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THE NERVOUS SYSTEM
CHAPTER 10
Joe Pistack MS/ED
STRUCTURE AND FUNCTION



Nervous System-acts as an interpreter for the
various organ systems.
Coordinates and directs the activity of the
nervous system.
Acts as a “conductor” for the nervous system, so
that the functions are perfomed correctly.
DIVISIONS OF THE NERVOUS SYSTEM
Central Nervous System
Peripheral Nervous
System

(CNS)-includes:


The brain
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
The Spinal cord

The brain is located in
the cranium and the
spinal cord is enclosed
in the spinal cavity.

(PNS)-includes:
Nerves that connect
the CNS with the rest
of the body.
The peripheral
nervous system is
located outside the
CNS.
DIVISIONS OF THE CENTRAL NORVOUS
SYSTEM
FUNCTIONS OF THE NERVOUS SYSTEM

The nervous system performs three general
functions:

(1)-Sensory function

(2)-Integrative function

(3)-Motor function
SENSORY FUNCTION

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
The nerves gather information from inside the
body and from the outside environment.
The nerves then carry the information to the
CNS.
Ex. You come in contact with a cat, you see the
cat and the information is picked up by the
special senses in the eye. The brain recalls how a
cat should act.
INTEGRATIVE FUNCTION

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Sensory information brought to the CNS is
processed or interpreted.
The brain recalls the information.
The brain integrates or puts together everything
it knows about the subject and then makes a
plan.
Ex. The brain recalls the information about how
a cat is to react and puts it together.
MOTOR FUNCTION



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The motor nerves convey information from the
CNS toward the muscle and glands of the body.
The motor nerves carry out the plan made by the
CNS.
The motor nerve converts the plan into action.
Ex. Person may decide that the cat needs to eat,
information travels along the motor nerves from
the CNS to the skeletal muscles needed so that
you have the movement to feed the cat.
FUNCTIONS OF THE NERVOUS SYSTEM
NEUROGLIA

Neuroglia or glial cells:

The nerve glue, holds the cell together.

Most glial cells are located in the CNS.


They support, insulate, nourish and care for
delicate neurons.
Some participate in phagocytosis, others assist in
the secretion of cerebrospinal fluid.
NEUROGLIA

Do not conduct electrical
impulses.

Astrocytes- most abundant
glial cell.


Supports the neurons and
forms a protective barrier
around the neurons of the
CNS.
Barrier helps to prevent
toxic substances in the
blood stream from entering
the nervous tissue of the
brain and the spinal cord.
NEURON



Second type of nerve cell.
Most important in the transmission of
information.
Enables the nervous system to act as a vast
communication network.

Have many shapes and sizes.

Nonmitotic, do not replicate when injured.
PARTS

OF A NEURON
Parts of a neuron:
(1) Dendrites
 (2) Cell Body
 (3) Axon
 (4) Axon Terminals

PARTS OF A NEURON


Axon-a long extension
that transmits
information away from
the cell body.
The end of the axon
undergoes extensive
branching to form
hundreds of thousands
of axon terminals, this
is where chemical
neurotransmitters are
stored.
PARTS OF A NEURON




Myelin sheath-layer of white fatty material that
encases most of the nerve fibers of the peripheral
and central nervous system.
Myelin-protects and insulates the axon.
Myelinated-when nerve fibers are covered with
myelin.
Unmyelinated-neurons that are not encased in
myelin.
TYPES OF NEURONS


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Three types of neurons:
(1) Sensory neuron-carries information from the
periphery toward the CNS. Also called, afferent
neurons.
(2) Motor neuron-carries information from the CNS
toward the periphery. Also called efferent neurons.
(3) Interneuron-found only in the CNS. Form
connections between sensory and motor neurons. In
the brain, they play a role in thinking, learning and
memory.
WHITE MATTER AND GRAY MATTER

The tissue of the CNS is
white and gray.

White matter is white
because of the myelin.


Myelinated fibers are
gathered together in the
CNS tracts.
The gray matter is
composed primarily of
cell bodies,
interneurons, and
unmyelinated fibers.
WHITE MATTER VERSUS GRAY MATTER
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Nuclei-clusters of cell bodies located in the CNS.
Ganglia-(singular-ganglion)-small clusters of cell
bodies located in the CNS.
Basal nuclei-patches of gray, located in the brain.
NERVE IMPULSES
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Neurons allow the nervous system to rapidly
convey information from one body part to the
next. Ex. Stubbed toe.
Information is carried along the neuron in the
form of a nerve impulse.
Nerve Impulse-an electrical signal that conveys
information along a neuron.
NERVE IMPULSE

Action potential-a process of polarization, depolarization, and
repolarization.
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Polarization-the resting state of a neuron. No nerve impulse
is being transmitted. The cell is quiet.

