Neurones

• 1. Receptors detect a stimuli (a change in in/external environment)
  2. Receptors are specific, they only detect one particular stimulus (eg light, pressure)
  3. Some receptors are cells, eg. photoreceptors connect to the nervous system. Some receptors are proteins on cell surface membranes, eg. glucose receptors are proteins found in the cell membranes of some prancreatic cells.
  4. Effectors bring a response, either muscles or glands
• Structure of a neurone

  Cell body- contains the nucleus surrounded by cytoplasm. Within cytoplasm there large amounts of endoplasmic reticulum and mitochondria which are involved in production of neurotransmitters.

  Dendrons- short extenstions that come from the cell body, which divide into smaller dendrites. These transmit electrical impulses towards the cell body

  Axon- singular elongated nerve fibre that transmit impulses away from the cell body.
• Sensory neurone

  Transmit impusles from sensory receptor cell to relay neurone, motor neurone or brain. Cell body in the middle (must be stuck up), dendrons from receptor to cell body, axon away from cell body to CNS

  
• Relay neurone

  Neurones which transmit impulses between neurones, eg. between sensory and motor. Short dendron and axon

  
• Motor neurone

  Transmit impulses from relay neurone or sensory neurone to an effector.

  One long axon and short dendrites

  
• Receptor -> sensory neurone -> CNS -> motor neurone -> effector
• Between each adjacent Schwann cell is a small gap known as nodes of Ranvier
• Saltatory conduction

  • Nodes of Ranvier- where sodium ion channels and potassium ion channels are concentrated. .
  • Action potentials occur only at the nodes of Ranvier - when one node is stimulated this triggers depolarisation of the next node, causing the impulse to ‘jump’ from node to node.
  • This type of nervous transmission is called saltatory conduction and is much faster than transmission along non-myelinated neurones, where the action potential has to travel along the entire length of the neurone in a wave of depolarisation.
• The speed at which an action potential moves along a neurone is known as the conduction velocity the higher the conduction velocity, the faster the action potential is travelling. This means that action potentials along myelinated neurones have a higher conduction velocity compared to those travelling along non-myelinated neurones.
• The role of neurones is to transmit electrical impulses rapidly around the bodt so that the organism can respond to changes in its in/external environment.