GIT 3
Innervation of GIT: Enteric Nervous System
2 major networks of nerve fibers
that innervate the GIT:
Intrinsic innervation
- Myenteric plexus (Auerbach’s plexus).
- It lies between longitudinal and
circular smooth muscle layers
- and innervates both theses layers.
- It is mainly motor in function.
- Its stimulation
increases the activity of gut by:
- increasing tone of gut wall
- increasing intensity of rhythmic contraction
- increasing rate of rhythmic contractions,
- increasing velocity of conduction of
excitatory waves along the gut wall.
Thus, it is concerned with control of peristaltic activity of the GIT.
- Submucous plexus (Meissner's plexus).
- It lies between the submucous layer and inner circular smooth muscle layer.
- It is mainly sensory in function
- and is concerned with control of
exocrine and endocrine secretions
by the cells in the GIT.
- It also innervate the submucosal blood vessels
to control local blood flow.
- Both the plexuses are interconnected
and are under the extrinsic autonomic nerves control, - by both parasympathetic and
sympathetic nerve fibers
Extrinsic innervation
- Parasympathetic (cholinergic) nerves,
- release acetylcholine (A-ch) at
their endings
- and by depolarization of smooth muscle membrane
produce contraction of GIT musculature.
- Stimulation of parasympathetic nerves to GIT produces:
- increase in motility and tone
- relaxation of sphincters
- increased secretions from the stomach (specially of enzymes) and of the intestine.
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Sympathetic (adrenergic) nerves,
- release epinephrine at their
endings
- which by hyperpolarization of smooth muscle membrane result
in relaxation of GIT musculature.
- Stimulation of sympathetic nerves to
GIT produces:
- decrease in motility and tone
- contraction of sphincters
- inhibition of secretions from the stomach and probably also inhibit intestinal secretions.
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together they form the Enteric nervous system
- the Little Brain