API12 THE CENTRAL NERVOUS SYSTEM (CNS)
I.
Development of the CNS
a. Cephalization
i. evolution of brain
ii. increased # neurons
b. embryonic development
i. ectoderm folds inward to form neural tube
ii. differentiation begins
iii. primary brain vesicles become secondary brain vesicles
1. forebrain
2. midbrain
3. hindbrain
iv. secondary brain vesicles
1. telencephalon
2. diencephalon
3. mesencephalon
4. metencephalon
5. myelencephlon
v. adult brain structures develop from secondary
1. cerebrum from telencephalon.
2. thalamus, hypothalamus, epithalamus from diencephalons
3. midbrain from mesencephalon.
4. pons, cerebellum from metecephalon
5. medulla oblongata from myelencephlon
c. Brain Ventricles
i. spaces within brain
ii. lined with ependymal cells
iii. lateral ventricles
1. into each hemisphere ofcerebrum
2. close
anteriorly
and
separated
by
septum
pellucidum
iv. third ventricle
1. in diencephalons
2. cerebral aqueduct connects to 4th
v. fourth ventricle
1. two lateral apertures and median aperture connect ventricle to
subarachnoid space of meninges
d. Spinal cord
i. passes through foramen magnum and continues to end in lumbar
vertebral formamen at conus medullaris
ii. central canal
1. cavity within the spinal cord
2. lined with ependymal cells
II.
Protection of the CNS
a. Bones
i. all cranial bones forming the crainial cavity
ii. vertebra
1. Vertebral canal
a. formed by stacked vertebral foramen
b. vertebral ligaments add support
b. Meninges
i. 3 connective tissue membranes
ii. function
1. covers and protects CNS
2. protects blood vessels
3. contain cerebrospinal fluid
iii. Dura mater
1. tough outer layer
2. dense connective tissue
3. epidural space in vertebral canal
iv. Arachnoid
1. delicate collage fibers
2. subarachnoid space
a. Cerebrospinal fluid and blood vessels
v. pia mater
1. thin transparent membrane that clings tightly to surface of
brain and spinal cord.
2. contains collagen and elastic fibers
c. Cerebrospinal Fluid (CSF)
i. Liquid cushion of brain and spinal cord
ii. protects from trauma
iii. nourishment
iv. equivalent to blood plasma
v. made at choroid plexus
1. capillary network at roof of third and fouth ventricle
vi. located in ventricles, central canal of spinal cord, and subarachnoid
space
vii. CSF must be produced and drained at constant rate
viii. returned to blood (veins) via dural sinuses
d. Blood brain barrier
i. helps maintain brain environment
ii. certain molecules pass freely, others do not
iii. easy pass by facilated diffusion through endothelial cells of
capillaries
1. glucose
2. essential amino acids
3. some electrolytes
4. fat soluble cross freely
a. oxygen
b. carbon dioxide
c. fats
d. alcohol
e. nicotine
f. anesthetics
g. drugs
i. toxic in newborns due to inefficient BBB
ii. to get drugs to crossBBB
iii. mannitol changes osmotic pressure of
endothelial cells and cells shrink to increase
junction and make more permeable
iv. antibiotics which cross are reserved to use to
treat bacterial mennigitis or encephalitis
I.Brain Regions
A.Cerebrum
1.Cerebral hemispheres
a.gyri-folds
b.sulci-grooves
c.fissure-deep groove
d.right and left hemispheres
(1)separated by longitudinal fissure
(2)joined by corpus callosum
e.transverse fissure
(1)between cerebrum and cerebellum
f.5 lobes divided by deep sulci
(1)frontal
(2)parietal
(3)temporal
(4)occipital
(5)insula
g.central sulcus divides frontal and parietal
h.temporal lobe is outlined by lateral sulcus
2.cerebral cortex
a.outer gray matter
(1)40% brain mass
b.concerned with conscious behavior
c.Brodmann areas
(1)map of functional regions
d.functional area classification
(1)motor
(2)sensory
(3)association
e.Right hemisphere
(1)controls left side of body
f.left hemisphere
(1)controls right side of body
g.symmetrical in structure not function
h.motor
(1)primary motor cortex
(a)precentralgyrus of frontal lobe
(b)conscious movement of Sk M
(c)axons down spinal cord
