Reflex Action

Reflex is involuntary and a sudden response to stimuli. It happens to be an integral component of the famed survival instinct. Most of the common reflexes are a response to all the well trained, accumulated knowledge of caution that we have internalized. It could be anything and ranges from the reflex action of abruptly withdrawing the hand as it comes in contact with an extremely cold or hot object. This action is termed as the reflex action. It has a subtle relation with instinct.

A point to be thought upon is that we all have our instincts differently depending on our past experience and understanding. A reflex is a reaction triggered by this instinct. At times we have no prior knowledge whether the pan is hot or not, nowhere instinct has little to do with reflex.

reflex action

Reflex Action

Action of the Neurons

Two neurons dominate the pathway, afferent nerves (receptor) and the efferent nerves (effector or excitor).

Below is a brief description of the events that take place:

  • Firstly, it begins with receptor detecting the stimulus or a sudden change in the environment, where the instinct again has a role to play. The stimulus is received from a sensory organ.
  • Then, the sensory neuron sends a signal to the relay neuron.
  • This is followed with the relay neuron sending the signal to the motor neuron.
  • Further, the motor neuron sends a signal to the effector.
  • The effector produces an instantaneous response, for example, pulling away of the hand or a knee-jerk reaction.

From the above explanations, it can be clearly summarized that the moment the afferent neuron receives a signal from the sensory organ; it transmits the impulse via a dorsal nerve root into the Central Nervous System. The efferent neuron then carries the signal from the CNS to the effector. The stimulus thus forms a reflex arc.

In reflex action, the signals do not route to the brain – it is directed into the synapse in the spinal cord, hence the reaction  is almost instantaneous.

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Practise This Question

Injury to vagus nerve in humans is not likely to affect: