Wk8 Enteric NS Flashcards
What is the enteric nervous system?
3rd division of ANS
- sometimes classed as parasympathetic - will be names intraneural plexus
Intrinsic innervation of the GI tract
- Oesophagus to rectum
- pancreas and biliary system (in part involved in this control)
- can communicate with brain
Network of neurones (80-100 million)
- considered the little brain - a neurotransmitter, much more complex than peripheral NS
Where is it?
Two major plexuses of ganglion cells and their fibre bundles
• Submucosal (Meissner’s) plexus - stomach and intestines • Myenteric (Auerbach’s) plexus - full length of GIT - extensively interconnected plexuses
What is a plexus?
Tangled or network
What is order of tissues?
Longitudinal muscle - myenteric plexus (muscle) Circular muscle - submucosal plexus - contains blood vessels, connective tissue etc Submucosa Mucosa Lumen
Types of neurones
Afférent (sensory) neurones - mechanoreceptors & chemoreceptors Interneurones - excitatory and inhibitory Efferent (secretomotor) neurones - excitatory or inhibitory — many neurotransmitters including ACh, various peptides etc Effectors - motor and secretory reflex effectors Components necessary for reflexes -most are reflexes and predominantly short neurones
What does it do?
• Controls motility,secretion and bloodflow
Matches blood flow to activity in the gut e.g. following a big meal vs not eating
• Motor reflex- myenteric plexus
E.g. peristalis
Sensory neurones
- can detect contents of lumen
- degree of stretch of wall of GI tract in response to food
Order of processing food
Food —> Sensory receptors - mechanoreceptors - chemoreceptors —> ENS - submucosal plexus —> Secretory neurones —> Secretion increased - mucus - enzymes - acid
What does it do?
Blood flow
- myenteric/submucosal plexus
- vasoactive neurotransmitters
- due to poor interactivity between enteric neurones and brain
Integration with CNS
- ENS SNS/PNSCNS
- you’re aware of eating - large meal so much be information transmitted to brain
- brain can overrule enteric NS - stop digestion etc if required
- Long reflex
CNS influence varies along GIT
- once swallowed, brain cannot stop digestion
- but can control when defecation takes place
What dysfunction/diseases are associated with it?
Age
- ENS appears to not function as well
- possibly due to decrease in number of neurones as some die or do not function as well
Disease
- pathology
- ENS specific - pathological process sometimes only changes ENS
- NS more generally - affected by body wide disease
Chaga’s disease e.g. South America
- try panosome parasite
- toxin causes neurone death - parasite can maintain in body as not expelled by GIT
Hirschprung’s disease (1 in 5 births) - manifests soon after birth
- also known as mégacôlon
- congenital absence of ENS neurones ~ genetic mutation
- distal colon cannot do peristalsis so excretion builds up and cannot leave
Congenital absence of ENS neurones
Peristaltic wave halts at the section missing ENS neurones
- starts in faeces movement
- distension
- scoliotis
Abolition of rectoanalreflex (babys pooing reflex)
- abnormal defection
- cannot open sphincter
- surgery - cannot create neurones so have to open colon
Achalasia- common in elderly
- affects swallowing - loss of inhibitory interneurones within myenteric plexus of Oesophagus or sphincter
- autoimmune?
General neurological conditions
- Parkinson’s disease
- peripheral neuropathies
- myasthenia gravis - appears to involve production of antibodies against nAChRs in skeletal muscle so normally associated with somatic nervous system
Irritable bowel syndrome
- dysfunctional interaction so enteric affected - CNS —>ENS
- mental health ? E.g. anxiety
ENS neurotransmission
Many drug targets
- endrogenenous opioids and receptors
Good —> anti-diahorrheol
Bad —> analgesic e.g. morphine —> causes interaction with opioid receptions in gut - constipation
