296
UNIT 3
Organ Systems
Inner circular muscle
Inner circular muscle
Inner circular muscle
Neuron cell bodies
Neuron cell bodies
Neuron cell bodies
Outer longitudinal muscle
Outer longitudinal muscle
Outer longitudinal muscle
Auerbach
Auerbach
plexuses
plexuses
Auerbach
plexuses
Glial cells
Glial cells
Glial cells
C
Figure 15-14A.
Submucosal/Meissner plexus, small
intestine.
H&E,
3
272; inset
3
544
The enteric nervous system is able to operate indepen-
dently, although it is usually infl
uenced by the para-
sympathetic and sympathetic nervous systems. The
two types of ganglia of the enteric nervous system are
found in the wall of the digestive tract. (1)
Submu-
cosal plexuses
(
Meissner plexuses
) are located in the
submucosal layer. (2)
Myenteric plexuses
(
Auerbach
plexuses
) are located between the two layers of the
muscularis externa. Here is an example of a submu-
cosal plexus in the submucosa of the wall of the small
intestine. Submucosal plexuses are scattered small
groups of neuron cell bodies (sensory and motor neu-
rons and interneurons) and unmyelinated nerve F bers.
The axons of the sensory neurons receive mechanical
and chemical signals from the glandular epithelium;
the axons of the motor neurons innervate the muscu-
laris mucosae and glandular epithelium.
S
u
b
m
u
c
o
s
a
Submucosa
Neuron cell body
Neuron cell body
Neuron cell body
Submucosal
Submucosal
plexus
plexus
Submucosal
plexus
Glandular
Glandular
epithelium
epithelium
Glandular
epithelium
Muscularis
Muscularis
mucosae
mucosae
Muscularis
mucosae
A
Submucosa
Submucosa
Submucosa
Inner circular muscle
Inner circular muscle
Inner circular muscle
Outer longitudinal muscle
Outer longitudinal muscle
Outer longitudinal muscle
Auerbach
Auerbach
plexus
plexus
Auerbach
plexus
Auerbach plexus
Auerbach plexus
Auerbach plexus
Muscularis
Muscularis
enterna
enterna
Muscularis
enterna
B
Figure 15-14B.
Muscularis externa, small
intestine.
H&E,
3
68; inset
3
354
Here is an example of the
muscularis externa
of the
small intestine, which contains two layers of smooth
muscle. (1)
Inner circular muscle layer
: When the
smooth muscle F bers in this layer contract, the diame-
ter of lumen of the small intestine decreases. (2)
Outer
longitudinal muscle layer
: This layer surrounds the
inner circular muscle layer. When the smooth muscle
F bers in this layer contract, the length of the intestine
is reduced. These two layers of muscle work together
to make successive waves of involuntary movements
called
peristalsis
, which force digestive contents to
move downward into the large intestine. The inner
circular and outer longitudinal muscles are innervated
by axons from neurons in the
myenteric/Auerbach
plexuses
of the enteric nervous system (see ±ig. 7-14).
Figure 15-14C.
Myenteric/Auerbach plexus, mus-
cularis externa of the small intestine.
H&E,
×
136;
inset
×
317
Myenteric plexuses
(
Auerbach plexuses
) are found
between the inner circular muscle and the outer longi-
tudinal muscle layers. Myenteric (Auerbach) plexuses
are much larger than submucosal plexuses. The
inset
shows several
neuron cell bodies
and
enteric glial cells
surrounded by connective tissues in a myenteric plexus.
Neurons in both the submucosal plexuses and the
myenteric plexuses are multipolar in shape. Like sub-
mucosal plexuses, they may have little or no encapsula-
tion and contain unmyelinated nerve F bers and gangli-
onic neurons mainly belonging to the enteric nervous
system. The enteric nervous system coordinates peri-
staltic refl exes, which evoke waves of contraction and
relaxation of the gut wall, moving the contents toward
the anus and also regulates enteroendocrine cells.
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