Autonomic nervous system fibers (ANS fibers)

Autonomic nervous system (ANS) fibers are the network of efferent and afferent nerves that regulate the body's involuntary physiological processes, including heart rate, blood pressure, respiration, digestion, and sexual arousal (Waxenbaum et al., 2023, StatPearls). These fibers are categorized into the sympathetic nervous system, which mediates the 'fight-or-flight' response, and the parasympathetic nervous system, which governs 'rest-and-digest' activities (McCorry, 2007, American Journal of Pharmaceutical Education). While 'ANS fibers' serve as a functional anatomical unit, they are not a single molecular target; instead, they express a wide variety of specific receptors such as adrenergic and muscarinic G protein-coupled receptors (GPCRs) that serve as the actual sites of drug action (NIH, 2022). Dysfunction of these fibers is a hallmark of diseases such as diabetic neuropathy, Parkinson's disease, and various forms of dysautonomia, where the signaling between the central nervous system and peripheral organs is impaired (Merck Manual, 2023). Pharmacological intervention typically involves small molecules that modulate neurotransmission at the synaptic junctions of these fibers to restore homeostatic balance or manage symptomatic conditions like hypertension or gastrointestinal motility disorders.

Other names

Visceral efferent fibersVisceral afferent fibersSympathetic nervesParasympathetic nervesVegetative nervous system fibers

Drugs modulate autonomic nervous system fibers by acting as agonists or antagonists at cholinergic (muscarinic/nicotinic) or adrenergic (alpha/beta) receptors located on the post-ganglionic or pre-ganglionic neurons, or by inhibiting the degradation or reuptake of neurotransmitters like acetylcholine and norepinephrine.