Functions and Physiologic Characteristics of Skeletal Muscle Tissue

  • The term muscle tissue refers to all the contractile tissues of the body: skeletal, cardiac, and smooth muscle. The muscular system, however, refers to the skeletal muscle system: the skeletal muscle tissue and connective tissues that makeup individual muscle organs, such as the biceps brachii muscle. 
  • Cardiac muscle tissue is located in the heart and is therefore considered part of the cardiovascular system. Smooth muscle tissue of the intestines is part of the digestive system, whereas smooth muscle tissue of the urinary bladder is part of the urinary system and so on. In this chapter, we discuss only the muscular system.

Functions of muscle tissue

  • Through sustained contraction or alternating contraction and relaxation, muscle tissue has three key functions: producing motion, providing stabilization, and generating heat.
  1. Motion: Motion is obvious in movements such as walking and running, and in localized movements, such as grasping a pencil or nodding the head. These movements rely on the integrated functioning of bones, joints, and skeletal muscles.
  2. Stabilizing body: Besides producing movements, skeletal muscle contractions maintain the body in stable positions, such as standing or sitting. Postural muscles display sustained contractions when a person is awake, for example, partially contracted neck muscles hold the head upright. In addition, the volumes of the body cavities are regulated through the contractions of skeletal muscles. For example muscles of respiration regulate the volume of the thoracic cavity during the process of breathing.
  3. Thermo genesis: As skeletal muscle contracts to perform work, a by-product is heat. Much of the heat released by muscle is used to maintain normal body temperature. Muscle contractions are thought to generate as much as 85% of all body heat.

The Three Connective Tissue Layers Bundles of muscle fibers, called fascicles, are covered by the perimysium. Muscle fibers are covered by the endomysium. Image Source: openstax.org

Physiologic Characteristics of muscle tissue

  1. Excitability: Excitability (irritability), a property of both muscle and nerve cells (neurons), is the ability to respond to certain stimuli by producing electrical signal called action potentials (impulses).
  2. Contractility: Contractility is the ability of muscle cells to forcefully shorten. Contractility is the ability of muscle tissue to shorten and thicken (contract), thus generating force to do work. Muscles contract in response to one or more muscle action potentials.
  3. Extensibility: Extensibility means that the muscle can be extended without damaging the tissue. Most skeletal muscles are arranged in opposing pairs. While one is contracting, the other not only relaxed but also usually is being stretched.
  4. Elasticity: Tissue elasticity is the ability to stretch a muscle to reach its full range of movement without restriction. Elasticity means that muscle tissue tends to return to its original shape after contraction or extension.

Further Readings