AQA A Level Biology

Revision Notes

6.1.5 Reflex Arcs

Reflex Arcs

  • There are three main types of neurone: sensory, relay and motor
    • Sensory neurones carry impulses from receptors to the Central Nervous System (CNS – the brain or spinal cord)
    • Relay (intermediate) neurones are found entirely within the CNS and connect sensory and motor neurones
    • Motor neurones carry impulses from the CNS to effectors (muscles or glands)
  • Sensory neurones, relay (intermediate) neurones and motor neurones work together to bring about a response to a stimulus
  • A reflex arc is a pathway along which impulses are transmitted from a receptor to an effector without involving ‘conscious’ regions of the brain
  • As it does not involve the brain, a reflex response is quicker than any other type of nervous response
  • Examples of simple reflex actions that are coordinated by these pathways are:
    • Removing the hand rapidly from a sharp or hot object
    • Blinking
    • Focusing the eye on an object
    • Controlling how much light enters the eye

A reflex, IGCSE & GCSE Biology revision notes

How sensory neurones, intermediate (relay) neurones and motor neurones work together to carry out a reflex action

  • In the example above:
    • A pin (the stimulus) is detected by a pain receptor in the skin
    • The sensory neurone sends electrical impulses to the spinal cord (the coordinator)
    • Electrical impulses are passed on to relay neurone in the spinal cord
    • The relay neurone connects to the motor neurone and passes the impulses on
    • The motor neurone carries the impulses to the muscle in the leg (the effector)
    • The impulses cause the muscle to contract and pull the leg up and away from the sharp object (the response)

The reflex pathway (1), downloadable AS & A Level Biology revision notes

The pathway of a reflex arc

Author: Lára

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.

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top