The gut communicates with the (blank)
CNS
(blank) innervation inhibits peristalsis and secretion, while (blank) innervation stimulates peristalsis and secretion
sympathetic; parasympathetic
a condition with microbial imbalances on or inside the body
dysbiosis
Vagal affarents synpase in the (blank), while pelvic afferents synapse in the (blank)
nodose; dorsal root ganglia
Gastric input to the CNS is represented in the brainstem and thoracic spinal cord by (blank) and (blank) inputs
vagal; splanchnic
(blank) percent of nerve fibers in the vagus nerve are sensory
80%
Three pathways connecting the gut to the CNS
- vagal afferents
- pelvic afferents
- splanchnic afferents
Make up 80% of nerve fibers, signal mainly from upper GI regions
vagal afferents
Regulate colon, rectum and internal anal sphincter
pelvic afferents
Throughout the GI tract, many are thought to be nociceptive
splanchnic afferents
Extrinsic afferents reach the gut via these four nerves
vagus
splanchnic
pelvic
pudendal
Differences between a generator potential and an action potential.
- generator potential does not propagate
- generator potential is “graded”–>larger when more transmitters are attached
- no refractory period
The spinal reflex arc that changes activity in an effector (5 steps)
- visceral afferent neuron plus sensory receptor
- interneuron
- preganglionic neuron
- postganglionic neuron
- effector
Information about conditions of the gut are signaled through extrinsic (blank) afferents to the brain stem and (blank) afferents to the spinal cord
vagal; spinal
Mechanical stimuli (stretch, pressure, distortion and shearing forces) can activate spinal, vagal and intrinsic primary afferents (IPANs) (blank) without intermediary cells.
directly
Function as detectors that analyze luminal contents, survey the mucosal status and activate afferent neurons
endocrine cells in the GI tract
release Cholecystokinin (CCK) in response to fat and protein digestion
I cells in the duodenum
release secretin from EC cells in response to duodenal acidification to enhance pancreatic exocrine secretion and bile flow
S cells of the stomach and intestine
Release ~20 different neuropeptides that can stimulate vagal afferents in a paracrine fashion, or when released into the circulation they can exert an endocrine effect
EE cells
Mechanical and chemical stimulation releases 5-HT to activate both intrinsic (peristalsis) and extrinsic afferent neurons to cause receptive relaxation of the stomach
EC cells
includes antigen-sampling M cells, macrophages, eosinophils, neutrophils, and mast cells
lymphoid tissue
(blank) nerve stimulation elicits severe pain in conscious humans, whereas (blank) nerve stimulation doesn’t produce pain
splanchnic; vagal
Afferents regulating visceral tone, distension, motility and secretion accompany the (blank) efferent nerves
parasympathetic
Most visceral afferent nerve fibers mediating sensation and nociception (pain) accompany the (blank) nerves
sympathetic
Bottom line: (blank) afferent nerve fibers cause pain, (blank) afferent nerve fibers do not.
sympathetic; parasympathetic
There are many more mechanosensory neurons than visceral sensory neurons, so visceral sensations are (blank) difficult to (blank).
diffuse; localize
(blank) afferents are considered to convey to the CNS the sensations of discomfort and pain.
spinal
Types of vagal, pelvic and spinal afferents
intramuscular arrays
intraganglionic endings
mucosal intravillous arbors
Located within the submucosal and myenteric plexuses
Activate enteric reflexes that regulate motility, secretion, and blood flow
intrinsic primary afferent neurons (IPANs)
Two types of extrinsic primary afferent neurons
Vagal afferents
Spinal afferents
Activated by mechanical, thermal and chemical stimuli
Cell bodies in nodose ganglion and central terminals to brainstem nucleus tractus solitarius
vagal afferents
Activated by low and high intensity chemical stimuli
Cell bodies in DRG and central terminals in superficial dorsal horn of spinal cord
Convey info about painful stimuli
spinal afferents
EC cells can release (blank) which can activate the vomiting center via vagal afferents directly, vagal afferents to the area postrema, or through the bloodstream to the area postrema
5HT
a type of chronic inflammatory bowel disease. It involves the formation of areas of patchy inflammation, primarily in the small intestine (terminal ileus) but sometimes in other parts of the digestive tract
Crohn’s disease
a form of IBD in which the inflammation is limited to the large intestine
Ulcerative colitis
T/F: irritable bowl syndrome = IBD
FALSE, While IBS can be painful, it doesn’t lead to other health problems or damage the GI tract
Inflammation sensitizes responses to gastric distension
visceral hyposensitivity
Following injury, there is complex sensitization of pain (nociceptive) fibers caused by a (blank)
inflammatory soup (bradykinins, histamine, prostaglandins, substance P)
Sensory (blank) channels sense how hot or mild different foods are.
TRP
exaggerated pain in response to a painful stimulus
hyperalgesia
pain in response to an innocuous stimulus
allodynia
Sensitization of peripheral visceral sensory neurons is defined by an increase in the number of (blank) triggered by a stimulus, a decrease in the (blank) required for AP generation, and a lowering of the (blank) for AP generation
action potentials; stimulus intensity; threshold
Sensitization of peripheral visceral sensory neurons may be associated with increase or change in (blank) release at central synapses or enhanced response of postsynaptic neurons
transmitter
Sensitization of central visceral sensory neurons is associated with (blank) in response magnitude of central neurons, (blank) in size of are of referred sensation, and (blank) excitability of spinal neurons.
increase
both somatic sensory fibers and visceral sensory fibers have the cell bodies in the same dorsal root ganglion and synapse on the same second-order neurons in the spinal cord causing (blank)
referred pain
T/F: Visceral organs, such as the bladder and colon, can become cross-sensitized
True
Theory attempting to explain why thoughts and emotions influence pain perception
gate control theory of pain
Used to manage gut pain and can relieve diarrhea
opioids
Some patients with inflammatory bowel disease (IBD) anecdotally report that they experience relief by smoking marijuana. What endogenous ligand is at work here?
cannabinoids
T/F: Low innervation density and polymodal character of visceral sensory neurons explain the poor discriminatory ability of sensory input
true
Convergence of different afferent input to higher order sensory neurons is responsible for (blank) pain
referred
(blank) of sensory pathways during acute episodes of gastroenteritis contributes to the development of postinfectious functional GI disorders
sensitization
Most gastric ulcers caused by a bacterial infection, usually (blank)
H. pylori
Emesis occurs as a result of (blank) acting on nerves from the intestines to the vomiting center in the brain
5HT
Detect stretch; are supplied by vagal afferents and innervate the smooth muscle layers of the GI tract
intramuscular arrays
Detect mechanical changes; are supplied by vagal afferents and innervate
intraganglionic endings
Sensitive to luminal chemicals and selective responses to fine tactile stimulation
vagal mucosal afferents