OCR A2 Nerve Mindmap

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  • Created by: Caitlin
  • Created on: 02-04-13 13:16
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  • Nerves
    • Structure
      • Sensory
        • cell body in centre of neurone
        • dendron carries nerve impulse from receptor toward cell body
        • axon carries impulse from cell body to CNS
      • Motor
        • cell body at end of neurone
        • many short dendrites carry impulse toward cell body
        • long axon carrying impulse away from cell body
    • Resting Potential
      • when not conducting impulse, at "resting potential" of -60mv
      • Na-K pumps actively transport 3Na out for every 2K in
      • axon contains large organic anions
      • membrane more permeable to K, so some diffuse back out
      • inside more negative than outside - polarised
    • Action Potential
      • 1. membrane polarised -resting state
      • 2. Na ion channels open - some Na diffuse out
      • 3. membrane depolarises and reaches threshold potential of --50 mV
      • 4. voltage gated Na channels open and many Na ions enter - inside more positive than outside
      • 5. potental difference reaches +40 mV - inside positive compared to outside
      • 6. Na ion channels shut and K ion channels open
      • 7. K+ ions diffuse out of cell - potential difference back to negative - repolarisation
      • 8. potential difference overshoots slightly - hyperpolarised
      • 9. orignal potential difference resotored - resting state
    • Frequency of transmission
      • all or nothing - once reaches threshold potential, action potential transmitted
      • size doesn't matter - only frequency of transmission
      • stimulus at higher intensity will cause more generator potentials
        • more frequent action potentials in sensory neurone
          • more vesicles released at synapse
            • higher frequency of action potentials in postsynaptic neurone
              • higher frequency of impulses to brain
    • Myelin sheath
      • fatty electrical insulating layer composed of Schwann cells
      • Na+ and K+ cannot pass through
      • speeds up transmission of action potential
      • action potential can only occur at nodes of Ranvier - between myelin sheath
      • action potential "jumps" from one node to next - SALTATORY CONDUCTION
      • myelinated neurones transmit much faster than non-myelinated
    • Synapse
      • synaptic knob
        • many mitochondria
        • large no of smooth ER
        • vesicles containing neurotransmitter, eg acetylcholine
        • voltage gated Na+ channels in membrane
      • Postsynaptic membrane
        • specialised Na+ channels that only open when acetylcholine binds to them
      • Neurotransmitter
        • chemical that diffuses across cleft of synapse to transmit signal to postsynaptic neurone
        • cause generation of new action potential
        • stored in vesicles in synaptic knob
      • Transmission of Action Potential
        • 1. action potential arrives at synaptic knob
        • 2. Calcium channels open and calcium ions diffuse into synapse
        • 3. Vesicles containing acetycholine move to presynaptic membrane
        • 4. vesicles fuse with membrane and release acetycholine via exocytosis
        • 5. acetylcholine diffuses across synaptic cleft
        • 6. acetylcholine binds to receptors on postsynaptic membrane - opening Na+ channels
        • 7. Na+ diffuse into postsynaptic neurone and depolarise membrane


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