Depolarization-the neuron is stimulated, a change occurs in
the cell’s electrical state.

Repolarization-cell returning to its resting place. Unless the
cell repolarizes, it cannot be stimulated again.

Refractory Period-the cell’s unresponsive period.

The phases of the nerve impulse are caused by the movement
of ions, particularly Na+ and K+.
NERVE IMPULSE
NERVE IMPULSE
Axons of most fibers
are wrapped in
myelin.
 At the nodes of
Ranvier, the axonal
membrane is bare, not
covered with myelin.
 The nerve impulse
arrives at the axon, it
cannot develop on any
part that is covered
with myelin.

NERVE IMPULSE

To convey
information, a nerve
impulse must move
the length of the
neuron, from the cell
body to the axon
terminal.
NERVE IMPULSE
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

The nerve impulse
will jump from node to
node to the end of the
axon.
Jumping from node to
node is called
saltatory conduction.
Saltatory conduction
increases the speed
with which the nerve
impulse travels.
EVENTS OF A SYNAPSE
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Many axons are myelinated to increase the speed
of the nerve impulse.
The nerve impulse travels along the neuron from
the dendrite to the end of the axon.
The impulse stimulates the release of
neurotransmitters into the synaptic cleft.
The transmitter diffuses across the synaptic cleft,
binds to the receptor and stimulates the dendrite
of the second neuron.
THE BRAIN
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The brain is located in
the cranial cavity.
Pinkish-gray, delicate
structure with a soft
consistency.
The surface of the
brain appears bumpy,
like a walnut.
Weighs about 3lb.
THE BRAIN


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Primary source of
energy for the brain is
glucose.
Low blood glucose
levels result in
hypoglycemia.
S/S patient will
exhibit are: mental
confusion, dizziness,
convulsions, loss of
consciousness, death.
THE BRAIN
THE BRAIN
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The brain is divided into four major areas:

The Cerebrum
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The Diencephalon
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The Brain Stem
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The Cerebellum
THE CEREBRUM
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The cerebrum contains both gray and white
matter.
Cerebral Cortex-thin layer of gray matter that
forms the outermost portion of the cerebrum.
The gray matter of the cerebral cortex allows us
to perform higher mental tasks such as learning,
reasoning, language, and memory.
The bulk of the cerebrum is composed of white
matter located directly below the cortex.
THE CEREBRUM
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
The bumps of the
cerebrum have several
markings, or
structures with
special names.
The surface of the
cerebrum is folded
into elevations called
convolutions or gyri.
THE CEREBRUM
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The extensive folding
increases the amount
of the cerebral cortex.
It is thought that
intelligence is related
to the amount of
cerebral cortex.
Sulci-the grooves that
separate the gyri.
LOBES OF THE CEREBRUM
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Frontal Lobe- located in the
front of the cranium under the
frontal bone.
Plays a key role in voluntary
motor function, personality,
behavior, emotional expression,
intellectual functions, and
memory storage. Also involved
with thinking learning and
making plans. These are called
“executive functions”
FRONTAL LOBE
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Broca’s area-the part of the
frontal lobe concerned with
speech.
In most people it is in the left
hemisphere.
(some people it is in the right
hemisphere).
If damaged, (CVA) the person
develops aphasia – the
person knows what they
want to say but can’t
FRONTAL LOBE
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

Frontal eye fieldlocated above Broca’s
area.
Controls voluntary
movements of the eyes
and the eyelids.
Ex. Ability to scan a
paragraph.
DECUSSATION
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Decussation-the crossing over of nerve fibers from
one side of the brain to the other side of the body.
Fibers leave the motor area of the left frontal lobe
cross over, and innervate the right side of the body.
The fibers from the right frontal lobe also cross over
and innervate the left side of the body.
Ex. Damage to the left side of the brain causes
paralysis to the right side of the body.
PARIETAL LOBE
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Located behind the
central sulcus.
Primarily concerned
with receiving general
sensory information
from the body.
Called the primary
somatosensory area
because it receives
sensations from the
body.
PARIETAL LOBE
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
The primary somatosensory area- receives
information from the skin and muscles and
allows you to experience the sensations of
temperature, pain, light touch, and
proprioception, (a sense of where your body is).
The parietal lobe is also concerned with reading,
speech and taste.
TEMPORAL LOBE
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
Located inferior to the lateral fissure in the area
above the ear.
Contains the primary auditory cortex, the area
that allows you to hear.

Receives sensory information from the ears.

