Nerves

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  • Created by: Liv Scott
  • Created on: 09-03-15 09:46
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  • Nerves
    • Converting energy
      • Light sensitive cells- light intensity & wavelength
      • Olfactory cells- presence of volatile chemicals
      • Taste buds-presences of chemicals
      • Pressure receptors- pressure on skin
      • Sound receptors in cochlea- vibrations in air
      • Transducotrs convert stimulus to nerve impulse
    • Structure
      • Motor neurone
        • Cell body at the end
        • Many short dendrites, impulse towards CB
        • Long axon
        • No dendron
      • Sensory neurone
        • Cell body in the center
        • Dendron, cimpulse from receptor to CB
        • Shorter axon, impulse from CB to CNS
    • Resting potential
      • -60/-70mV
      • Sodium-Potassium pump actively pumps 3Na+ ions out & 2K+ ions in
      • Membrane more permeable to K+ ions so some K+ ions move back out of neurone
    • Action potential
      • Frequency of transmission
        • All or nothing response
        • Threshold potential reached = action potential
        • Strength of stimulus is proportional to the frequency of action potential
        • Refectory period
          • Brief time when an action potenail can't be generated
      • -60mV
      • 1) Na+ ion channels open, Na+ diffuses in
      • 2) Membrane depolarises, reaches threshold potential, -50mV
      • 3) Voltage-gated Na ion channels open, many Na+ enter
      • 4) Membrane potential, +40mV
      • 5) Na+ channel shut, K+ channels open
      • 6) Repolarisation, K+ diffuse out of cell
      • 7)Hyperpolarisation
      • 8) Resting potential restored
    • Myelin
      • Non-myelinated
        • Slower response time
        • Used in breathing & digestion
      • Myelinated
        • Faster response
        • Used in movement
      • Schwann cells wrap around the axon, forms many layer
      • Ions can't pass through, action potential can only occur at node of Ranvier
      • Action potential jumps, causing larger local current - salutatory conduction
    • Cholinergic synapse
      • Synaptic knob
        • Many mitochondria
        • Lots of smooth ER
        • Vesicles containing acetylcholine
      • Postsynaptic membrane
        • Specialised Na+ channel
    • Neurotransmitters
      • A chemical that diffuses across the synapse to postsynaptic neurone
        • Cause a new action potential
      • 1) Ca+ channels open
        • 2) Ca+ diffuse into synapse
          • 3) Vesicles move to presynaptic membrane & fuse with it
            • 4) Acetylcholine released by exocytosis, diffuses across cleft
              • 5) Binds to specific receptors on postsynaptic membrance
                • 6) Na+ channels open, Na+ ions diffuse in, causes action potential
                  • 7) Acetycholine removed by acetycholinesterase, returns to presynaptic membrane
    • Synapse
      • Ensure one way transmission, only transmitters on pre-synaptic membrane
      • Several neurones go into one post synaptic neurone
      • One presynaptic neurone diverge into several postsynaptic neurones
      • Can filter out low level signals
      • Summation- low level signals amplified
        • Temporal summation- several action potentials in quick succession
        • Spatial summation- several action potential from several neurones
      • Acclimatisation-  run out of neurotransmitter, prevents overstimulation

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