Speed of nerve impulse

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  • Speed of nerve impulse
    • Refractory period
      • Period after AP  generation  anywhere in axon, inward movement of Na+ ions prevented d.t closure of Na+ voltage-gated channel.
        • AP can't be generated
      • Limits strength of stimulus detected
      • 3 Purposes
        • 1. ENSURES AP- 1D ONLY
          • AP - Can only pass from active region to resting region as they can only move in forward direction
            • Prevents AP spreading both directions
          • Refractory period ensures APs are seperated
        • 3. LIMITS NO. OF APs
          • APs are separate -> limits AP frequency -> limits strength of stimulus detected
    • Factors effecting speed action potential travels
      • 2* Myelin sheath- acts as an electrical insulator, prevents action potential  forming on axon covered in myelin
      • 1* Greater axon diameter -> faster conductance
      • 3* Temp- (effects diffusion rate of ions)- higher-> faster nerve impulse
        • Energy for active transport -> from resp -> controlled by enzymes-> efficient at high temps but can denature -> impulses fail to be conducted
    • nerve impulse- transmission of an action potential along axon
    • once action potential set up, moves from 1 end of axon to other (action potential at end same as at start)
      • All or nothing principal
        • Certain level of stimulus- THRESHOLD VALUE = Action potential
          • below TV, no AP -> no impulse generated
          • Any stimulus of whatever strength, below TV-> fail to make AP
          • Any stimulus above TV -> generate action potential -> nerve impulse will travel
        • Action potentials
          • Are all about same size, so strength of stimulus can't be detected by size of action potentials
            • How organisms perceive size of stimulus
              • 1. Impulse frequency:     + -> larger stimulus
              • 2. Having diff neurons with diff TV
        • Filter: prevents setting up nerve impulses for minor stimuli   -> not overloaded


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