nervous communication

• neurones - specialised cells that transmit an action potential from one part of the body to another
• adaptations of neurones

  • long
  • sodium potassium pumps 3sodium out 2potassium in
  • gated ion channels
  • organelles - mitochondria, ribosomes, ER, Golgi
  • myelin sheath
• sensory neurone - from sensory receptor to CNS

  • cell body just outside CNS
  • long dendrites
  • short axon
• relay neurone - carries impulses from sensory neurones to motor neurones

  • cell body inside CNS
  • short dendrites
  • short axon
• motor neurone - carries impulses from the CNS to the effector

  • cell body inside CNS
  • short dendrites
  • long axon
• nerve impulse - a temporary reversal of the electrical potential difference across the neurone membrane
• resting membrane potential - the potential difference across the neurone cell membrane while at rest, -70mv.
• threshold potential - the minimum strength of stimulus required to trigger an action potential
• refractory period - time during which another nerve impulse cannot be initiated
• channel proteins

  • voltage gated - whether they are open/closed is dependent on the voltage across the membrane
  • ligand gated - open in the response to the binding of a neurotransmitter
  • stimulus sensitive - when a receptor receives a stimulus the channel will open
• action potential - a brief reversal of the potential across the membrane of a neurone causing a peak of +40mv
• depolarisation - sodium diffuse down electrical gradient into cell causing the membrane to become less negative
• repolarisation - potassium diffuse out of the cell through channels, potential difference becomes more negative inside the cell
• hyperpolarisaiton - too many k leave, sodium potassium pump restore
• all or nothing - below the threshold value no impulse is generated
• non myelinated neurone transmission

  1. during an action potential sodium ions move sideways = local currents
  2. depolarising the next voltage gated channel so the action potential spreads
• saltatory conduction - long local currents

  voltage gated channels only occur at nodes of ranvier causing the action potential to jump in myelinated neurones therefore faster
• factors affecting transmission of action potentials

  • myelin sheath - saltatory conduction is quick
  • diameter of axon - the greater the diameter the faster the rate of transmission
  • temperature - causes increase in kinetic energy which increases speed of neurotransmitter
• sensory receptors - detect changes in the surrounding, energy transducers = convert one from of energy to electrical
• pacinian corpuscle

  • mechanoreceptor
  • found in the skin
  • detects pressure
• how does the pacinian corpuscle work

  1. pressure applied changes the shape
  2. membrane is stretch mediated and causes stimulus sensitive sodium ion channels to open
  3. the membrane becomes depolarised
• transmission across the synapse

  1. action potential arrives at synaptic knob
  2. calcium ions diffuse into the synaptic knob
  3. calcium ions cause vesicles to fuse with the presynaptic membrane, releasing acth by exocytosis
  4. acth binds to receptors on the postsynaptic membrane
  5. sodium channels open, action potential generated