The cells responsible for transmitting messages to the effectors are

Step 1: Analyze the question The question asks which cells carry messages to the effectors. Effectors are the muscles and glands that carry out a response, such as muscle contraction or hormone secretion.

Step 2: Explain the concept A reflex arc or nerve pathway has three main types of neurons:

• Sensory (afferent) neurons carry impulses from receptors (such as skin, eyes, ears) to the central nervous system (brain or spinal cord).
• Relay (intermediate/association) neurons connect sensory and motor neurons inside the CNS.
• Motor (efferent) neurons carry impulses from the CNS to the effectors (muscles or glands).

Step 3: Apply to the options

• A. Motor neurons: carry messages from the CNS to effectors. ✔
• B. Sensory neurons: carry messages from receptors to the CNS, so this is wrong.
• C. Hair cells: these are sensory receptor cells, for example in the inner ear, and they detect stimuli rather than transmit to effectors.
• D. Relay neurons: they pass messages within the CNS, not to the effectors.

Step 4: Answer The correct option is A. motor neurons.

Tip: Remember "S-A-M-E": Sensory = Afferent (arrives at the CNS), Motor = Efferent (exits to the Effectors). Motor and Effector both relate to "action", so the motor neuron leads to the effector.