Cardiac Muscle

Although cardiac muscle is striated, it differs markedly from skeletal muscle in appearance. Cardiac muscle is found only in the heart, where the myocardial cells are short, branched, and intimately interconnected to form a continuous fabric. Special areas of contact between adjacent cells stain darkly to show intercalated discs (fig. 1.8), which are characteristic of heart muscle.

The Study of Body Function

The Study of Body Function

Myocardial Intercalated Disc

Nucleus

Striations

Nucleus

Striations

■ Figure 1.7 Three skeletal muscle fibers showing the characteristic light and dark cross striations. Because of this feature, skeletal muscle is also called striated muscle.

Striated Muscle Intercalated Discs

Nucleus

Intercalated disc

Nucleus

Intercalated disc

■ Figure 1.8 Human cardiac muscle. Notice the striated appearance and dark-staining intercalated discs.

Intercalated Disc
Nucleus

■ Figure 1.9 A photomicrograph of smooth muscle cells. Notice that these cells contain single, centrally located nuclei and lack striations.

The intercalated discs couple myocardial cells together mechanically and electrically. Unlike skeletal muscles, therefore, the heart cannot produce a graded contraction by varying the number of cells stimulated to contract. Because of the way it is constructed, the stimulation of one myocardial cell results in the stimulation of all other cells in the mass and a "wholehearted" contraction.

Was this article helpful?

0 0
Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment