• A?reflex response?(also known as an?involuntary response) does not involve the?conscious part of the brain?as the?coordinator?of the reaction
• Awareness of a response having happened occurs?after?the response has been carried out
• Responses are therefore?automatic?and?rapid?– this helps to?minimise damage?to the body and?aids survival
  • Pain-withdrawal, blinking and coughing are all examples of reflex responses that help us to avoid serious injury, such as damage to the eye or choking

   

The reflex arc

• A?reflex arc?is the?pathway of a reflex response?(specifically, the pathway taken by?electrical impulses?as they travel along?neurones)
• An example of a reflex response is the pain-withdrawal reflex that occurs when someone steps on a pin. The reflex arc for this response is outlined below 
  1. The pin (the?stimulus) is detected by a (pain/pressure/touch)?receptor?in the skin on the person's foot
  2. A?sensory?neurone sends electrical impulses to the spinal cord (the?coordinator)
  3. An electrical impulse is passed to a?relay?neurone in the spinal cord (part of the?CNS)
  4. A relay neurone?synapses?with a motor neurone
  5. A?motor?neurone carries an impulse to a muscle in the leg (the?effector)
  6. When stimulated by the motor neurone, the muscle will contract and pull the foot up and away from the sharp object (the?response)
  7. This all occurs within a fraction of a second

   

The reflex arc pathway (in this case for a pain-withdrawal reflex). Reflex actions are automatic and rapid; they do not involve the conscious part of the brain

The neurones of the reflex arc

• There are three main types of neurone in a reflex arc: sensory, relay and motor
  • Sensory?neurones carry impulses?from sense organs to the CNS?(brain or spinal cord)
  • Relay?neurones are found inside the CNS and?connect sensory and motor neurones
  • Motor?neurones carry impulses?from the CNS to effectors?(muscles or glands)

   

You need to be able to recognise the three types of neurone in a reflex arc