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8/12/2019 14 the Central Nervous System
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Chapter 14
The Central Nervous System
Overview of the central
nervous system
Meninges, ventricles,cerebrospinal fluid &
blood supply
Spinal cord Hindbrain and midbrain
Forebrain
Higher brain functions
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Brain Description
Brain weighs 3 to 3.5 pounds Major portions of the brain--brainstem, cerebrum, and
cerebellum cerebrum is 83% of brain volume; cerebellum contains 50% of the
neurons
brainstem = medulla oblongata + pons + midbrain (mesencephalon)
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Brain
Longitudinal fissure separates 2 cerebral hemispheres.
Central sulcus separates frontal and parietal lobe.
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Embryonic Development
Nervous system develops from ectoderm
by 3rd week, neural plate becomes a
groove with neural folds along each
side
by 4th week, neural folds join toform neural tube
lumen of the neural tube develops
into central canal of
spinal cord & ventricles of the brain
cells along the margin of the neural
groove is called the neural crest
develop into sensory and sympathetic neurons & schwann cells
by 4th week, neural tube exhibits 3 anterior dilations
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Brain Development
4th week
forebrain
midbrain
hindbrain
5th week
telencephalon
diencephalon
mesencephalon
metencephalon
myelencephalon
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Meninges
Dura mater -- outermost, tough membraneouter periosteal layer against bone
where separated from inner meningeal layer forms
dural venous sinuses draining blood from brain
supportive structures formed by dura mater
falx cerebri, falx cerebelli and tentorium cerebelli
epidural space filled with fat in lower back region
epidural anaesthesia during childbirth
Arachnoid mater is spider web filamentous layer
Pia mater is a thin vascular layer adherent to
contours of brain
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Cranial Meninges
CSF in subarachnoid space
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Meninges of Vertebra & Spinal Cord
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Brain Ventricles
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Ventricles and Cerebrospinal Fluid
Internal chambers within the CNS
lateral ventricles found inside cerebral hemispheres
third ventricle is single vertical space under corpus
callosumcerebral aqueduct runs through midbrain
fourth ventricle is small chamber between pons &
cerebellumcentral canal runs down through spinal cord
Lined with ependymal cells and containing
choroid plexus of capillaries that produce CSF
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Cerebrospinal Fluid
Clear liquid fills ventricles and canals & bathes
its external surface (in subarachnoid space)
Brain produces & absorbs about 500 ml/day
filtration of blood through choroid plexus
has more Na+ & Cl- but less K+ & Ca+2 than plasma
Functions
buoyancy -- floats brain so it neutrally buoyant
protection -- cushions from hitting inside of skull
chemical stability -- rinses away wastes
Escapes from 4th ventricle to surround the brain
Absorbed by arachnoid villi into venous sinus
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Flow of Cerebrospinal Fluid
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Blood-Brain and Blood-CSF Barriers
Blood-brain barrier is tightly joined endothelium
permeable to lipid-soluble materials (alcohol, O2,
CO2, nicotine and anesthetics)
administer drugs through nasal sprayscircumventricular organs in 3rd & 4th ventricles at
breaks in the barrier where blood has direct access
monitoring of glucose, pH, osmolarity & other variations
allows route for HIV virus to invade the brain
Blood-CSF barrier at choroid plexus is
ependymal cells joined by tight junctions
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Functions of the Spinal Cord
Conductionbundles of fibers passing information up & down
spinal cord
Locomotionrepetitive, coordinated actions of several muscle
groups
central pattern generators are pools of neurons
providing control of flexors and extensors (walking)
Reflexes
involuntary, stereotyped responses to stimuli
remove hand from hot stove
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Gross Anatomy of the Spinal Cord
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Anatomy of the Spinal Cord
Ropelike bundle of nerve tissue within the
vertebral canal (thick as a finger)
vertebral column grows faster so in an adult the spinal
cord only extends to L1
31 pairs of spinal nerves coming from cervical,
thoracic, lumbar or sacral regions of the cord
named for level of vertebral column where nerves exit
Cervical & lumbar enlargements in cord
Medullary cone is tapered tip of spinal cord
Cauda equinae is L2 to S5 nerve roots resemble
horses tail
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Cross-Sectional Anatomy of the Spinal Cord
Central area of gray matter shaped like a butterfly and
surrounded by white matter in 3 columns
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Gray Matter Pair of dorsal or posterior horns
dorsal root of spinal nerve is totally sensory fibers
Pair of ventral or anterior horns
ventral root of spinal nerve is totally motor fibers
Connected by gray commissure punctured by a
central canal continuous above with 4th ventricle
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White Matter
Bundles of myelinated axons that run up & down Dorsal or posterior columns or funiculi
Lateral columns or funiculi
Anterior columns or funiculi
Each column is filled with tracts or fasciculi
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Spinal Tracts
