Transcript Nervous System

Nervous System
Transmits information from 1
part of the body to another,
rapid communication
2 major divisions
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Central Nervous system (CNS)– brain and
spinal cord
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Peripheral (PNS)– nerves of the body
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Autonomic nervous system (ANS)– regulates
involuntary functions
Cells of nervous system
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Neurons – made of dendrites, cell body,
axons
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Dendrites – take information to cell body
Axons – take information away from cell body
3 types of neurons
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Sensory – to brain or spinal cord (afferent)
Motor – away from brain/spinal cord (efferent)
Interneuron – conduct impulses from sensory
to motor neurons.
Structure of neuron
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See handout
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Myelin – white fatty substance that covers
some axons outside of CNS
Schwann cell – forms myelin
Nodes of Ranvier – indentions between
schwann cells
Neurilemma – outer cell membrane of a
schwann cell
Neuroglia cells (glia)
Support cells for neurons, do not transmit
impulses.
 3 types of glia
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Astrocytes – star like extensions that hold
neurons and blood vessels together.
Microglia – small, used as microphages
(microbe eating scavengers)
Oligodendrocytes – hold nerve fibers
together and produce fatty myelin sheath that
envelops nerve fibers in the brain and spinal
cord (instead of schwann cells)
Disorders of nervous tissue
Neuromas – tumors of nervous system,
seen mostly in glia cells (glioma)
 Multiple neurofibromatosis – inherited
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Numerous fibrous neuromas
Multiple sclerosis –
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(CNS) disorder of oligodendroglia
Myelin lost and destroyed
becomes plaque like lesions
Nerve conduction impaired
Nerves – see figure 9-6
Group of peripheral nerve fibers (axons) in
PNS
 Look white, covered in myelin
 CNS – called “tracts”,
 White matter – part of CNS covered in
myelin, axons
 Grey matter – dendrites and cell bodies
not covered in myelin sheath
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Nerve structure
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Endoneurium – thin fibrous connective tissue
covering of each axon
Fascicles – group of
wrapped axons
Perineurium – thin,
fibrous covering of
fascicles
Epineurium – tough
fibrous covering of
entire nerve
Reflex arc
Specialized type of neuron pathway that
nerve impulses travel
 2 neuron arc, simplest, ex – knee jerk
 3 neuron arc, ex. Withdrawal reflex
 impulse ->receptor (end of dendrite) ->
sensory neuron ->cell body (ganglion)->
axon-> synapse ->chemicals sent across
gap ->dendrite -> cell body (ganglion) ->
axon of motor neuron -> creates reflex.
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Nerve impulses
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Self propagating wave of electrical disturbance
that travels along the surface of a neuron’s
plasma membrane.
Must be initiated by a stimulus (pressure…
At rest, the membrane has slightly + charge
(Na+) outside and – inside
When stimulated, inside membrane becomes +
and – outside temporarily.
Impulses travel in 1 direction across neurons
surface.
Saltatory conduction – faster impulses when
nerve has myelin covering.