Transcript The Central Nervous System

The Central Nervous System
Honors Biology Chapter 12
CNS
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brain & spinal cord
cephalization: concentration of sense organs
and nervous control at the anterior end of
the body, (rostral end) forming a head and
brain, both during evolution and
development of embryo
Embryonic Development of CNS
brain & spinal cord begin as embryonic
structure called the neural tube
 as neural tube forms rostral end expands 
3 primary brain vesicles
1. Prosencephalon: forebrain
2. Mesencephalon: midbrain
3. Rhombencephalon:hindbrain
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remaining caudal portion  spinal cord
Secondary Brain Vesicles
develop from the 3 primary vesicles
1. Forebrain  cerebral hemispheres, basal
nuclei & the diencephalon (thalamus,
hypothalamus, epithalamus, retina)
2. Midbrain does not divide
3. Hindbrain  brain stem, cerebellum
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https://www.youtube.com/watch?v=Cu4lQ
YbOzzY
Development of the Brain
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Brain grows more rapidly than the
membranous skull surrounding it causing
folding to occupy available space
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http://www.hhmi.org/biointeractive/develo
pment-human-embryonic-brain
Ventricles of the Brain
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spaces in brain filled with
CSF
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are continuous w/each other
connected to subarachnoid
space (around brain &
spinal cord) and central
canal of spinal cord
paired lateral ventricles
3rd ventricle
4th ventricle
Lateral Ventricles
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anteriorly are very close separated only by a
thin membrane called the septum pellucidum
each communicates with 3rd ventricle via
channel called interventricular foramen
3rd Ventricle
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continuous with 4th ventricle through canal-like
cerebral aqueduct which runs through midbrain
4th Ventricle
continuous with central canal of spinal cord
inferiorly
 3 openings which connect this ventricle to the
subarachnoid space (fluid-filled space
surrounding brain & spinal cord
 1.median apeture in roof
2 & 3: paired lateral apertures on sides
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CSF: Cerebral Spinal Fluid
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forms liquid cushion in & around brain & spinal
cord
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gives buoyancy to brain reducing its weight by 97%
prevents injury to delicate nervous tissue from trauma
provides nourishment
carries chemical signals from 1part of brain to another
clears waste products or unnecesssary solutes
watery broth similar to blood plasma with less
protein & a different ion composition
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> Na+, Cl-, H+
< Ca++ and K+
Choroid Plexus
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hangs from top of each ventricle
broad, thin-walled capillaries
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leaky capillaries
filter fluid from blood  CSF
CSF
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volume in adults ~150 mL (4 oz)
replaced every8 hrs forming ~500 mL/day
moves freely thru ventricles  subarachnoid
spaces (4th ventricle) where it bathes outer
surfaces of brain & spinal cord  returns to
blood in the dural sinuses via arachnoid villi
Brain: unremarkable appearance
~ 3 lbs
4 major regions
1. Cerebral Hemispheres: Gross Structures
right & left connected by large fiber
tract: corpus callosum
 cover most of other 3 parts (83% of total
brain mass)
 surface: elevated ridges = gyri separated
by shallow grooves = sulci
 fissures deeper grooves separate regions
of brain
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Gyri, Sulci, & a Fissure
Longitudinal Fissure
separates cerebral hemispheres
 other fissures separate brain into lobes
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Cerebral Cortex
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“conscious mind”
 awareness, memory, communication,
understanding, initiation of voluntary
movements
composed of gray matter
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neuron cell bodies with associated glial cells,
dendrites, blood vessels, (no fiber tracts)
~40% of total brain mass
convolutions triple its surface area
Gray Matter of the Brain
PET Scans
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Positron Emission Tomography
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using radioactive tracer to show activity in
brain
MRI of Brain
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reveals blood flow
Lobes of the Cerebral Cortex
The Brain’s Functional Areas
1.
2.
3.
Motor Areas
Sensory Areas
Association Areas
3 Functional Areas of Cerebral Cortex
Motor Areas
Primary(Somatic) Motor Cortex
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control precise or skilled voluntary
movements of skeletal muscles
long axons form voluntary motor tracts called
pyramidal or corticospinal tracts
Premotor Cortex
2.
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anterior to precentral gyrus
planning of movements/ coordination of
different muscle groups
Motor Areas continued
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3. Broca’s Area
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anterior to inferior region of premotor area
usually only in left hemisphere
directs muscles involved with speech (becomes
active even when thinking of saying something)
4. Frontal Eye Field
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partially in & anterior to premotor cortex/
superior to Broca’s
controls voluntary motion of the eyes
Humunculus: Primary Motor Cortex
Homeostatic Imbalances
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1◦ Motor Cortex
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damage  paralysis of area
motor tracts cross so damage to left motor
cortex  paralysis on right
Premotor Cortex
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loss of motor skills programmed by region
damaged
does not impair muscle strength or ability to do
the activity just the agility or speed (activity can
be re-learned by using undamaged neurons in
area)
Sensory Areas
Primary Somatosensory Cortex
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1.