Ascending & descending tract head up or down whiledecussation means that the fibers cross sides
Contralateral means from the opposite side whileipsilateral means 2 regions on same side
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Deep touch,vibration, limb
movement & position
(proprioception)
Fasciculus gracilis &
cuneatus carry signals
from arm & leg
respectively
Decussation of 2nd order
neuron in medulla
CNS Ascending Pathway
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CNS Ascending Pathway 2
Spinothalamic tract
Pain, pressure,
temperature, light
touch, tickle & itch
Decussation is in
spinal cord
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Corticospinal tract
Motor signals from
cerebral cortex for
limb movements
Decussation in medulla
forms lateral tract
anterior tract uncrossed
Tectospinal, reticulospinal & vestibulospinal
tracts maintain posture & balance and provide
reflex movements of the head
CNS Descending Pathway
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Medulla Oblongata
3 cm extension of spinal cord Ascending & descending nerve tracts
Nuclei of sensory & motor cranialnerves (IX, X, XI, and XII)
Cardiac center adjusts rate & force of heart beat
Vasomotor center adjusts blood vessel diameter
Respiratory centers control rate & depth of
breathing Reflex centers for coughing, sneezing, gagging,
swallowing, vomiting, salivation, sweating,movements of tongue & head
Pyramids and olive visible on surface
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Medulla and Pons
Olive
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Pons
Bulge in the brainstem, rostral tothe medulla
Ascending sensory tracts
Descending motor tracts Pathways in & out of cerebellum
Nuclei concerned with sleep, hearing, balance,
taste, eye movements, facial expression, facialsensation, respiration, swallowing, bladder
control & posture
cranial nerves V, VI, VII, and VIII
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Cerebellum
Right & left hemispheres connected by vermis
Parallel surface folds called folia are gray matter
all of output comes from deep gray nuclei
large cells in single layer in cortex are purkinje cells
synapse on deep nuclei
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Cerebellum
Connected to brainstem by cerebellar peduncles
White matter (arbor vitae) visible in sagittal section
Sits atop the 4th ventricle
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Mesencephalon Central aqueduct
CN III and IV
eye movement
Cerebral peduncles hold corticospinal tract
Tegmentum connects to cerebellum & helps
control fine movements through red nucleus
Substantia nigra sends inhibitory signals to basal
ganglia & thalamus (degeneration leads to
tremors and Parkinson disease)
Midbrain, Cross Section
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Superior & Inferior Colliculus
Tectum (4 nuclei) called corpora quadrigeminasuperior colliculus (tracking moving objects )
inferior colliculus (reflex turning of head to sound)
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Reticular Formation
Clusters of gray matter
scattered throughout pons,
midbrain & medulla
Regulate balance & posture
relaying information from
eyes & ears to cerebellum
gaze centers allow you to track moving object
Includes cardiac & vasomotor centers
Origin of descending analgesic pathways
Regulates sleep & conscious attention
in ur leads to irreversible coma
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Thalamus-the integrator
Oval mass of gray matter protruding into lateralventricle (part of diencephalon)
Receives nearly all sensory information on its
way to cerebral cortex integrate & directs information to appropriate area
Interconnected to limbic system so involved in
emotional & memory functions
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Walls & floor of 3rd ventricle
Functions
hormone secretion & pituitary
autonomic NS control
thermoregulation (thermostat)
food & water intake (hunger & satiety)
sleep & circadian rhythms
memory (mammillary bodies)
emotional behavior
Hypothalamus
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Epithalamus (Pineal Gland)
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Tracts of Cerebral White Matter
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Cerebral Cortex Surface layer of gray matter -- 3 mm thick
Neocortex (six-layered tissue)
newest part of the cortex (paleocortex & archicortex)
layers vary in thickness in different regions of brain
2 types of cells
stellate cells
have dendrites projecting
in all directions
pyramidal cells
have an axon that passes
out of the area
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Basal Nuclei
Masses of gray matter deep to cerebral cortex Receive input from substantia nigra & motor
cortex & send signals back to these regions
Involved in motor control & inhibition of tremors
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Limbic System
Loop of cortical structures surrounding deep brain
amygdala, hippocampus, fornix & cingulate gyrus
Amydala important in emotions and
hippocampus in memory -- rest are not sure
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Brain Waves & Sleep
States of consciousness can be correlated with EEG
4 types of brain waves
alpha occur when awake & resting with eyes closed
beta occur with eyes open performing mental tasks
theta occur during sleep or emotional stress
delta occur during deep sleep
Sleep is temporary state of unconsciousness
coma is state of unconsciousness with no possible arousal
reticular formation seems to regulate state of alertness
suprachiasmatic nucleus acts as biological clock to set our
circadian rhythm of sleep and waking
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Sleep Stages and Brain Waves
