The Three Types of Muscle

There are two general classes of muscle in the body: striated and smooth. Both are named for the characteristic appearance of the individual cells making up the muscle tissue when viewed through a microscope. Striated muscle cells

Figure 10-1 Microscopic structure of skeletal muscle. Muscle components are viewed at increasing magnification in (a) through (d).

(a) Intact muscle

(a) Intact muscle

Muscle consists of muscle fibers

Stripes or striations

Muscle consists of muscle fibers

Muscle fiber is a bundle of myofibrils

(c) Myofibril

Z lines

Z lines

A band

I band

A band

(d) Two sarcomeres

I band

Enlarged view

Z line M line

Z line

M line Z line

Z line M line

Z line

M line Z line

Smooth Muscle Band Band

Sarcomere A band

Sarcomere A band

(Figure 10-1) exhibit closely spaced, crosswise stripes (striations). Smooth muscle cells have no striations and have a smooth appearance. Smooth muscle is found in the gut, blood vessels, the uterus, and other locations where contractions are usually slow and sustained. The muscles that move and support the skeletal framework of the body the skeletal muscles are made up of striated muscle cells. This chapter will focus on the structure and properties of skeletal muscle cells.

The cells that make up the muscle of the heart are also striated, like skeletal muscle. Because the membranes of cardiac muscle cells are electrically quite different from those of skeletal muscle cells, cardiac muscle is usually regarded as a distinct class of muscle in its own right. The characteristics of cardiac muscle will be discussed in Chapter 12.

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