2.
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in postcentral gyrus (just posterior to 1◦ motor
cortex)
neurons receive info from:
general (somatic) sensory receptors
proprioceptors in skeletal muscles, joints &
tendons
spatial discrimination: identification of area
being stimulated
Humunculus:Primary Somatosensory
Sensory Areas continued
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2. Somatosensory Association Cortex
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lies posterior to 1◦ Somatosensory Cortex
integrates sensory inputs (from #1) & makes
sense of info
3. 1◦ Visual Area
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extreme posterior tip of occipital lobe& deep
w/in the occipital lobe
receives info from retina
optic tracts partially cross so there is a
contralateral map
Sensory Areas continued
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4. Visual Association Area
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surrounds 1◦ Visual Cortex
uses past visual experiences to interpret visual
stimuli
complex visual processing involves entire
posterior ½ of hemispheres
5. 1◦ Auditory Cortex
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superior margin of temporal lobe
receives impulses from inner ear
interpret pitch, loudness, & location
Sensory Areas continued
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6. Auditory Association Area
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posterior to #5
storage of memories of sound
Sensory Areas continued
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7. Vestibular Cortex
posterior part of insula & adjacent parietal
cortex
 conscious awareness of balance & position of
head
8. Olfactory Cortex
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medial aspect of temporal lobe
 afferent fibers from smell receptors  olfactory
tract  here
 conscious awareness of odors
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Sensory Areas continued
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8. Gustatory Cortex
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insula deep to temporal lobe
perception of taste
9. Visceral Sensory Area
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just posterior to gustatory cortex in insula
conscious awareness of visceral sensations
(nausea, feeling your bladder is full)
Homeostatic Imbalances of 1◦ Visual Cortex
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damage results in functional blindness
in contrast a damaged visual association
area  can see but cannot interpret what
they see
Lateralization of Cortical Functioning
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division of labor in cerebral hemispheres:
cerebral dominance: designates the
hemisphere that is dominant for language
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~90% people have left dominance
~10%: right dominance or equally functioning
generally: rt dominance people are males & left
handed / equally functioning: ambidexterous
2 hemispheres instantly communicate via
connecting fiber tracts
Cerebral White Matter
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internal to gray matter
responsible for communication w/in brain &
between brain and lower CNS centers
(brainstem & spinal cord)
consists mainly of myelinated fibers
bundled into large tracts
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classified (#3)according to direction in which
they run
Association Fibers
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connect different parts of same hemisphere
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short: connect adjacent gyri
long: bundled into tracts connecting different
lobes
Commisural Fibers
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connect corresponding gray areas of the 2
hemispheres
Corpus Callosum: largest commissure
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superior to lateral ventricles , deep w/in
longitudinal fissure
anterior & posterior commissures: smaller
Projection Fibers
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enter cerebral cortex from lower brain or
cord centers or descend from cortex to lower
areas
sensory info reaches cortex & motor output
leaves cortex thru these tying cortex to rest
of nervous system
run vertically
Basal Nuclei (Ganglia)
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group of subcortical gray matter
receive input from entire cerebral cortex &
each other thru thalamus
functions:
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motor: starting, stopping, & monitoring
intensity of movements
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disorders: Huntington’s chores (too much
movement) Parkinson’s (too little movement)
cognition
emotion
Diencephalon
forms central core of forebrain
 3 paired structures:
1. Thalamus
2. Hypothalamus
3. Epithalamus
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Thalamus
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bilateral egg-shaped nuclei joined (in most
people) by intermediate mass
form superolateral walls of 3rd ventricle
information received (motor, sensory,
cortical arousal, learning, memory) is
sorted, “edited”, then relayed via internal
capsule to specific cortical association areas
allows for stimulus localization &
discrimination
Thalamus
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relay station for sensory impulses
passing thru to sensory cortex
Hypothalamus
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below thalamus
caps brain stem forming inferrolateral walls
of 3rd ventricle
extends from optic chiasma (crossover point
of optic nerves)  mammary bodies (nuclei
that bulge anteriorly from hypothalamus &
are relay stations in olfactory pathway)
infundibulum: stalk of hypothalamus that
connects to pituitary gland
Hypothalamus Functions
main visceral control center of body
(homeostasis)
1. controls ANS
2. initiates physical response to emotions
3. regulates body temperature
4. regulates food intake
5. regulates sleep/wake cycles
6. controls endocrine function
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Epithalamus
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most dorsal part of diencephalon
forms roof of 3rd ventricle
includes Pineal Gland (pineconeshaped)which secretes melatonin which is
released in response to darkness  helps
regulate sleep cycle
Brain Stem
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3 major regions
1.
