Key ideas

• The nervous system has two major divisions: the central nervous system (brain and spinal cord) and the peripheral nervous system, which connects the CNS to the rest of the body.
• The peripheral nervous system carries sensory information to the CNS and carries instructions back out to the muscles.
• The somatic nervous system controls skeletal muscles; its movements are usually voluntary, but reflexes, triggered through the spinal cord before the brain gets the message, are an exception.
• The autonomic nervous system runs internal functions like heart rate and digestion automatically.
• The sympathetic division prepares the body for action (fight or flight), while the parasympathetic division calms the body back toward rest (rest and digest).

Key terms

central nervous system (CNS)

The brain and spinal cord; the brain processes information and the spinal cord is a major pathway to and from the body.

peripheral nervous system (PNS)

The nerves outside the brain and spinal cord, connecting the CNS with the rest of the body.

somatic nervous system

The PNS division that controls skeletal muscles, which move your body; usually voluntary.

reflex

An automatic response, like yanking your hand from a hot pan, triggered through the spinal cord before the brain gets the message.

reflex arc

The quick loop from the body to the spinal cord and back that produces a reflex.

autonomic nervous system

The PNS division that runs internal bodily functions like heart rate and digestion automatically (autonomic = automatic).

sympathetic nervous system

The autonomic division that prepares the body for action: pounding heart, dilated pupils, slowed digestion (fight or flight).

parasympathetic nervous system

The autonomic division that calms the body and returns it toward its normal resting state (rest and digest).

fight-or-flight response

The sympathetic nervous system's preparation of the body for action in response to a threat.