Question

Which is the correct sequence of components of the reflex arc ?
A. $Receptors{\text{ }} \to {\text{ }}muscles{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}spinal{\text{ }}cord$
B.$Receptors{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}spinal{\text{ }}cord{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}muscle$
C. $Receptors{\text{ }} \to {\text{ }}spinal{\text{ }}cord{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}muscle$
D. $Receptors{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}spinal{\text{ }}cord{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}muscle$

Answer 1

The entire process of response to a peripheral neural stimulation, that occurs involuntarily, i.e., without conscious effort or thought and requires the involvement of a part of the central neural system is called the reflex action. The pathway followed during generation of reflex action is commonly known as reflex arc.

Complete answer:
Which structures in our body participate in the reflex action? This question can be answered by studying the reflex pathway or reflex arc. In a particular withdrawal reflex discussed above, the following actions are carried out:
The stimulus is detected by sensory receptors present in the skin.
These initiate nerve impulses in the sensory or afferent neurons leading from them to the spinal cord.
These impulses enter the spinal cord and initiate impulses in one or more interneurons.
Interneurons initiate impulses in one or more motors or different neurons.
The motor neurons then carry these impulses to the effectors or skeletal muscles in which response will be shown.

Now let us match this information with given options:-
A.$Receptors{\text{ }} \to {\text{ }}muscles{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}spinal{\text{ }}cord$:- the information after detecting on the receptor goes to sensory neuron and muscles do not participate in this process. Thus this option is not correct.
B.$Receptors{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}spinal{\text{ }}cord{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}muscle$:- sensory neuron carries information to the brain after taking information from receptor and motor neuron send information to the affected part. Thus this option is not correct.
C, $Receptors{\text{ }} \to {\text{ }}spinal{\text{ }}cord{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}muscle$:- sensory neuron carries information to the brain after taking information from receptor and the spinal cord receives information and not act as carrying source. Thus this option is not correct.
$Receptors{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}spinal{\text{ }}cord{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}muscle$: sensory neuron carries information to the brain after taking information from receptor and motor neuron send information to the affected
part. Thus this option is correct.

Our required answer is d that is $Receptors{\text{ }} \to {\text{ }}sensory{\text{ }}neuron{\text{ }} \to {\text{ }}spinal{\text{ }}cord{\text{ }} \to {\text{ }}motor{\text{ }}neuron{\text{ }} \to {\text{ }}muscle$.

Note: The entire pathway from sensory receptor to sensory neuron to spinal cord (having interneurons) to motor neuron to effectors is called the reflex pathway or reflex arc. Hence, the reflex pathway comprises at least one afferent neuron (coming from receptor) and one efferent neuron (going to effector or excitor) appropriately arranged in a series.