (Merkel’s discs)
– type II cutaneous (Ruffini’s corpuscles)
– mechanoreceptors,
– lamellated (Pacinian) corpuscles,
– free nerve endings
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Touch
• Crude touch refers to the ability to perceive that something
has simply touched the skin
• Discriminative touch (fine touch) provides specific
information about a touch sensation such as location,
shape, size, and texture of the source of stimulation.
• Receptors for touch include corpuscles of touch (Meissner’s
corpuscles) and hair root plexuses; these are rapidly
adapting receptors.
• Type I cutaneous mechanoreceptors (tactile or Merkel
discs) and type II cutaneous mechanoreceptors (end organs
of Ruffini) are slowly adapting receptors for touch (Figure
16.2).
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Pressure and Vibration
• Pressure is a sustained sensation that is felt over a larger
area than touch.
– Pressure sensations generally result from stimulation of
tactile receptors in deeper tissues and are longer lasting
and have less variation in intensity than touch sensations
– Receptors for pressure are type II cutaneous
mechanoreceptors and lamellated (Pacinian) corpuscles.
• Like corpuscles of touch (Meissner’s corpuscles),
lamellated corpuscles adapt rapidly.
• Vibration sensations result from rapidly repetitive sensory
signals from tactile receptors
– receptors for vibration sensations are corpuscles of touch
and lamellated corpuscles, which detect low-frequency
and high-frequency vibrations, respectively.
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Itch and Tickle
• Itch and tickle receptors are free nerve endings.
– Tickle is the only sensation that you may not elicit on
yourself.
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Meissner’s Corpuscle
• Dendrites enclosed in CT in dermal papillae of hairless skin
• Discriminative touch & vibration-- rapidly adapting
• Generate impulses mainly at onset of a touch
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Hair Root Plexus
•Free nerve endings found around follicles, detects
movement of hair
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Merkel’s Disc
• Flattened dendrites touching cells of stratum basale
• Used in discriminative touch (25% of receptors in hands)
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Ruffini Corpuscle
• Found deep in dermis of skin
• Detect heavy touch, continuous touch, & pressure
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Pacinian Corpuscle
• Onion-like connective tissue capsule enclosing a dendrite
• Found in subcutaneous tissues & certain viscera
• Sensations of pressure or high-frequency vibration
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Somatic Tactile Sensations - Summary
• Touch
– crude touch is ability to perceive something has touched
the skin
– discriminative touch provides location and texture of
source
• Pressure is sustained sensation over a large area
• Vibration is rapidly repetitive sensory signals
• Itching is chemical stimulation of free nerve endings
• Tickle is stimulation of free nerve endings only by someone
else
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Thermal Sensations
• Free nerve endings with 1mm diameter receptive fields on
the skin surface
– Cold receptors in the stratum basale respond to
temperatures between 50-105 degrees F
– Warm receptors in the dermis respond to temperatures
between 90-118 degrees F
• Both adapt rapidly at first, but continue to generate
impulses at a low frequency
• Pain is produced below 50 and over 118
degrees F.
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Pain Sensations
• Pain receptors (nociceptors) are free endings that are
located in nearly every body tissue
– Free nerve endings found in every tissue of body
except the brain
– adaptation is slight if it occurs at all.
• Stimulated by excessive distension, muscle spasm, &
inadequate blood flow
• Tissue injury releases chemicals such as K+, kinins
or prostaglandins that stimulate nociceptors
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Types of Pain
• Fast pain (acute)
– occurs rapidly after stimuli (.1 second)
– sharp pain like needle puncture or cut
– not felt in deeper tissues
– larger A nerve fibers
• Slow pain (chronic)
– begins more slowly & increases in intensity
– aching or throbbing pain of toothache
– in both superficial and deeper tissues
– smaller C nerve fibers
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Types of Pain
• Somatic pain that arises from the stimulation of
receptors in the skin is superficial, while somatic
pain that arises from skeletal muscle, joints, and
tendons is deep.
• Visceral pain, unlike somatic pain, is usually felt in or
just under the skin that overlies the stimulated organ
– localized damage (cutting) intestines may cause
no pain, but diffuse visceral stimulation can be
severe
• distension of a bile duct from a gallstone
• distension of the ureter from a kidney stone
– pain may also be felt in a surface area far from the
stimulated organ in a phenomenon known as
referred pain (Figure 16.3).
