Simple Reflex Arc (Edexcel IGCSE Biology)

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Simple Reflex Arc

  • 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)
  • This all occurs within a fraction of a second

A reflex arc

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.

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Lára

Author: Lára

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.