The Pain Reflex Arc
Reflexes
- Reflex responses are actions of the body that occur without conscious thought
- Reflexes are automatic and rapid, minimising damage to the body and therefore aiding survival
- Awareness of a reflex response occurs after it has been carried out; this is because the information takes longer to reach the conscious parts of the brain
- Examples of reflexes include blinking, coughing, and the pupil and knee reflexes
- Blinking prevents the outer surface of the eye from drying out as well as protecting it from foreign objects
- Coughing prevents food from entering the airways and removes mucus from the airways during infection or an allergic reaction
- The pupil reflex prevents damage to the eye from bright light
- The knee reflex aids balance when standing upright
What is a reflex arc
- A reflex arc is a pathway along which impulses are transmitted from a receptor to an effector without involving conscious regions of the brain
- A reflex arc therefore brings about a reflex response
- Sensory neurones, relay neurones and motor neurones work together in a reflex arc
Order of a reflex arc
- A pain reflex arc is another example of a reflex response
- The skin has receptors for pressure, touch, and pain
- The receptor involved is the pain receptor called a nocireceptor
- The stimulus may be a sharp pin or hot flame which is detected by the nocireceptor in the skin of the hand
- An afferent (sensory) action potential is sent along a sensory neurone to the CNS
- An electrical impulse is passed to a relay neurone in the spinal cord
- Relay neurones are found entirely within grey matter of the spinal cord
- A relay neurone synapses with a motor neurone
- A synapse is the junction between neurones; nerve impulses cross synapses by diffusion of a chemical called a neurotransmitter
- A motor neurone carries an impulse to an effector muscle in the hand
- When stimulated by the motor neurone the muscle will contract and pull the hand away from the sharp object or heat; this is the reflex response
- The receptor involved is the pain receptor called a nocireceptor
- The reflex arc for a spinal reflex is as follows:
A Reflex Arc Diagram
Spinal reflexes involve relay neurones in the spinal cord as part of a pain reflex