Which of the following sequences is the correct route of the transmission of impulses along a reflex arc?

Step 1: Analyze the question You are asked for the correct order in which an impulse travels along a reflex arc, which is the pathway for an automatic, rapid response (for example, pulling your hand away from a hot object).

Step 2: The concept A reflex arc has these components, in this order:

1. Receptor – detects the stimulus (e.g., heat receptors in the skin).
2. Sensory (afferent) neuron – carries the impulse toward the spinal cord (central nervous system).
3. Synapse – the gap where the impulse passes chemically to the next neuron.
4. Intermediate (relay/association) neuron – located in the spinal cord, connects the sensory and motor neurons.
5. Synapse – another junction.
6. Motor (efferent) neuron – carries the impulse away from the spinal cord.
7. Effector – a muscle or gland that carries out the response.

Step 3: Check the options

• A. Receptor → sensory neuron → synapse → intermediate neuron → synapse → motor neuron → effector. This matches the correct order.
• B. The motor neuron comes right after the receptor, and the sensory neuron comes right before the effector. This is wrong.
• C. It starts at the effector and runs backwards. This is wrong.
• D. It also starts at the effector, and the neuron order is wrong. This is wrong.

Step 4: Answer The correct option is A.

Exam tip: Remember the order as R-S-I-M-E: Receptor, Sensory, Intermediate, Motor, Effector. Also, "Sensory goes in, Motor goes out" of the spinal cord. An impulse always starts at a receptor and ends at an effector.