Organization of the
Nervous System
Anatomy & Physiology
Mrs. Halkuff
The nervous system is the master
controlling and communicating system
of the body.
 The nervous system has 3 main
functions:

– Uses sensory receptors to monitor
changes inside and outside of the body.
(Sensory Neurons)
– Intergration: Processes and interprets
sensory input and makes decision.
– Motor output: Responds by muscles or
glands. (Motor Neurons)
Organization of the Nervous
System
1. Central Nervous
System (CNS):
– Brain and spinal cord
– Command center
– Interprets incoming
sensory information
– Make decisions based
on past experiences
Organization of the Nervous
System
2. Peripheral Nervous
System (PNS):
– Nerves that extend from the
brain and spinal cord.
1. Sensory (Afferent)
Division:
Deliver impulses to the CNS
from various parts of the
body.
2. Motor (Efferent)
Division: Carries impulses
from the CNS to muscles
and glands.
Neuron
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Dendrites: Increase the surface area for
receiving incoming information.
Axon: Carries information from the cell body to
a neighboring neuron.
Myelin Sheath: Insulating fat cells that
increase the rate of signal transmissions.
Node of Ranvier: Bare axon; allows action
potential to jump from node to node.
Axon Terminals: Release
chemicals called
neurotransmitters.
Supporting Cells: CNS

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6 Cell Types Total: 4 CNS; 2 PNS
Microglia: Destroy invading microorganisms that
could be harmful to the CNS. A type of
macrophage.
 Astrocytes: Most abundant; Anchors the
neurons in place by attaching to capillaries. Also
serve as a nutrient (blood supply) to neurons.
 Ependymal Cell: Line the brain & spinal cord
cavities (dorsal). Have cilia that help to circulate
the cerebro-spinal fluid.
 Oligodendrocytes: Wrap around axons of
neurons to form myelin sheaths.
Supporting Cells: PNS
Schwann Cells: Help form myelin
sheath; also engulf deteriorating cell
debris & aid in regeneration.
 Satellite Cells: Surround the cell
bodies and regulate chemical
environment.
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Resting Potential
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A neuron sends messages electrochemically.
Ions are Na & K (positive)
A neuron is at rest when it is not sending a
signal and is in a negatively charged state.
Even at rest, the neuron allows K to pass.
Neuron pumps 3 Na ions out for every 2 K ions
it pumps in.
At rest, there are more Na ions outside and
more K ions inside
Resting & Action Potential
Action Potential
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Occurs when a neuron sends information down
the axon.
Electrical activity created by a depolarizing
current.
A stimulus must make the neuron reach its
threshold in order to fire an action potential.
Stimulus causes Na channels to open and Na+
rushes into the neuron, depolarizing it.
K rushes out of the cell, reversing the
depolarization.
Autonomic Nervous System

Part of the PNS.
 Has 2 divisions: Sympathetic &
Parasympathetic
 Controls heart rate, digestion, respiration
rate, salivation, & perspiration.
Sympathetic
Neurons begin in the Thoracic &
Lumbar region of the spinal cord
 Functions in actions that require a quick
response.
 “Fight or Flight” response.

Parasympathetic
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Neurons begin in the cervical
& sacral regions of the spinal
cord.
Functions in actions that do
not require an immediate
response.
“Rest & Digest”
Constant opposition to
Sympathetic N.S.
Sympathetic &
Parasympathetic Clip
Reflexes
Involuntary, rapid actions; usually for
survival.
 Most reflexes don’t have to travel to the
brain, as they need to happen quickly.
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– Reflex Arc:
1.
2.
3.
4.
Receptors are excited.
Signal travels along sensory neuron to spinal cord
Signal is passed onto a motor neuron
Muscle/Gland is stimulated.