Biology · Coordination and Control

In a reflex action, the stimulus is sansed by receptors, travels via sensory and relay neurons within the spinal cord, and activates the effector, without involvement of the brain.

This option mentions receptors and effectors but omits the critical role of the spinal cord in the reflex arc. While receptors detect stimuli and effectors respond, the spinal cord is essential for the transmission of the nerve impulse.

This is the correct option. A reflex action involves receptors that sense the stimulus, a spinal cord pathway that includes sensory neurons and motor neurons, and effectors that produce the response. This pathway is designed for speed, bypassing the brain.

This option incorrectly includes the brain, which is not involved in reflex actions. Reflexes are meant to be quick responses and thus operate through the spinal cord alone, minimizing the delay that would occur if the brain were involved.

While this option mentions receptors and neurons correctly, it incorrectly includes the brain. Reflex actions operate through a more direct pathway involving the spinal cord to ensure rapid responses, hence the brain's involvement is not necessary.