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- Innervates heart, eye and internal organ systems
- constricts pupil of eye
- slows heart rate
- increased salivation
- cooperates in ejaculation
- moderates heart rate
- selectively regulates and promotes functioning of internal organ
systems
- More restricted and focal than the sympathetic system
- ganglia all lie close to or enclosed within structures they innervate
- Pre-ganglionic neurones situated either within brainstem or in middle
sacral segments of spinal cord
- enteric ganglia innervated by parasympathetic pre-ganglionic neurones
- Cranial outflow:
- occulomotor (III) nerve to iris (sphincter pupillae) and ciliary
muscles of eye, via small cilliary ganglion
- facial and glossopharyngeal nerves (VII and IX) innervate lacrimal
gland of orbit and salivary and mucus glands of mouth, nose and
pharynx via three ganglia (pterygopalatine, submandibular, otic)
- vagus (X) caries extensive preganglionic outflow to pacemaker and
nodal regions of heart, ganglia in lung (pulmonary plexuses) and
enteric ganglia in alimentary tract (submucosal and myenteric) from
pharynx to end of midgut (oesophagus,
stomach, duodenum
and pancreas, small intestine and part of
colon)
- Sacral outflow
- Middle sacral segments of spinal cord (S2-4).
- Cell bodies of preganglionic neurons in intermediate zone of grey
matter
- axons distributed to enteric ganglia of intrinsic plexuses (submucosal
and myenteric) plexuses of hindgut (caudal part of colon and rectum)
and to ganglia in wall of urinary bladder and associated with accessory
reproductive organs (pelvic ganglia
- B fibres like those of sympathetic
- cholinergic
- Postganglionic axons unmyelinated and usually very short.
- many are cholinergic (e.g. to sphincter pupillae)
- wide variety of other transmitters,
- VIP, substance P, cholecystokinin, somatostatin
- NO : responsible in some sites for non-adrenergic non-cholinergic
inhibitory responses
- Preganglionic ratio 1:1 of 1:few
- Enteric ganglia in
- 2 nerve plexuses
- Myenteric
- between longitudinal and circular smooth muscle layers of
gut wall
- submucosal plexus
- lying in the submucosal layer of the gut wall
- can allow peristalsis independent of external innervation
- innervated by preganglionic parasympathetic nerve fibres
- increase peristalsis and blood flow to gut wall
- innervated by postganglionic sympathetic nerve fibres
- decrease peristalsis and blood flow
- increases tone of pyloric and anal sphincters.
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