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Referred Pain
• Visceral pain that is felt just deep to the skin overlying the stimulated
organ or in a surface area far from the organ.
• Skin area & organ are served by the same segment of the spinal cord.
– Heart attack is felt in skin along left arm since both are supplied by
spinal cord segment T1-T5
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Pain Relief
Multiple sites of analgesic action:
• Aspirin and ibuprofen block formation of prostaglandins that
stimulate nociceptors
• Novocaine blocks conduction of nerve impulses along pain
fibers
• Morphine lessen the perception of pain in the brain.
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Proprioceptive Sensations
• Receptors located in skeletal muscles, in tendons, in and
around joints, and in the internal ear convey nerve impulses
related to muscle tone, movement of body parts, and body
position. This awareness of the activities of muscles,
tendons, and joints and of balance or equilibrium is provided
by the proprioceptive or kinesthetic sense.
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Proprioceptive or Kinesthetic Sense
• Awareness of body position & movement
– walk or type without looking
– estimate weight of objects
• Proprioceptors adapt only slightly
• Sensory information is sent to cerebellum & cerebral
cortex
– signals project from muscle, tendon, joint capsules
& hair cells in the vestibular apparatus
– receptors discussed here include muscle spindles,
tendon organs (Golgi tendon organs), and joint
kinesthetic receptors (Figure 16.4).
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Muscle
Spindles
• Specialized intrafusal muscle fibers enclosed in a CT capsule and
innervated by gamma motor neurons
• Stretching of the muscle stretches the muscle spindles sending sensory
information back to the CNS
• Spindle sensory fiber monitor changes in muscle length
• Brain regulates muscle tone by controlling gamma fibers
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Golgi Tendon Organs
• Found at junction of tendon & muscle
• Consists of an encapsulated bundle of collagen fibers laced with
sensory fibers
• When the tendon is overly stretched, sensory signals head for the
CNS & resulting in the muscle’s relaxation
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Joint Receptors
• Ruffini corpuscles
– found in joint capsule
– respond to pressure
• Pacinian corpuscles
– found in connective tissue around the joint
– respond to acceleration & deceleration of joints
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SOMATIC SENSORY PATHWAYS
• Somatic sensory pathways relay information from somatic
receptors to the primary somatosensory area in the cerebral
cortex.
• The pathways consist of three neurons
– first-order,
– second-order, and
– third-order
• Axon collaterals of somatic sensory neurons simultaneously
carry signals into the cerebellum and the reticular formation
of the brain stem.
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Somatic Sensory Pathways
• First-order neuron conduct impulses to the CNS
(brainstem or spinal cord)
– either spinal or cranial nerves
• Second-order neurons conducts impulses from brain stem
or spinal cord to thalamus
– cross over to opposite side of body
• Third-order neuron conducts impulses from thalamus to
primary somatosensory cortex (postcentral gyrus of
parietal lobe)
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Posterior Column-Medial Lemniscus
Pathway to the Cortex
• The nerve impulses for conscious proprioception and most
tactile sensations ascend to the cortex along a common
pathway formed by three-neuron sets (Figure 16.16a).
• These neurons are a part of the posterior (dorsal) columns
– consist of the gracile fasciculus and cuneate fasciculus
• Impulses conducted along this pathway
– fine touch,
– stereognosis,
– proprioception, and
– vibratory sensations
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Posterior Column-Medial
Lemniscus Pathway of CNS
• Proprioception, vibration,
discriminative touch, weight
discrimination & stereognosis
• Signals travel up spinal cord
in posterior column
• Fibers cross-over in medulla
to become the medial
lemniscus pathway ending in
thalamus
• Thalamic fibers reach cortex
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Anterolateral Pathways to the Cortex
• 3-neuron pathway
• The anterolateral or spinothalamic pathways carry
mainly pain and temperature impulses (Figure 16.5b).
• They also relay the sensations of tickle and itch and
some tactile impulses.
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Spinothalamic
Pathway of CNS
• Lateral spinothalamic tract
carries pain & temperature
• Anterior tract carries tickle,
itch, crude touch & pressure
• First cell body in DRG with
synapses in cord
• 2nd cell body in gray matter
of cord, sends fibers to other
side of cord & up through
white matter to synapse in
thalamus
• 3rd cell body in thalamus
projects to cerebral cortex
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Somatosensory Map of Postcentral Gyrus
• Relative sizes of cortical
areas
– proportional to number of
sensory receptors
– proportional to the
sensitivity of each part of
the body
• Can be modified with learning
– learn to read Braille & will
have larger area
representing fingertips
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Somatic Sensory Pathways to the Cerebellum
• The posterior spinocerebellar and the anterior
spinocerebellar tracts are the major routes whereby
proprioceptive impulses reach the cerebellum.
