Autonomic nervous system

The Autonomic division of peripheral nervous system or autonomic nervous system is a complex network responsible for regulating involuntary physiological functions. It is divided into three main components: the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system.

1. Sympathetic Nervous System: This division is often associated with the "fight or flight" response. It originates in the thoracolumbar region of the spinal cord and is characterized by short preganglionic and long postganglionic fibers. The sympathetic chain, or trunk, runs alongside the vertebral column, and its ganglia are connected to spinal nerves via rami communicantes.

2. Parasympathetic Nervous System: This system is involved in "rest and digest" activities. It originates in the brainstem and sacral spinal cord, with long preganglionic and short postganglionic fibers. The vagus nerve is a major component, providing extensive parasympathetic innervation to thoracic and abdominal organs.

3. Enteric Nervous System: Often referred to as the "second brain," it is embedded in the gastrointestinal tract and can function independently of the central nervous system. It regulates digestive processes through a complex network of neurons.

The ANS is integrated with the central nervous system through the central autonomic network, which includes cortical and subcortical structures such as the insular cortex and hypothalamus.