Types of Muscle Tissue

Skeletal Muscle

Skeletal muscle tissue is packaged into skeletal muscles, which are organs attached to bones and skin. These muscles are responsible for voluntary movements and are under conscious control.

• Skeletal muscle fibers are the longest muscle cells and have striations (striped appearance).

• Also called voluntary muscle because it can be consciously controlled.

Cardiac Muscle

Cardiac muscle tissue is found only in the heart and makes up the bulk of the heart walls.

• Striated like skeletal muscle.

• Involuntary: cannot be consciously controlled.

Smooth Muscle

Smooth muscle tissue is found in the walls of hollow organs such as the stomach, urinary bladder, and airways.

• Not striated.

• Involuntary: cannot be consciously controlled.

Characteristics & Functions of Muscle Tissue

Main Characteristics

All muscle tissues share four main characteristics:

• Excitability (responsiveness): Ability to receive and respond to stimuli.

• Contractility: Ability to shorten forcibly when stimulated.

• Extensibility: Ability to be stretched.

• Elasticity: Ability to recoil to resting length after being stretched.

Important Functions

• Produce movement: Responsible for all locomotion and manipulation (e.g., walking, digesting, pumping blood).

• Maintain posture and body position.

• Stabilize joints.

• Generate heat as they contract.

Skeletal Muscle Anatomy

Overview

Skeletal muscle is an organ composed of different tissues with three main features: nerve and blood supply, connective tissue sheaths, and attachments.

• Each muscle receives a nerve, artery, and veins.

• Every muscle fiber is supplied by a nerve ending to control activity.

• Contracting muscle fibers require large amounts of oxygen and nutrients and need waste products removed quickly.

Connective Tissue Sheaths

Connective tissue sheaths support cells and reinforce the whole muscle. They are organized from external to internal as follows:

• Epimysium: Dense irregular connective tissue surrounding the entire muscle; may blend with fascia.

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

• Endomysium: Fine areolar connective tissue surrounding each muscle fiber.

Attachments

Muscles span joints and attach to bones at two or more places:

• Insertion: Attachment to the movable bone.

• Origin: Attachment to the immovable or less movable bone.

Attachments can be:

• Direct (fleshy): Epimysium fused to periosteum of bone or perichondrium of cartilage.

• Indirect: Connective tissue wrappings extend beyond muscle as a ropelike tendon or a sheetlike aponeurosis.

Illustration: Connective Tissue Sheaths

The connective tissue sheaths of skeletal muscle (epimysium, perimysium, and endomysium) are shown in cross-sectional and longitudinal diagrams, highlighting their relationship to muscle fibers, fascicles, and tendons.