– impulses conveyed to the cerebellum are critical for
posture, balance, and coordination of skilled
movements.
• Table 16.3 summarizes the major sensory tracts in the
spinal cord and pathways in the brain.
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Sensory Pathways to the Cerebellum
• Major routes for proprioceptive
signals to reach the cerebellum
– anterior spinocerebellar tract
– posterior spinocerebellar
tract
• Subconscious information used
by cerebellum for adjusting
posture, balance & skilled
movements
• Signal travels up to same side
inferior cerebellar peduncle
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Clinical Application - Syphilis
Syphilis causes a progressive degeneration of the posterior
portions of the spinal cord.
– Sexually transmitted disease caused by bacterium
Treponema pallidum.
– Third clinical stage known as tertiary syphilis
– Progressive degeneration of posterior portions of spinal
cord & neurological loss
• loss of somatic sensations
• proprioceptive impulses fail to reach cerebellum
– People watch their feet while walking, but are still
uncoordinated and jerky
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SOMATIC MOTOR PATHWAYS
• Lower motor neurons extend from the brain stem or spinal
cord to skeletal muscles.
• These lower motor neurons are called the final common
pathway because many regulatory mechanisms converge
on these peripheral neurons.
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Somatic Motor Pathways - Overview
• Control of body movement
– motor portions of cerebral cortex
• initiate & control precise movements
– basal ganglia help establish muscle tone &
integrate semivoluntary automatic movements
– cerebellum helps make movements smooth &
helps maintain posture & balance
• Somatic motor pathways
– direct pathway from cerebral cortex to spinal cord
& out to muscles
– indirect pathway includes synapses in basal
ganglia, thalamus, reticular formation &
cerebellum
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SOMATIC MOTOR PATHWAYS
• Four distinct neural circuits (somatic motor pathways)
participate in control of movement by providing input to
lower motor neurons (Figure 16.7).
– Local circuit neurons are located close to lower motor
neuron cell bodies in the brain stem and spinal cord.
– Local circuit neurons and lower motor neurons receive
input from upper motor neurons.
– Neurons of the basal ganglia provide input to upper
motor neurons.
– Cerebellar neurons also control activity of upper motor
neurons.
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SOMATIC MOTOR PATHWAYS
• Organization of upper motor neuron pathways
– Direct motor pathways provide input to lower motor
neurons via axons that extend directly from the cerebral
cortex.
– Indirect pathways provide input to lower motor neurons
from motor centers in the brain stem
• Paralysis: damage of lower motor neurons produces flaccid
paralysis while injury to upper motor neurons causes spastic
paralysis.
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Primary Motor Cortex
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• The primary motor area is located in
the precentral gyrus of the frontal
lobe (Figure 16.6b)
– upper motor neurons initiate
voluntary movement
• The adjacent premotor area and
somatosensory area of the
postcentral gyrus also contribute
axons to descending motor
pathways.
• The cortical area devoted to a
muscle is proportional to the number
of motor units.
– More cortical area is needed if
number of motor units in a
muscle is high
• vocal cords, tongue, lips,
fingers & thumb
258
Direct motor pathways
• The direct pathways (pyramidal tracts) include (Figure
16.8).
– lateral and anterior corticospinal tracts
– corticobulbar tracts
• The various tracts of the pyramidal system convey impulses
from the cerebral cortex that result in precise muscular
movements.
• Table 16.4 summarizes the functions and pathways of the
tracts in the direct motor pathways.
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Direct Pathways (Pyramidal Pathways)
• 1 million upper motor neurons in cerebral cortex
• Axons form internal capsule in cerebrum and pyramids
in the medulla oblongata
• 90% of fibers decussate (cross over) in the medulla
– right side of brain controls left side muscles
• Terminate on interneurons which synapse on lower
motor neurons in either:
– nuclei of cranial nerves
– anterior horns of spinal cord
• Integrate excitatory & inhibitory input to become final
common pathway
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Details of Pyramidal Pathways
• Lateral corticospinal tracts
– cortex, cerebral peduncles, 90%
decussation of axons in medulla,
tract formed in lateral column.
