The Myenteric Nervous System. Flashcards
What are the 2 nervous systems that control the GI tract?
The autonomic nervous system.
The enteric nervous system.
What are the components of the enteric nervous system?
The myenteric plexus.
The submucosal plexus.
The enteric nervous system is found in what parts of the gut?
It is found in the gut wall between the oesophagus and the anus.
What 2 things are regulated by the enteric nervous system?
The smooth muscles of the gut wall.
The endocrine and secretory cells associated with the gut.
What allows different organs of the digestive system to communicate with each other?
The enteric nervous system.
Where in the GI tract wall is the submucosal plexus found?
In the submucosa.
Where in the GI tract wall is the myenteric plexus found?
In the muscular layer.
What does the enteric nervous system use to control the digestive system?
Neurotransmitters.
Is acetylcholine an excitatory or inhibitory neurotransmitter?
An excitatory neurotransmitter.
Is norepiniephrine an excitatory or inhibitory neurotransmitter?
An inhibitory neurotransmitter.
What kind of nervous system is the enteric nervous system?
A simple reflex system with sensory neurons and receptors and motor neurons and receptors.
What are the steps of the reflex system involving the myenteric plexus of the GI tract?
Mechanoreceptors are stimulated by stretching.
Afferent neurons travel to the nerve cell body.
Efferent neurons travel to the muscle cells.
Gut motility is stimulated.
What are the steps of the reflex system involving the submucosal plexus of the GI tract?
Chemoreceptors detect chemicals.
Afferent neurons travel to the nerve cell body.
Enzymes etc are secreted.
The myenteric plexus governs what major digestive process?
Gut motility.
The submucosal plexus governs what major digestive process?
GI secretions.
The myenteric plexus will be activated by what kind of receptors?
Mechanoreceptors.
The submucosal plexus will be activated by what kind of receptors?
Chemoreceptors.
What are the 2 nervous systems that supply the GI tract?
The enteric nervous system.
The autonomic nervous system.
What nerves supply the parasympathetic nervous system?
The Vagus nerve.
The pelvic nerves.
What is the main neurotransmitter of the parasympathetic nervous system?
Acetylcholine.
What information from the GI tract is transmitted through the parasympathetic nervous system?
Sensory information from chemoreceptors or mechanoreceptors.
Motor information to muscle cells and gland cells.
What is the origin of parasympathetic nerves?
Craniosacral.
Parasympathetic and sympathetic nerves are only found in what division of the nervous system.
The motor division.
Will the parasympathetic nervous system help or hinder digestion?
It helps with digestion.
What is the origin of the sympathetic nervous system?
Thoracolumbar.
What is the main neurotransmitter of the sympathetic nervous system?
Norepinephrine.
What are the 3 major effects that the parasympathetic nervous system has on the GI tract?
Increased gut motility.
Increased secretion rates.
Decreased muscle sphincter tone.
What kind of fibres are found in the sympathetic nervous system?
Sensory and motor fibres.
What are the 3 major effects that the sympathetic nervous system has on the GI tract?
Decreases gut motility.
Decreases gut secretions.
Increases sphincter tone.
Does the sympathetic nervous system help or hinder digestion?
It hinders digestion.
What controls the autonomic and enteric reflexes in the GI tract?
The same receptors affect both nervous systems.
Which nervous system provides local reflexes for the GI tract?
The enteric nervous system.
Which nervous system provides central reflexes for the GI tract?
The autonomic nervous system.
What is the main stimulus for GI movements?
Stretching of the gut wall.
What cells produce the gastro-intestinal hormones?
Specialised epithelial cells called GI endocrine cells.
What is responsible for stimulating the GI endocrine cells?
The enteric and autonomic nervous systems.
Where will the GI endothelial cells secrete their hormones into?
Into the blood.
What happens once GI hormones have been secreted into the blood?
They signal to other organs that something is going on and these organs will respond.
What name is given to the signalling that involves releasing substances into the blood?
Endocrine signalling.
What is paracrine signalling?
When signalling occurs between 2 cells that are next to each other.
