THE HUMAN NERVOUS SYSTEM

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THE HUMAN NERVOUS SYSTEM

• CHAPTER 35

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The Human Nervous System

• Controls and coordinates functions throughout
  body and responds to internal and external stimuli

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Neurons

• Cells which transmit electrical signals, or
  impulses
• Sensory carry impulses from sense organs to
  spinal cord or brain.
• Motor carry impulses from brain or spinal cord
  to muscles and glands.
• Interneurons connect sensory and motor neurons,
  carrying impulses between them.

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Neuron Structure

• Cell body contains nucleus and cytoplasm
• Dendrites carry impulses from environment to
  cell body
• Axon carry impulses away from cell body
• Myelin Sheath insulating membrane surrounding
  axon

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A
H
B
G
F
D
E
C
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Resting Neuron

• Outside cell positive charge, inside negative
  charge resting potential
• Na ions pumped out of cell, K pumped inside
  cell through active transport Sodium-Potassium
  Pump

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Moving Impulse

• Begins when a neuron is stimulated by another
  neuron or environment
• Na allowed in, inside becomes temporarily
  positive
• Reversal of charges action potential
• Impulse passes, K flows out, restoring resting
  potential
• Self-propagating, ex dominoes falling

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Nerve Impulse
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Moving Impulse
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Animation
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• Stimulus must be strong enough to produce impulse
• Follows all-or-none principle, either stimulus
  will produce impulse or not
• Threshold minimal level of a stimulus required
  to activate neuron

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Synapse

• Location where neuron transfers impulse to
  another cell
• Space between neurons synaptic cleft
• Axon terminal contains tiny sacs filled with
  neurotransmitters, chemicals used to transmit
  impulse
• Animation

Synaptic Cleft
Axon terminal
Neurotransmitters
Dendrites next neuron
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Nerve Impulse