The Nervous System
Eric Mennen
Introduction
The nervous system is the master
controlling and communication system of
the body
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Communicates through electrical impulses
Every thought, action, and emotion reflects its
activity
Functions
Monitor changes (sensory input)
Process and interpret sensory input
(integration)
Effects a response (motor output)
Structural Classification
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Central Nervous System (CNS) – brain and
spinal cord
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Occupies the dorsal body cavity
Acts as the command center of the nervous
system
Peripheral Nervous System (PNS) – nerves
that extend from brain and spinal cord
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Consists mainly of the nerves that extend from the
brain and spinal cord
Spinal Nerves – carry impulses to and from the
spinal cord
Cranial Nerves – carry impulses to and from the
brain
Functional Classification
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Afferent (sensory) Division - nerve fibers
that carry impulses to the CNS
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Keeps the CNS constantly informed on events
inside and outside the body
Efferent (motor) Division - nerve fibers that
carry impulses from the CNS to the effector
organs
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These impulses activate or bring about a motor
response
Functional Classification cont..
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Two Motor Subdivisions
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Somatic Nervous System - allows us to
consciously or voluntarily control our muscles
Autonomic Nervous System – regulates events
that are automatic or involuntary
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Sympathetic- mobilizes the body during extreme
situations
Parasympathetic- allows us to unwind and conserve
energy
Nervous Tissue
Supporting Cells (neuroglia) - cells that support,
insulate, and protect delicate neurons
4 types
 Astrocytes - (star shaped) protect neurons from
harmful substances in the blood
 Microglia - dispose of debris and foreign
substances (ex. Dead brain cells)
 Ependymal cells - helps circulate cerebrospinal
fluid and create a cushion
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Line cavities of the brain and spinal cord
Oligodendrocytes - insulated covering of nerve
cells called myelin sheaths
Nervous Tissue
Neurons (nerve cells) - transmit messages
called a nerve impulse from one part of the
body to another
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Neurons differ structurally but have many
common features
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(Ex. They all possess a cell body and one or more
processes extending from the cell body)
Neurons communicate with each other through
tiny gaps called synaptic clefts (Synapses).
Neurons Anatomy
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Cell Body (perikaryon) - the metabolic
center of the neuron
Contains the usual organelles
Contains neuroplasm which is the cytoplasm
of the neuron
Nissl Substance (rough ER) – produce
proteins
Neurofibrils – intermediate filaments that are
important in maintaining cell shape
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abundant in the cell body
Neurons Anatomy cont.
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Processes – arm like extension of the cell
body that sends and receive electrical signals
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Can be 3 to 4 feet (Ex. Lumbar – Big toe)
Two Types:
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Dendrites – convey incoming messages
(electrical signals) – afferent process
Axons – generate nerve impulses and send them
away from the cell body - efferent process
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Each neuron can have hundreds of dendrites but only 1
axon
Neurons Anatomy Cont.
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Axon hillock – conelike region where axon
meets cell body
Axon terminals – branches at the end of the
axon
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Contain neurotransmitters
Each axon terminal is separated from the next
neuron by a tiny gap called the synaptic cleft
(synapse)
Schwann cells are supporting cells that wrap
themselves around the axon and form the myelin
sheath encloses the axon
The Central Nervous System
Consists of the Brain and Spinal Cord
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They act as a control center for all activities
The Brain is divided into four major regions
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Cerebral hemispheres
Diencephalon
Brain stem
Cerebellum
The Central Nervous System
Fun Facts!
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The brain weighs
roughly 3 lbs and is
about the size of your
two fist put together
The brain gives us
consciousness,
memory, perception,
and the ability to
evaluate situations and
feel emotions
Cerebral Hemispheres
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Together called the cerebrum, the most
superior part of the brain
Frontal lobe: Conscience choice, motor
movements, speech, language
comprehension.
Temporal lobe: auditory, olfactory, long
term memory.
Parietal lobe: somatic sensory (pain, temp.,
touch), gustatory,
Occipital lobe: vision , spatial interpretation
Diencephalon (Interbrain)
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Thalamus: recognizes pleasant and
unpleasant senses, sleep, alertness
Hypothalamus: regulation of temperature,
water balance,metabolism, moods,regulates
sex drive and emotional memory (Limbic
system)
Pituitary gland: important in hormone
production “Master Hormone Gland”
Brain Stem
Midbrain: vision and hearing reflexes
Pons: breathing
Medulla Oblongata: regulates heart rate,
blood pressure, breathing, swallowing, and
vomiting
Reticular Formation: motor control of the
visceral organs (abdomen)
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Damage to this area can result in permanent
unconsciousness (coma)
Cerebellum
Large cauliflower projection under the
occipital lobe
Functions:
1. Skeletal muscle activity
2. Balance and equilibrium (Coordination)
3. Regulates body position and tension of
body parts
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The Spinal Cord
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A continuation of the
brain stem
Extends from brain to
just below ribs (L1)
Enclosed in vertebral
column
Creates a two way
pathway to and from
the brain
Gray Matter
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Butterfly in shape
Surrounds central the central canal of the
spinal cord
Damage can cause loss of sensation from
body area
Contains motor neurons of the somatic
(voluntary) nervous system
White Matter
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Surrounds the gray matter
Conducts impulses to the brain for sensory
(afferent) and motor (efferent)
Peripheral Nervous System
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Consists of nerves and scattered neuronal
cell bodies found outside of the Central
Nervous System
Cranial nerves- 12 pairs of nerves that
extend from the brain
Spinal nerves- 31 pairs of nerves that
extend from the spinal cord
Cranial Nerves
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Olfactory nerve - carries impulse for sense
of smell
Optic nerve - carries impulse for vision
Oculomotor nerve - supplies motor fibers for
eye muscles
Facial nerve - activates muscle for facial
expression and impulse for taste
Vagus nerve - sensory and motor impulses
for respiratory, cardiac and digestive activity
Cranial Nerves Cont’d
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Trochlear – supplies motor fibers for one
external eye muscle
Trigeminal – conducts sensory impulses
from the skin of the face and mucosa of the
nose and mouth: activates chewing muscles
Abducens – supplies motor fibers to the
lateral rectus muscle – rolls the eye laterally
Vestibulocochlear – sensory; transmits
impulses for the sense of balance and
hearing
Cranial Nerves Cont’d
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Glossopharyngeal – supplies motor
fibers to the pharnyx to promote
swallowing and saliva production
Accessory – motor fibers that activate
sternocleidomastoid and trapezius muscle
Hypoglossal – motor fibers control tongue
movements
Spinal Nerves
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Named from vertebrae from which the extend
C1-C5 (Cervical)- serves muscles of shoulder
and neck
C5-C8, T1 (Brachial)- serves shoulder and arm
muscles
T2-T12 (Thoracic)- serves muscles between
ribs and mid trunk
L1-L4 (Lumbar)- serves muscles of abdomen,
hips and upper leg
Spinal Nerves Cont.
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S1-S4- (Sacral)- serves
muscles of lower leg
and feet
Sciatic Nerve - largest
nerve in the body,
serves muscles of the
legs