Download Muscular System Module 7: Smooth Muscle

Connexions module: m48588
1
Muscular System Module 7: Smooth
∗
Muscle
Donna Browne
Based on Smooth Muscle† by
OpenStax College
This work is produced by The Connexions Project and licensed under the
‡
Creative Commons Attribution License 3.0
Abstract
By the end of this section, you will be able to:
•
•
•
•
Describe a dense body
Explain how smooth muscle works with internal organs and passageways through the body
Explain how smooth muscles dier from skeletal and cardiac muscles
Explain the dierence between single-unit and multi-unit smooth muscle
Smooth muscle (so-named because the cells do not have striations) is present in the walls of hollow
organs like the urinary bladder, uterus, stomach, intestines, and in the walls of passageways, such as the
arteries and veins of the circulatory system, and the tracts of the respiratory, urinary, and reproductive
systems (Figure 1 (Smooth Muscle Tissue )ab). Smooth muscle is also present in the eyes, where it functions
to change the size of the iris and alter the shape of the lens; and in the skin where it causes hair to stand
erect in response to cold temperature or fear.
∗ Version
1.1: Jan 2, 2014 2:33 pm -0600
† http://cnx.org/content/m46478/1.3/
‡ http://creativecommons.org/licenses/by/3.0/
http://cnx.org/content/m48588/1.1/
Connexions module: m48588
2
Smooth Muscle Tissue
Figure 1:
Smooth muscle tissue is found around organs in the digestive, respiratory, reproductive tracts
©
and the iris of the eye. LM
Medical School
×
1600. (Micrograph provided by the Regents of University of Michigan
2012)
Smooth muscle bers are spindle-shaped (wide in the middle and tapered at both ends, somewhat like
a football) and have a single nucleus. They shorter than skeletal muscle bers. Although they do not have
striations and sarcomeres, smooth muscle bers do have actin and myosin contractile proteins, and thick
and thin laments. These thin laments are anchored by dense bodies. A dense body functions like a
Z-discs of skeletal and cardiac muscle bers. Because most smooth muscles must function for long periods
without rest, their power output is relatively low, but contractions can continue without using large amounts
of energy.
http://cnx.org/content/m48588/1.1/
Connexions module: m48588
3
Muscle Contraction
Figure 2:
The dense bodies and intermediate laments are networked through the sarcoplasm, which
cause the muscle ber to contract.
Motor Units
Figure 3:
A series of axon-like swelling, called varicosities or boutons, from autonomic neurons form
motor units through the smooth muscle.
Glossary
Denition 1: dense body
sarcoplasmic structure that attaches to the sarcolemma and shortens the muscle as thin laments
slide past thick laments
Denition 2: visceral muscle
smooth muscle found in the walls of visceral organs
http://cnx.org/content/m48588/1.1/