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Nervous System
Principles of Health Science 2012
What is the Nervous System?
•Complex, highly organized system
•Coordinates all of the many
activities of the body
•Allows body to respond and adapt
to changes that occur both inside
and outside the body
•Also known as nerve cell
•Basic structural unit of the nervous system
Parts of neuron
• Cell body
• Nucleus inside
cell body
• Nerve fibers
Nerve fibers continued:
Dendrites – carry impulses toward cell
Axon – single nerve fiber that carries
impulses away from the cell body
•Covered with lipid (fat) covering called a
myelin sheath
•Increases rate of transmission of an
•Insulates and maintains the axon
Axon of a neuron lies close to the dendrites of
many other neurons
•Space between them is known as synapse
•Impulses coming from an axon
“jump” the synapse to get to the
dendrite of a neuron that will carry
the impulse in the right direction
•Special chemicals called
neurotransmitters located at end of
each axon allow nerve impulses to
pass from one neuron to another
•Impulses may follow many
different routes.
•Combination of many nerve fibers
•Located outside brain and spinal cord
Nerves cont.
•Afferent or sensory nerves carry
messages from all parts of the body
to the brain and spinal cord
•Efferent or motor nerves carry
messages from the brain and spinal
cord to muscles and glands
Associative or
internuncial nerves
carry both sensory
and motor messages