Autonomic Nervous System: Overview and Target Organs

Primary Target Organs and Effectors

The "targets" of the ANS are the specific tissues that respond to autonomic stimulation. These targets are generally categorized into three distinct types of tissue: glands, cardiac muscle, and smooth muscle.

1. Smooth Muscle

Smooth muscle is found throughout the walls of hollow organs, known as the viscera. The ANS regulates the contraction and relaxation of this muscle to control vital processes such as digestion, blood pressure, and airway diameter. For example, when you are startled, the ANS triggers smooth muscle in your blood vessels to constrict, redirecting blood flow to your muscles.

2. Cardiac Muscle

The heart is composed of cardiac muscle, which requires constant regulation to ensure that cardiac output meets the metabolic needs of the body. The ANS can increase the heart rate and the force of contraction (to pump more blood) or decrease them (to conserve energy) depending on the physiological state.

3. Glands

The ANS controls both exocrine and endocrine glands. This includes the regulation of sweat glands (to manage body temperature), salivary glands (to aid digestion), and various endocrine glands that release hormones into the bloodstream.

Target Locations: Viscera and Beyond

The term "viscera" refers to the internal organs located within the thoracic, abdominal, and pelvic cavities. Most of the ANS's work is concentrated here. By modulating the activity of the viscera, the ANS manages complex processes like peristalsis (the movement of food through the gut) and bladder contraction.

However, the targets are not limited to deep internal organs. The ANS also reaches the periphery to manage specialized structures like sweat glands located in the skin. This allows the body to respond to external stimuli—such as heat—by activating thermoregulatory mechanisms through the skin.

Summary Table of ANS Targets

In summary, the ANS is an essential motor system that maintains the body's internal equilibrium by targeting smooth muscle, cardiac muscle, and glands throughout the viscera and skin.