transmission of AP

• • once AP is generated, it can be transmitted along axon
  • depolarisation of membrane at site of first AP causes NA+ to diffuse along cytoplasm ino next section of axon
  • this depolarises membrane in new section- causing voltage gated NA+ channels to open
  • triggers another AP repeating along length of axon
• transmission in ONE direction

  • any NA+ which diffuses backwards along the membrane is unable to initiate a new AP due to hyperpolarised nature of membrane following previous AP
• ALL OR NOTHING PRINCIPLE

  • impulse is only transmitted if intial stimulus is efficient enough to increase membrane potential above threshold potential
  • if stimulus is weak, only few NA+ channels open and membrane wont efficiently depolarise, no AP generated
  • if stimulus size increases so does the frequency of APs transmitted along the neurone however doesnt increase the intensity of impulse
• preventing impulse transmission

  • eg pain killers
  • some drugs bind to sodium ions channels preventing opening and influx of NA+ when stimulated
  • this prevents membrane depolarisation and AP cannot be generated
• myelination

  • increases the speed of APs travelling along neurone
  • where axons are surrounded by myelin sheath depolarisayion cannot occur as it stops the diffusion of ions
  • AP can only occur at nodes of ranvier
  • NA+ diffuse along axon within schwann cells, membrane of the node of ranvier depolarises when NA+ arrive
  • so APs jump from nodes of ranvier= saltatory conduction