Yfh Muscle Contraction

1 f Most behavioral and many physiological responses depend on muscle cells. Muscle cells are specialized for contraction and have high densities of actin and myosin. Muscle cells are found throughout the animal kingdom. Wherever whole tissues contract in animals, muscle cells are responsible.

In muscle cells, actin and myosin molecules are organized into microfilaments consisting of two or more molecules. Actin filaments consist of a twisted chain of actin molecules. Myosin filaments are bundles of many myosin molecules. The actin and myosin filaments lie parallel to each other. When contraction is triggered, the actin and myosin filaments slide past each other in a telescoping fashion. This sliding is the mechanism by which muscle cells contract. Like those of neurons, muscle cell plasma membranes can generate action potentials, and it is these action potentials that trigger the contractile machinery.

There are three types of vertebrate muscle: smooth muscle, cardiac (heart) muscle, and skeletal muscle (Figure 47.1). Although they all use the same contractile mechanism, these three muscle types have important differences that adapt them to their particular functions.

Muscle cell Intercalated discs

Types Muscle Cell

Skeletal muscle

47.1 Types of Vertebrate Muscle Tissue The cells of cardiac,or heart, muscle (top), branch and create a meshwork that resists tearing or breaking. Intercalated discs provide strong mechanical adhesion between the cells. In smooth muscle (center), the cells are usually arranged in sheets. Skeletal muscle (bottom) appears striped, or striated.The individual cells, called muscle fibers, are very large and are multinucleated.

Muscle cell Intercalated discs

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