Muscle Tissue: Structure, Types, and Function

Muscle Tissue

Prefix Review

Understanding common prefixes helps in identifying muscle-related terminology in anatomy and physiology.

• Myo-: Refers to muscle.

• My-: Also refers to muscle.

• Sarc-/Sarco-: Means flesh or muscle, often used for cellular components (e.g., sarcoplasm, sarcolemma, sarcomere).

Types of Muscle Tissue

Muscle tissue is classified into three main types, each with distinct structure and function.

• Skeletal Muscle

  • Attached to bones, skin, and other structures.

  • Longest muscle fibers.

  • Striated (visible stripes).

  • Voluntary control.

  • Tires easily, but endurance improves with muscle tone.

  • Also called: striated, skeletal, voluntary muscle.

• Cardiac Muscle

  • Located in the heart only.

  • Involuntary—does not require conscious control.

  • Striated and branched fibers (unique structure for heart function).

• Smooth Muscle

  • Found throughout the body: organs, tubes, vessels, digestive system, etc.

  • Non-striated and highly elastic.

  • Responsible for moving substances through organs (e.g., peristalsis).

  • Involuntary.

Functional Overview of Muscle Types

• Skeletal Muscle: Voluntary muscle attached to bones; responsible for body movement and posture.

• Cardiac Muscle: Involuntary muscle found only in the heart; responsible for pumping blood throughout the body.

• Smooth Muscle: Involuntary muscle found in walls of hollow organs (e.g., intestines, blood vessels); responsible for regulating internal movement.

Microscopic Structure Overview

Muscle tissue types differ in microscopic appearance and organization.

• Skeletal muscle: Highly striated, long parallel fibers.

• Smooth muscle: Long diagonal fibers, non-striated.

• Cardiac muscle: Branched fibers with striations.

Muscle Characteristics

All muscle tissue shares four key physiological properties:

• Excitability: Ability to respond to stimuli.

• Contractility: Ability to shorten (muscles only pull, never push).

• Extensibility: Ability to stretch.

• Elasticity: Ability to recoil to original shape.

Muscle Attachment Terminology

• Origin: The fixed attachment point of the muscle to a bone.

• Insertion: The movable attachment point where the muscle exerts its action.

• Direct Attachment: Muscle attaches directly to bone.

• Indirect Attachment: Muscle attaches to bone via tendons or aponeuroses.

General Notes on Muscle Function

• Muscles often work in pairs: one contracts while another relaxes.

• Elasticity decreases with age.

Functions of Muscle

Muscle tissue serves several essential functions in the body:

• Movement

• Posture

• Joint stabilization

• Heat generation (caused by ATP production during contraction)

Examples of Muscle Function

• Eye muscles controlling rotation: lateral, medial, inferior, superior muscles.

• Internal eye muscles control pupil size.

Skeletal Muscle Structure: Innervation & Blood Supply

• Each muscle fiber has nerve supply (innervation).

• Muscles require large amounts of energy (ATP).

• Waste products are removed through the bloodstream and processed (e.g., kidneys).

Connective Tissue Layers (Outer → Inner)

Muscles are organized into layers of connective tissue for support and function.

• Epimysium: Dense irregular connective tissue; surrounds the entire muscle.

• Perimysium: Fibrous connective tissue; surrounds fascicles (groups of muscle fibers).

• Endomysium: Areolar connective tissue; surrounds individual muscle fibers.

Muscle Attachment

• Muscles attach to bones and joints through:

  • Direct attachment

  • Indirect attachment

Muscle Diagram Summary

• The whole muscle is covered by epimysium.

• Inside are fascicles, each covered by perimysium.

• Inside fascicles are muscle fibers, each wrapped in endomysium.

Additional info:

• ATP (adenosine triphosphate) is the primary energy source for muscle contraction. The breakdown of ATP releases energy required for the sliding filament mechanism in muscle fibers.

• Muscle contraction is explained by the sliding filament theory, where actin and myosin filaments slide past each other to shorten the muscle fiber.

• Muscle tone refers to the continuous and passive partial contraction of muscles, which helps maintain posture.