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Chapter 12: NERVOUS SYSTEM - Fundamentals & Neural Tissue
Master controlling communicating system of the body
 Responsible for every

Cells respond quickly
1. Monitors changes (stimulus)
o Gathered information is called
2. Processes and interprets, then decides what should be done
o A process called integration
3. Causes a response by activating effector organs (motor output)
Two divisions of our Nervous System
1. CNS (central nervous system)

Integrating and command center
2. PNS (peripheral nervous system)

Nerves that extend from the brain and spinal cord
Two functional subdivisions
 Sensory (afferent) division
o Somatic – skin, muscles, joints
o Visceral – organs inside ventral cavity

Motor (efferent) division
Two main parts
 SNS (Somatic nervous system) – somatic motor nerves

ANS (autonomic nervous system) – consists of visceral motor nerve fibers
Two functional subdivisions
 Sympathetic –

Parasympathetic –
*Both are always in counterbalance of each other, not necessarily equal
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Two types of cells - supporting cells and neurons
I. Neurons (nerve cell)
 basic structural and functional component

excitability (irratibility)

amitotic

Increased metabolic rate

Longevity
Structure of a Neuron - 3 distinct portions:
1. cell body (soma):
 perikaryon – cytoplasm surrounding the nucleus

contains most organelles of a typical cell except

The high # of mitochondria, fixed and free ribosomes
Nissl bodies (chromatophilic substance) -
2. dendrites:
3. axon:

conduct impulses

axon hillock

axon collaterals

telodendria

axon terminals (synaptic bulbs)
Synapse:
- mediates the information transfer from
1. presynaptic neuron
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2. postsynaptic neuron
- typical synapse has: axon terminals & receptor regions (ie. dendrites; sarcolemma)
- specialized for the release and reception of
- neurotransmitters
Axoplasmic Transport – movement of materials between the cell body and synaptic knob
 anterograde – cell body to

retrograde – synaptic bulb to
Neurons are classified by structure and function
Structural classification:
1. Anaxonic – small and do not distinguish dendrites from axons. Located in the brain and
special sense organs
2. Bipolar – 2 processes; cell body in between. Associated with special sense organs
3. Unipolar – continuous, fused dendrite and axon with the cell body off to the side. Most
sensory neurons of the PNS; may extend a meter or more
4. Multipolar – 2 or more dendrites and a single axon; most common type of all neurons; may
extend a meter or more
Functional classification:
1. sensory (afferent) neurons – afferent division of the PNS (~10 million neurons)
a. cell bodies of sensory neurons are located in peripheral ganglia
b. somatic vs. visceral
c. Categorized as Exteroceptors, Proprioceptors, or Interoceptors
2. motor (efferent) neurons – (~500,000 neurons)
a. cell bodies are located in the CNS
b. Somatic (SNS) vs. Visceral (ANS)
c. Pre and Postganglionic fibers
3. Interneurons (association) - (~20 billion neurons)
a. Located in the brain and spinal cord
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b. shuttle information between sensory and motor neurons
c. also involved in memory, planning and learning
II. Supporting cells also called neuroglia or glial cells
Neuroglia of the CNS

ependymal cells – single layer of ciliated cells that
o have slender processes that branch and make contact with other neuroglia which
use is unknown

astrocytes- connection between neurons and capillaries
o
o
o
o
o

Maintain blood-brain barrier
Create framework for the CNS
Repair damaged neural tissue
Guide neuron development
Control interstitial environment
Oligodendrocytes -
myelin sheath
nodes of Ranvier
grey vs white matter

Microglia – small with long thorny processes; monitor the health of neurons; police
much like macrophages
Neuroglia of the PNS

Satellite cells – regulate the environment around the neurons much like astrocytes do in
the CNS; surround neuron cell bodies

Schwann cells
-neurilemma or sheath of Schwann
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NEURAL RESPONSE TO INJURIES
Wallerian degeneration -
NEUROPHYSIOLOGY
Basic Principles of Electricity 
The measure of potential energy of a separated charge is known as

The

Current –

Resistance –

Ohm’s Law: current = voltage/resistance
the difference; the
the voltage
Resting membrane potential (Polarized State) 

more K inside the neuron
more Na outside the neuron
(membrane is more permeable to K than Na )

passive forces such as diffusion pulls K out of neuron

electrochemical gradient for Na to enter neuron

active transport of Na –K pump
Membrane potentials as Signals – stimulus can change resting potential by:
1. changing
2. altering

depolarization

repolarization

hyperpolarization
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Membrane channels – control the movement of ions across the cell membrane

leak channels (passive) –

gated channels (active) –
1. Chemical
2. Voltage
3. Mechanical
Graded Potentials (summary table 12-2)
- short lived
- signal decreases over distance
- called graded potential because
- essential in initiating
Action Potentials (summary table 12-3)
-wave of negativity
-don't decrease in
-only
Generation of an action potential
1.
2.
3.
4.
Threshold
All or None Principle
with
generate action potentials
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Absolute refractory period
Relative refractory period
Propagation –

Continuous – on unmyelinated axon

Saltatory – on myelinated axons
Conduction velocities of Axons
1. axon diameter
2. myelin sheath
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Group A, B, or C fibers:
A:
B:
C:
Electrical vs Chemical Synapses
Cholinergic synapses:
• uses Ach
• action potential arrives at synaptic knob which opens voltage gated _______ channels
and
__is pumped into the synaptic knob
• this triggers exocytosis of Ach which is then released into the synaptic cleft
Neurotransmitters
 Excitatory or inhibitory

Ach

Norepinepherine

Dopamine

Serotonin

GABA
Neuromodulators
 Alter the rate of neurotransmitter release or change the postsynaptic sensitivity

Four classes of opioids:
Postsynaptic Potentials – graded potentials that develop in the postsynaptic membrane in
response to a neurotransmitter
Excitatory postsynaptic potential (EPSP):
- local event
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-a single EPSP cannot induce an action potential but:
Inhibitory postsynaptic potential (IPSP):
Temporal vs Spatial summation
Information Processing (Summary Table 12-7)
Factors that disrupt Neural Function

Environmental

Metabolic