The Nervous System
(rev 6/10)
Control of the cells of our body is carried out by
2 communication systems, the nervous
system and the endocrine system.
Both systems transmit information from one
part of the body to another, but they do it
differently.
• Nervous System: transmits information very
rapidly by nerves which send impulses from
one part of the body to another.
• Endocrine System: transmits information
through chemicals secreted into the blood;
glands without ducts secrete the chemicals.
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Divisions of the Nervous System
Central nervous system (CNS)—brain and spinal
cord
– is the integrating and command center of the nervous system
– it interprets incoming sensory information and
produces motor responses
Peripheral nervous system (PNS) —all nerves
which extend from the CNS to all parts of the
body
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Subdivisions:
– Autonomic nervous system (ANS) --controls involuntary functions of the body:
heart rate, stomach and intestine
contractions, gland secretions
– Is further sub-divided into the
• SYMPATHETIC NERVOUS SYSTEM which
mobilizes body systems during emergency
situations
• the PARASYMPATHETIC NERVOUS SYSTEM
which primarily conserves our energy
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• the PNS has 2 functional subdivisions
– the sensory or afferent division carries
impulses TO the CNS and keeps the CNS
informed of events going on inside and
outside of the body
– The motor or efferent division carries
impulses FROM the CNS
• this division enables us to respond to stimuli
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Cells of the Nervous System
2 types of cells: Neurons and Glia (also
called Neuroglia)
Neurons
 Consist of three main parts
 dendrites, which conduct impulses to the
cell body of neuron;
 cell body;
 and axon, which conducts impulses away
from cell body of neuron
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Myelin Sheath:
wrapping around
axon; formed by
Schwann Cells;
called
Myelinated
Fibers. Myelin is
white in color.
Nodes of
Ranvier
Saltatory
Conduction
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Neurons are classified according to
function:
• Sensory or afferent: conduct
impulses TO the spinal cord and brain;
• Motor or efferent: conduct impulses
AWAY FROM the brain and spinal cord
to muscles and glands;
• Interneurons: conduct impulses from
sensory neurons to motor neurons
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Glia (neuroglia)
 Support cells;
 Attaches neurons to nearby structures
 protects them
 Three main types of glial cells
 Astrocytes—anchor small blood vessels to
neurons
 Microglia—in inflamed or degenerating
brain tissue they act as phagocytes and
remove this tissue
 Oligodendrocytes—form myelin sheaths on
axons in the CNS
 Schwann cells form myelin sheaths of
axons in the PNS

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Nerves
• Nerve —group of peripheral axons
bundled together. The bundles are
usually called “tracts”.
• In the CNS, these bundles of axons
are called “tracts”.
• White matter —tissue composed
primarily of myelinated axons
(nerves or tracts)
 Gray matter —tissue composed
primarily of cell bodies, dendrites
and unmyelinated fibers
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Nerve coverings—fibrous connective
tissue
 Endoneurium—surrounds
individual fibers within a nerve
 Perineurium—surrounds a
group (fascicle) of nerve fibers
 Epineurium—surrounds the
entire nerve
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The Reflex Arc
Many of the body’s control systems belong to a
general category known as reflexes.
• A reflex is a rapid, predictable motor response
to a stimulus.
– It is automatic, involuntary, and protective.
– Both the spinal cord and the brain are reflex
centers.
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Reflexes
• Nerve impulses are conducted from RECEPTORS
(receive stimulus)
• to EFFECTORS (muscle or gland) over neuron
pathways (specific route frequently traveled by
nerve impulses);
• The simplest reflexes are two-neuron arcs-consist of sensory neurons synapsing in the spinal
cord with an interneuron and then a motor neuron;
•
• Complex or three-neuron reflexes consist of
sensory neurons synapsing in the spinal cord with
interneurons that synapse with motor neurons and
send a signal to the spinal cord and the brain.
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Nerve Impulse Conduction
Definition—self-generating wave of electrical impulses
that travel along the surface of a neuron
Mechanism:
• The plasma membrane of a resting neuron has a slight
positive charge on the outside and a negative charge
on the inside.
• A stimulus triggers the opening of sodium (Na+)
channels in the plasma membrane of the neuron.
• Positively charged sodium ions move into the cell
leaving a more negative charge outside the cell.
• This causes an electrical impulse to start moving
down the nerve cell (neuron).
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Nerve signals need to jump across a space, called a
synapse or a synaptic cleft, between the neurons.
 The first neuron is called the pre-synaptic neuron
and the neuron after the synapse is called the
postsynaptic neuron.
