Types and stru c tu re o f sm o o th m uscle cells • Figure 6.1 0
Whether arranged as single- or multi-unit smooth muscle tissue, the structure of
individual smooth muscle cells is the same.
Autonomic
neurons
Nucleus
Muscle
fibers
Sarcolemma
Dense body -
Intermediate
filament
Nucleus
Visceral (single-unit) smooth
muscle tissue:
• Most common
• Found in sheets that form
walls of hollow organs
• Tightly bound together
• One neuron to many smooth
muscle cells
• Smooth muscle cells
communicate via gap junctions
• Many cells contract in unison
• Found in small arteries, veins,
stomach, intestines, uterus,
bladder
Multi-unit smooth
muscle tissue:
• Loosely bound together
• One neuron to one
smooth muscle cell
• Individual cells contract
independently
• Found in blood vessels,
airways, arrector pili of
hairs, and internal eye
muscles
Thick filament
Thin filament
Relaxed
Contracted
skeletal muscle. Some of the dense bodies are within
the cytoplasm, and others are attached to the cell
membrane. This arrangement gives the intermediate
filament network a net-like appearance.
Smooth muscle cells do not have a well-developed
sarcoplasmic reticulum.
Smooth Muscle Tissue Comes in Two
Varieties: Visceral and Multi-unit
There are two types of smooth muscle tissue: visceral
(single-unit) muscle tissue and multi-unit smooth
muscle tissue (Figure 6.10). The smooth muscle cells
CONCEPT CHECK
1.
Why
do smooth muscle cells lack striations?
of both types have the structural features listed above,
but the appearance of the contraction differs between the
two. Visceral smooth muscle cells are interconnected by
gap junctions and function as a group to produce a wave-
like contraction known as
p e rista lsis.
Multi-unit smooth
muscle does not contain gap junctions, so the cells func-
tion independently, allowing more pinpoint control of the
contraction.
Smooth muscles contract or relax involuntarily in
response to stimulation by neurons of the autonomic (invol-
untary) nervous system. Smooth muscles also respond to
hormones and local events, such as changes in pH, carbon
dioxide levels, temperature, and ion concentrations.
2.
Which
type of smooth muscle tissue would you
find in the walls of your stomach?
166 CHAPTER 6
The Muscular System
previous page 201 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online next page 203 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online Home Toggle text on/off