THE BIG PICTURE OF NERVE IMPULSES

 

  1. Neurons function to conduct impulses from one part of the body to another
    1. while traveling along the neuron, the impulse is electrical
    2. when crossing the synapse, the impulse is chemical (don’t want electricity to jump the space and accidently land on an uninsulated cell
  2. Stimulus is applied to a neuron which causes Na+ to rush into the neuron at point A
    1. this current causes a chain reaction, allowing Na+ to enter at point B, and so on down the line
    2. This switching of Na+ and K+ is called depolarization
  3. By the time the action potential has moved from one point to the next (only 1/1000 of a second), the first point has repolarized (gone back to normal)
    1. this happens because of K+
    2. when Na+ rushes in, the positive charge of the Na+ pushes the positive charge of K+ out of the cell due to the fact that like charges repel
    3. the cell doesn’t like to be “backwards”, so the Na+-K+ pump pumps the Na+ back out and the K+ back in (repolarization)
    4. The amount of time needed to do this repolarization = the refractory period
  4. An impulse will only begin if the stimulus is strong enough to cause Na+ to enter
    1. when this occurs- Threshold is reached
    2. threshold varies from person to person
    3. if stimulus is too weak to cause the threshold= subliminal
    4. the threshold can be reached by summation (several subliminals immediately after each other occurring so fast your brain thinks it is one big stimulus)
  5. Impulses move from one neuron to another
    1. the space between them (the synapse) is only 1/100000 of an inch wide
    2. the collaterals at the ends of the axons have knob like structures called boutons that contain the neurotransmitters
    3. you don’t want the electrical current jumping over the synapse, so the electricity opens the boutons and the neurotransmitters are released
    4. the neurotransmitter moves across the synapse to the nerve or cell on the other side
    5. the most common neurotransmitter is acetylocholine
    6. the chemical cholinesterase destroys acetylocholine once it has carried the info across the synapse
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