Autonomic Nervous System

The Autonomic Nervous System (ANS) is an integral part of the peripheral nervous system, controlling many unconscious physiological processes, such as heart rate, digestion, respiratory rate, pupil dilation and constriction, urination, and sexual arousal^[1]. This system plays a pivotal role in upholding homeostasis within the body.

The ANS is fundamentally divided into two main subsystems: the Sympathetic Nervous System (SNS) and the Parasympathetic Nervous System (PNS). These systems typically manifest opposing effects to maintain a harmonious internal balance within the body.

The Sympathetic Nervous System (SNS) is frequently referred to as the "fight or flight" system. The primary neural substrates that control the SNS are located in the spinal cord, specifically the thoracic and lumbar regions^[2]. In response to stress or danger, the SNS is activated, resulting in an increased heart rate and blood pressure, slowed digestion, and a surge of glucose for immediate energy needs.

On the other hand, the Parasympathetic Nervous System (PNS) is known as the "rest and digest" system. Its control centers lie in the brainstem, within the medulla oblongata, and the sacral spinal cord^[3]. Activation of the PNS conserves and replenishes the body's energy reserves. It reduces heart rate, boosts intestinal and glandular activity, and relaxes the digestive tract's sphincter muscles.

A lesser-known but significant component of the ANS is the Enteric Nervous System (ENS). This component comprises an intricate network of neurons and nerve networks located within the gastrointestinal tract walls and is responsible for the regulation of gastrointestinal function.

The ANS operates in dynamic interplay with the Central Nervous System (CNS), which includes the brain and spinal cord. The CNS controls the body's internal environment^[4]. The ANS receives input from the limbic system, among other brain regions involved in emotional processing. This intricate communication allows psychological states and stress to influence physiological function reciprocally.