Reflex Actions

Components of the Reflex arc

1. Receptor - detects stimulus and creates an action potential in the sensory neurone

2. Sensory neurone - carries impulse to spinal cord

3. Relay neurone - connects sensory neurone to motor neurone in the CNS

4. Motor neurone - carries impulse to the effector to carry out the appropriate response

Knee jerk reflex

1) The leg is tapped just below the kneecap, it stretches the patellar tendon and acts as a stimulus

2) This stimulus causes the quadriceps muscles to contract and the antagonistic hamstring muscle to relax, causing the muscle to extend and the leg to kick

5) After the tap of the hammer, the leg is normally extended once and comes to rest.

What does the knee-jerk reflex indicate?

If there is no response, it indicates nervous problems

Multiple oscillation of the leg may be a sign of cerebellar disease.

Suggest how and why someone would react to an object coming towards their face.

They would blink to protect the eye from the object

Survival importance of Reflexes

1. Involuntary responses

   The decision making regions of the brain are not involved

2. Not having learnt

   They are present at birth and therefore provide immediate protection

3. Extremely fast

   The reflex arc is short and normally involves only one or two synapses, the slowest part of transmission