NERVOUS SYSTEM
Chapter 7
I. OVERVIEW
A.
Three overlapping functions
1.
2.
3.
B.
Monitor changes inside and outside of the body
(sensory input)
Processes sensory input and makes decisions about
what to do (integration)
Then effects a response called a motor output
Works with the endocrine system to maintain
homeostasis
II. ORGANIZATION OF THE NERVOUS
SYSTEM
A.
Structural Classification
Central nervous system – brain and spinal cord
1.
a.
Interpret incoming sensory information and issues
instructions based on past experiences and current
conditions
Peripheral nervous system – outside of CNS
2.
a.
b.
Spinal nerves – impulse to and from spinal cord
Cranial nerves – impulse to and from brain
II. ORGANIZATION OF THE NERVOUS
SYSTEM
B.
Functional Classification
Concerned only with PNS
Sensory (afferent) division – convey impulses to the
CNS from sensory receptors
1.
2.
a.
b.
Somatic sensory fibers – from skin, skeletal, and joints
Visceral sensory fibers – from visceral organs
Motor (efferent) division – carries impulses from the
CNS to effector organs, muscles, and glands
3.
a.
b.
Somatic nervous system (voluntary nervous system) –
allows us to consciously, or voluntarily, control our
skeletal muscles (except for those reflex muscles)
Autonomic nervous system (involuntary nervous system)
– regulates events that are automatic or involuntary
i.
sympathetic and parasympathetic
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
A.
Supporting Cells
1.
Neuroglia (glia) –
literally “nerve glue”,
generally support,
insulate, and protect
a.
b.
Resemble neurons, but
not able to transmit
nerve impulses
Never lose ability to
divide, thus most brain
tumors are gliomas or
formed from neuroglia
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
c.
Astrocytes – abundant, star-shaped, nearly half of neural tissue
i.
Numerous swollen projections that cling to neurons and
anchor them to capillaries for nutrients
ii. Form a barrier between capillaries to protect the neurons
from substances in the blood
iii. Control chemical environment by picking up excess ions and
released neurotransmitters
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
d.
Microglia – spider-like
phagocytes that dispose of
debris, including dead brain
cells and bacteria
e.
Ependymal cells – line
cavities of brain and spinal
cord, cilia help to circulate
cerebrospinal fluid and
forms a protective cushion
around the CNS
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
f.
g.
Oligodendrocytes – wrap
flat extensions tightly
around nerve fibers,
producing fatty insulating
coverings called myelin
sheath
PNS supporting cells
e. Schwann cells – form
myelin sheaths
f. Satellite cells – act as
protective, cushioning
cells
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
B.
Neurons
1.
Anatomy
a.
b.
Neurons (nerve cells) – highly specialized to transmit messages
from one part of the body to another
i.
All include a cell body and one or more processes
Cell body is metabolic center of neuron containing organelles
except for centrioles
i.
Particularly abundant are
rough ER (Nissl substance),
neurofibrils, and
intermediate filaments for
cell shape
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
c.
Arm-like processes vary from microscopic to 3-4 feet
i.
Longest from lumbar region to big toe
ii. Processes conveying incoming messages are dendrites,
contains hundreds per neuron
iii. Processes generating nerve impulses are axons, only one per
neuron, arises from axon hillock
iv. Most long nerve fibers are covered with whitish, fatty
material, with a waxy material called myelin – protects,
insulates, and increases transmission rates
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
v.
Axons outside CNS are surrounded by Schwann cells which
wrap their membranes tightly around the axon, forming a
myelin sheath; the cytoplasm ends up on the outside and the
outer layer is called the neurilemma
vi.
There are gaps between the Schwann cells called nodes of
Ranvier at regular intervals
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
vii.
Myelinated fibers also found in
CNS, but formed from
oligodendrocytes, which can
coil around as many as 60
fibers with their flat
extensions, but lack a
neurilemma which means they
are not protected and cannot
regenerate
vii.
Axons occasionally give off collateral branches along its
length, but branch profusely at their terminal end to form
axonal terminals which contain hundreds of tiny vesicles, or
membranous sacs, containing neurotransmitters which are
released when stimulated; they are separated from next
neuron by a tiny gap called synaptic cleft (synapse)
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
d.
