Excitation and Contraction of Smooth Muscle Contraction of Smooth Muscle In Chapters 6 and 7, the discussion was concerned with
skeletal muscle. We now turn to smooth muscle, which is composed of far smaller fibers—usually 1 to
5 micrometers in diameter and only 20 to 500 micrometers in length. In contrast, skeletal muscle fibers
are as much as 30 times greater in diameter and hundreds of times as long
Types of Smooth Muscle The smooth muscle of each organ is distinctive from that of most other or ans in several ways: (1)
physical dimensions, (2) organization into bundles or sheets, (3) response to different types of stimuli,
(4) characteristics of innervation,
and (5) function.
Figure 8-1 Multi-unit (A) and unitary (B) smooth muscle.
Unit II Membrane Physiology, Nerve, and Muscle 92 Contractile Mechanism in Smooth Muscle Chemical Basis for Smooth Muscle Contraction
Smooth muscle contains both actin and
myosin filaments, having chemical characteristics similar to those of the actin and myosin filaments in
skeletal muscle. It does not contain the normal troponin complex that is required in the control of
skeletal muscle contraction, so the mechanism for control of contraction is different. This is discussed
in detail later in this chapter. Chemical studies have shown that actin and myosin filaments derived
from smooth muscle interact with each other in much the same way that they do in skeletal muscle.
