Difference between symathetic and parasympathetic nervous systems, and how did they get those name
Executive summary
The sympathetic and parasympathetic systems are the two main motor divisions of the autonomic nervous system that coordinate involuntary functions across the body: the sympathetic mobilizes for rapid action (“fight-or-flight”) while the parasympathetic promotes restoration and digestion (“rest-and-digest”) [1] [2]. They differ in anatomical origin, wiring patterns, neurotransmitters, timing and typical physiological effects, though real physiology contains many exceptions and coordinated co‑activation [3] [4] [5].
1. What each system does: opposing but complementary roles
The sympathetic division is classically described as the body’s rapid mobilizer—raising heart rate and blood pressure, dilating pupils, diverting blood to muscles and inhibiting digestion—functions that support escape or exertion [1] [3]; the parasympathetic division generally slows the heart, stimulates digestion and supports energy storage, sexual arousal and other “rest-and-digest” processes when safety and recovery are the priority [2] [6].
2. Anatomy and wiring: thoracolumbar versus craniosacral outflow
Anatomically the systems arise from different CNS regions: sympathetic fibers come from thoracic and lumbar spinal segments (often described as thoracolumbar outflow, roughly T1–L2), while parasympathetic fibers arise from cranial nerves (III, VII, IX, X) and sacral segments S2–S4—hence the labels craniosacral for the parasympathetic outflow [7] [4] [8]. This difference produces distinct ganglionic layouts: sympathetic ganglia lie nearer the spinal trunk enabling rapid multi‑organ activation, whereas parasympathetic ganglia tend to sit in or near target organs for more focused control [9] [8].
3. Neurochemistry and signal timing
Both systems use two‑neuron efferent chains (preganglionic → postganglionic), and acetylcholine is the common transmitter at the preganglionic synapse for both divisions, but many sympathetic postganglionic fibers primarily release norepinephrine (noradrenaline) at end organs while parasympathetic postganglionic terminals usually use acetylcholine; cotransmitters and peptides complicate the picture [6] [5] [10]. Functionally this maps onto speed and breadth: sympathetic architecture supports fast, widespread effects, while parasympathetic control is often slower, more targeted and geared to restoration [2] [4].
4. Interaction, exceptions and modern nuance
The textbook idea of neat antagonism—one system on, the other off—is an oversimplification: many organs receive dual innervation and the two divisions can be co‑active or show complex coordination depending on context (for instance some aspects of sexual function involve both systems) [4] [10]. Contemporary reviews stress flexible modulation of sympathetic and parasympathetic activity across tasks and emotions rather than a simple binary opposition [10] [5].
5. Origins of the names — what sources say and what they do not
Historical classification work that established sympathetic and parasympathetic divisions (for example Langley’s tripartite scheme) is noted in modern reviews, but the provided sources do not document a clear etymological or historical narrative explaining exactly how the English names “sympathetic” and “parasympathetic” were coined or popularized [8]. Because the listed material focuses on physiology, anatomy and function rather than linguistic history, this reporting cannot authoritatively state the naming provenance; further investigation in historical physiology texts or etymological sources would be required to firmly trace the origin and semantic intent behind the English labels.