Receptors detect stimuli in sensory neurons

Steps:

• Identify receptors as specialized structures that detect environmental changes.
• Recall that sensory neurons transmit signals from receptors to the CNS.
• Note that receptors are located at the start of sensory pathways.
• Confirm motor and relay neurons process signals without direct receptor attachment.

Why D is correct:

• Receptors are defined as sensory endings at the dendrite end of sensory neurons, converting stimuli into electrical impulses per neural transmission basics.

Why the others are wrong:

• A: Receptors are not along all neurons; they are specific to sensory input sites.
• B: Relay neurons connect sensory and motor neurons in the CNS without receptors.
• C: Motor neurons carry signals to effectors, lacking receptors at their ends.

Final answer: D