What happens during autocrine signalling?
The cell signals to itself.
What is neurocrine signalling?
When the cell signalling involves neurons.
Where in the GI tract are the GI mucosa found?
Throughout the length of the GI tract.
What is the function of the GI mucosa?
They sample the contents of the gut and release hormones via endocrine secretion or paracrine secretion.
Can the GI mucosa be stimulated by the enteric plexus?
Yes.
What is the function of the regulatory peptides that are secreted by the GI mucosa?
To affect the secretions of the GI tract and the accessory organs and their motility.
What is the stimulus for endothelial cells in the duodenum?
Low pH.
What happens when the endothelial cells in the duodenum are stimulated by low pH?
It stimulates the pancreas and the liver to release their secretions into the duodenum.
Secretin is produced in what part of the GI tract?
The duodenum and upper jejunum.
What stimulates the release of secretin?
Acids, fats and proteins in the duodenum.
What is the action of secretin?
It stimulates the release of bicarbonate and prevents more acid secretion.
Gastrin is produced in what part of the GI tract?
Stomach and duodenum.
What stimulates the release of gastrin?
Proteins and high pH in the stomach.
What is the action of gastrin?
Release of stomach acid and increase in gastric secretions.
Choleocystokinin is produced in what part of the GI tract?
Duodenum, jejunum and ileum.
What stimulates the release of choleocystokinin?
Fats and proteins in the duodenum.
What is the action of choleocystokinin?
It leads to the release of pancreatic enzymes and and gall bladder secretions.
It also inhibits food intake and the release of stomach contents into the duodenum.
What hormone helps to increase the pH of food in the duodenum?
Secretin.
What are the 2 processes associated with GI motility?
Segmentation/mixing.
Peristalsis/propulsion.
What muscles are involved in the segmentation phase of GI motility?
The circular muscles.
What are the characteristics of segmentation GI motility?
Food travels over a short distance.
It mixes the food up.
What are the characteristics of peristalsis GI motility?
It moves the food along the GI tract.
What name is given to the reflex that is associated with peristalsis?
Adaptive relaxation.
Where are cajal cells located in the GI tract?
In the muscle layer.
Digestion breaks food into what?
Into acidic chyme.
What muscle layer is mainly responsible for peristalsis?
The longitudinal muscles.
What can cajal cells be thought of as?
As pacemaker cells as they control the rate of contractions of the GI tract.
How do cajal cells carry out their function?
They communicate with other cells via tight junctions.
Ions pass through these junction leading to depolarisation and stimulation.
The cajal cells control the membrane potential.
Can cajal cells lead to action potentials?
No.
What is created by the partial depolarisation that is created by the cajal cells?
An undulating wave which creates very slow waves in the smooth muscle in the GI tract.
How does the resting membrane potential of smooth muscle compare to that of skeletal muscle?
It is higher than skeletal muscle and is at around -60.
What generates the slow waves of contraction in the GI tract?
The cajal cells.
When will a full action potential be generated in the GI tract?
When certain hormones arrive.
What ion is responsible for the contraction of the smooth muscle in the GI tract?
Calcium.
What part of the brain is mainly responsible for controlling food intake?
The arcuate nucleus of the hypothalamus.
What tells the animal when to start eating?
Signals from the appetite centre.
What tells the animal when to stop eating?
Signals from the satiety centre.
What hormone is responsible for stimulating appetite?
Ghrelin.
What hormone is responsible for inhibiting food intake?
Leptin.
What actions lead to an increase in GI blood flow?
Increase in gut motility.
Certain hormones such as bradykinin.
Decreased O2 or increased CO2.
How will sympathetic stimulation affect blood flow in the GI tract?
It leads to vasoconstriction.
Can the GI organs survive with reduced bloodflow for a long time?
No.
What is ischemia?
When there is not enough blood arriving at an organ.
What might an animal suffer from if it is in a sympathetic state for a long time?
Ischemia.
What state must the body be in to send blood to the GI tract?
A relaxed (parasympathetic) state.
