Nervous System

• Nervous System


  Enables animals to react to changes in their surroundings so they are able to survive and coordinate their behaviour
• Senses


  Collections of receptor cells that enable us to detect the changes in environment
• Senses and Receptor Cells


  • Sight (Receptor cells in the eye detect changes in light)
  • Hearing (Receptor cells in the ear detect changes in sound)
  • Balance (Receptors in the ear detect changes in position)
  • Touch (Receptor cells in the skin detect changes in pressure, changes in temperature and pain)
  • Smell (Receptor cells in the nose detect changes in chemicals)
  • Taste (Receptor cells in the tongue detect changes in chemicals)
• Nerve Cells (Neurones)


  • Different types make up the nervous system and enable electrical nerve impulses to travel to and from the central nervous system (the brain and spinal cord) where the coordination takes place
  • Sensory neurone - carry electrical nerve impulses from the receptors to the CNS
  • Relay neurone - carry electrical nerve impulses from the sensory neurone to the motor neurone. They are found within the CNS
  • Motor neurone - carry electrical nerve impulses from the CNS to the effectors (muscles or glands)
  • The long axons enable electrical nerve impulses to travel over long distances
  • The branches enable one cell to be connected to many others

  
• Nerve Impulse Pathway


  1. Stimulus

  2. Receptor

  3. Co-ordinator

  4. Effector

  5. Response

  
• Synapse


  • A gap between neurones i.e. a gap between a sensory neurone and a relay neurone
  • Electrical nerve impulses cannot cross the gap
  • Chemicals called neurotransmitters move across the gap and stimulate an electrical nerve impulse to be generated in the next neurone

  
• Transmission across a synapse

  1. Electrical nerve impulse arrives at the end of a neurone (at the synaptic knob)

  2. Vesicles (sacs of chemical) move to the end of the synaptic knob and fuse with the cell membrane

  3. This releases chemical (neurotransmitter) into the gap (into the synapse)

  4. The chemical (neurotransmitter) diffuses across the gap and binds with receptors on the surface of the next neurone

  5. The chemical has a complementary shape to the receptor

  6. The binding causes the electrical nerve impulse to be generated in the next neurone

  
• Reflex Action


  • A fast, automatic response to a stimulus
  • It does not involve conscious thought by the brain
  • Reflex actions are important as they protect us from harm and damage to our tissues
• Reflex Actions


  • Coughing to prevent choking
  • Removing your hand from a hot or sharp object to prevent damage to the skin tissues
• Reflex Arc


  1. Receptor

  2. Sensory neurone

  3. Synapse

  4. Relay neurone (or inter neurone)

  5. Synapse

  6. Motor neurone

  7. Effector

  
• The gap between the neurones is a synapse. The synapses are in the grey matter of the spinal cord.