Dr. Matt and Dr. Mike's Medical Podcast Autonomic Nervous System (Parasympathetic & Sympathetic Divisions))
Nov 10, 2017
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Craniosacral Layout Of Parasympathetic Fibres
- Parasympathetic outflow is craniosacral: cranial nerves III, VII, IX, and X plus sacral S2–S4.
- Parasympathetic preganglionic fibres run long and synapse near or within target organs; postganglionic fibres are short.
Acetylcholine Mediates Ganglionic Transmission
- Both divisions use ACh from preganglionic neurons acting on nicotinic receptors at the ganglion.
- Parasympathetic postganglionic neurons also release ACh acting on muscarinic receptors at the effector organ.
Adrenergic Targets Determine Opposing Effects
- Sympathetic postganglionic neurons predominantly release noradrenaline (norepinephrine) which acts on adrenergic receptors (alpha and beta subtypes).
- Different adrenergic receptors produce excitatory or inhibitory effects depending on target tissue.