When a nerve impulse arrives at the end of the neuron
to an area called the synaptic knob (a tiny bulge at
the axon terminals), it releases a neurotransmitter
(chemicals by which neurons communicate) into the
synaptic cleft (the space between the first and
second neuron).
 The second, or postsynaptic neuron, has protein
molecules embedded in it opposite each synaptic
knob. These are receptors and the neurotransmitter
binds to them. The binding begins an impulse in the
postsynaptic neuron.
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• Names of neurotransmitters:
 Acetylcholine, catecholamines
(epinephrine, norepinephrine, dopamine, and
serotonin), and other compounds
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Central Nervous System
Divisions of the brain
I. Brainstem:
Consists of the medulla oblongata,
pons, and midbrain
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A. Medulla
1. Two way conduction pathway between the spinal cord
and higher brain centers
2. contains the cardiac, respiratory, and vasomotor
(blood vessels) control centers
B. Pons
1. Two way conduction pathway between areas of
the brain and other areas of the body; Aids
information flow--coordinates information flow
between cerebellum and higher brain centers
2. Works with the medulla in regulating respiration
C. Midbrain
1. Two way conduction pathway—relay for visual and
auditory pathways
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II. Cerebellum
A. Helps control coordinated movements,
balance, and normal posture
III. Diencephalon
A. Hypothalamus
1. Consists mainly of the posterior
pituitary gland and gray matter
2. Acts as the major center for control of
the Autonomic Nervous System
(ANS---the ANS controls the
functioning of most internal organs)
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3. Controls hormone secretion by
anterior and posterior pituitary gland
and therefore helps control hormone
secretion by most other endocrine
glands
4. Contains centers for controlling
body temperature, water balance,
appetite, wakefulness, pleasure, and
many other body emotions
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B. Thalamus
1. Dumbbell-shaped mass of gray matter in
each cerebral hemisphere
2. Produces sensations by relaying sensory
impulses to the cerebral cortex
3. Associates sensations with the emotions
of pleasantness or unpleasantness
4. Plays a part in the arousal or alerting
mechanism
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Central Nervous System
IV. Cerebrum
A. Largest part of the human brain
B. Outer layer of gray matter is the
cerebral cortex;
1. composed mainly of dendrites and cell
bodies of neurons
2. made up of lobes as well as gyri
(ridges) and sulci (grooves);
3. Interior of the cerebrum composed
mainly of white matter
4. Functions—
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a. Frontal lobes initiate motor activity and are
responsible for speech, conscious thought,
and personality
b. Parietal lobes contain the somatosensory
cortex; interpretation of sensory information
from the skin and from the muscles and joints.
c. Occipital lobes contain the primary visual
cortex and the visual association area
• association areas allow us to
interpret/understand information
d. Temporal lobes interpret auditory information
and are responsible for perceptual judgment
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• Spinal cord
 Is the center for all spinal cord reflexes
 Outer part is composed of white matter
made up of many nerve tracts (bundles of
axons);
 Interior composed of gray matter made up
mainly of dendrites and cell bodies
 Sensory tracts conduct impulses TO the
brain
 Motor tracts conduct impulses FROM the
brain
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Coverings and fluid spaces of the brain and
spinal cord
 Coverings
 Skull and vertebrae
 Cerebral and spinal meninges—the dura
mater, the arachnoid mater, and the pia
mater
Form protective covering for the brain
and the spinal cord
 Cerebrospinal Fluid
Blood-brain barrier
Hydrocephalus
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Autonomic Nervous System
• Composed of two divisions—
• the sympathetic system —the “fight or flight”
system and
• the parasympathetic system —the “normal
functioning” system
• regulates the body’s automatic or involuntary
functions
• conducts impulses from the central nervous
system to cardiac muscle, smooth muscle,
and glandular epithelial tissue
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• Sympathetic nervous system
 Sympathetic preganglionic neurons are
located in the thoracic and upper lumbar
segments of the spinal cord
 Parasympathetic nervous system
 Parasympathetic preganglionic neurons are
located in the brainstem and in the sacral
segments of the spinal cord
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Nervous System Disorders--Psychoactive Drugs
• Action: affects higher brain functions; work by
influencing the actions of brain
neurotransmitters; can cross the blood brain
barrier
• Psychological dependence: user craves the
feeling associated with the drug
• Tolerance: takes more of the substance to achieve
the same affect
• Addiction: the need to continue obtaining and using
a substance; no free choice
• Withdrawal: physical symptoms that occur upon
stopping the drug
Disorders of the Nervous System
Autoimmune Disorders:
Multiple Sclerosis (MS):
• An autoimmune disease that mainly affects young
adults
– The sheaths of myelinated neurons in the brain
and spinal cord become progressively damaged
until they form hardened (sclerotic) scar tissue.