Clustered neuron cell bodies in the CNS are called nuclei, a few small
clusters outside the CNS in the PNS are called ganglia
e.
Bundles of nerve fibers running through CNS are called tracts and in
PNS are called nerves
f.
Cell body carries out most of the metabolic functions, so if it is
damaged or dies it is not replaced
g.
Regions of the CNS
i.
ii.
White matter is dense
collections of myelinated
fibers
Gray matter is mostly
unmyelinated fibers and cell
bodies
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
2.
Homeostatic Imbalance
a. Importance of myelin sheaths is seen in people with
multiple sclerosis (MS)
i.
3.
Myelin sheaths are gradually destroyed, converted to
hardened sheaths (scleroses) and when this happen the
electrical current is short-circuited, which causes loss of
muscle control and they become increasingly disabled
Classification
a. Functional Classification
i.
Groups neurons according to the direction the nerve
impulse is traveling
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
ii.
Sensory neurons – cell body found outside the CNS in a
ganglion, dendrite endings have specialized receptors that are
activated by changes nearby
a) Complex receptors of special sense organs (vision, hearing,
equilibrium, taste, and smell)
b) Skin – cutaneous sense organs, extreme heat, cold or
excessive pressure can be interpreted as pain
c)
Muscles and tendons – proprioceptors, detect amount of
stretch or tension so proper adjustments can be made to
maintain balance and normal posture
d) Pain – bare dendrite endings, most numerous
iii.
Motor neurons – carry nerve impulses from CNS to viscera,
muscles, and/or glands, cell bodies are always located in CNS
iv.
Associations neurons (interneurons) – connect motor and
sensory neurons, cell bodies always located in CNS
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
Structural classification – based on number of processes
extending from the cell body
b.
i.
ii.
Multipolar neuron – several processes, most common
structural type, include all motor and association neurons
Bipolar neurons – two processes (axon and dendrite), rare in
adult, only in special sense organs (eye, ear)
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
iii.
Unipolar neurons – single process, very short and divides
almost immediately into proximal (central) and distal
(peripheral) fibers; only the small branches at the end of the
peripheral process are dendrites, remainder act as axons
a) Conduct nerve impulses toward and away from the cell body,
included are sensory neurons in the PNS ganglia
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
4.
Physiology
a. Nerve impulses – two major functions
i.
Irritability - the ability to respond to a stimulus and
convert it into a nerve impulse
a)
A neuron is polarized when it is resting, or inactive;
this also means that there are fewer positive ions inside
the plasma membrane than out
b)
Ions inside are K+ and ions outside are Na+, and as long
as the inside remains more negative the neuron stays
inactive
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
c)
Nerves are excited by many
different types of stimuli, but
most of the neurons in the body
are excited by neurotransmitters
released by other neurons
d)
Nerve impulses are an all-ornone response and either
happens over the whole axon or
not at all
e)
When a neuron is adequately
stimulated, the “sodium gates”
open and Na+ quickly diffuses
into the neuron, changing the
polarity of the membrane; this
process is called depolarization
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
f)
If this stimulus is strong
enough, and there’s a large
enough Na+ in-rush, then
depolarization activates the
neuron to initiate and
transmit an action potential
(nerve impulse)
g)
Once Na+ ions rush in the
membrane permeability
changes again and is no
longer permeable to Na+,
but permeable to K+, which
diffuse out and the
electrical charge is restored;
this is called repolarization
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
h)
Until repolarization occurs there cannot be another nerve
impulse conducted
i)
The initial concentrations must still be restored, so the Na-K
pump is activated, which uses ATP
j)
This nerve impulse is along unmyelinated fibers
k)
Nerve impulses occur much faster though down myelinated
fibers because it leaps from node to node since the current
cannot flow across myelin insulation – this is called saltatory
conduction
Nerve Impulses
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
ii.
Conductivity – the ability
to transmit the nerve
impulse to other neurons,
muscles, or glands
a)
Impulses from one
neuron travel across the
synapse to another by
means of a
neurotransmitter
b)
Dendrite of the next
neuron receives the
neurotransmitter and
an action potential is
then started
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
iii.
