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Reflex Action

A reflex action or reflex is a biological control system linking stimulus to response and mediated by a reflex arc. It is any action performed involuntarily in consequence of an impulse or impression transmitted along afferent nerves to a nerve center, from which it is reflected to an efferent nerve, and so calls into action certain muscles, organs, or cells. Reflexes can be built-in or learned. For example, a person stepping on a sharp object would initiate the reflex action through the creation of a stimulus, within specialized sense receptors located in the skin tissue of the foot. The resulting stimulus would be transmitted through afferent, or sensory neurons to the spinal cord. This stimulus is usually processed by an interneuron to create an immediate response to pain by initiating a motor response, which is acted upon by muscles of the leg, retracting the foot away from the object. This retraction would occur as the pain sensation is arriving in the brain, which would process a more cognitive evaluation of the situation.
  1. Voluntary Co-ordination
    These responses are a result of ones though processes, e.g. making a choice of questions in the examination paper. Walking, talking, eating, writing and speaking are some other examples.
  2. Involuntary Co-ordination
    These responses occur without the thought process being involved. Some involuntary co-ordinations continue to occur all the time without our being aware of them, e.g. working of heart, lungs and most other internal organs. This part of the nervous system is called autonomous, i.e. it works all by itself. Many other responses are instantaneous in nature. They occur within fractions of seconds. These are called reflex actions.
Most reflex actions are controlled by the spinal cord but it does not interpret the stimulus in the form of a sensation. In the given figure the feeling of pain due to the pin-prick comes after the withdrawal of the finger. The interpretations of pin-prick into pain is done in the brain. The brain is made aware of reflex actions by impulses that travel through fibers within the spinal cord to and from the brain. The brain is the centre for interpreting all sensations.

Eyes, ears, nose, tongue and skin are our sense organs. They contain special types of receptor cells which receive stimuli and send their impulses to specific areas of the brain where they are interpreted. These sense organs constantly help us in being aware of our environment. 


A Reflex Action


Receptor - The pain receptor in skin of thumb.

Sensory Route - Through a sensory nerve tract from the receptor to the spinal cord. This is dorsal root.

Motor Route - The ventral root with the motor tract reaching the muscles of the foot.

Effector - The muscles which on being stimulated by motor nerve fibres contract and bring about jerking removal of the foot.


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