– skilled movements (hands & feet)
• Anterior corticospinal tracts
– the 10% of axons that do not cross
– controls neck & trunk muscles
• Corticobulbar tracts
– cortex to nuclei of CNs
• III, IV, V, VI, VII, IX, X, XI & XII
– movements of eyes, tongue,
chewing, expressions & speech
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Location of Direct Pathways
• Lateral corticospinal tract
• Anterior corticospinal tract
• Corticobulbar tract
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Application
• Amyotrophic Lateral Sclerosis (ALS) is a disease hat attacks
motor areas of the cerebral cortex, axons of upper motor
neurons and cell bodies of lower motor neurons.
• It causes progressive muscle weakness.
• There are several theories as to its cause. While there is no
cure, several drugs are used to treat the symptoms.
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Paralysis
• Flaccid paralysis = damage lower motor neurons
– no voluntary movement on same side as damage
– no reflex actions
– muscle limp & flaccid
– decreased muscle tone
• Spastic paralysis = damage upper motor neurons
– paralysis on opposite side from injury
– increased muscle tone
– exaggerated reflexes
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Indirect Pathways
• Indirect or extrapyramidal pathways include all somatic
motor tracts other than the corticospinal and corticobulbar
tracts.
– involve the motor cortex, basal ganglia, thalamus,
cerebellum, reticular formation, and nuclei in the brain
stem (Figure 16.8).
– indirect tracts are the rubrospinal, tectospinal,
vestibulospinal, lateral reticulospinal and medial
reticulospinal tracts.
• Table 16.4 summarizes the major motor tracts, their
functions, and pathways in the brain.
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Indirect Pathways
• All other descending motor
pathways
• Complex polysynaptic circuits
– include basal ganglia,
thalamus, cerebellum,
reticular formation
• Descend in spinal cord as 5
major tracts
• All 5 tracts end upon
interneurons or lower motor
neurons
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Final Common
Pathway
• Lower motor neurons
receive signals from both
direct & indirect upper
motor neurons
• Sum total of all inhibitory &
excitatory signals
determines the final
response of the lower
motor neuron & the
skeletal muscles
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Roles of the basal ganglia
• The circuit from the cerebral cortex to basal ganglia to
thalamus to cortex seems to function in initiating and
terminating movement.
– basal ganglia also suppress unwanted movements
– basal ganglia may influence aspects of cortical function
including sensory, limbic, cognitive, and linguistic
functions.
• Damage to the basal ganglia results in uncontrollable,
abnormal body movements, often accompanied by muscle
rigidity and tremors.
• Parkinson disease and Huntington disease result from
damage to the basal ganglia.
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Basal Ganglia
• Helps to program automatic movement sequences
– walking and arm swinging or laughing at a joke
• Set muscle tone by inhibiting other motor circuits
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Basal Ganglia Connections - Review
• Circuit of connections
– cortex to basal ganglia to
thalamus to cortex
– planning movements
• Output from basal ganglia to
reticular formation
– reduces muscle tone
– damage produces rigidity
of Parkinson’s disease
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Modulation of Movement by the Cerebellum
• The cerebellum is active in both learning and performing
rapid, coordinated, highly skilled movements and in
maintaining proper posture and equilibrium.
• The four aspects of cerebellar function (Figure 16.9)
– monitoring intent for movement,
– monitoring actual movement,
– comparing intent with actual performance, and
– sending out corrective signals
• Damage to the cerebellum is evidenced by ataxia and
intention tremors.
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Cerebellar
Function
Aspects of Function
• learning
• coordinated &
skilled movements
• posture &
equilibrium
1. Monitors intentions for movements -- input from cerebral
cortex
2. Monitors actual movements with feedback from
proprioceptors
3. Compares intentions with actual movements
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INTEGRATIVE FUNCTIONS OF THE CEREBRUM
• The integrative functions include sleep and wakefulness,
memory, and emotional responses.
(discussed in Chapter 14).
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Wakefulness and Sleep
Role of the Reticular Activating System (RAS)
• Sleep and wakefulness are integrative functions that are
controlled by the reticular activating system (Figure 16.10).
– Arousal, or awakening from a sleep, involves increased
activity of the RAS.
– When the RAS is activated, the cerebral cortex is also
activated and arousal occurs.
– The result is a state of wakefulness called
consciousness.
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Reticular Activating System
• RAS has connections to
cortex & spinal cord.