Homeostatic Imbalance – impact on conduction of impulses
a)
b)
alcohol, sedatives, and anesthetics all reduce membrane
permeability
Cold and continuous pressure interrupt blood circulation, so
after warming up or pressure removed then prickly feeling
comes when impulses are transmitted again
III. NERVOUS TISSUE: STRUCTURE
AND FUNCTION
Reflex arc – direct route from a sensory neuron, to an
interneuron, to an effector
b.
Reflexes are rapid, predictable, and involuntary responses to
stimuli that always travel in the same direction
ii. Autonomic reflexes regulate the activity of smooth muscles,
the heart, and glands, saliva, eye pupils, digestion,
elimination, blood pressure, sweating
iii. Somatic reflexes are all reflexes that stimulate skeletal
muscles
i.
IV. CENTRAL NERVOUS SYSTEM
A.
Composed of brain
and spinal cord
1.
During embryonic
development, appears
as a simple tube
(neural tube) that
extends down the
dorsal median plane,
and by the fourth
week the anterior
end begins to expand
and brain formation
begins
IV. CENTRAL NERVOUS SYSTEM
B.
Functional Anatomy of the Brain
Opening of the neural tube becomes the four
chambers of the brain called ventricles, filled with
cerebrospinal fluid (CSF)
2. Cerebral hemispheres – paired, superior part of the
brain, larger than all other regions combined
1.
IV. CENTRAL NERVOUS SYSTEM
a.
Surface has ridges called
gyri seperated by shallow
grooves called sulci, and
few deeper grooves called
fissures that separate
large regions of the brain
i.
these all serve as
landmarks
ii. Single, deep fissure
(longitudinal fissure)
separates hemispheres
iii. Other fissures or sulci
divide hemispheres into
lobes named for cranial
bones that lie over them
IV. CENTRAL NERVOUS SYSTEM
IV. CENTRAL NERVOUS SYSTEM
b.
Parietal lobe lies posterior
to the central sulcus and is
home to the somatic
sensory area
i.
all of the body’s sensory
receptors (except special
senses) are localized and
interpreted here, and all
of the pathways are
upside-down and
backwards
IV. CENTRAL NERVOUS SYSTEM
c.
Frontal lobe lies anterior to
the central sulcus and is
home to the primary motor
area
i.
Axons of these motor
neurons form major
voluntary motor tract –
the pyramidal, or
corticospinal tract, which
descends to the cord
ii. Like the somatic sensory
cortex, all of the
pathways are upsidedown and backwards
IV. CENTRAL NERVOUS SYSTEM
iii.
iv.
Broca’s area is involved in the ability to speak, damage causes
inability to say words properly
Higher intellectual reasoning located in anterior of frontal lobe,
and language comprehension
d.
Speech area is at the
junction of temporal,
parietal, and occipital
lobes, it allows you to
sound out words
e.
Cell bodies of neurons
involved in cerebral
hemisphere functions
are found only in the
outermost gray matter –
the cerebral cortex
IV. CENTRAL NERVOUS SYSTEM
f.
g.
Most of the remaining
cerebral hemisphere –
cerebral white matter – is
composed of fiber tracts
carrying impulses to/from
the cortex
i.
Corpus callosum – large
fiber tract connecting
cerebral hemispheres
Basal nuclei – islands of
gray matter deep in white
matter, help regulate
voluntary motor activities
by modifying instructions
sent to the skeletal muscles
by the primary motor cortex
IV. CENTRAL NERVOUS SYSTEM
1. Cerebral hemisphere
2.Corpus callosum
3.Thalamus
4.Midbrain
5.Pons
6.Cerebellum
7.Medulla oblongata
IV. CENTRAL NERVOUS SYSTEM
3.
Diencephalon
(interbrain) – sits atop
brain stem and enclosed
by cerebral hemispheres
a.
Thalamus – encloses
shallow third ventricle,
relay station for sensory
impulses passing to
sensory cortex and
recognizes whether the
impulse in pleasant or
unpleasant
IV. CENTRAL NERVOUS SYSTEM
Hypothalamus makes up
floor of diencephalon, plays
role in regulation of body
temperature, water balance,
and metabolism
b.
