A level nerves and action potentials

• Sensory neurons


  Neurones that carry incoming information from the sense receptors to the central nervous system
• Relay neurone


  Short nerve cell that connects sensory and motor neurones.
• Motor neurones


  Neurones that carry outgoing information from the brain and spinal cord to the muscles and glands
• Reflex arc

  receptor --> sensory neurone --> relay neurone --> motor neurone --> effector
• resting potential


  The difference in electric charge between the inside and outside of a neuron's cell membrane (-70mV)
• Establishing the resting membrane potential

  Na/K pump: 3 x Na+ out of axon, 2 x K+ into axon. K+ ions flow down electrochemical gradient but pumped back in. Overall more positive on outside of axon
• Depolarisation


  A temporary and local reversal of the resting potential difference of the membrane that occurs when an impulse is transmitted along the axon
• How depolarisation occurs

  Stimulus causes the influx of Na+, causing a reversal of charge along the axon membrane. Voltage gated Na+ channels open allowing Na+ to flow into axon
• Depolarisation is an example of

  Positive feedback
• Repolarisation


  A change in potential difference from positive back to negative across the membrane of a neurone
• How repolarisation occurs

  when +40mV reached, voltage gated Na+ channels close and Voltage gated K+ channels open. K+ diffuse down the electrochemical gradient. Inside the axon is now more negative
• Hyperpolarisation

  Too many K+ move outside of the axon, causing the inside of the axon to become more negative than the outside (-90mV). Voltage gated K+ channels now close.
• threshold potential


  The minimum membrane potential that must be reached in order for an action potential to be generated (-55mV)
• Saltatory conduction


  The propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.
• As axon diameter increases

  the speed of conduction increases
• Structure of sensory neurone

  Cell body off the middle of axon, dendrites connected to axon, short axon
• Structure of motor neurone

  Cell body at the end of axon, dendrites connected to cell body, long axon
• myelin sheath


  A layer of tissue encasing the fibers of neurons; enables greater transmission speed of neural impulses as the impulse hops from one node to the next.