Introduction to Muscle Tissue

 

Learning Objectives

  • Describe the properties of muscle tissue.
  • Compare and contrast the three types of muscle tissue.
  • Describe the significant events of a skeletal muscle contraction within a muscle in generating force
  • Describe the Nervous System Control of muscle tension
  • Describe the types of skeletal muscle fibers
  • Identify the major muscles of the human body and their actions.
  • Compare and contrast agonist and antagonist muscles
  • Explain the structure and function of smooth muscle and cardiac muscle tissue.

 

Muscle is one of the four primary tissue types of the body. Muscle cells are specialized for contraction. Muscles allow for motions such as walking, and they also facilitate bodily processes such as respiration and digestion.

Properties of muscle tissue

All muscle cells share several properties: contractility, excitability, extensibility, and elasticity:

  1. Contractility is the ability of muscle cells to forcefully shorten. Contractility allows muscle tissue to pull on its attachment points and shorten with force.( muscles can only pull, never push.)
  2. Excitability is the ability to respond to a stimulus, which may be delivered from a motor neuron or a hormone.
  3. Extensibility is the ability of a muscle to be stretched or extended.
  4. Elasticity is the ability to a muscle to return to its original length when relaxed

Three types of muscle tissue:

Muscle cells are specialized for contraction. Muscles allow for motions such as walking, and they also facilitate bodily processes such as respiration and digestion. The body contains three types of muscle tissue: (a) skeletal muscle tissue (b) smooth muscle tissue (c) cardiac muscle tissue.

This figure show the micrographs of skeletal muscle, smooth muscle, and cardiac muscle cells.

Figure 1. The Three Types of Muscle Tissue. The body contains three types of muscle tissue: (a) skeletal muscle, (b) smooth muscle, and (c) cardiac muscle. From top, LM × 1600, LM × 1600, LM × 1600. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)

  • Skeletal muscle tissue forms skeletal muscles, which attach to bones or skin and control locomotion and any movement that can be consciously controlled. Because it can be controlled by thought, skeletal muscle is also called voluntary muscle. Skeletal muscles are long and cylindrical in appearance; when viewed under a microscope, skeletal muscle tissue has a striped or striated appearance. The striations are caused by the regular arrangement of contractile proteins (actin and myosin). Actin is a globular contractile protein that interacts with myosin for muscle contraction. Skeletal muscle also has multiple nuclei present in a single cell
  • Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels. Smooth muscle has no striations, is not under voluntary control, has only one nucleus per cell, is tapered at both ends, and is called involuntary muscle.
  • Cardiac muscle tissue is only found in the heart, and cardiac contractions pump blood throughout the body and maintain blood pressure. Like skeletal muscle, cardiac muscle is striated, but unlike skeletal muscle, cardiac muscle cannot be consciously controlled and is called involuntary muscle. It has one nucleus per cell, is branched, and is distinguished by the presence of intercalated disk.

                              Table 1:  Comparison of Structure and Properties of Muscle Tissue Types
Tissue Histology Function Location
Skeletal Long cylindrical fiber, striated, many peripherally located nuclei Voluntary movement, produces heat, protects organs Attached to bones and around entrance points to body (e.g., mouth, anus)
Cardiac Short, branched, striated, single central nucleus Contracts to pump blood Heart
Smooth Short, spindle-shaped, no evident striation, single nucleus in each fiber Involuntary movement, moves food, involuntary control of respiration, moves secretions, regulates flow of blood in arteries by contraction Walls of major organs and passageways