Anatomy Unit: Muscle Tissue Overview

Anatomy of Muscle Tissue

• Muscle tissue consists of muscle fibers grouped together, enabling contractility due to myofibrils in the cytoplasm.
• The muscle cell membrane is referred to as the sarcolemma, while the cytoplasm is called sarcoplasm.
• Muscle fibers can be categorized as striated or non-striated, and as voluntary or involuntary.

Types of Muscle Fibers

• Skeletal Muscle Fibers:

  • Striated with transverse dark and light bands.
  • Primarily voluntary, except in the upper third of the esophagus, pharynx, and cremaster muscle.
  • Generally do not branch, with exceptions in the tongue and face.
  • Attached to bones in the skeleton, and found in the eye and tongue.

• Cardiac Muscle Fibers:

  • Distinctive striations but branched; involuntary control.

• Smooth Muscle Fibers:

  • Non-striated, involuntary, and spindle-shaped.

Structure of Skeletal Muscle Fibers

• Composed of individual muscle cells (fibers) bundled by connective tissue.

• Connective Tissue Components:

  • Epimysium: Dense connective tissue encapsulating the entire muscle.
  • Perimysium: Dense connective tissue that divides the muscle into bundles.
  • Endomysium: Loose connective tissue separating individual muscle fibers.

• Microscopic Structure:

  • Longitudinal section: Skeletal muscle fibers are elongated, multinucleated cells (syncytium) with flattened oval nuclei located peripherally.
  • Regular transverse striations are visible; sarcoplasm is acidophilic and contains glycogen granules and myoglobin.
  • Transverse section: Polyhedral shape with possible visibility of nuclei; dark areas (Cohnheim’s areas) indicate myofibril grouping.

Myofibrils (Sarcostyles)

• Contractile elements arranged longitudinally within the sarcoplasm of skeletal muscle fibers.

• Structure:

  • Display alternating light and dark bands: the light band (I-band) is pale, while the dark band (A-band) is prominent.
  • Adjacent myofibrils’ dark bands align to create cross-striation observable under a light microscope.

• Band Structure:

  • Each dark band is bisected by a light disc termed the H-zone.
  • Each light band is divided by a dark line known as the Z-line, indicating the boundaries of sarcomeres.

This quiz covers the fundamental aspects of muscle tissue, including the basic structure and types of muscular tissues. It highlights the relationship between the structure and function of various muscular tissues, essential for understanding human anatomy. Test your knowledge on the characteristics and components of muscle tissue.