Transcript Central Nervous System

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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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 (page 699 or next slide)
• 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
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Subarachnoid Haemorrhage
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Middle Meningeal Artery –epidural
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Venous Drainage
• Superior saggital sinus etc- in subdural
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Bridging Veins – subdural space
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Subdural Haemorrhage
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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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Meninges
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Blood Brain Barrier
• 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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What goes in and What Doesn’t
• Lipid Soluble- O2, CO2, ETOH, anesth all pass
easily the BBB
• Watersoluble, glucose, urea, creatinine, ions
pass slowly or in the case of glucose, via active
transport only
• BBB is not uniform throughout, some areas are
more permeable and thus bacteria can get in
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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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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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Cerebral Perfusion Pressure
• CPP = MABP – ICP
• Cerebral auto regulation
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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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Medulla Oblongata
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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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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
• 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 thru 7
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Midbrain
• One inch in length
• Extends from pons to
diencephalon
• Cerebral aqueduct
connects 3rd
ventricle above to
4th ventricle below
• Visual reflex centers
and auditory relay
(startle reflex)
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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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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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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
• 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
• 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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Functions of Hypothalamus
• Controls and integrates activities of the ANS which
regulates smooth, cardiac muscle and glands
• Synthesizes regulatory hormones that control the
anterior pituitary
• Contains cell bodies of axons that end in posterior
pituitary where they secrete hormones
• Regulates rage, aggression, pain, pleasure & arousal
• Feeding, thirst & satiety centers
• Controls body temperature
• Regulates daily patterns of sleep
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Cerebrum
(Cerebral Hemispheres)
• Cerebral cortex is gray matter
overlying white matter
– 2-4 mm thick containing billions
of cells
– grew so quickly formed folds
(gyri) and grooves (sulci or fissures)
• Longitudinal fissure separates left
& right cerebral hemispheres
• Corpus callosum is band of white matter connecting
left and right cerebral hemispheres
• Each hemisphere is subdivided into 4 lobes
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Lobes and Fissures
• Longitudinal fissure (green)
• Frontal lobe
• Central sulcus (yellow)
– precentral & postcentral gyrus
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Parietal lobe
Parieto-occipital sulcus
Occipital lobe
Lateral sulcus (blue)
Temporal lobe
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Basal Ganglia
• 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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Limbic System
• Parahippocampal & cingulate gyri & hippocampus
• Emotional brain--intense pleasure & intense pain
• Strong emotions increase efficiency of memory
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Brain Injuries
• Causes of damage
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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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Types of Injuries Cont
• Epidural bleed –arterial- Middle meningeal
artery – retrograde unconsiousness -treated
Burr holes
• SubDural Bleed –venous- bridging veins
• Subarchnoid bleed- arterial-Circle of Willis
• Moderate axonal injury
• Diffuse axonal tearing injury
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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 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
(FYI)
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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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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
• Functional
specialization of each
hemisphere more
pronounced in men
• Females have larger
connections between 2
sides
• Damage to left side
produces aphasia
• Damage to same area
on right side produces
speech with little
emotional inflection
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The Spinal Cord
• Extends from the foramen magnum of the
skull to L¹ or L² ; the dural and arachnoid
membranes extend to the level of S², well
beyond the end of the spinal cord which
makes this an ideal location for a lumbar tap
• 31 pairs of spinal nerves attach to the cord
by paired roots and exit from the vertebral
column via the intervertebral foramina to
travel to the body regions they serve
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The Spinal
Cord
• It is about the
width of a thumb
for most of its
length, but is
enlarged in the
cervical and
lumbosacral
regions, where the
nerves serving the
upper and lower
limbs arise
• The collection of
nerve roots at the
inferior end of the
vertebral canal is
named the cauda
equina
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The Spinal Cord: Gray Matter and
Spinal Roots
• Looks like the
letter “H” or a
butterfly with the
cross-bar of gray
matter called the
gray commissure
that encloses the
central canal
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The Spinal Cord: Gray Matter and
Spinal Roots
• Dorsal and Ventral Roots: very short
and fuse laterally to form the spinal
nerves
• The spinal nerves form the peripheral
nervous system
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The Spinal Cord: White Matter
• Composed of myelinated and unmyelinated
nerve fibers that allow communication between
different parts of the spinal cord and between
the cord and brain
• (1) Ascending: up to higher centers (sensory
inputs) (2) Descending: down to the cord from
the brain or within the cord to lower levels
(motor outputs) (3) Transversely: across from
one side of the cord to the other (commissural
fibers)
• Ascending and descending make up most of
the white matter
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Spinal cord Injuries
The following list outlines which muscle functions may be retained at
progressively lower levels of spinal cord transection.
C1–C3: no function maintained from the neck down; ventilator needed
for breathing
C4–C5: diaphragm, which allows breathing
C6–C7: some arm and chest muscles, which allows feeding, some
dressing, and propelling wheelchair
T1–T3: intact arm function
T4–T9: control of trunk above the umbilicus
T10–L1: most thigh muscles, which allows walking with long leg braces
L1–L2: most leg muscles, which allows walking with short leg braces
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