• Many types of inputs can
activate the RAS---pain,
light, noise, muscle
activity, touch
• Coma is sleep-like state
– A person in a deep
coma has no reflexes.
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Wakefulness and Sleep
• Circadian rhythm
– 24 hour cycle of sleep and awakening
– established by hypothalamus
• EEG recordings show large amount of activity in
cerebral cortex when awake
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Sleep
• During sleep, a state of altered consciousness or partial
unconsciousness from which an individual can be aroused
by different stimuli,
• During sleep activity in the RAS is very low.
• Normal sleep consists of two types:
– non-rapid eye movement sleep (NREM) and
– rapid eye movement sleep (REM)
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Sleep
• Triggers for sleep are unclear
– adenosine levels increase with brain activity
– adenosine levels inhibit activity in RAS
– caffeine prevents adenosine from inhibiting RAS
• Non-rapid eye movement or slow wave sleep consists of
four stages, each of which gradually merges into the
next.
• Most dreaming occurs during rapid eye movement
sleep.
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Non-Rapid Eye Movement Sleep
• Stage 1
– person is drifting off with eyes
closed (first few minutes)
• Stage 2
– fragments of dreams
– eyes may roll from side to side
• Stage 3
– very relaxed, moderately deep
– 20 minutes, body temperature & BP have dropped
• Stage 4 = deep sleep
– bed-wetting & sleep walking occur in this phase
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REM Sleep
• Most dreams occur during REM sleep
• In first 90 minutes of sleep:
– go from stage 1 to 4 of NREM,
– go up to stage 2 of NREM
– to REM sleep
• Cycles repeat until total REM sleep totals 90 to 120
minutes
• Neuronal activity & oxygen use is highest in REM sleep
• Total sleeping & dreaming time decreases with age
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Learning and Memory
• Learning is the ability to acquire new knowledge or skills
through instruction or experience.
• Memory is the process by which that knowledge is retained
over time.
• For an experience to become part of memory, it must
produce persistent functional changes that represent the
experience in the brain.
• The capability for change with learning is called plasticity.
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Learning and Memory
• Memory occurs in stages over a period and is described as
immediate memory, short term memory, or long term
memory.
– Immediate memory is the ability to recall for a few
seconds.
– Short-term memory lasts only seconds or hours and is
the ability to recall bits of information; it is related to
electrical and chemical events.
– Long-term memory lasts from days to years and is
related to anatomical and biochemical changes at
synapses.
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Amnesia
• Amnesia refers to the loss of memory
• Anterograde amnesia is the loss of memory for events that
occur after the trauma; the inability to form new memories.
• Retrograde amnesia is the loss of memory for events that
occurred before the trauma; the inability to recall past
events.
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DISORDERS: HOMEOSTATIC IMBALANCES
• Phantom pain is the sensations of pain in a limb that has
been amputated; the brain interprets nerve impulses arising
in the remaining proximal portions of the sensory nerves as
coming from the nonexistent (phantom) limb. Another
explanation is that the neurons in the brain that received
input from the missing limbs are still active.
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Spinal Cord Injury
• Spinal cord injury can be due to damage in a number of
ways, such as compression or transection, and the location
and extent of damage determines the type and degree of loss
in neural abilities.
– tumor, herniated disc, clot, trauma …
• Paralysis
– monoplegia is paralysis of one limb only
– diplegia is paralysis of both upper or both lower
– hemiplegia is paralysis of one side
– quadriplegia is paralysis of all four limbs
• Spinal shock is loss of reflex function (areflexia)
– slow heart rate, low blood pressure, bladder problem
– reflexes gradually return
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Cerebral Palsy
• Loss of motor control and coordination
• Damage to motor areas of the brain
– infection of pregnant woman with rubella virus
– radiation during fetal life
– temporary lack of O2 during birth
• Not a progressive disease, but irreversible
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Parkinson Disease
• Parkinson’s disease is a progressive degeneration of CNS neurons of
the basal nuclei region due to unknown causes that decreases
dopamine neurotransmitter production.
– Environmental toxins may be the cause in some cases
• Neurons from the substantia nigra do not release enough dopamine
onto basal ganglia
– tremor, rigidity, bradykinesia (slow movement) or hypokinesia
(decreasing range of movement)
– may affect walking, speech, and facial expression
• Treatments
– drugs to increase dopamine levels (L-Dopa), or to prevent its
breakdown
– surgery to transplant fetal tissue or removal of part of globus
pallidus to slow tremors
– acetylcholine inhibitors
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