▶️ Answer/Explanation
The central nervous system (CNS) consists of the brain and spinal cord. In a reflex arc, sensory neurons carry information to the CNS, and motor neurons carry signals away from it. The structure that lies entirely within the CNS—connecting sensory and motor neurons—is the relay neuron (also called an interneuron). The provided table indicates the correct choice corresponds to a value of \(20\%\), which identifies the relay neuron in the diagram as part C.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
A reflex arc is the nerve pathway followed by a reflex action. The sequence is highly specific to ensure a rapid, involuntary response to a stimulus:
- Sensory neurone: Carries the impulse from the receptor (e.g., skin) to the Central Nervous System (spinal cord).
- Relay neurone: Located within the spinal cord, it connects the sensory neurone to the motor neurone.
- Motor neurone: Carries the impulse from the spinal cord to the effector (e.g., a muscle), which then carries out the response.
✅ Answer: (D)
▶️ Answer/Explanation
Structure $P$ is a receptor because its role is to detect a stimulus (the hot object) and convert it into an electrical signal. Structure $Q$ is a sensory neurone because it carries that electrical impulse away from the receptor toward the central nervous system (CNS). In a reflex arc, effectors and motor neurones only come into play after the CNS has processed the signal to coordinate a response, such as moving the hand away. Therefore, row D correctly identifies the roles of both structures based on the direction of the impulse.
✅ Answer: (D)