Also center for many drives
and emotions, called limbic
system – thirst, appetite, sex,
pain, and pleasure centers
ii. Regulates pituitary gland or
hypophysis (endocrine organ)
iii. Mammillary bodies involved
in olfaction (smell) bulge
from floor
i.
IV. CENTRAL NERVOUS SYSTEM
c.
4.
Epithalamus – roof of third
ventricle, includes pineal body
(endocrine) and choroid plexus
(knots of capillaries in each
ventricle that form the CSF)
Brain Stem – about the size of
a thumb in diameter and
about 3 inches long
a.
Pathway for tracts, many
small gray matter areas,
control vital activities such
as breathing and blood
pressure
IV. CENTRAL NERVOUS SYSTEM
b.
Midbrain – small part of brain
stem
Cerebral aqueduct is a tiny
canal that travels through
the midbrain and connects
the third and fourth ventricle
ii. Cerebral peduncles – two
anteriorly bulging fiber
tracts which convey
ascending and descending
impulses
iii. Corpora quadrigemina – four
rounded dorsal protrusions,
these are reflex centers
involved with vision and
hearing
i.
IV. CENTRAL NERVOUS SYSTEM
c.
Pons – means bridge, rounded structure
protruding just below midbrain, mostly
fiber tracts, nuclei for breathing
d.
Medulla oblongata – most inferior of
brain stem, merges into spinal cord,
fiber tract area, control center for heart
rate, blood pressure, breathing,
swallowing, vomiting, and others
e.
Reticular formation – extends length of
brain stem, diffuses mass of gray
matter, involved in motor control of
visceral organs
i.
Reticular activating system (RAS)
plays a role in consciousness and the
awake/sleep cycles and damage to
this area can result in coma
IV. CENTRAL NERVOUS SYSTEM
5.
Cerebellum – large, cauliflower-like
projection dorsally from under
occipital lobe of cerebrum
Much like cerebrum – two
hemispheres, convoluted surface,
outer cortex of gray matter and
inner white matter
b. Provides precise timing for
skeletal muscle activity and
controls balance and equilibrium
c. Fibers come here from the
equilibrium apparatus of the inner
ear, the eye, the proprioceptors,
and other areas
a.
IV. CENTRAL NERVOUS SYSTEM
C.
Protection of the Central Nervous System
1.
Meninges – three connective tissue membranes
covering and protecting the CNS
a.
Dura mater – leathery, outermost layer, double-layered
membrane surrounding the brain
i.
One layer is attached to the inner surface of the
skull forming the periosteum
ii.
Other layer is outermost covering of the brain that
continues as the dura mater of the spinal cord,
called meningeal layer
iii. Fused together except where they separate to
enclose dural sinuses (collects venous blood)
iv.
Dural sinuses fold inward in several places to
attach brain to cranial cavity – falx cerebri and
tentorium cerebelli
IV. CENTRAL NERVOUS SYSTEM
IV. CENTRAL NERVOUS SYSTEM
b.
c.
Arachnoid mater – web-like middle meningeal layer
i.
Thread-like extensions span subarachnoid space, which is
filled with CSF, and attach to pia mater
ii.
Arachnoid villi – protrude through dura mater, CSF
absorbed into venous blood in dural sinuses
Pia mater – delicate, innermost membrane, clings tightly to
surface of brain following every fold
IV. CENTRAL NERVOUS SYSTEM


Pneumococcal
meningitis in an
alcoholic patient.
Head opened at autopsy
revealing purulent
inflammation of
leptomeninges beneath
reflected dura mater.
IV. CENTRAL NERVOUS SYSTEM
2.
Cerebrospinal Fluid – similar to blood plasma, but less
protein, more vitamin C, and different ion composition
a.
b.
c.
d.
e.
Continually formed from blood by choroid plexuses, which
are capillaries hanging from the top in each ventricle
Continually moving by circulating through lateral ventricles
in cerebral hemispheres, third ventricle (diencephalon), and
fourth ventricle (brain stem)
Some fluid reaching fourth ventricle travels down central
canal of spinal cord, but most stays in subarachnoid space
which leaves through holes in fourth ventricle
Fluid is recycled through arachnoid villi into blood in the
dural sinuses
Normal volume is about 150 mL or ½ cup
IV. CENTRAL NERVOUS SYSTEM
f.
