Transmission of a Nerve Impulse

Transmission of a Nerve Impulse

All or Nothing Principle:

• The stimulus has to be above a certain threshold value to cause an action potential
• Below the threshold value, no action potential occurs
• Once the threshold value is reached, the action potential generated is always the same size regardless of the strength of the stimulus
• All - it doesn't matter how much above the threshold value the stimulus is, it will still generate the same intensity action potential
• Nothing - any stimulus of any strength below the threshold value will not generate an action potential

Actions Potentials are:

• Unidirectional transmissions -
  • action potentials can only travel in one direction
  • the "backwards" part of the axon will be in the refractory period so cannot be reactivated
  • myelination means that sodium ion channels are seperated by the Schwann cells
  • neurotransmitters are only released at the axon terminals
• Discrete - 
  • refractory period ensures action potentials are seperated
  • after an action potential is passed, small section of time when neurone cannot be stimulated again

Factors Affecting Speed of Nerve Impulse Transmission:

• Myelination - 
  • action potentials jump from node to adjacent node
• Temperature - 
  • high temperature means faster speed of nerve impulses and faster diffusion of ions
  • after optimum temperature means channel proteins denature
• Axon…