General structure
Central portion is located in:
- Hypothalamus
- Brain stem (medulla oblongata, and ?others)
- Spinal cord
Preganglionic neurons have
-> cell bodies in brain stem or spinal cord
-> axons are thinly myelinated
Postganglionic neurons have
-> cell bodies in the autonomic ganglia
-> axons are unmyelinated
Sympathetic ganglia are located close to CNS
-> short preganglionic fibres, long postganglionic fibres
Parasympathetic ganglia are located close to the effector tissues
-> long preganglionic fibres, short postganglionic fibres
Anatomy
Sympathetic motor neurons
- Located in the intermediolateral horn of the spinal cord from T1 to L2
- Send axons via the ventral root, then white ramus, then either:
(1) synapse in sympathetic chain at the same or different level,
OR
(2) go through sympathetic chain, and exit via splanchnic nerve and synapse in a prevertebral ganglion,
OR
(3) go through sympathetic chain and splanchnic nerve, and end directly on modified neuronal cells in adrenal medulla
Parasympathetic motor neurons
- Located in discrete brain stem nuclei or in S2-S4
- Axons leave brain stem via cranial nerves III, VII, IX, and X
OR
leave sacral spinal cord via pelvic nerves
Parasympathetic fibres in CN III innervate
- pupillary sphincters and ciliary muscles of the eye
Parasympathetic fibres in CN VII innervate
- lacrimal, nasal, and submandibular glands
Parasympathetic fibres in CN IX innervate
Parasympathetic fibres in CN X (vagus nerve) innervate
- heart
- lungs
- oesophagus
- stomach
- small intestines
- colon proximal to splenic flexure
- liver and gallbladder
- pancreas
- upper portion of ureter
Sacral parasympathic fibres innervate
- descending colon
- rectum
- bladder
- lower portion of ureter
- external genitalia