i)pyrimidal tracts
ii)large cell bodies in brain
a)pyrimidal cells
(2)premoter cortex
(a)practiced motor skills
(b)typing
(c)musical instrument
(3)Broca's area
(a)motor speech area
(b)in only one hemisphere
(c)dominant side (usually left)
i.sensory
(1)parietal, temporal, occipital lobes
(2)primary somatosensory cortex
(a)sensory
input
from
receptors
use this cortex to tell where stimuli are
(3)visual- occipital lobe
(4)auditory - temporal lobe
(5)smell - temporal lobe ; olfactory cortex
(6)gustatory (taste) parietal
j.association areas
(1)makes association with senses and cortex
(2)analyzes
(3)prefrontal cortex
(a)complex learning(cognition)
(b)personality
(4)general interpretation area
(a)generally left hemisphere
(b)all
sensory
input
makes
and decisions here
(5)language areas
(a)Wernicks
(b)sounding out unfamiliar words
k.laterilization
in
body
conclusions
(1)one hemisphere is dominant over the other
(2)hemisphere with language is dominant
(3)left hemisphere is dominant in 90%
(a)language
(b)math skills
(c)logic
(4)right hemisphere
(a)visual spatial skills
(b)intuition
3.cerebral white matter
a.tracts
(1)myelinated fibers
(2)communication between cortex areas
(3)commissures
(c)connect areas between hemispheres
(d)corpus callosum
(4)association fibers
(a)within hemispheres
(5)projection fibers
(a)leave brain to spinal cord
(b)form ascending and descending tracts
(6)decussation of the pyramids
(a)crossing over of projection fibers so that right brain
controls muscles on left side
4.Basal nuclei (called ganglia)
(1)deep within cerebral hemispheres
(2)several nuclei
(3)influence motor function
(4)impaired nuclei results in
(a)disturbances in posture and muscle tone
(b)tremors
(c)slowness
B.Diencephalon
1.thalamus
a.superior to midbrain
b.nuclei here serve as relay stations for all sensory impulses except
smell to cerebral cortex
c.most all input comes via thalamic nuclei
d.registers conscious recognition of pain and temperature
e.some awareness of light touch and pressure
2.hypothalamus
a.inferior to the thalmus
b.connection to pituitary gland
(1)infundibulum
(a)stalk from hyothalamus to pituitary
c.production of some hormones
d.outside is mammillary bodies associated with sense of smell
e.controls and regulates visceral autonomic nervous system to
include contraction of smooth and cardiac muscle and secretion of many glands.
f.reception
and
integration
of
sensory
impulses
of
viscera
g.many functional nuclei
(1)autonomic control center
(2)emotional response
(3)body temperature regulation
(4)thirst and water balance
(5)food intake
(6)sleep/wake cycle
(7)endocrine control
h.Epithalamus
(1)roof of third ventrical
(2)choroid plexus
(a)
in 3rd ventrical
(b)production of cerebrospinal fluid
(3)pineal gland extends from epithalamus
(a)produces melatonin
(b)sleep/wake cycle regulation
C.Brain Stem
1.midbrain
a.cerebral pedunles
(1)hold up cerebrum
b.cerebral aqueduct runs through midbrain
c.nuclei involved in visual and auditory reflexs
d.substantia nigra
(1)dark color with melanin
(2)linked to basal nuclei
2.pons
a.anterior wall of 4th ventricle
b.bridge
c.conduction tracts between highter and lower
brain
centers
d.cranial nerves V, VI, VII
3.Medulla oblongata
a.most inferior
b.brain stem joins spinal cord at foramen magnum
c.forms part of wallof 4th ventricle
d.pyramids
(1)ridges seen on ventral side
(2)decussation of pyramids
e.autonomic reflex center
(1)cardiac center
(2)vasomotor center
(3)respiratory center
(4)vomitting
(5)swallowing
(6)sneezing
f.hypothalamus controls over medulla basic reflex
D.Cerebellum
1.small brain
2.inferior to occipital lobe of cerebrum
3.11% of brain mass
4.dorsal to pons and medulla
5.processes input from cerebral motor cortex,brain stem
nuclei
and sensory receptors
6.provides precise regulation of skeletal muscle
7.cerebellar hemispheres
a.connect by vermis
(1)all transverse gyri are called folia
