Name the reflex action in which the flexer muscle contracts and the extensor muscle relax in withdrawing limb?

MP NHM CHO-2024 (Shift-1)

Applied Physiology

Easy

Appeared in: MP NHM CHO-2024 (Shift-1)

Explanation

The question describes the precise mechanism of the flexor reflex, which is a protective action to remove a limb from a painful stimulus.
This reflex involves activating motor neurons to the flexor muscles, causing them to contract.
Simultaneously, through a process called reciprocal inhibition, inhibitory interneurons are activated to prevent the motor neurons of the antagonist extensor muscles from firing.
This coordinated contraction of flexors and relaxation of extensors ensures a swift and efficient withdrawal of the limb.

Option A: The crossed extensor reflex describes the response in the limb opposite to the one receiving the stimulus. It involves extension of the contralateral limb to support the body's weight, not withdrawal of the stimulated limb.
Option B: The Golgi tendon reflex is a protective reflex that responds to excessive tension in a muscle. It causes the muscle to relax to prevent injury to the muscle or its tendon.
Option D: While the flexor reflex is a type of withdrawal reflex, 'Flexor reflex' is a more specific and precise answer. The question details the specific muscle actions (flexor contraction, extensor relaxation), which is the definition of the flexor reflex itself.

Visual 1: Diagram: A flowchart showing the neural pathway of the flexor reflex. It would start with a painful stimulus to the foot, show the sensory neuron traveling to the spinal cord, synapsing with an interneuron, which then excites the flexor motor neuron and inhibits the extensor motor neuron, resulting in leg flexion.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Spinal cord reflexes, specifically the mechanism of the flexor (withdrawal) reflex and reciprocal inhibition as background academic context rather than a clinical decision trigger.
Assessing reflexes is a fundamental part of a neurological examination. The presence, absence, or exaggeration of the flexor reflex can help a nurse or doctor localize lesions in the nervous system (e.g., spinal cord injury).
Understanding this reflex is crucial for patient safety, as it is a primary protective mechanism. A patient with a diminished reflex is at higher risk for injury from heat, pressure, or sharp objects.
What if? If a patient shows a flexor reflex but no crossed extensor reflex, it could indicate a more severe spinal cord injury where the pathways that cross the midline of the cord are damaged.

How to Approach the Question

First, identify the key actions described in the question stem: 'flexer muscle contracts', 'extensor muscle relax', and 'withdrawing limb'.
Recall the definitions of the different types of spinal reflexes provided in the options.
Analyze the relationship between the muscles: flexors and extensors are antagonist pairs. The described action (one contracts, the other relaxes) is called reciprocal inhibition.
Compare the options. 'Crossed extensor reflex' involves the opposite limb. 'Golgi tendon reflex' involves relaxation due to tension.
Differentiate between 'Flexor reflex' and 'Withdrawal reflex'. Recognize that 'Flexor reflex' is the specific physiological name for the mechanism described, while 'Withdrawal reflex' is a broader functional term. In a multiple-choice question, the most precise and specific correct answer is preferred.

Concept Tested & Keywords

Concept Tested: Spinal cord reflexes, specifically the mechanism of the flexor (withdrawal) reflex and reciprocal inhibition.
Stem keywords: reflex action, flexer muscle contracts, extensor muscle relax, withdrawing limb
Lead-in keywords: Name
Negative lead-in flag: false

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