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Describe the anatomy and histology of the muscular layers to the extent they are discussed in your text.
longitudinal and concentric
Indicate the role of the Interstitial Cells of Cajal in generating the slow wave or basic electrical rhythm (BER).
- couple the longitudinal and circular muscles
- determines: max frequency, direction of propagation, speed of propagation
Discuss the conditions that permit a slow wave to produce a contraction or generate action (spike) potentials.
the depolarization is strong enough to reach the threshold
Compare the functional differences between tonic and phasic smooth muscle. Compare the frequency of the BER in stomach, small and large intestine and sphincters.
tonic can provide sustained contraction - segmentation
phasic is on and off, repetitive and slow - peristalsis
stomach < large intestine < small intestine < sphincters
Explain the role of neurocrines or endocrines in modulating slow wave activity
ACh, CCK, gastrin: excitatory, depolarize, stim contraction, make the contraction longer and stronger
Epi, GIP, VIP, secretin: inhibitory, hyperpolarize, inhibit contraction, make the contraction weaker and shorter
The functions of motility are:
- agitate the lumenal contents
- mix the contents with secretions from the various GI organs
- optimize the time necessary for digestion and absorption and promote the orderly movement of contents from mouth to anus
Each section of the GI tract expresses a unique electrical activity that normally moves the contents in an _______ direction.
The resting membrane potential in smooth muscle is not constant but _______, which is termed, ________, an inherent property of the smooth muscle cell that occurs without neurochemical mediation.
- depolarizes and repolarizes with time
The oscillations are known as _______ or _________ and originate in the ______.
- slow waves
- the basic
- electrical rhythm (BER)
- Interstitial Cells of Cajal (ICC)
Interstitial Cells of Cajal (ICC) are specialized ________ cells that determine _____________.
- the maximal contractile frequency or how often contractions can develop, the propagation velocity and direction of propagation
ICCs have properties of ______ and ________. The branched processes of the cells form _______ with _________ and thus _________.
- smooth muscle cells
- gap junctions
- smooth muscle cells
- couple the electrical activity of the longitudinal and circular layers
Two distinct types of motility: segmentation and peristalsis.
- sphincter, proximal stomach
- contraction: long, tonic
- spike rate: high
- esophagus, gastric antrum, small intestine
- contraction: phasic
- spike rate: low
Neurocrine regulation on smooth muscle activity
- ACh, gastrin and CCK
- stimulate contraction
- increase the amplitude of the slow wave and the frequency of spike -> longer and stronger contractions
- epinephrine, VIP, secretin and GIP
- inhibit contraction
- decrease slow wave amplitude and decrease or abolish spike potential -> decrease the force and frequency of action potentials
In the stomach, the slow frequency promotes _______.
The fast frequency in the small intestine is instrumental in ________.
The slow frequency in the colon promotes _________.
- slow mixing
- rapidly removing acid contents and preventing ulcers
- net water absorption and controlled emptying of waste products