Any changes in CSF can indicate a problem in brain or spinal
cord, and a sample can be obtained through a lumbar (spinal)
tap, and checked for blood cells
g.
Since the fluid is decreased with this test, patient must remain
horizontal for 6 – 12 hours to prevent a headache
IV. CENTRAL NERVOUS SYSTEM
IV. CENTRAL NERVOUS SYSTEM
3.
Hydrocephalus
a.
b.
c.
d.
If the CSF cannot drain it accumulates and causes pressure on the
brain, this is called hydrocephalus, which literally means water on
the brain
In babies the head enlarges to allow for the extra spinal fluid
because of the soft bones
In adults though the condition can lead to brain damage because of
hardened skull
A shunt to drain excess fluid is then placed
IV. CENTRAL NERVOUS SYSTEM
4.
The Blood-Brain Barrier
a.
b.
c.
Separates neurons from blood-borne substances, composed of
least permeable capillaries in the whole body which provide
most of the protection and the astrocytes help with this
Only water, glucose, and essential amino acids pass easily,
but urea, toxins, proteins, and most drugs are prevented
from entering
Useless against fats, respiratory gases, and other fat-soluble
molecule (alcohol, nicotine, anesthetics)
IV. CENTRAL NERVOUS SYSTEM
D.
Brain Dysfunctions
1.
Traumatic Brain Injuries
a.
b.
c.
d.
Leading cause of accidental
death in US
Concussion – slight brain
injury, cause dizziness and
brief loss of consciousness but
no permanent brain damage
Contusion – result of marked
tissue destruction
Hemorrhage or cerebral
edema – individuals usually
alert then deteriorate
neurologically, caused from
compression of vital brain
tissue
IV. CENTRAL NERVOUS SYSTEM
2.
Cerebrovascular Accident (CVAs) – strokes
a.
b.
c.
d.
e.
Third leading cause of death in the US
Occur when blood circulation to a brain area is blocked by clot,
rupture, or tissue dies
Area of brain damage can be determined by patient’s symptoms
Fewer than 1/3 of those that survive are alive three years later, but
not hopeless, undamaged neurons take over some of the lost
function
Not all strokes are “completed”, result in
temporary restriction of blood flow called a
transient ischemic attack (TIA) that last
from 5 to 50 minutes, these are red flags
though for impending more serious CVAs
IV. CENTRAL NERVOUS SYSTEM
Spinal Cord
E.
1.
2.
3.
4.
5.
Approximately 17 inches long, glistening white continuation
of brain stem
Provides two-way conduction pathway to/from brain
Only extends to the 1st/2nd lumbar vertebrae because it grows
slower than vertebral column, spinal nerves at inferior end
are called cauda equina
Cushioned and protected by
meninges, which continue
past end of spinal cord
31 pairs of spinal nerves
arise from cord
IV. CENTRAL NERVOUS SYSTEM
6.
Gray Matter of the
Spinal Cord and Spinal
Roots
a.
b.
Gray matter looks like a
butterfly or “H” in cross
section, posterior
projections are
posterior/dorsal horns,
anterior projections are
anterior/ventral horns
Surrounds the central
canal of the cord
IV. CENTRAL NERVOUS SYSTEM
c.
d.
e.
Cell bodies of sensory neurons, whose fibers enter the cord by the
dorsal root, are found in an enlarged area called the dorsal root
ganglion
i.
If damaged then sensation from the body area will be lost
Ventral horns of gray matter contain
cell bodies of motor neurons of the
somatic system extend their axons
out of the ventral root
i.
If damaged then flaccid paralysis
results and voluntary movement is
impossible and will begin to
atrophy
Dorsal and ventral roots fuse to form
spinal nerves
IV. CENTRAL NERVOUS SYSTEM
7.
White Matter of the Spinal Cord
a.
b.
8.
Composed of myelinated fiber tracts
Because of irregular shape of gray matter, white matter
divided into three regions
i.
Posterior column – ascending tracts that carry sensory
input to the brain
ii.
Lateral and anterior columns – contain ascending and
descending motor tracts
Homeostatic Imbalance
a.
b.
c.
