01:377:213 Lecture Notes - Lecture 17: Muscularis Mucosae, Enteric Nervous System, Muscular Layer
13 May 2018
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A. Muscular Layers and the Movement of Digestive Materials
1. The muscularis mucosae and muscular layer of the digestive tract contain
smooth muscle
a) Smooth cell contractions are as strong as skeletal/cardiac muscle
contractions
b) Because the contractile filaments of smooth muscle are not rigidly
organized, a stretch smooth muscle cell soon adapts to its new
lengths and still retains its ability to contract on demand. This
ability to tolerate extreme stretching is called plasticity.
(1) A smooth muscle can be strectec several times its length
but can still contract when stimulated
(2) Plasticity is important for stomach
c) Smooth muscle along digestive tract are involuntary and have no
nervous system motor innervation
2. Pacesetter cells are located in the muscularis mucosae and muscular layer
that surround the lumen of the digestive tract
a) These pacesetter cells go through spontaneous depolarization,
triggering contraction of smooth muscle and adjacent muscle cells
that are electrically connected. Therefore when one smooth muscle
cell contract the contraction spreads like a wave along tissue.
b) The initial stimulus can be a pacesetter cell or a neuron in the
region
3. Peristalsis (Like toothpaste)
a) Smooth muscle contractions that move a bolus (small, oval mass
of food) along the digestive tract
b) During peristaltic wave the circular muscles contract behind
digestive contents,
c) then longitudinal muscles contract next contracting adjacent
segments.
d) Wave of contractions in the circular muscles forces material in
desired direction.
(1) Peristalsis propels materials along the length of the
digestive tract by coordinated contractions of the circular
and longitudinal layers
4. Segmentation
a) Most regions of small and some large intestine
b) Movements that churn and fragment the digestive materials
c) Mix contents with intestinal secretions
d) Involve circular muscle layer
e) Unlike peristalsis, they do not move bolus in particular way.
(1) No net movement
5. Enteric nervous system
a) Afferent and efferent fibers of glossopharyngeal, vagus or pelvic
nerve initiate these peristaltic waves
b) Sensory receptors in the wall of the digestive tract trigger local
peristaltic movements that are limited to a few centimeters of the
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