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NERVOUS SYSTEM
I.
Functions
A. Sensory Input – monitors all
information about change occurring
inside and outside the body
B. Integration – processes and
interprets the information received
and integrates it in order to make
decisions
C. Motor Output – commands
responses by activating muscles,
glands, and other parts of the
nervous system
II.
Structural Classification
A. Central Nervous
System (CNS)
1. brain
2. spinal cord
B. Peripheral Nervous
System (PNS)
1. spinal nerves
2. cranial nerves
III.
Nervous System Cells
A. Neurons
1. Structure:
a. dendrites – receive impulses and
conduct them to cell body.
b. cell body- contains the nucleus and
organelles; regulates cell.
c. axon – conducts impulses away from
cell body by means of axonal terminals.
i. Axon terminals - distal
terminations of the branches of
an axon
ii. Synaptic end bulbs - terminal
enlargements of nerve fibers that are in
contact with the dendrites or cell bodies of
other nerve cells, muscles, or glands.
iii. myelin – lipid-protein covering that protects,
insulates, and speeds transmissions
iv. Schwann cells (outside CNS) – segments
along the axon separated from one another
by Nodes of Ranvier (produce myelin
sheaths)
v. Nodes of Ranvier - are the gaps (approximately
1 micrometer in length) formed between the
Schwann cells.
vi. neurolemma – outermost layer (sheath)
around Schwann cell in PNS
2.
Types of Neurons
a. sensory (afferent) – conduct impulses to
the brain and spinal cord
b. motor (efferent) – conduct impulses away
from brain and spinal cord to muscles and
glands
c. interneurons (association) – conduct
impulses from sensory neurons to motor
neurons
B. Neuroglia (glial) – function in support, insulation, and protection
1. Types in the CNS
a. Astrocytes – star-shaped cells that anchor small blood
vessels to neurons
b. Microglia – small cells that move in inflamed brain tissue
and carry on phagocytosis
c. Oligodendroglia – form myelin sheaths around axons in the
CNS
d. Ependymal cells – line the cavities of the brain & spinal cord
and produce cerebrospinal fluid.
2. Types in the PNS
a. Schwann Cells- produce myelin sheaths for
the PNS
b. Satellite Cells – support neurons in ganglia of
PNS
C. Axon bundles
1. In the PNS the bundles form White Matter.
They are white because of the myelin, the
white matter propagates the never signals.
2. In the CNS the cell bodies and unmyelinated
axons are called Gray Matter. This tissue
performs integrative functions.
C. Disorders of Nervous Tissue
1. Multiple Sclerosis – characterized by myelin loss in
central nerve fibers resulting in conduction impairment
a. loss of muscle control/coordination, visual
impairment, and speech problems
b. autoimmune disease triggered by a viral infection
c. chronic, prolonged, can be relapsing/remitting
d. most common in women age 20-40
e. no known cure
2. Tumors – general name for nervous system tumor is
neuroma
a. most neuromas are gliomas (neuroglial tumor)
b. multiple neurofibromatosis – characterized by
numerous benign tumors that can progress to
disfiguring, crippling soft tissue tumors
1. inherited (a.k.a. Elephant Man’s disease)
IV. Nerve – bundle of peripheral nerve fibers
(axons) bundled together like strands of a
cable (in CNS referred to as tracts)
A. White matter – tissue composed mainly of
myelinated axons (nerves/tracts)
B. Gray matter – tissue composed of cell
bodies and unmyelinated fibers
C. Coverings – fibrous connective tissue
1. Endoneurium – surrounds individual
fibers within a nerve
2. Perineurium – surrounds a group
(fascicle) of nerve fibers
3. Epineurium – surrounds the entire nerve
V. Reflex Arcs – conduction of nerve impulse
results in a reflex
A. responses can be contraction by a muscle
or secretion by a gland
B. simplest reflex arcs are two-neuron:
sensory neurons synapsing in the spinal
cord with motor neurons. Ex: “knee-jerk”
response
C. three-neuron arcs consist of sensory
neurons synapsing with interneurons that
synapse with motor neurons.
Ex: withdrawal response
VI. Nerve Impulse – a self-propagating
wave of electrical disturbance that
travels along the surface of a neuron
membrane
A.Physiology – neurons have two
major functional properties:
1.Irritability – the ability to
respond to a stimulus and
convert it into a nerve impulse
(electrochemical event)
a. stimuli causes change in the
neuron plasma membrane
permeability allowing sodium ions
(Na+) to enter the cell – depolarization
b. action potential/nerve impulse
(all-or-none response) continues
over the entire length of the cell
c. electrical conditions of the resting
stage (polarized) are restored by
the diffusion of potassium ions (K+)
out of the cell – repolarization
d. ion concentration is restored by the
sodium-potassium pump
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2. Conductivity – the ability to transmit the
impulse to other neurons, muscles, or
glands.
a. neurotransmitters released by axonal
terminals of a presynaptic neuron into
synaptic cleft.
b. neurotransmitter binds to specific
molecules in the membrane of a
postsynaptic neuron. This stimulates
impulse conduction by the membrane.
c. names of neurotransmitters –
acetylcholine, catecholamines
(norepinephrine, dopamine, serotonin)
d. Parkinson’s disease – chronic
disorder brought on by a deficiency of
the neurotransmitter dopamine
1. signs include:
- rigidity and trembling of the head
and extremities
- forward tilt of the trunk
- shuffling manner of walking
2. treatments include:
- L-dopa
- surgical grafting of normal
dopamine-secreting neurons
- surgery to cauterize affected areas