Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

Skeletal Muscle Tissue Skeletal muscles are coordinated tissues under voluntary control. Skeletal muscle tissue contains very large muscle cells. Because the individual muscle cells are relatively long and slender, they are usually called muscle fibers. Each muscle fiber is described as multinucleate because it has several hundred nuclei distributed just inside the plasma membrane. Skeletal muscle fibers are incapable of dividing, but new muscle fibers are produced through the divisions of myosatellite cells. These are stem cells that reside in adult skeletal muscle tissue. As a result, skeletal muscle tissue can partially repair itself after an injury. Cardiac Muscle Tissue Cardiac muscle tissue is located only in the heart. A typical cardiac muscle cell, also known as a cardiocyte, is smaller than a skeletal muscle cell. A typical cardiac muscle cell has one centrally positioned nucleus. Cardiac muscle cells form extensive connections with one another. As a result, cardiac muscle tissue consists of a branching network of interconnected muscle cells. The connections occur at specialized regions known as intercalated discs . Cardiac muscle tissue has a very limited ability to repair itself. Although some cardiac muscle cells divide after an injury to the heart, the repairs are incomplete, and some heart function is usually lost. Cardiac muscle cells do not rely on nerve activity to start a contraction. Instead, specialized cardiac muscle cells called pacemaker cells establish a regular rate of contraction. The nervous system can alter the rate of pacemaker cell activity, but it does not provide voluntary control over individual cardiac muscle cells. Therefore, cardiac muscle is called striated involuntary muscle. Smooth Muscle Tissue Smooth muscle tissue is located in the walls of blood vessels, around hollow organs, such as the urinary bladder, and in layers around the respiratory, circulatory, digestive, and reproductive tracts. A smooth muscle cell is a small, spindle-shaped cell with tapering ends and a single, oval nucleus. They can divide; hence, smooth muscle tissue can regenerate after an injury. Smooth muscle cells may contract on their own. Because the nervous system usually does not provide voluntary control over smooth muscle contractions, smooth muscle is known as non-striated, involuntary muscle.

©2018 Achieve Test Prep Page 42 of 367