reflex actions

• A reflex action 


  where the body responds to a stimulus without making a conscious decision to respond.
• a reflex action takes place because the pathway of communication doesn't involve conscious parts of the brain - instead it goes through unconscious parts of the brain or the spinal cord. Because you don't have to spend time deciding how to respond, information travels really fast from receptors to effectors. Reflex actions are protective - they help organisms to avoid damage to the body because the response happens so quickly.
• Blinking reflex


  1. Stimulus - something touches your eye

  2. Receptors - sensory nerve endings in the cornea detect the touch stimulus, send nerve impulse along sensory neurone to relay neurone in CNS

  3. CNS - impulse passed from relay neurone to motor neurones

  4. Effectors - motor neurones send impulses to orbicularis oculi muscles that move eyelids

  5. Response - muscles contract causing eyelids to close quickly to prevent eye damage
• Knee-jerk reflex


  1. Stimulus - quadriceps muscle is stretched

  2. Receptors - stretch receptors in quadriceps detect stretch, nerve impulse passed along sensory neurone

  3. CNS - sensory neurone communicates directly with motor neurone in spinal cord

  4. Effectors - motor neurone carries nerve impulse to quadriceps muscle

  5. Response - quadriceps muscle contracts, lower leg moves forward quickly
• Knee-jerk reflex


  • Works to quickly straighten leg if body detects quadriceps is suddenly stretched
  • Helps maintain posture and balance
• Knee-jerk reflex


  • If knees buckle after landing from a jump, reflex causes quadriceps to contract to keep you upright