Pages Below:
Greater Splanchnic Nerve
Least Splanchnic Nerve
Lesser Splanchnic Nerve
| |
Innervates
- smooth muscle coat of all blood vessels (except interior of brain)
- Mainly vasoconstrictor
- Important in maintaining systemic blood pressure and in
distribution of blood flow to different vascular beds
- eccrine sweat glands
- Pineal gland
- Heart
- eye
- internal organs
Sympathetic ganglia
- lie close to central axis of body
- In 2 sympathetic chains (paravertebral ganglia)
- unpaired prevertebral ganglia surrounding bases of great arteries
- coeliac,
- superior mesenteric
- inferior mesenteric
- aortico-renal ganglia (renal arteries)
- pelvic ganglia (short adrenergic neurones)
- chromaffin cells of adrenal medulla (innervated by preganglionic
sympathetic neurones)
Preganglionic neurones
- lie within 12 thoracic and upper 2-3 lumbar
segments of spinal cord
- in lateral horns of grey matter
- small (1-4mm) myelinated (B) fibres
- leave by ventral roots of T1 to L3 and run to sympathetic chain as
white rami communicantes
- fibres run in sympathetic chain and terminate on ganglia there or
leave as splanchnic nerves to terminate on prevertebral ganglia and
adrenal medulla
- Thoracic splanchnic nerves (T5-T12) are subpleural
Ganglionic neurones
- outnunber preganglionic and each preganglionic
innervates a number of ganglionic neurons
- Each ganglionic neurone may recieve input from up to 10 or more
preganglionic fibres
- Vasomotor and sudomotor controlled separately
Postganglionic axons
- relatively long, unmyelinated, <1mm
in diameter (C fibres)
- mostly adrenergic
- exception is eccrine sweat glands which are cholinergic
- travel in mixed spinal nerves or along blood vessels
|