reflex arc

• the simplest situation where impulses cross synapse to produce action is the reflex arc
• a reflex action is an automatic response to a stimulus
• it provides means of rapidly integrating and coordination a stimulus with the responses of an effector without the need for thought of decision
• the nervous pathway such reflexes are called reflex arc
• hitting the tendon stretches the muscles and stimulates a stretch receptor:

  • the receptor sends off impulses in a sensory fibre
  • the sensory impulses travel in the nerve to the spinal cord
  • in the central region of the spinal cord, the sensory fibre passes the impulse across a synapse to a motor neurone which conducts the impulse down the fibre back to the thigh muscle (effector)
  • the arrival of the impulses as the muscle makes it contract and jerk
• order :

  stimulus -> receptor -> sensory neurones -> coordinator (spinal cord) -> motor neurone -> effector -> response
• the reflex arc may only require one syapse