What are reflexes and how do they work?

Reflexes are quick and automatic reactions to harmful stimuli. Reflexes are important as they protect the body from harm. We don’t have to learn reflexes because they occur automatically from the moment we are born. An example of a reflex is if you step on a pin without shoes on, you will automatically jump away. So, how does this happen? When you first step on the pin, a mechanoreceptor on the skin surface is activated. A mechanoreceptor is a type of receptor that responds to changes in pressure, such as a pin pushing on the skin. The receptor will activate a sensory neurone which sends the information, via an electrical impulse, towards the spinal cord (a part of the central nervous system). At the spinal cord the sensory neurone meets a relay neurone and passes on the information. There is a small gap between the two neurones known as a synapse. The relay neurone passes the information onto a motor neurone at another synapse. The motor neurone transmits the information away from the spinal cord towards the effector. The effector will cause the physical protective response. In this case, the effector will be muscles in the leg that cause you to step off the pin. The journey of the electrical impulse from sensory neurone to relay neurone to motor neurone is known as a reflex arc. You will notice the reflex arc does not involve neurones in the brain. This is because if the information had to travel from the spinal cord into the brain and we had to consciously decide to step off the pin, it would take much longer, risking more damage to the body. Bypassing the brain allows the reflex to occur more quickly.