Autonomic nervous system

The autonomic nervous system (ANS) is the part of the nervous system responsible for the involuntary control of internal organs.

The autonomic nervous system controls:

• Smooth muscle (e.g., blood vessels, gut wall, urinary bladder)
• Cardiac muscle
• Glands (e.g., sweat glands, salivary glands)

The ANS has two major divisions:

• Sympathetic
• Parasympathetic

The enteric nervous system, which controls the gastrointestinal tract, is also part of the autonomic nervous system.

Figure 1: Sympathetic and Parasympathetic divisions

Autonomic nerves release different neurotransmitters, such as acetylcholine and epinephrine, to fire an action potentials that will initiate the contraction mechanism.

Besides the nervous control, the smooth and cardiac muscles can also contract due to hormones, pacemaker cells, drugs, or mechanical stretching.