Autonomic Nervous System: Physiology

The autonomic nervous system controls involuntary bodily functions, including heart rate, respiration, digestion, and excretion. This system is divided into two main branches: sympathetic and parasympathetic.

Sympathetic System

• Higher center: Located in the posterior hypothalamus.

• Lower center: Located in the lateral horn of the gray matter of the spinal cord from thoracic segment 1 to lumbar segment 2.

• Chemical mediator:

• Pre-ganglionic fibers: Acetylcholine.

• Post-ganglionic fibers: Norepinephrine (except sweat glands and skeletal muscle blood vessels).

• Post-ganglionic fibers going to sweat glands and skeletal muscle blood vessels: Acetylcholine.

Parasympathetic System

• Higher center: Located in the anterior hypothalamus.

• Lower center:

• Upper part: Located in the brainstem.

• Lower part: Located in the lateral horn of the gray matter of the spinal cord from sacral segment 2 to sacral segment 4.

• Chemical mediator: Acetylcholine in both pre- and post-ganglionic fibers.

The sympathetic and parasympathetic systems act antagonistically, creating a dynamic balance for bodily functions. The sympathetic system prepares the body for stress, while the parasympathetic system maintains normal activities and recovers from stress.