What is a reflex and what do you mean by a reflex arc? (both "reflex" and "reflex arc" are on the CCEArevised GCSE Biology specification)
1. A reflex is an automatic response to a stimulus. For example: If I touch a hot plate, my hand will automatically pull away from the heat. Another example is the pupillary light reflex. If you turn on a light in a room, your pupils will shrink in order to limit the amount of light entering them. This helps the eye adapt to rapidly changing light. So from this, you can see that reflexes generally function to protect the body, and allow it to react quickly without conscious thought.
- A reflex arc is the mechanism by which a reflex can occur. The spinal reflex arc is the most basic, and the one you need to learn about. A receptor detects a stimuli (stretch/heat etc) in the environment, and produces a nerve impulse that travels along a sensory neurone ( a neurone that brings information towards the spine). This is then connected to an association or interneuron by a synapse (A gap between neurones), which is then connected to a motor neurone by another synapse. The impulse then travels along the motor neurone (a neurone bringing information from the spine) and reaches an effector. An effector is usually a muscle or gland that will respond to impulses from the neurone.
So in our example with touching something hot, a heat receptor produces a nerve impulse that will travel along a sensory neurone to the spine, which will then be connected by an interneuron by a synapse which is connected to a motor neurone by another synapse, and the impulse will travel from the motor neurone into the effector (in this case, muscle) and cause it to contract and move away from the heat.
