L23 - 24 ENS Flashcards
Are there more neuron cell bodies in ENS or spinal cord
ENS
6 Layers of ENS (Superficial to Deep)
1) Muscosal layer - vili, site of secretion and absorption
2) Muscularis mucosae - thin layer of muscle
3) Submucosal plexis - Regulation of secretion of water and salts, 20% of neurons in ENS
4) Circular muscle - Mechanical work moving material in GIT
5) Myenteric plexus - Regulation of GIT motility, 80% of neurons in ENS
6) Longitutidinal muscle - Mechanical work moving material in GIT
Two ganglionated plexuses and what do they do?
1) Myenteric (Auerbach’s) plexus provides motor innervation to both layers of the muscular layer of the gut, having both parasympathetic and sympathetic input. It is in between the longitudinal and circular layers of muscularis externa.
2) Submucosal (Meissner’s) plexus – in between mucosa and muscle layer, has only parasympathetic fibres and provides secretomotor innervation to the mucosa nearest the lumen of the gut. q
Submucousal begins at stomach but is ganglionated at? Myenteric is ganglionated at
Pylorus
Upper Oesophageal Sphnicter
Lack of secretion leads to
Constipation and cystic fibrosis
Too much secretion (overactivity of submucosal plexus) leads to
Diarrhoea
Several non-ganglionated plexuses innervate?
Muscle, mucosa, blood vessela
EXTRINSIC NERVE SUPPLY
- Symp: innervates?
- Para: innervates?
Symp innervates whole length of GIT
Para innervates most but less prominent in Jeujunem and ileum
__% of vagal afferents are primary afferents
90
Dorsal root ganglion cell afferents run in ____ and ____ nerves and are often thought to be ____
Splanchnic and pelvic, nociceptive
Secretion is an active/passive process when water and salt moves from ___ into ___
Active, Body into lumen
ENS contributes to control of acid secretion in _____, mucus secretion along ______and bicarbonate secretion in _____
Stomach, gut, duodenum
Contractions abolished by ______, which blocks neural action potentials (by inhibiting __ channels), but not those of smooth muscle because ____
Tetrodotoxin, voltage gated Na+ channels, Smooth muscle AP are Ca2+ dependent not Na+ dependent
•Jejunum contains entire circuit for generation of a complex behaviour
–Circuit involves two types of cholinergic neurons (Ach onto neurons – nicotinic muscles and Ach on the muscle –muscarinic receptors)
•Jejunum contains entire circuit for generation of a complex behaviour
–Circuit involves two types of cholinergic neurons (Ach onto neurons – nicotinic muscles and Ach on the muscle –muscarinic receptors)
Intrinsic sensory neurons - What are they sensitive to?
Distention, mucosal deformation, nutrients
Interneurons - what directions do they run in?
–Running orally, ascending
–Running anally, descending
Secretomotor neurons - what do they aid with?
-2 classes, neurons that drive the movement of water and salt across the intestinal mucosa
Latch effect of smooth muscle
When it contracts, it doesn’t relax without an active intervention. Actin-myosin crossbridges don’t break when Ca2+ is removed – hence inhibitory motor neurons are needed.
NOS - inhibitory or excitatory?
Inhibitory
NOS neurons make vasoactive intestinal peptide, but vasoactive intestinal peptide neurons in submuscousal plexus not found in NOS
NOS neurons make vasoactive intestinal peptide, but vasoactive intestinal peptide neurons in submuscousal plexus not found in NOS
Main secretatory motor neurons in the ENS
Vaso-active intestinal peptide
When have not eaten for 3 – 4 hours have the fasted state or interdigestive motor pattern is known as
MMC, begins at upper duodenum, last for 90 mins
Interstitial cells of Cajal (ICC)
- In addition to neural pattern generators have pacemakers intrinsic to muscle layers – ICC
- ICC near myenteric plexus are electrically coupled via gap junctions to each other & to smooth muscle cells
- ICC generate rhythmic membrane potential changes (slow waves) in muscle
- Neural activity has little effect on slow wave frequency, but alters probability of slow waves generating action potentials and hence contractions
Segementation circuit has 2 rhythmic pattern generators. There is a band of active excitatory motor neurons at site of contraction and 2 inhibitory bands on each side
Segementation circuit has 2 rhythmic pattern generators. There is a band of active excitatory motor neurons at site of contraction and 2 inhibitory bands on each side
Key logic point – if neuron responds to sensory stimulus without synaptic transmission it must have a sensory function, in addition to any other functions
Key logic point – if neuron responds to sensory stimulus without synaptic transmission it must have a sensory function, in addition to any other functions
