The tendency to reflexively startle at a loud noise is controlled by which part of the nervous system?

The tendency to reflexively startle at a loud noise is primarily controlled by the spinal cord through a reflex arc. When a loud noise occurs, sensory receptors in the auditory system detect the sound and send signals directly to the spinal cord. This allows for an immediate response without the need for the brain to process the information first. The reflex arc bypasses the higher brain functions, enabling a quick reaction, which is crucial for survival in response to potential threats.

The spinal cord's role in processing this reflexive response allows for a rapid reaction to the stimulus (the loud noise). While the brain (including parts like the cerebrum and medulla) is involved in processing sounds and emotions related to them, the immediate startle reflex is a mechanism that relies primarily on the neural pathways coordinated by the spinal cord. This is why the correct answer highlights the spinal cord's importance in controlling such reflex actions.