Reflex Action

Reflex action is an automatic, quick and involuntary action in the body brought about by a stimulus.

For example,

1. You instantaneously withdraw your hand on accidentally touching a hot plate or a sharp thorn.
2. Watering (salivation) of the mouth takes place on seeing or just smelling a familiar tasty food.

There are two types of reflexes - simple and conditioned. The first one is inborn or natural, which did not require previous learning. Such reflexes are called simple reflexes. The other example is the outcome of repeated experience. Here the brain actually remembers the taste of food and works in an unconscious manner. Such reflexes are called conditioned reflexes.

Mechanism of Reflex Action

Some reflexes are brought about through the brain (cerebral reflexes) such as the closing of the eyelids due to approaching objects while other are brought about through the spinal cord (spinal reflexes). The pathway in a simple spinal reflex action is:

The stimulus (prick, heat, etc.) → receptor in the sensory organ → the afferent (sensory) nerve fibre running through the dorsal root of the spinal nerve bringing the impulse into the spinal cord → a (motor) neuron sending out the command through its efferent fibre in the ventral root of the spinal nerve → a muscle or the gland.

Mostly there occur an intermediate neuron between the axon ending of the afferent fibre and the motor neuron inside the spinal cord.