(2)lobes
(a)anterior
(b)posterior
(c)flocculonodular
b.dentate nuclei
(1)regulates output of cerebellum
(2)compares
higher
brain
intentions
with
body's performance
c.superior cerebellar peduncle
(1)connect cerebellum and midbrane
(2)no direct contact with cerebral cortex
(3)nuclei
linked
to
cerebral
cortex
via
hypothalamus
d.middle cerebellar peduncles
(1)connects pons and cerebellum
e.inferior cerebellar peduncles
(1)connects cerebellum and medulla
E.Functional brain systems
1.limbic system
a.emotional brain
b.relates sensory input to emotion
c.hippocampus
2.reticular formation
a.nuclei projects to many areas of brain
b.acts inarousal of brain
c.Reticular Activation System RAS
(1)all
ascending
sensory
tracts
synapse
with
RAS neurons
(2)filters
out
sensory
garbage
or
background
noise
F.Disorders
1.CVA
a.cerebrovascular acident
(1)stroke
(2)ischemia
2.TIA
a.transcient ischemic attack
b.temporary impairment
3.Alzheimer's
a.progressive degeneration of brain
b.presence ofsenile plaques
c.decrease in cerebal mass
4.Aging
a.loss of neurons
b.decreased capacity to send impulses
c.decreased conduction velocity
d.degernative diseases affect sense organs
6.Parkinson's Disease
e.degeneration
of
dopamine
the substantia nigra
f.insufficient dopamine in basal nuclei
g.tremor, slowed movement, rigidity
producing
II.Spinal Cord
A.2-way conduction pathyway
B.foramen magnum to conus medullaris (tapered end)
C.3 meninges cover
1.dura mater not attached to verterae
2.epidural space
a.withfat, BV
3.between arachnoid and pia mater is CSF
4.below conus medullaris
a.meninges extend to S2
b.lumbar puncture or tap less likely
to damage spinal cord
5.filum terminale
a.extension of pia mater to attach to coccyx
D.Spinal nerves
1.31 pairs
a.from paired roots off spinal cord
b.exit intervertebral foramina to body
2.segments or enlargements in spinal cord
neurons
in
a.cervical
b.lumbar
c.cauda equina (horse's tail)
E.Anatomy
1.grooves divide into left and right
a.anterior median fissure
b.posterior median sulcus
2.gray matter (H shape)
a.draw a cross section of the spinal cord
b.gray commissure
(1)enclsoes central canal
c.horns
(1)osterior horns
(2)anterior ventral horns
(3)lateral horns
(a)additional
in
thoracic
lumbar regions
d.amount of gray matter related to amount of SK M
3.signal goes out
a.ventral roots
b.to SK M
c.efferent fibers
4.signal enters CNS
a.dorsal rots
b.sensory input
c.afferent fibers
d.cell bodies in dorsal root ganglia
5.Dorsal and Ventral roots fuse
a.form spinal nerves
b.mixed nerves with both sensory and motor function
6.White matter
a.outside, unlike cerebral cortex
b.tracts
(1)myelinated and unmyelinated processes
(2)ascending
(a)sensory in from spinal cord to brain
(3)descending
(a)motor from brain to spinal cord
(4)tracts may also be across spinal cord
(5)tracts cross over
(a)decussate
at
some
pont
cord
and
uper
in
spinal
c.white columns
(1)posterior funiculi
(2)lateral funiculi
(3)anterior funiculi
(4)each column has several tracts
d.neurons may be chain of 2 or 3
(1)place in chain
(a)first,second or third order
e.examples of tracts
(1)spinothalamic
(a)ascending
(b)pain,temp,deep pressure
(2)pyramidal tracts
(a)descending
(b)motor impulses from cerebrum to SKM
F.Disorders
1.paralysis
a.loss of motor function
b.flacid paralysis
(1)damage at ventral root
(2)nerve impulses do not reachmuscle
c.spastic paralysis
(1)damage at upper neuron
(2)muscle stimulated by spinal reflexes
d.location of damage
(1)paraplegia
(a)T1-L1
(2)quadraplegia
(a)cervical reion
(b)paralysis of all 4 limbs
2.spina bifida
a.incomplete formation of vertebral arches at
lumbosacral region
b.lamina and spinous processes missing
III.Diagnostics for CNS
A.reflex tests
1.to asses neural function
a.patellar reflex
B.Cerebral angiogram
1.inject radioopaque dye
2.assess arteries from neck (Carotids)
3.view arteries for arteriosclerosis or clots
4.following TIA or stroke