Question

Which is the correct sequence of the components of a reflex arc

• A. Receptors → muscles → sensory neuron → motor neuron → spinal cord
• B. Receptors → motor neuron → spinal cord → sensory neuron → muscle
• C. Receptors → sensory neuron → spinal cord → motor neuron → muscle
• D. Stimulus → receptor → sensory neuron → relay neuron → motor neuron → muscle

Answer 1

The correct option is D

Stimulus → receptor → sensory neuron → relay neuron → motor neuron → muscle

The correct option is D.

The explanation for the correct option:

1. The neural arc is responsible for a reflex action, which at its most basic level consists of a synapse connecting a motor neuron to a sensory nerve.
2. When a receptor is stimulated, it sends a signal to the central nervous system, where the brain coordinates the response. But sometimes a very quick response is needed, one that does not need the involvement of the brain. This is called reflex action.
3. In a reflex action, the receptor recognizes the stimuli and generates the impulses which are carried by the sensory neuron to the spinal cord. The Relay neuron then connects the sensory neuron and the motor neuron and generates quick responses according to the sensory impulses.
4. The motor neuron carries the information from the spinal cord to the effector also known as the effector. As a response, the effector responds to the stimulus like withdrawing the hand when we touch a hot object.

The explanation for the incorrect options

Option A

1. The muscle is an effector involved in a reflex action. It is the part that is responsible for the response to the stimulus.
2. Hence this flow of components in the reflex arc is incorrect.

Option B

1. Motor nerves are the nerves that transmit information from the brain or spinal cord in the form of a reaction to other body components like the muscles and glands. They are in charge of transmitting data from the CNS to the PNS.
2. It is responsible for the response, not the stimulus. It should come after the sensory neuron. Hence this option is incorrect.

Option C

1. Anything that causes an organism, or a cell or tissue of an organism, to respond is referred to as a stimulus. These impulses may come from within or outside. Hunger and pain are examples of internal sensations that originate within an organism.
2. It is the beginning of a reflex arc that results in a sympathetic action. Since it is missing here, this option is incorrect.

Final answer: The correct sequence of the components of a reflex arc is Stimulus → receptor → sensory neuron → relay neuron → motor neuron → muscle.