synapses

• stages


  1)AP arrives at end of axon of the presynaptic neurone and membrane becomes depolarised causing voltage gated CA+channels to open

  2)CA+ diffuse into synaptic knob via channels

  3)calcium ions cause vesicles in synaptic knob to move towards presynaptic membrane, vesicles fuse with it and release NTs into synaptic cleft via exocytosis

  4)NTs diffuse across synaptic cleft and bind with receptor molecules on post synaptic membrane- causing NA+ channels of postsynaptic membrane to open- NA+ ions diffuse in
• stages continued(2)


  5)if enough NT binds with receptors, AP is generated- travels down axon of post synaptic neurone

  • many AP in presynaptic knob causes more NT released by exocytosis
  • large amount of NT=increased NA+ channels open
  • many channels open=large influx of NA+ ions
• role of synapses

  • enable unidirectionality of impulse transmission
  • NT released on one side and receptors on other so can only travel 1 direction
• amplification of nerve signals by summation

  • effect of multiple impulses can be added together to overcome summation(not reaching threshold potential)
  • summation achieved by:

  -several presynaptic neurones converging to meet single post synaptic neurone

  -many AP's arrive at post synaptic knob in quick succession