2.
3.
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Midbrain
Pons
Medulla Oblongata
connects brain to spinal cord
Midbrain
smallest, uppermost part of brain stem
 cerebral aquaduct: tiny canal that runs
thru midbrain connecting 3rd & 4th
ventricles
 contains reflex centers for vision,
hearing
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Midbrain
Pons
“bridge”
 rounded structure that protrudes below
midbrain
 contains apneustic (produces deep,
prolonged inspirations) & pneumotatic
center (inhibits inspiration)
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Medulla Oblongata
most inferior part of brain stem
 with the pons form the ventral wall of 4th
ventricle
 inferior border merges into spinal cord
 site where corticospinal tracts cross
 centers: heart rate, BP, breathing,
swallowing, vomiting
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Cerebellum
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“small brain”
~11% brain mass
dorsal to pons & medulla protruding under
occipital lobe (separated by transverse
cerebral fissure)
Functions: (all unconscious)
1.
2.
processes input from motor cortex, brain stem
nuclei, & sensory receptors
provides timing & patterns of skeletal muscle
allowing smooth, coordinated movements &
agility
Cerebellar Anatomy
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bilaterally symmetrical
vermis (worm-like)connects the 2 cerebellar
hemispheres
surface is convoluted with pleat-like gyri
called folia (“leaves”)
thin outer cortex of gray matter, internal
white matter with small, deeply situated
paired masses of gray matter: dendate
nuclei
Purkinje Cells
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large cells with extensively branched
dendrites called arbor vitae
*only cortical neurons that send axons
through white matter to synapse with
central nuclei in cerebellum
Ataxia
loss of ability to control body movements
 occurs with damage to cerebellum
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cannot touch finger to nose with eyes closed
have trouble keeping balance
appear drunk
Limbic System
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group of structures in medial aspect of each
cerebral hemisphere & diencephalon
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encircle upper brain stem (limbus = ring)
includes:
1. amygdaloid body
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important in emotions
hypothalamus
fornix :
2.
3.
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fiber tract connecting limbic regions
cingulate gyrus
4.
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important in expressing emotions thru gestures &
resolving mental conflicts when frustrated
The Emotional Brain (Limbic System)
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odors often trigger emotions/memories
due to extensive connections with lower&
higher regions of brain its able to respond to
a variety of stimuli
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connections with frontal lobe account for
intimate relationship between feelings &
thought
output from limbic system  hypothalamus
psychosomatic illnesses: emotion-induced
illness
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example: stress headaches, high blood pressure
The Reticular Formation
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loosely clustered neurons in white matter
extending through central portion of
brainstem
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their axons  diencephalon, cerebral cortex,
cerebellum, spinal cord
Reticular Activating System or RAS sends
continuous stream of impulses to cerebral
cortex
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keeps cortex alert & conscious
filters ascending sensory information but sends
unusual, significant, or strong impulses to
reach awareness
Reticular Activating Center
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inhibited by:
1.
2.
3.
4.
5.
sleep centers(hypothalamus, epithalamus))
alcohol
sleep-inducing drugs
tranquilizers
irreversible coma (twisting injury to brainstem)
Reticular Activating Center continued
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motor function: helps control skeletal
muscles during coarse limb movements
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autonomic functions: vasomotor, cardiac,
respiratory centers (medulla)  regulate
visceral motor functions
EEG
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electroencephalogram: recording of electrical
activity of brain
electrodes placed on scalp measure
voltage differences between different cortical
areas
patterns called brain waves: generated by
synaptic activity at surface of cortex
Normal EEG
EEG during a Seizure
Epilepsy
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Seizures: reflect a torrent of electrical
charges by groups of brain neurons
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while happening no other messages can get
through
1% of world population affected
causes: head trauma, tumor, stroke,
infection, metabolic, fever
Types of Epilepsy
Absence / Petit Mal
1.
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mild form: patient gets blank expression for
few seconds
unconscious during this
most commonly seen in young children, often
resolve when >10 yo
Tonic-Clonic/ Grand Mal
2.
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most severe
loss of consciousness, possibly injure self, loss
of bowel/bladder, biting of tongue
Aura of Seizures
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many epileptics experience a sensory
hallucination (smell, flashes of light, taste)
just prior to onset
Epilepsy Treatment
Anticonvulsants
1.
