Reflex action

Correct answer: A. The stimulus will be detected, but the response may be blocked

The governing concept is the reflex arc, which includes a receptor, sensory neuron, relay neuron, motor neuron and effector. A normal sensory nerve can carry information from the receptor to the nervous system, so the stimulus may be detected. However, blockage in the relay pathway prevents or weakens transmission to the motor neuron and effector. Therefore, option A is correct; B ignores the need for a nerve signal, while C and D are unrelated.

Correct answer: B. Medulla

The cerebrum is chiefly associated with conscious activities such as thinking, memory and voluntary speech, so preserved thinking and speaking suggest that it is not the main affected part. Breathing is an involuntary, vital activity regulated by centres in the brainstem, especially the medulla. Thus option B is most suitable. The cerebellum coordinates movement and balance, while the tongue is an effector, not the main respiratory control centre.

Correct answer: A. Reflex action is fast and involuntary while voluntary action is linked with will and thought

The governing concept is the difference between involuntary protective responses and consciously controlled actions. A reflex action follows a rapid pathway, usually through the spinal cord, so it can occur without waiting for deliberate thought. A voluntary action involves conscious planning or choice by the brain. Therefore option A is correct; B incorrectly assigns reflexes to plants, C denies the brain’s role, and D ignores nervous control.

Correct answer: A. Receptor then sensory nerve then spinal cord then motor nerve then effector

The governing concept is the direction of information flow in a reflex arc. A receptor first detects the stimulus. The sensory nerve carries the impulse to the spinal cord, which coordinates the rapid response; a motor nerve then carries the command to the effector, such as a muscle. Thus A gives the correct sequence. The other options reverse stages or incorrectly insert blood, hormones or an unsuitable order.

Correct answer: A. Spinal cord forms the message and muscle pulls the hand away

In a withdrawal reflex, the spinal cord acts as the rapid control centre that receives and processes the sensory signal, while a skeletal muscle acts as the effector. The muscle contracts and pulls the hand away from the harmful stimulus. Thus option A represents the correct relationship, although the spinal cord coordinates the response rather than literally creating the original stimulus message. The other pairs assign impossible functions.

Correct answer: A. Because spinal cord works as a quick control centre in reflex arc

In many reflex actions, the spinal cord acts as a rapid integration and coordination centre. A sensory impulse enters through a sensory neuron, is processed through the reflex pathway, and a motor impulse is sent quickly to the effector, often before conscious brain processing is complete. Injury to the relevant spinal region can interrupt this communication and impair the reflex. Thus A is correct; B, C and D assign plant or endocrine functions to the spinal cord.