The nervous system

• Motor neurone

  • Many short dendrites carry nerve impulses from the CNS to the cell body
  • One long axon carries nerve impulses from the cell body to effector cells

  A) cell body

  B) dendrites

  C) myelin sheath

  D) axon

  E) effector cells

  
• Sensory neurone

  • One long dendron carries nerve impulses from receptor cells to the cell body, which is located in the middle of the neurone
  • One short axon carries nerve impulses from the cell body to the CNS

  A) receptor cells

  B) dendron

  C) axon

  D) cell body

  
• Relay neurone

  • Many short dendrites carry nerve impulses from sensory neurones to the cell body
  • An axon carries nerve impulses from the cell body to motor neurones

  A) dendrites

  B) cell body

  C) axon

  
• Synapses


  Synapses are the connection between two neurones. The nerve signal from a neurone is transferred by chemicals called neurotransmitters, which diffuse across the gap. These neurotransmitters then set off a new electrical signal in the next neurone. This process slows a nervous impulse down because the diffusion of neurotransmitters takes time.
• Axon


  Carry nerve impulses away from the cell body
• Dendrites and dendrons


  Carry nerve impulses towards the cell body
• Myelin Sheath


  Some axons are surrounded my myelin sheath which acts as an electrical insulator speeding up the impulse
• Nervous system order of response

  Stimulus>Receptor>Sensory neurone> Relay neurone> CNS> Motor neurone> effector> response
• What is in the CNS?

  Brain and spinal cord
• Reflex Arcs

  1. The receptors detect a stimulus and send an impulse to the sensory neurones
  2. The sensory neurones carry this signal to a relay neurone -via a synapse- which carries it to the spinal cord or an unconscious part of the brain
  3. The impulse is then carried from relay neurone to motor neurone- via a synapse-
  4. The motor neurone sends the impulse to effector cells (e.g a muscle)
  5. A response is made immediately (e.g a muscle contracting)
• Sensory receptors

  A group of cells that detect a change in the environment. Different receptors detect different stimuli. Receptors in your eyes detect light whereas receptors in your skin detect touch and temperature change.