Reflex Arcs (AQA A Level Biology): Revision Note

Simple reflexes

• Simple reflexes allow rapid, automatic responses to stimuli, the purpose of which is to protect an organism from harm, e.g.:

  • the pupil reflex prevents bright light from damaging the retina

  • the coughing reflex prevents obstructions from entering the airways

• Reflexes nerve pathways are known as reflex arcs

  • Reflex arcs do not involve conscious parts of the brain, meaning that reflexes are faster than any other type of nervous response

• In a reflex arc a stimulus brings about a response when a nerve impulse is sent as follows:

receptor → sensory neurone → relay neurone → motor neurone → effector

• Reflex arcs involve three types of neurone:

  • sensory neurones carry impulses from receptors to the central nervous system (CNS)

  • relay neurones connect sensory and motor neurones, and are found within the CNS

  • motor neurones carry impulses from the CNS to effectors