Types of muscle tissue

Introduction

Muscle cells convert chemical energy into mechanical tension. This makes them necessary for many functions: body movement, blood circulation, transport of materials through hollow organs, continence, etc.

All muscle cells share some properties:

• Excitability: they respond to external stimuli
• Conductivity: action potentials propagate along their membrane
• Contractility: they shorten to produce force
• Extensibility: they can lengthen without sustaining structural damage
• Elasticity: they return to their initial length after being stretched

In addition, calcium ions regulate contraction and relaxation, myosin interacts with actin to create mechanical tension, and ATP is the primary energy source in all muscle cells.

To better support the functions of the organs they are part of, muscle tissues in different organs have specific characteristics. Muscle tissues can be classified into:

• Skeletal muscle has long cylindrical cells organized into repeating units called sarcomeres, which create alternating light and dark bands. Somatic motor neurons activate individual bundles of muscle fibers. Skeletal muscle contracts when calcium ions bind to troponin, promoting actin-myosin interaction.
• Cardiac muscle also has striated cells and relies on calcium ions binding to troponin to trigger contraction. These branched cells are tightly connected to spread action potentials and mechanical forces between adjacent cells, so that the heart contracts as a single unit. Some cardiac cells are autorhythmic, meaning that they spontaneously generate action potentials that cause contraction.
• Smooth muscle cells are spindle-shaped and lack striations. They are often activated by the autonomic nervous system, but they also respond to other stimuli including hormones and stretch. Some cells are tightly connected like cardiac muscle tissue; others are controlled independently like skeletal muscle. Instead of relying on troponin, calcium binds calmodulin, which activates myosin light chain kinase to enable smooth muscle contraction.

Explore concepts

Muscle tissue histology

Review the histology of different types of muscle tissues.

Location of the types of muscle tissues

Organs rely on different types of muscle tissue to perform their functions.

Comparison of muscle tissue types

Structure, activation and contraction mechanisms often differ across muscle tissues.

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Summary