SB2i- Neurotransmission speeds

• Describe how the nervous system responds to stimuli

  Impulses travel through the CNS along relay neurones

  The CNS sends information to an effector (muscle or Gland) along a motor neurone

  The effector responds accordingly
• Relay neurone structure

  3 main parts

  • Dendrite, cell body, axon
  • Dendrites receive signals, the cell body processes them and the axons sends the signal to other neurones
• Motor neurone structure

  • Motor neurones have a cell body which contains the nucleus
  • Branching out, there are dendrites (which receive signals from other neurones)
  • Long axon is surrounded by a MYELIN SHEATH
  • Myelin sheath- electrical impulses jumps from one gap in the myelin sheath to another, speeding up the rate of transmission
  • Nerve endings which transmits the impulse to an effector
• Sensory neurone structure


  • Skin receptor cells have dendrites which collect impulses from receptor cells
  • The impulse moves along a LONG DENDRON (carries impulse TOWARDS cell body)
  • Then there is a cell body
  • The impulse then moves father along the SHORT AXON (carries impulse AWAY from cell body)
  • To the axon endings which pass impulses to other neurones
  • The short axon is insulated with a myelin sheath
• Synapses


  • A synapse is a gap between two neurones
  • The eletrical nerve impulse cannot cross the gap, so the impulse needs to be carried out by NEUROTRANSMITTERS
• How synapses work


  • An electrical nerve impulse reaches the end of the neurone
  • The electrical impulse causes chemical neurotransmitters to be released from vesicles in the neurone into the gap between neurones
  • The neurotransmitter DIFFUSES across the gap and fits into receptors, causing a new electrical impulse in the next neurone
• The reflex arc


  A reflex action follows this general sequence and does not involve the conscious part of the brain. This is why the response is so fast.

  1. Receptor in the skin detects a stimulus (the change in temperature).
  2. Sensory neuron sends electrical impulses to a relay neuron, which is located in the spinal cord of the CNS. Relay neurons connect sensory neurons to motor neurons.
  3. Motor neuron sends electrical impulses to an effector.
  4. Effector produces a response (muscle contracts to move hand away).