The Structure and Function of Muscular Tissue Types

Posted on Dec 21, 2025 in Human Biology

Muscular Tissue: Structure and Components

Muscles are made up of highly specialized, thin, and elongated cells called muscle fibers. The muscle fibers contain specialized cytoplasm called sarcoplasm that contains a network of membranes called the sarcoplasmic reticulum. The muscle fibers may be bounded by the cell membrane called the sarcolemma. Each muscle fiber may contain numerous longitudinal fibrils called myofibrils.

Basic Physiological Properties of Muscle Tissue

  1. Contractility
  2. Excitability
  3. Extensibility
  4. Elasticity

Types of Muscle

  1. Skeletal Muscle
  2. Smooth Muscle
  3. Cardiac Muscle

1. Skeletal Muscle

  • It acquires its name because most of these muscles are attached to the skeleton, enabling movement.
  • Also known as Striated Muscle because its cells (fibers) are composed of alternating light and dark bands (stripes).
  • Also known as Voluntary Muscle.
Structure of Skeletal Muscle
  1. Composed of muscle fibers. Each muscle fiber is long, cylindrical-shaped, and contains numerous nuclei.
  2. Each fiber is approximately 1.2 inches long and 0.004 inches in diameter. (The longest fiber is the Sartorius muscle, 12 inches; the shortest fiber is the Stapedius muscle, 0.04 inches.)
  3. Each fiber contains numerous myofibrils, which are made up of thick and thin threads called myofilaments.
  4. Thick myofilaments are composed of larger proteins (e.g., Myosin).
  5. Thin myofilaments are composed of smaller proteins, such as actin.
  6. An overlapping of thick myosin and thin actin myofilaments produces the dark A band (anisotropic band), which does not allow light to pass.
  7. When viewed with a light microscope, skeletal tissue shows a pattern of alternating light and dark bands. The bands are caused by the arrangement of actin and myosin myofilaments in the muscle fiber.
  8. Thin actin myofilaments alone produce the light I band (isotropic band), which allows light to pass.
  9. Cutting across each I band is a dark Z line.
  10. Within the A band is a somewhat lighter H zone (Hensen’s disk), which consists only of myosin myofilaments.
  11. The area between two Z lines is known as the sarcomere, which is the fundamental contractile unit of the myofibril.
Functions of Skeletal Muscle

Skeletal muscles are voluntary in function. They bring about the movement of organs and locomotion of the body.

  1. Skeletal muscles undergo powerful and rapid contractions with short rest periods, and hence get fatigued easily.
  2. They are supplied by the Voluntary Nervous System (CNS and PNS).
  3. They require a large amount of energy, so they are supplied with blood vessels and numerous elongated mitochondria and glycogen granules.
  4. Found attached to the head, trunk, and limbs, and also in the body wall, tongue, pharynx, and esophagus.

2. Smooth Muscle

  • It gets its name because it is not striated and appears smooth under a microscope.
  • Also called Involuntary Muscle because it is controlled by the Autonomic Nervous System (ANS).
Structure of Smooth Muscle
  1. The muscle fiber is long (but not nearly as long as skeletal muscle fiber), spindle-shaped, and slender. It contains only one nucleus, situated at the center of the fiber at the broadest part.
  2. The smooth muscle fiber is enclosed by the sarcolemma and contains numerous longitudinal myofibrils.
  3. Actin and myosin myofilaments within the myofibrils are very thin and are arranged more randomly than in skeletal muscle, resulting in no visible stripes or striations.
Main Characteristics of Smooth Muscle
  1. Its contraction and relaxation periods are slower.
  2. Its action is rhythmical. Its contraction may last for 30 seconds or more, but it does not tire easily. Such sustained contraction plus the ability to stretch makes it suitable for the muscular control of organs like the stomach, intestine, urinary bladder, and uterus.

3. Cardiac Muscle

It is present only in the heart.

Structure and Function of Cardiac Muscle
  1. Under a microscope, they have similar striations as skeletal muscle.
  2. Cardiac muscle cells are closely packed, but each cell is nucleated and separated from others.
  3. The cells are joined end-to-end by specialized cell junctions called intercalated disks. These disks attach one cell to another with desmosomes, connect the myofibril filaments of adjacent cells, and contain gap junctions that help to synchronize the contraction of cardiac muscle by allowing impulse transmission from one cell to another.
  4. They contain light I bands and dark A bands; the intercalated disk always occurs at the location of the Z-line.
  5. Supplied by the Central and Autonomic Nervous Systems.
  6. The rhythmic contraction occurs on its own (autorhythmicity).
  7. They do not fatigue, so they are often called fatigue-less muscle.