The CNS, PNS, SNS, and ANS
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A control and communications system
◦ Consists of the brain, spinal cord, nerve cells, and
nerve fibers that run throughout the body
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Originates and coordinates physical reactions
to the environment
Controls involuntary muscles and organs
Maintains homeostasis
◦ A balanced state within the body
 C.S. 24
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Nerve cells are called neurons
◦ Star-shaped bodies with 2 long nerve fibers projecting
from them
◦ Messages to the cell body are carried by nerve fibers
called dendrites (part of the star)
◦ Messages that travel away from the cell body are carried
by nerve fibers called axons (the tail)
 The axon is covered by a myelin sheath for protection –
deterioration of this sheath is called MS
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The dendrite receives a message, transmits it to
the cell body, and the cell body sends the
message along to another neuron or to the organ
that is to be affected (such as a muscle)
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The neurons and their fibers form a network
that covers the entire inside of the body and
all of the skin
The long fibers of neurons are arranged in
bundles called nerves
◦ The fibers of neurons within the nerves don’t
actually touch
◦ They meet at a place called a synapse, which is a
space where an electrical impulse is transmitted
from an axon to a dendrite
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Classified according to the direction in which
they transmit impulses
Afferent neuron: sensory neurons – transmits
impulses TO the brain and spinal cord from the
sensory organs
Efferent neuron: motor neurons – transmits
impulses AWAY from the brain and spinal cord or
other nerve centers
◦ Transmit only to muscles and organs
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Interneuron: transmits impulses from sensory to
motor neurons
◦ Used in reflexes for defensive purposes
 C.S. 25
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It is divided into categories depending upon
function
Central Nervous System (CNS)
◦ Brain
◦ Spinal cord
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Peripheral Nervous System (PNS)
◦ Somatic Nervous System (SNS)
◦ Autonomic Nervous System (ANS)
 Sympathetic Nervous System
 Parasympathetic Nervous System
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Made up of:
◦ The brain
◦ The spinal cord
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Control center for the movement and actions
of the entire body
◦ Messages come to the CNS from throughout the
body, where they are interpreted
◦ the CNS then sends out reaction impulses
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The most complex and specialized organ in
the body
3 areas – forebrain, midbrain, hindbrain
Divided into specialized sections
◦ Cerebrum
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 2 hemispheres – right and left
 4 ventricles/lobes – frontal, parietal, temporal, and
occipital
Cerebellum
Corpus Callosum
Pons
Medulla
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1. Frontal lobe of
cerebrum (f)
2. Pituitary gland
3. Temporal lobe of
cerebrum (f)
4. Pons (h)
5. Medulla oblongata
6. Parietal lobe of
cerebrum (m)
7. Corpus callosum (f)
8. Occipital lobe of
cerebrum (m)
9. Cerebellum (h)
10. Spinal cord
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Main part of the brain
Divided into hemispheres
Outer surface is called the cortex
◦ Wrinkled with deep furrows to increase the surface
area of the brain
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Consists of the forebrain and the midbrain
Has 4 lobes (aka ventricles)
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Frontal lobe
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Parietal lobe
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Temporal lobe
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Occipital lobe
◦ Top, front regions of each of the cerebral hemispheres.
