Transcript Chapter 14 Part 1

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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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: 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
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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


chemical protection


floats brain & softens impact with bony walls
optimal ionic concentrations for action potentials
circulation

nutrients and waste products to and from
and Physiology,
bloodstream Principles of Human Anatomy
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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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 20 ml/hour reabsorption rate
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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
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 Reflex centers for coughing,
sneezing,
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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 arisePrinciples
fromof Human
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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Tests of Cranial Nerve Function
Nerve
Name
Function
How to test
I
Olfactory
olfaction
with an odorous substance
II
Optical
vision
vision chart
III
Oculomotor
most eye muscles
"follow the moving finger"
IV
Trochlear
superior oblique
look down at the nose
facial sensation
touch the face
V
Trigeminal
muscles of mastication
clench the teeth
lateral rectus
look to the side
facial expression
smile, raise the eyebrows
taste
sugar or salt
hearing
a tuning fork
balance
look for vertigo
VI
Abducens
VII
Facial
VIII
Vestibulocochlear
IX
Glosopharyngeal
pharynx sensation
gag reflex
X
Vagus
Muscles of larynx and pharynx,
parasympathetic
check for hoarseness, open wide
and say "AH"
XI
Accessory
Trapezius and sternocleidomastoid
test shoulder raise or turning the
head
XII
Hypoglossal
tongue
muscles
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stick out the tongue
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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 36
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sending information here from
the cortex and cerebellum
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
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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.
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It regulates circadian rhythms and states of consciousness.
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
the corpus callosum,
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bundle of transverse white fibers. Figure 14.12)
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