Reflexes

• Required practical =Measure how quickly nerve impulses travel in the body using a ruler drop test to measure reaction time
• People claim that activities such as drinking cola, talking on the phone & listening to music affect reaction time
• Reflexes


  • Help you avoid danger because they happen so fast
  • Examples: breathing, moving food through digestive system
  • Automatic and rapid - they don't involve the conscious part of the brain
• Simple reflex arc


  1. Sensory neuron

  2. Relay neuron

  3. Motor neuron

  4. Electrical impulse passes from receptor along sensory neuron to the CNS

  5. Impulse passes along relay neuron (usually in spinal cord)

  6. Impulse travels back along motor neuron to effector organ
• Reflex arc


  The pathway that bypasses conscious areas of the brain so that the time between stimulus and reflex action is as short as possible
• Neurons


  • Not joined up directly, have synapses which form physical gaps between them
  • Electrical impulses travelling along neurons have to cross synapses
  • Diffusion of chemicals across the synapse is slower than the electrical impulse in the neurons
• Reflex process


  1. Receptor in skin stimulated

  2. Electrical impulse passes along sensory neuron to CNS

  3. Impulse reaches synapse with relay neuron, chemical released which diffuses across synapse to relay neuron

  4. Impulse reaches synapse between relay neuron & motor neuron, another chemical released which diffuses across synapse

  5. Impulse reaches effector, which responds (muscle contracts or gland secretes)