The Reflex Arc (Cambridge (CIE) IGCSE Biology): Revision Note

The reflex arc

Voluntary responses

• A voluntary response is a response where a conscious decision is made to carry out a particular action

• Voluntary responses start in the brain

  • An example is reaching out to pick up a cup of coffee

Reflex responses

• An involuntary (or reflex) response does not involve the brain as the coordinator of the reaction

• A person is not aware they have completed a reflex response until after the response has been carried it out

• Reflexes are automatic and rapid responses to a stimulus; such as touching something sharp or hot

• As it does not involve the brain, a reflex response is quicker than any other type of nervous response

• This helps to minimise the damage to the body

• An example of a reflex arc is:

1. The pin (the stimulus) is detected by a pain/pressure/touch receptor in the skin.

2. The sensory neurone sends electrical impulses to the spinal cord (the coordinator).

3. The electrical impulse is passed on to a relay neurone in the spinal cord.

4. The relay neurone connects to a motor neurone, transmitting the impulse onward.

5. The motor neurone carries the impulse to a muscle in the leg (the effector).

6. The muscle contracts and pulls the foot up and away from the sharp object (the response).

Synapses

• Where two neurones meet or join, they do so at a junction called a synapse

• Synapses are important because they allow the nervous system to function as a connected network of neurones

• Impulses can pass from one neurone to another across a synapse, allowing them to be directed along the appropriate route, e.g. to the correct part of the brain