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various drugs
may require >1
Vagus Nerve Stimulator or Deep Brain
Stimulator
2.
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possible treatment options if drugs fail
deliver pulses to vagus nerve or directly to the
brain in effort to stabilize brain’s electrical
activity
Protection of the Brain
Nervous tissue: very delicate and easily
damaged
 Protection:
1. Skull
2. Meninges (membranes)
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3.
cover &protect the CNS
protect blood vessels & enclose venous sinuses
contain CSF
form partitions in the skull
CSF
Meninges
3 layers:
1. Dura Mater
2. Arachnoid Mater
3. Pia Mater
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Dura Mater
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“tough mother”
tough, leathery, fibrous CT
surrounds brain in 2 layers
Dura Septa: #3,extend inward to form flat
partitions that subdivide the cranial cavity
1.
2.
3.
Falx cerebri: dips into longitudinal fissure
between hemispheres
Falx cerebelli: along vermis of cerebellum
Tentorium cerebelli: horizontal fold extends
between cerebellar hemispheres
Arachnoid Mater
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web-like
projections span subarachnoid space & attach
to pia mater
subarachnoid space filled with CSF
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spinal taps insert needle into this space between
lumbar vertebrae to either;
1. withdraw fluid for analysis
2. inject anesthetic (spinal anesthesia)
3. inject medications that cannot cross blood brain
barrier (bbb)
Pia Mater
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“gentle mother”
delicate CT layer clinging tightly to brain
and spinal cord
Meningitis
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inflammation of meninges
bacterial or viral
could spread to brain tissue
diagnosed by spinal lumbar tap &
examining for WBC’s and microbes
Blood Brain Barrier
protective mechanism that helps maintain a
stable environment for the brain
 all blood-borne substances in capillaries in
brain must pass through 3 layers b/4
reaching neurons:
1. endothelium of capillary: held together by
tight jcts  key to BBB
2. relatively thick basal lamina surrounding
capillary
3. astrocytes clinging to cappilary
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BBB
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selective barrier
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pumps removing
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allows fats, fatty acids, O2, CO2, other small,
fat-soluble molecules
K+
nonessential amino acids
passing via facilitated diffusion:
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glucose
essential amino acids
some electrolytes
BBB
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absent in tissue around 3rd & 4th ventricles
examples:
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Vomiting Center
 monitors blood for poisonous substances
Hypothalamus
 monitors: temperature, water balance, other
metabolic activities
Traumatic Brain Injuries (TBI)
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head injuries are leading cause of accidental
death in North America
victim suffers a coup and a contra-coup
Concussion
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alteration in brain function, usually
temporary, following a blow to the head
multiple concussions over time can produce
cumulative damage
symptoms:
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+/- dizziness
+/- loss of consciousness
Brain Contusion
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bruising of brain tissue
+/- remain conscious if injury in brain
if involves brain stem  coma (hours to
lifetime) depending on damage to RAS
Subdural or Subarachnoid Hemorrhage
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injury that involves bleeding from ruptured
vessels in spaces betwee dura mater &
arachnoid mater or between arachnoid
mater and pia mater
treatment: surgically removing hematoma
& repairing ruptured vessels
Cerebral Edema
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swelling of the brain
usually associated with contusion but also
2◦ to infection
Cerebral Vascular Accidents (CVA)
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strokes
single most common nervous system
disorder and the #3 cause of death in North
America
occur when blood circulation to area of
brain is blocked  tissue dies
#1 cause: blood clots block a cerebral artery
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clot could form inside brain artery or travel to
brain
less commonly CVA 2◦ to bleeding within brain
causing compression
Transient Ischemic Attacks
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TIA’s or “minnie strokes”
temporary episodes of reversible brain
ischemia ( deprivation of blood supply to any
tissue)
characterized by temporary:
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numbness or tingling
paralysis
impaired speech
Alzheimer’s Disease
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progressive degenerative disease of brain
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~50%nursing home patients
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leads to dementia
5- 15% > 65 yo / ~50% >85 yo
Symptoms:
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memory loss: past > recent
shortened attention span
disorientation
eventually loss of language
confusion, irritability
+/- hallucinations
Alzheimer’s Disease
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Pathology:
extracellular plaques of amyloid
 1 form ass’c with gene mutation (codes for
precursor molecule to amyloid)
 Prion (infective protein) may
1. neurofibillary tangles inside neurons
 eventually kill neuron  brain shrinks
1.