Brain waves change as we pass through 4 stages
of sleep: alpha, to sleep spindles, to theta and
finally to delta waves during deep sleep
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Sleep Stages
Notice how REM sleep periods become longer
and more frequent in the second half of the night
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Cognition
Cognition is mental processes such as awareness,perception, thinking, knowledge & memory
75% of brain is association areas where integration
of sensory & motor information occurs
Examples of effects of brain lesions
parietal lobe -- contralateral neglect syndrome
temporal lobe -- agnosia (inability to recognize objects)
or prosopagnosia (inability to recognize faces)
frontal lobe -- problems with personality (inability to
plan & execute appropriate behavior)
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Memory Information management requires learning,
memory & forgetting (eliminating the trivia)pathological inability to forget have trouble with
reading comprehension
anterograde amnesia -- can not store new dataretrograde amnesia -- can not remember old data
Hippocampus is important in organizing sensory
& cognitive information into a memorylesion to it causes inability to form new memories
Cerebellum helps learn motor skills
Amygdala important in emotional memory
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Emotion
Prefrontal cortex controls how emotions areexpressed (seat of judgement)
Emotions form in hypothalamus & amygdala
artificial stimulation produces fear, anger, pleasure,love, parental affection, etc.
electrode in median forebrain bundle in rat or human
and a foot pedal
press all day to the exclusion of food (report a quiet,
relaxed feeling)
Much of our behavior is learned by rewards and
punishments or responses of others to them
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Somesthetic Sensation
Somesthetic signals travel up gracile and cuneatefascicui and spinothalamic tracts of spinal cord
Somatosensory area is postcentral gyrus
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Sensory Homunculus
Demonstrates thatthe area of the
cortex dedicated to
the sensations ofvarious body parts
is proportional to
how sensitive that
part of the body is.
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Special Senses
Organs of smell, vision, hearing & equilibriumproject to specialized regions of the brain
Locations
taste is lower end of postcentral gyrus
smell is medial temporal lobe & inferior frontal lobe
vision is occipital lobe
hearing is superior temporal lobeequilibrium is mainly the cerebellum, but to unknown
areas of cerebral cortex via the thalamus
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Sensory Association Areas
Association areas interpret sensory information
Somesthetic association area (parietal lobe)
position of limbs, location of touch or pain, and
shape, weight & texture of an object
Visual association area (occipital lobe)
identify the things we see
faces are recognized in temporal lobe
Auditory association area (temporal lobe)
remember the name of a piece of music or identify a
person by his voice
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Motor Control
Intention to contract a muscle begins in motor
association (premotor) area of frontal lobes
Precentral gyrus (primary motor area) processes
that order by sending signals to the spinal cord
pyramidal cells called upper motor neurons
supply muscles of contralateral side due to decussation
Motor homunculus is
proportional to number
of muscle motor units in
a region (fine control)
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Input to Cerebellum
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Output from Cerebellum
Smoothes muscle contractions, maintains muscle tone &
posture, coordinates motions of different joints, aids in
learning motor skills & coordinates eye movements
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Language
Includes reading, writing, speaking &understanding words
Wernickes area permits recognition of spoken
& written language & creates plan of speechangular gyrus processes text into a form we can speak
Brocas area generates motor program for
larynx, tongue, cheeks & lipstransmits that to primary motor cortex for action
Affective language area lesions produce aprosodia
area as Brocas on opposite hemisphere
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A h i
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Aphasia Any language deficit resulting from lesions in
same hemisphere as Wernickes & Brocas areas
Lesion to Brocas = nonfluent aphasia
slow speech, difficulty in choosing words
entire vocabulary may be 2 to 3 words
Lesion to Wernickes = fluent aphasia
speech normal & excessive, but makes little sense
Anomic aphasia = speech & understanding are
normal but text & pictures make no sense
Others = understanding only 1st half of words or
writing only consonants
L li i f C b l F i
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Lateralization of Cerebral Functions
C b l L li i
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Cerebral Lateralization Left hemisphere is categorical hemisphere
specialized for spoken & written language, sequential &analytical reasoning (math & science), analyze data in linear way
Right hemisphere is representational hemisphere
perceives information more holistically, perception of spatial
relationships, pattern, comparison of special senses,
imagination & insight, music and artistic skill
Highly correlated with handedness
91% of people right-handed with left side is categorical Lateralization develops with age
trauma more problems in males since females have more
communication between hemisphere (corpus callosum is thicker