Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: When a flexor muscle is excited, the probability of excitation decreases in the paired extensor muscle.
Reason R: The interneuron that excited a motor neuron to the flexor muscle also inhibited a motor neuron connected to the extensor muscle.
In the light of the above statements, choose the most appropriate answer from the options given below

• A. Both A and R are correct and R is the correct explanation of A
• B. Both A and R are correct but R is NOT the correct explanation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Hint:

Reciprocal inhibition is a fundamental spinal reflex mechanism. Inhibitory interneurons are the biological "switches" that turn off the antagonist muscle when the agonist muscle is turned on.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks us to analyze an Assertion-Reason pair explaining how antagonistic muscle groups (flexors and extensors) are coordinated during motor reflexes.

Step 2: Detailed Explanation:

• Antagonistic muscle pairs, such as the biceps (flexor) and triceps (extensor), must work in a coordinated, opposite fashion to produce smooth limb movement.

• Assertion A states that when a flexor muscle is excited, the probability of excitation in its paired extensor muscle decreases. This is a true statement describing the phenomenon of reciprocal inhibition.

• Reason R explains the physiological mechanism behind this reflex. When sensory neurons detect a stimulus, they project into the spinal cord.

• In the spinal cord, sensory neurons synapse with interneurons. One pathway of interneurons excites the motor neuron of the flexor muscle, causing it to contract.

• Simultaneously, collateral branches of these interneurons activate inhibitory interneurons, which directly inhibit the motor neurons controlling the antagonistic extensor muscle, preventing it from contracting.

• This reciprocal wiring ensures that muscles do not pull against one another, making the Reason a biologically accurate and direct explanation of the Assertion.

Step 3: Final Answer:
Both Assertion A and Reason R are correct, and Reason R provides the exact neurological explanation of Assertion A.