<s>[INST] describe the structure and the functions of the autonomic nervous system [/INST] Hello, welcome to Chat Doctor. The autonomic nervous system (ANS or visceral nervous system) is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, micturition (urination), and sexual arousal. Whereas most of its actions are involuntary, some, such as breathing, work in tandem with the conscious mind. It is classically divided into two subsystems: the parasympathetic nervous system (PSNS) and sympathetic nervous system (SNS). Relatively recently, a third subsystem of neurons that have been named non-a Chat Doctor.  </s>