These areas can’t effectively insulate the neurons
and so impulse transmission is slowed and
disrupted.
– People with MS experience a variety of symptoms
depending on which area of the CNS are
damaged.
Multiple Sclerosis
• Symptoms include visual disturbances,
weakness, loss of muscular control, and
urinary incontinence
TREATMENT
• The advent of disease-modifying drugs
including interferon beta-1a and -1b, Avonex,
Betaseran, and Copazone:
– Hold symptoms at bay
– Reduce complications
– Reduce disability
Amyotrophic Lateral Sclerosis (ALS)
• Similar to MS but the sclerotic areas
begin in areas of the spinal cord
involved in the motor control of skeletal
muscles
• Primary symptom is progressive
weakening and wasting of skeletal
muscles, especially those responsible
for breathing
Trauma:
• Concussion: caused by a violent blow to the
head or neck
– Usually see a short loss of consciousness due
to a disruption of the electrical activity of brain
neurons.
– After regaining consciousness, person may
have blurred vision, confusion, nausea and
vomiting
– Typically concussions don’t have permanent
damage unless there is a subdural hematoma:
bleeding into the space between the meninges
• Bleeding increases pressure within
headsquashes brain tissue and
disrupts function of brain
–Symptoms: drowsiness, headache
and weakness of 1 side of body
• Treatment: surgery for immediate relief
of pressure and repair of bleeding blood
vessels
• Spinal cord injuries: will impair sensation and
function below the level of injury
– Paraplegia or quadriplegia; can be fatal; will
always cause problems with bladder and bowel
control
Infections: Brain and spinal cord typically do not
get infected due to the blood-brain barrier.
• Encephalitis: inflammation of the brain; typically
caused by a virus
– Symptoms: headache, fever, fatigue,
hallucinations, confusion, disturbances in
speech, memory or behavior, epileptic
seizures
– Treatment: Hospitalization with IV
medications
• Meningitis: Inflammation of the meninges; can
be viral or bacterial
– Symptoms: headache, fever, nausea and
vomiting, light sensitivity, stiff neck
– Treatment: hospitalization. If viral, mild
symptoms and will improve in few weeks
–If bacterial, can be fatal; IV antibiotics
needed ASAP
• Rabies: infectious viral brain disease
– Transmitted to humans by direct contact, either bite or
lick over broken skin
• Virus attacks the sensory neurons in the bite region then
travels to the spinal cord, then to the brain where it multiplies
and kills cells
– Symptoms: swollen lymph glands, painful swallowing,
vomiting, choking, spasms of throat and chest
muscles, fever, becomes irrational. Death within 2-20
days
– Treatment: wash wound thoroughly ASAP, go to
emergency room or doctor, have animal tested,
receive rabies immunization ASAP
Neural and synaptic transmission disorders:
action potentials can’t be properly sent.
Symptoms depend on which nerves are affected
• Epilepsy: recurring episodes of abnormal
electrical activity in brain
– Seizure triggers: fatigue, stress, flashing lights
– Seizures vary widely due to which part of brain
is affected
– Treatment: EEG, medications
• Parkinson’s disease: progressive degenerative
illness; loss of dopamine releasing neurons in the
area of the midbrain that coordinates muscle
movements; can’t perform smooth, coordinated
movement
– Symptoms: stiff joints, muscle tremors in
hand, loss of mobility, depression and other
mental impairments
– Treatment: L-dopa, a drug which the body
converts to dopamine. Will become ineffective
eventually
• Alzheimer’s disease: disorder of mental
impairment, especially memory due to a shortage
of the neurotransmitter acetylcholine. Primarily
affects neurons in the limbic system and frontal
lobe. See plaques (beta amyloid) in brain tissue
and abnormal, tangled neurons.
– Symptoms: Progresses from memory lapses
to severe memory loss, especially of STM.
LTM affected very slowly. Disorientation,
dementia, personality changes, loss of ability
to function independently
– Treatment: medications which increase the
brain’s production of acetylcholine
Brain tumors: abnormal growth in or on the
brain
• Can be cancerous or benign
– Problems due to increased pressure within
the brain
– Symptoms: headache, vomiting, visual
impairment, confusion, muscle weakness,
difficulty speaking, seizures
– Treatment: Surgical removal, radiation and
chemotherapy to try to shrink the tumor.