Question

Which is the correct sequence of components of a reflex arc?
A) Receptor- muscle- sensory neuron- motor neuron- spinal cord
B) Receptor- motor neuron- spinal cord- sensory neuron- muscle
C) Receptor- spinal cord- sensory nerve- motor neuron- muscle
D) Receptor- sensory neuron- spinal cord- motor neuron- muscle

Answer 1

Sensory neuron carries signal away from the receptors. The motor neuron carries signals towards the site of action, which is muscle in this case. One of the two neurons brings signal to the spinal cord and the other carries it away from it.

Complete answer:
When a body part comes in contact with extremely hot or cold or pointed objects, a sudden withdrawal of the body part is observed. This process is called involuntary as it happens on its own, no thought or conscious effort is involved in this. It is a response to stimulus generated by the peripheral nervous system, the conscious involvement of the central nervous system does not happen in this process. This particular action is called reflex action. In a reflex action, at least one afferent neuron and an efferent neuron, also called excitor neuron are involved. The afferent neuron or the sensory neuron receives signal from receptors present on the sensory organ, muscle in this case and transmits the impulse into the central nervous system, at the spinal cord. The spinal cord then initiates an impulse in order to send it to the sensory organ. This impulse is carried via the efferent neuron, also known as motor neuron. A reflex arc is thus formed by the stimulus and response produced.

Thus, the correct option is- D. Receptor- sensory neuron- spinal cord- motor neuron- muscle.

Note: A reflex action carried by neural pathways which is known as the reflex arc. The reflex arc acts on a stimulus before the impulse reaches the brain. The reflex action is an automatic involuntary response to an impulse that occurs without a conscious thought.