LECTURE 25!!!! Flashcards
What type of muscle is found in the pharynx, UES, oral third of the esophageal body, and external anal sphincter?
Skeletal (striated) muscle
What type of subunits are GI sphincters made of?
Multi-unit
___: single unit smooth muscle contracts and relaxes within seconds. Contraction INCREASES pressure on luminal contents while relaxation DECREASES pressure on luminal contents. Pressure gradients are required!!
A. Phasic contractions
B. Tonic contractions
A. Phasic contractions
Which type of contractions are used by sphincters?
Tonic contractions
If a sphincter is closed, it is ___ and the strength of tonic contraction has___
contracted; increased
The enteric circuit requires which 4 enteric neurons?
Sensory neuron
Interneuron
Excitatory motor neuron
Inhibitory motor neuron
___: sensory neurons of the ENS
Intrinsic primary afferent neurons (IPAN’s)
True or false: There are IPAN’s that are mechanosensitive (sense distension) and those that are chemosensitive (sense nutrition)
True
What NT is released by excitatory motor neurons? Inhibitory?
Excitatory = Ach
Inhibitory = NO
What do the UES and the Esophageal body have in common?
Made of skeletal muscle
- Esophageal body (upper 1/3)
Why is the UES usually closed?
High frequency of AP in vagus nerve (increased Ach)
Why does the UES open after a swallow?
Decrease in AP frequency (decreased Ach)
Which has no resting tone and is flaccid?
A. Esophageal Body
B. UES
C. LES
D. Stomach
A. Esophageal Body
Why does the LES relax during swallow?
Inhibitory enteric motor neurons make NO
How is the LES tone maintained?
Tonic input from enteric inhibitory (NO) and excitatory (Ach) neurons
How is the swallowing reflex started?
Activation of sensory afferent nerves innervating the oropharynx
The vagus n in the Nucleus Ambiguus binds to striated muscle of the ___ and ___
UES; upper 1/3 of esophageal body
The vagus n in the Dorsal Motor Nucleus binds to Myenteric Plexus, which acts on smooth m in the ___, ____, and ____
fundus, LES, and lower 2/3 of esophageal body
The skeletal m of the esophagus is innervated ___ by the efferent vagus n
The vagus n forms _____ on skeletal muscle
directly
motor endplates
Which neurons directly innervates the myenteric neurons? Which neurons directly innervate smooth muscle?
Myenteric neurons = vagus n
Smooth muscle = myenteric n
Three stages of deglutition? Which stages are voluntary? involuntary?
1) Oral stage - voluntary
2) Pharyngeal stage - involuntary
3) Esophageal stage - involuntary
Extrinsic afferent nerves with sensory endings in the oropharynx are activated by pressure from bolus of food to initiated which stage of deglutition?
A. Oral
B. Esophageal
C. Pharyngeal
C. Pharyngeal
Cranial sensory afferent n innervating oropharynx are activated by ____
food bolus
Vagal ___ pathways include:
1) Direct vagal innervation of striated m
2) Indirect vagal innervation of smooth m
Excitatory
Vagal ___ pathways immediately open LES and __ fundus
Inhibitory; relax
Which type of peristalsis always follows a swallow and is mediated by long neural reflex?
Primary Peristalsis
Which type of peristalsis is initiated by distension of esophageal body and occurs in absence of pharyngeal peristalsis?
Secondary Peristalsis
Which cell generate and establish the frequency of the slow wave?
Interstitial cells of Cajal - found in the wall of the GIT and connected via gap junctions
Smooth muscles of the ____ and ____ exhibit continuous oscillations of the resting membrane potential known as the slow wave
stomach; small intestines
True or False: The esophagus, stomach, and GI sphincters have slow waves
False
True or False: The slow wave is always occurring, regardless of presence or absence of smooth muscle phasic contractions
True
What is requires to generates smooth muscle AP burst?
Membrane depolarization
___ sets the max frequency that action potential bursts can occur in the smooth muscle
Slow wave
__ is the underlying basis for all phasic contractions
Slow Wave
How is the frequency of phasic contractions affected by damaged ICC’s?
Decreased phasic contractions
Where in the small intestines can you generate the most contractions? least?
most = duodenum (12) = higher pressure
least = ileum (8) = lower pressure
True or False: Slow waves help est. pressure gradient
True
What four factors influence motility?
1) Slow wave
2) Enteric neurons
3) Extrinsic nerves: sympathetic and parasympathetic
4) Hormones and paracrines
Which drugs will decrease phasic contractions?
Opioids
Orad of the stomach is for ___ while the caudad is for ___
storage; emptying
In the small intestines, the slow wave ___ from the duodenum to the jejunum to the ileum. This helps move chyme DOWN the small intestines
decreases
In the large intestines, the slow wave ___ from the ascending to the transverse to the descending colon. This helps RETAIN fecal matter in the large intestine.
increases
