Control 2 Flashcards
Enteric and autonomic nervous system
What are rich plexuses?
dense local network of nerves and supporting cells
what are ganglia?
nerve cells which carry signals
What are ganglia in enteric nervous system interconnected by?
tracts of fine, unmyelinated nerve fibres.
What is the enteric nervous system?
“second brain” capable of independence, consists of rich plexus of ganglia interconnected by unmyelinated fibres and integrates function
What is an interesting feature of the enteric nervous system?
produce a coordinated response to specific stimuli independent of the central nervous system.
What can cause dysfunction?
Inflammation (ulcerative colitis; Crohn’s disease)
Following invasive abdominal surgery
Irritable bowel syndrome
Ageing (constipation)
What are the two main plexuses of the gut?
the myenteric plexus and the submucosal plexus.
Where is the myenteric plexus located
between the circular and longitudinal smooth muscle layers, and has efferent innervation of both
What does the myenteric plexus do?
allows for coordinated control of motor function, and hence, motility.
What are the afferent functions of the submucosal plexus?
senses the environment within lumen using mechanoreceptors, chemoreceptors and osmoreceptors.
What are the efferent functions of the submucosal plexus?
Can fine tune local blood flow, epithelial transport and secretory/paracrine/endocrine cell function.
What are the functions of the entire enteric system?
SPAM
Secretion - controlling secretions of enzymes, paracrine signals, endocrine hormones to regulate local and non local gut functions
Perfusion - blood flow carfully controlled to ensure high perfusions
Absorption - of nutrients, vitamins, minerals and ions by adjusting expression of luminal transport proteins
Motility - smooth muscle cells in circular and longitudinal muscle layers can contract and relax to cause effective gut transit
What do sensory neurones respond to?
Mechanical, thermal, osmotic and chemical stimuli
What do motor neurones do?
Axons terminate on SMC of circular or longitudinal layers, secretatory cells of GI tract or GI blood vessels
Interneurones dunction?
Neurones between neurones integrate the sensory input and effector output
Where are SNS preganglionic cell bodies found?
located in the spinal cord in the lower thoracic and upper lumbar spinal cord
Where are SNS postganglionic cell bodies found?
pre- and paravertebral ganglia
Where are PNS preganglionic cell bodies found?
Brainstem and sacral spinal chord
Where are PNS postganglionic cell bodies found?
V close to target organs
Where are SNS pre-ganglionic nerves arising from and where do they innervate?
Pre-ganglionic neurons are in the splanchnic nerves arising from the thoracic and lumbar regions. Thoracic branches innervate the foregut and associated organs, and the lumbar branches innervate the hindgut.
Where does most PNS GI tract inervation come from?
Most GI tract innervation in the branch of the ANS arises from the vagus nerve (CNX).
What structures receive PNS innervation from pelvic splanchnic nerves?
Structures from the descending colon onwards receive innervation from the pelvic splanchnic nerves.
What does the difference between blood supply and nervous innervation between structures before and after splenic flexure of large intestine reflect?
Embryological origins of the gut
What is the major neurotransmitter of the SNS?
Norepinephrine
What do synapses of the sympathetic chain of the SNS use to communicate - neurotransmitters?
acetylcholine (ACh), but most synapses between the SNS and the enteric nervous system use Norepinephrine
What is the major neurotransmitter of PNS branch of the ANS
Acetylcholine
What is the general impact of SNS on gut?
Reduce activity
What is the general impact of PNS on gut
Increase activity
How does the enteric nervous system interact with the autonomic nervous system
The ANS typically inputs into the enteric nervous system, allowing integration with local afferent signals to provide a coordinated response
What is an exception of how the enteric nervous system interacts with ANS
Sympathetic innervation of vascular smooth muscle. This allows the ANS to rapidly shut down gut perfusion in high stress situations, allowing blood to be redirected to brain, heart and muscle (SURVIVAL response)
What would a disruption in ANS innervation cause?
only a small decrease in functionality. The enteric nervous system is very INDEPENDENT!
What do glial cells do
provide insulate, protective, nutritional and structural support