AD Pathology
Parkinson’s Disease
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50 -60 yo’s
Cause: unknown
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degeneration of dopamine-releasing neurons in
substantia nigra (basal ganglion)
Symptoms:
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tremor at rest  “pill-rolling”
forward – bent walking
slow @ initiating & executing movement
Parkinson’s Treatment
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L-Dopa  crosses bbb converted to
dopamine
if not working:
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deep brain stimulation via implanted electrodes
decreases abnormal brain activity
gene therapy insert normal genes into
patient’s brain cells  secrete GABA a
inhibitory neurotransmitter (same as implants)
The Spinal Cord
Gross Anatomy
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enclosed in
vertebral column
extends from
foramen magnum 
L1-L2
Meninges
same layers as CNS
 exceptions:
1. dura mater not
attached to
vertebrae so there
is an epidural
space (between
bone & dura)
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Meninges of Spinal Cord
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other exceptions:
2. inferiorly, dural&
arachnoid layers
extend lower than
spinal cord
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cord ends ~L1 – L2
meninges extend to
upper sacrum
Conus Medullaris / Filum Terminale
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inferior border of
spinal cord ends in
cone-shaped point
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fibrous extension of
conus, covered by pia
mater extends from
conus to coccyx
where it anchors the
spinal cord
pegs of pia mater
called denticulate
ligaments secure cord
to dura materthrough
out its length
Spinal Nerves (PNS)
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31 pair attach to cord by “roots”
nerves exit cord passing superior to its
corresponding vertebra  part of body it
innervates
Spinal Cord Enlargements
Cauda Equina
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collection of nerve roots @ inferior end
spinal cord
Transverse Section of Spinal Cord
2 grooves mark surface:
1. ventral median fissure
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2.
deeper of the 2
dorsal median fissure
Gray Matter of the Spinal Cord
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butterfly shaped (or H) on cross section
lateral gray masses
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dorsal horns
ventral horns
both columns of gray matter running entire
length of cord
thoracic & upper lumbar have additional pair of
gray columns = lateral horns
crossbar : gray commissure
Neurons in the Spinal Cord
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*all neurons with cell bodies in spinal cord
are multipolar neurons
*dorsal horns: all neurons are interneurons
*ventral horns: some interneurons but
mostly somatic motor neurons  axons to
skeletal muscle via ventral roots
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larger in cervical & lumbar regions
*lateral horns contain cell bodies of
sympathetic division of ANS serving visceral
organs, axons  thru ventral root
Dorsal Roots
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carry afferent fibers from all peripheral
sensory receptors
dorsal root ganglion:
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enlargement containing cell bodies of associated
sensory neurons
their axons  enter spinal cord 
 to dorsal white matter  higher cord or brain
to synapse
 synapse with interneurons in dorsal horn
Spinal Cord Trauma
cord slightly elastic but very sensitive to
pressure
 injury results in:
1. paralysis: loss of motor control
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flaccid paralysis: motor neurons do not send
impulses to skeletal muscle  no voluntary or
involuntary movement
spastic paralysis: when only 1° motor cortex
neurons damaged loss of voluntary control
but still have spinal reflexes
paresthesias
2.
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abnormal sensations
Transection of Spinal Cord
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spinal shock: transient period of functional loss
following injury (most recover w/in 48 hrs, rest
permanent paralysis)
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depression of all reflexes caudal to injury
BP drops
all muscles below injury paralyzed & insensitive
depends on level
T1  L1 affect upper & lower limbs =
paraplegia
any cervical level = quadriplegia
hemiplegia: paralysis one side of body due to
brain injury only
Poliomyelitis
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polio – gray matter
myelitis –
inflammation
poliovirus: destroys
ventral horn motor
neurons
Polio (poliomyelitis) mainly affects children under 5 years of
age.
One in 200 infections leads to irreversible paralysis. Among
those paralysed, 5% to 10% die when their breathing
muscles become immobilized.
Polio cases have decreased by over 99% since 1988, from an
estimated 350 000 cases then, to 359 reported cases in
2014. The reduction is the result of the global effort to
eradicate the disease.
Today, only 2 countries (Afghanistan and Pakistan) remain
polio-endemic, down from more than 125 in 1988.
As long as a single child remains infected, children in all
countries are at risk of contracting polio. Failure to
eradicate polio from these last remaining strongholds could
result in as many as 200 000 new cases every year, within 10
years, all over the world.
ALS: Amyotrophic Lateral Sclerosis
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


condition that progressively destroys ventral
horn motor neurons + fibers of the
corticospinal tracts
patient progressively loses ability to speak,
swallow, breathe
death usually w/in 5 yrs
cause: environmental + genetic factors

10% have mutation: genes involved in RNA
processing