Transection or crushing of the cord results in spastic
paralysis where affected muscles stay healthy because of
reflex arcs, meaning movements are involuntary
Quadriplegic – all 4 limbs affected
Paraplegic – only legs are paralyzed
V. PERIPHERAL NERVOUS SYSTEM
A.
Structure of a Nerve
1.
Nerve – bundle of nerve fibers
outside the CNS
a.
b.
c.
Each process is wrapped in a
connective tissue sheath called
the endoneurium
Groups of fibers are bound by
coarser connective tissue called
the perineurium to form fiber
bundles or fascicles
Fascicles are bound together by a
tough fibrous sheath called the
epineurium for form a cord-like
nerve
V. PERIPHERAL NERVOUS SYSTEM
V. PERIPHERAL NERVOUS SYSTEM
2.
Like neurons, nerves are classified by direction in
which impulses are transmitted
a.
b.
c.
B.
Mixed nerves carry both sensory and motor fibers
Afferent or sensory nerves carry impulses toward the CNS
Efferent or motor nerves carry impulses away from CNS
Autonomic Nervous System
1.
Motor subdivision of the PNS that controls body
activities automatically, thus also called the
involuntary nervous system
V. PERIPHERAL NERVOUS SYSTEM
2.
Somatic and Autonomic Nervous Systems Compared
a.
b.
c.
Neurons
i.
Somatic – cell bodies are inside the CNS, axons extend all
the way to the skeletal muscle they serve
ii.
Autonomic – chain of two motor neurons, first is in brain
or spinal cord and its axon (preganglionic axon) leaves
CNS to synapse with second motor neuron in a ganglion
outside the CNS, the axon of this neuron is the
postganglionic axon
Effector organs
i.
Somatic – skeletal muscle
ii.
Autonomic – smooth muscle, cardiac muscle, glands
Neurotransmitters
i.
Somatic – acetylcholine
ii.
Autonomic – acetylcholine, epinephrine, norepinephrine
V. PERIPHERAL NERVOUS SYSTEM
d.
Autonomic system is broken into sympathetic and
parasympathetic divisions, but they both serve the same
organs, but counterbalance each other’s activities
i.
Sympathetic mobilizes the body during extreme situations
(fear, exercise, or rage)
ii. Parasympathetic allows us to unwind and conserve energy
V. PERIPHERAL NERVOUS SYSTEM
3.
Anatomy of the Sympathetic Division
a.
b.
c.
d.
4.
Originates from T1 through L2
Ganglia are at the sympathetic trunk (near the spinal cord)
Short preganglionic neuron and long postganglionic neuron
transmit impulse from CNS to the effector
Norepinephrine and epinephrine are neurotransmitters to
the effector organs
Anatomy of the Parasympathetic Division
a.
b.
c.
Originates from the brain stem and S1 through S4
Terminal ganglia are at the effector organs
Always uses acetylcholine as a neurotransmitter
V. PERIPHERAL NERVOUS SYSTEM
5.
Autonomic Functioning
Sympathetic – “fight-or-flight”
i.
Response to unusual stimulus
ii.
Takes over to increase activities
iii. Remember as the “E” division – exercise, excitement,
emergency, and embarrassment
b.
Parasympathetic – housekeeping activities
i.
Conserves energy
ii.
Maintains daily necessary body functions
iii. Remember as the “D” division – digestion, defecation,
diuresis
a.
VI. DEVELOPMENTAL ASPECTS OF
THE NERVOUS SYSTEM
A.
Embryonic development
1.
2.
3.
4.
5.
Nervous system is formed during the first month of
embryonic development
Any maternal infection can have extremely harmful
effects
The hypothalamus is one of the last areas of the
brain to develop, which regulates body temperature,
thus preemies have trouble with this
No more neurons are formed after birth, but growth
and maturation continues for several years
The brain reaches maximum weight as a young
adult
VI. DEVELOPMENTAL ASPECTS OF
THE NERVOUS SYSTEM

The apparent enlargement of the ventricles seen
here is due to atrophy of the head of the caudate
from neuronal loss with Huntington's disease, an
autosomal dominant condition characterized
clinically by choreiform movements.