Damage to the temporal lobe causes deafness.
TEMPORAL LOBE
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Olfactory area-receives sensory information from
the nose. Area that controls smell.
Sensory information from the taste buds- are
located in the tongue. Interpreted in both the
temporal and parietal lobes.
Wernicke’s area-broad region located in both
parietal and temporal lobes; concerned with the
translation of thoughts into words.
Damage to this area can cause deficits in
language comprehension.
TEMPORAL LOBE
OCCIPITAL LOBE
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
Located in the back of
the head, underlying
the occipital bone.
Contains the visual
cortex.
Sensory fibers from
the eye send
information to the
visual cortex of the
occipital lobe, where it
is interpreted as sight.
OCCIPITAL LOBE
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
Concerned with visual reflexes and vision-related
functions such as reading.
Damage to the occipital lobe causes blindness.
ASSOCIATION AREAS
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Large areas of
the cerebral
cortex that are
concerned
primarily with
analyzing,
interpreting
and
integrating
information
from the ear.
PATCHES OF GRAY
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Basal Nuclei-gray matter scattered throughout
the cerebral white matter.
Help to regulate body movement and facial
expression.
Dopamine is largely responsible for the activity of
the basal nuclei.
A deficiency in dopamine within the basal nuclei
is called Parkinson’s Disease.
PARKINSON’S DISEASE
Characterized by:
 A shuffling and
uncoordinated gait.
 Rigidity
 Slowness of speech.
 Drooling.
 Masklike facial
expression.
 Usually treated with
dopamine or
dopamine-like drugs.
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DIENCEPHALON
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Second main area of
the brain.
Located beneath the
cerebrum above the
brain stem.
Includes the thalamus
and the
hypothalamus.
THALAMUS
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
Serves as a relay station for most of the sensory
fibers traveling from the lower brain and spinal
cord region to the sensory areas of the cerebrum.
The thalamus sorts out the sensory information,
gives us a hint of the sensation we are to
experience, and then directs the information to
the specific cerebral areas for more precise
interpretation.
THALAMUS
HYPOTHALAMUS
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Second structure in
the diencephalon.
Situated below the
thalamus.
Regulates body
temperature, water
balance, and
metabolism.
BRAIN STEM
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Connects the spinal
cord with higher brain
structures.
Composed of the
midbrain, pons and
medulla oblongata.
The white matter of
the brain stem
includes tracts that
relay both sensory and
motor information.
MIDBRAIN
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Extends from the
lower diencephalon to
the pons.
Relays sensory and
motor information.
Contains nuclei that
function as reflex
centers for vision and
hearing.
PONS
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
Extends from the
midbrain to the
medulla oblongata.
Plays a role in
regulation of
breathing rate and
rhythm.
MEDULLA OBLONGATA
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

Connects the spinal
cord with the pons.
Act as a relay for
sensory and motor
information.
Often called the vital
center, controls heart
rate, BP, and resp.
MEDULLA OBLONGATA
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
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Extremely sensitive to certain drugs, especially
narcotics.
Overdose causes depression of the medulla
oblongata resulting in death if the patient stops
breathing.
Always assess the respiratory rate before
administering a narcotic, if less than 10 do not
administer.
MEDULLA OBLONGATA
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Also contains the vomiting center.
Vomiting center can be activated directly or
indirectly.
Direct activation includes stimuli from the
cerebral cortex such as fear, distressing sights,
bad odors, pain or spinning sensation from the
equilibrium apparatus of the inner ear.
MEDULLA OBLONGATA
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Indirect stimulation of the vomiting center comes
from the chemoreceptor trigger zone.
The (CTZ) can be stimulated by anticancer drugs,
and narcotics.
Signals in the digestive tract may send signals to
the vagus nerve to the (CTZ), this in turn may
activate the vomiting center.
Antiemetic agents can work on the (CTZ) and the
vomiting center to relieve nausea and vomiting.
CEREBELLUM
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
Fourth major area.
Protrudes from under
the occipital lobe at
the base of the skull.
Concerned primarily
with coordination of
voluntary muscle
activity.
CEREBELLUM
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Information is sent to the cerebellum from many
areas throughout the body.
The cerebellum integrates all of the incoming
information to produce a smooth, coordinated,
muscle response.
Damage to the cerebellum produces jerky muscle
movements, staggering gait, and difficulty
maintaining balance or equilibrium.
CEREBELLUM
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The person with cerebellar dysfunction may
appear intoxicated.
Diagnose cerebellar dysfunction-have the patient
touch the tip of the nose with finger.
The cerebellum normally coordinates muscle
activity, a patient with cerebellar dysfunction
may overshoot , first to one side and then the
other.
STRUCTURES THAT OVERLAP
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Limbic system:
Made up of parts of
the cerebrum and the
diencephalon, form a
wishbone-shaped
structure.
Called the emotional
brain-functions in
emotional states and
behavior.
RETICULAR FORMATION
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

Special mass of gray
matter.
Extends through the
entire brain stem.
Concerned with the
sleep-wake cycle and
consciousness.
RETICULAR FORMATION


Signals passing up to
the cerebral cortex
from the reticular
formation stimulate
us, keeping us awake.
This area is sensitive
to tranquilizers and
alcohol, can cause
damage to the
reticular formation
causing permanent
unconsciousness.
CONSCIOUSNESS


Consciousness-state of wakefulness. Depends
on our reticular activating system (RAS).
The RAS is continuously receiving information
from all over the body, it will send any unusual
signals to the cerebral cortex for interpretation.
Different levels of consciousness:
 Attentiveness
 Alertness
 Relaxation
 Inattentiveness

SLEEP


Sleep- occurs when the reticular activating
system is inhibited or slowed.
Coma-sleeplike state with several stages,
ranging from light to deep.