◦ Used for reasoning, emotions, judgment, and voluntary
movement
◦ Middle lobe of each cerebral hemisphere between the
frontal and occipital lobes
◦ Contains important sensory centers
◦ Region at the lower side of each cerebral hemisphere
◦ Contains centers of hearing and memory
◦ Region at the back of each cerebral hemisphere
◦ Contains the centers of vision and reading ability
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Part of the brain below the back of the
cerebrum
Regulates balance, posture, movement, and
muscle coordination
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A large bundle of nerve fibers that connect
the left and right cerebral hemispheres
Allows for communication and coordination
between the hemispheres
In the lateral section, it looks a bit like a "C"
on its side
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The part of the brainstem that joins the
hemispheres of the cerebellum and connects
the cerebrum with the cerebellum
It is located just above the Medulla oblongata
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The lowest section of the brainstem (at the
top end of the spinal cord)
It controls automatic functions including
heartbeat, breathing, etc
 C.S. 26
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Descends from the medulla oblongata down
into the canal formed by the vertebrae
Made up of white (nerve tissue) and gray
matter (same matter as brain tissue)
Has 2 functions:
◦ Serves as the sensory-motor mechanism for reflex
actions
◦ Is the 2-way transmitter of impulses, reactions, and
stimuli triggered by various internal and external
conditions
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Surround the brain and spinal cord for
protection
Dura mater – Outer layer
Arachnoid – Middle layer
Pia mater – Inner layer
Cerebrospinal fluid (CSF) – between pia mater
and arachnoid (sub-arachnoid space)
Meningitis – an infection of the meninges
◦ Can be in any of the layers
◦ Can involve the CSF as well
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Made up of the nerves of the body that
connect the CNS to the other parts of the
body
Includes the cranial and spinal nerves
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Cranial nerves link the brain with sensory
receptors and muscles
There are 12 cranial nerves
Designated by Roman numerals I-XII and
names
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I Olfactory
Smell
II Optic
Vision
III Oculomotor
Eye/eyeball movements
IV Trochlear
Eyeball movements
V Trigeminal
Chewing; facial sensation
VI Abducens
Eyeball movements
VII Facial
Taste; facial expression
VIII
Auditory/Vestibulocochlear
Hearing; balance
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IX Glossopharangeal
Taste; swallowing;
saliva secretion
X Vagus
Swallowing; voice; gag
reflex; slowing of
heartbeat
(parasympathetic)
XI Spinal accessory
Muscles of
neck/shoulder
XII Hypoglossal
Tongue movements
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Mnemonic device:
“On Old Olympus Towering Tops A Fin And German
Viewed Some Hops”
- OR –
“Oh Oh Oh To Touch And Feel A Girl’s V……. So
Happy”
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Olfactory (I) – Identify smells
Optic (II) – Eye chart; reading
Oculomotor, Trochlear, Abducens (III, IV, VI) –
With head still, follow a finger
up/down/left/right; pupillary response (III)
Trigeminal (V) – Bite down; Light touch on
face
Facial (VII) – Smile, frown; Taste on tip of
tongue
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Vestibulocochlear (VIII) – Check hearing;
stand on one leg with eyes closed, then the
other leg
Glossopharangeal and Vagus (IX, X) –
Swallow; taste on back of tongue
Spinal Accessory (XI) – Resisted shrug
Hypoglossal (XII) – Stick out tongue and move
it side to side
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Spinal nerves link the spinal cord with various
structures
Conduct impulses between the spine and the
parts of the body not supplied by the cranial
nerves
◦ Transmit sensory info to the spinal cord through
afferent neurons and transmit motor signals to
muscles and organs through efferent neurons
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Make sensation and movement possible
31 pairs
◦ One root of each pair goes to each side of the body
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31 pairs come from the spinal cord as
follows:
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8 cervical nerve roots
12 thoracic nerve roots
5 lumbar nerve roots
5 sacral nerve roots
1 coccygeal nerve root
Each nerve divides to form several branches
called rami
◦ Dorsal rami – control muscles and skin of the back
◦ Ventral rami – innervate all structures of the limbs
and torso
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Ventral rami and adjacent nerves form
networks called plexuses that go to general
areas
◦ Cervical plexus – serves neck, upper shoulders, and
diaphragm
◦ Brachial plexus – serves upper limbs, neck, and
shoulder muscles
◦ Lumbar plexus – serves abdominal area and part of
the legs
◦ Sacral plexus – serves buttocks area and lower legs
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Dermatome – Area of skin supplied by a
single spinal nerve root
Myotome – Specific muscle supplied by a
single nerve root
Sclerotome – Area of bone supplied by a
single nerve root
 C.S. 27
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Subdivision of the PNS
Made up of motor nerves that control the
voluntary actions of skeletal muscles
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Subdivision of the PNS
Made up of certain motor neurons of the PNS
that conduct impulses from the spinal
cord/brain stem to
◦ Cardiac muscle tissue
◦ Smooth muscle tissue
◦ Glandular epithelial tissue (tissue that forms glands)
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Regulates the body’s automatic/involuntary
functions such as heart rate, breathing,
contractions of intestinal musculature, and
secretions of hormones from the glands
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Responsible for “fight or flight” mechanism
Triggered by strong emotional situations (i.e.
anger, fear, anxiety, hate, etc.) and by
strenuous exercise
Increases heart rate, blood pressure, sweat
excretion
Decreases digestion
Charges you up!
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Opposite of sympathetic nervous system
Decreases heart rate and blood pressure
(Vagus nerve)
Increases digestion processes
Calms you down