The part of the central nervous system that controls unconscious actions in humans is the

Step 1: Analyze the question We need the part of the central nervous system (CNS) that controls unconscious (involuntary/reflex) actions.

Step 2: Key concepts

• The CNS consists of the brain and the spinal cord.
• Cerebrum: controls voluntary actions, thinking, memory, and conscious sensation.
• Cerebellum: coordinates balance, posture, and muscle coordination. It works automatically, but it is mainly responsible for coordination and balance, not reflex actions.
• Spinal cord: coordinates reflex actions (e.g., withdrawing your hand from a hot object). These are automatic and happen without conscious thought. The spinal cord is the reflex centre.
• Optic nerves: part of the peripheral nervous system. They carry impulses from the eye to the brain and are not part of the CNS.

Step 3: Eliminate options

• D is out because optic nerves are not part of the CNS.
• B is out because the cerebrum controls conscious, voluntary activities.
• A is mainly for balance and coordination of voluntary movement.
• C fits: the spinal cord controls reflex (unconscious) actions.

Step 4: Answer The spinal cord is the correct choice.

Note: The medulla oblongata (in the brain) controls involuntary actions such as breathing and heartbeat, but it is not listed here. Among the options given, the spinal cord is the best answer.

Exam tip: Remember "Cerebrum = Conscious, Cerebellum = Coordination/balance, Spinal cord = Spontaneous reflexes." Also, always check whether an option is part of the CNS (brain and spinal cord) or the peripheral nervous system (nerves).