Light stages- some reflexes are intact, patient may
respond to light, sound, touch, or painful stimuli.

As coma deepens the patient gradually becomes
unresponsive to all stimuli.
STAGES OF SLEEP

Two types of sleep:
1. Non-Rapid Eye Movements (NREM) sleep.
2. Rapid Eye Movement (REM) sleep.
Four stages of NREM sleep progress from light to
deep.
 In a typical 8-hour sleep period a person cycles
through various stages of sleep from light to deep
and deep to light.


REM sleep is characterized by fluctuating blood
pressure, resp. rate and rhythm and pulse rate.
SLEEP



REM sleep is
characterized by rapid
eye movements.
Most dreaming occurs
during REM sleep .
Deprivation of REM
sleep is is associated
with mental and
physical distress.
MEMORY

Ability to recall thoughts and images.
Areas of the brain concerned with memory:
 Frontal
 Parietal
 Occipital
 Temporal lobes
 Limbic system
 Diencephalon

MEMORY

Two categories:
1. Short-term-lasts for short periods of time,
(seconds to a few hours).Allows you to recall
such things as prices or telephone numbers.
Cramming for tests!
2. Long-term-lasts years or decades. Learned
over a longer period of time.
PROTECTION OF THE CENTRAL NERVOUS
SYSTEM


Tissue of the brain and spinal cord are very
delicate.
Has an elaborate protective system that consists
of four structures:
1. Bone
2. Meninges
3. Cerebrospinal fluid
4. Blood-brain barrier
FIRST LAYER OF PROTECTION

First layer is
bone, the
brain is
encased in
the cranium
while the
spinal cord
is encased in
the
vertebral
column.
LAYERS OF PROTECTION



Meninges-three layers of connective tissue that
surround the brain and the spinal cord.
Dura mater-the outermost layer of the thick,
tough, connective tissue. (Meaning “hard
mother”)
Arachnoid- (spiderlike). Middle layer, forms a
web for protection.
LAYERS OF PROTECTION



Pia mater-innermost layer, soft. (Meaning “gentle
mother”).
Pia mater is a very thin membrane and contains
blood vessels and lies delicately over the brain
and spinal cord. Blood vessels supply the brain
with much of it’s blood.
Subarachnoid space-lies between the arachnoid
space and the pia mater. Cerebrospinal fluid
circulates within this space.
LAYERS OF PROTECTION



Cerebrospinal fluid circulates around the brain
and forms a cushion.
Ex. Protects if the brain is jarred.
Arachnoid villi-projections of the arachnoid
membrane that protrude up into the blood filled
dural spaces.
Brain Pad
P-pia mater
A-arachnoid
D-dura mater
THREE LAYERS OF THE MENINGES
MENINGITIS

Meningitis-inflammation of the meninges.

Serious infection that may spread to the brain.

Diagnosis by testing the cerebrospinal fluid
obtained by lumbar puncture.
CEREBROSPINAL FLUID

Formed in the Choroid Plexus

Third layer of protection:

Formed from the blood within the brain.

CSF is a clear fluid, consistency of plasma.


.
Composed of water, glucose, protein, and several
ions.
Adult circulates about 500ml every 24 hours.
CEREBROSPINAL FLUID




Formed in the choroid plexus in the ventricles of
the brain.
Choroid plexus is a grapelike collection of blood
vessels and ependymal cells.
The rate at which CSF is formed must equal the
rate at which it is drained.
If drainage is impaired, CSF will accumulate in
the ventricles of the brain, increasing pressure
within the skull, may result in brain damage or
death if not treated.
BLOOD-BRAIN BARRIER




Fourth layer of protection:
Arrangement of cells, particularly glial
astrocytes.
Cells select the substances allowed to enter the
CNS from the blood.
The blood-brain barrier is successful in screening
many harmful substances, but not all toxic
substances are blocked.
Ex. Alcohol can cross the blood-brain barrier and
affect brain tissue.
BLOOD-BRAIN BARRIER


Most antibiotics cannot cross the blood-brain
barrier and therefore cannot reach the site of
infections within the CNS.
May need to inject antibiotic directly into the
subarachnoid space.