Structure

Each smooth-muscle fiber is a spindle-shaped cell with a diameter ranging from 2 to 10 ¡m, as compared to a range of 10 to 100 ¡m for skeletal-muscle fibers (see Figure 11-3). While skeletal-muscle fibers are multi-nucleate cells that are unable to divide once they have differentiated, smooth-muscle fibers have a single nucleus and have the capacity to divide throughout the life of an individual. Smooth-muscle cells can be stimulated to divide by a variety of paracrine agents, often in response to tissue injury.

Two types of filaments are present in the cytoplasm of smooth-muscle fibers (Figure 11-35): thick myosin-containing filaments and thin actin-containing filaments. The latter are anchored either to the plasma

Relaxed

Contracted

Dense body

Thick and thin filaments

Contracted

Dense body

Thick and thin filaments

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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.

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