Divisions of the Nervous System

Key vocabulary terms and definitions covering the central, peripheral, somatic, automatic, sympathetic, and parasympathetic divisions of the human nervous system.

Nervous system

An interacting network of neurons that conveys electrochemical information throughout the body.

Central nervous system (CNS)

The division composed of the brain and spinal cord that receives sensory information from the external world, processes and coordinates it, and sends commands to the skeletal and muscular systems for action.

Spinal reflexes

Simple pathways in the nervous system that rapidly generate muscle contractions without requiring input from the brain, mediated by connections between sensory inputs and motor neurons in the spinal cord.

Reflex arc

A neural pathway that controls reflex actions; it can include sensory neurons, motor neurons, and interneurons, though some simple forms consist only of sensory and motor neurons.

Peripheral nervous system

The division that connects the central nervous system to the body's organs and muscles, consisting of two main subdivisions: the somatic nervous system and the automatic nervous system.

Somatic nervous system

A set of nerves that conveys information between skeletal muscles and the central nervous system, over which humans have conscious control to think, perceive, and coordinate behavior.

Automatic nervous system

A set of nerves that carries involuntary and automatic commands that control blood vessels, body organs, and glands, operating largely outside of conscious control.

Sympathetic nervous system

A set of nerves that prepares the body for action in challenging or threatening situations by dilating pupils, increasing heart rate and respiration, diverting blood flow to the brain and muscles, inhibiting salivation and bowel movements, and suppressing response to pain and injury.

Parasympathetic nervous system

A set of nerves that helps the body return to a normal resting state by constricting pupils, decreasing heart rate and respiration, diverting blood flow to the digestive system, and decreasing sweat gland activity.