Structure and Organization of Skeletal Muscle

Structure and Organization of Skeletal Muscle

Overview of Skeletal Muscle Composition

Skeletal muscle is a discrete organ composed of several types of tissues. The primary components include muscle fibers, nerves, blood vessels, and connective tissues. These elements work together to enable muscle contraction, provide nutrients, and remove waste products.

• Skeletal muscle fibers: The contractile cells responsible for movement.

• Nerves: Each muscle fiber is supplied by a nerve ending that controls its activity.

• Blood vessels: Arteries deliver oxygen and nutrients; veins remove metabolic waste.

• Connective tissues: Support and reinforce the muscle, preventing damage during strong contractions.

Nerve and Blood Supply

Innervation and Vascularization of Skeletal Muscle

Each skeletal muscle is served by one nerve, one artery, and one or more veins. These structures enter or exit near the central part of the muscle and branch extensively through the connective tissue sheaths.

• Nerve supply: Unlike cardiac and smooth muscle, every skeletal muscle fiber requires a nerve ending for stimulation and contraction.

• Blood supply: Skeletal muscles have a rich blood supply to meet their high energy demands. Arteries provide continuous delivery of oxygen and nutrients, while veins remove large amounts of metabolic waste.

• Capillaries: These small blood vessels have a winding path through muscle, straightening when the muscle stretches and contorting when it contracts. This design accommodates changes in muscle length.

Connective Tissue Sheaths

Types and Functions of Connective Tissue Sheaths

Connective tissue sheaths in skeletal muscle support each cell, reinforce the muscle, and prevent it from bursting during strong contractions. These sheaths are organized from external to internal as follows:

• Epimysium: An "overcoat" of dense irregular connective tissue that surrounds the entire muscle. It sometimes blends with the deep fascia between neighboring muscles or with subcutaneous tissue beneath the skin.

• Perimysium and Fascicles: Muscle fibers are grouped into bundles called fascicles. Each fascicle is surrounded by a layer of dense irregular connective tissue called perimysium.

• Endomysium: (Additional info: Not explicitly described in the provided text, but typically, the endomysium is a fine sheath of connective tissue surrounding each individual muscle fiber.)

These sheaths are continuous with one another and with the tendons that attach muscles to bones. When muscles contract, the sheaths transmit the pulling force to the bone, contributing to the muscle's elasticity and providing routes for blood vessels and nerves.

Table: Structure and Organizational Levels of Skeletal Muscle

Level	Structure	Connective Tissue Sheath
Muscle (organ)	Bundle of fascicles	Epimysium
Fascicle (portion of muscle)	Bundle of muscle fibers	Perimysium
Muscle fiber (cell)	Elongated multinucleate cell	Endomysium

Additional info: Table inferred from standard textbook content and the reference to Table 9.1 in the images.

Attachments of Skeletal Muscle

Types of Muscle Attachments

Most skeletal muscles span at least one movable joint and attach to bones or cartilage. The connective tissue sheaths play a crucial role in these attachments.

• Direct attachments: The muscle's connective tissue fuses directly with the periosteum of a bone or perichondrium of a cartilage.

• Indirect attachments: The connective tissue wrappings extend beyond the muscle as a ropelike tendon or a sheetlike aponeurosis. These structures anchor the muscle to the connective tissue covering of a skeletal element or to the fascia of other muscles.

• Advantages of indirect attachments: Tendons are durable, made mostly of tough collagen fibers, and can withstand abrasion. Their small size allows more tendons than fleshy muscles to pass over a joint, conserving space.

Self-Check: Section 9.2

• Which connective tissue sheath surrounds the whole muscle? Epimysium

• Which of the following is NOT found within a skeletal muscle? (Options not fully visible; typically, options might include structures not present in skeletal muscle, such as intercalated discs.)