10.2 Skeletal Muscle Tissue

Muscle Fibers

Building blocks of skeletal muscles

Subcutaneous layer/hypodermis

separates muscle from skin

Fascia

Dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles

Epimysium

Outermost layer, surrounds entire muscle

Perimysium

Surrounds groups of 10-100 muscle fibers called fascicles

Endomysium

penetrates the interior of each fascicle and separates individual muscle fibers from one another

Tendon

Extension of epimysium, perimysium, and endomysium combined; connects muscle to bone

Average length of a mature muscle fiber

10cm

Top length of a mature muscle fiber

30cm

Myoblasts

muscle stem cells; fuse to form muscle fibers

Sarcolemma

Plasma membrane of a muscle cell

Transverse Tubules

Invagination of the sarcollema; tunnel in from surface toward the center of the muscle fiber

Sarcoplasm

cytoplasm of muscle fiber, contains glycogen and myoglobin

Glycogen

Large molecule composed of many glucose molecules

Myoglobin

Red-colored protein that releases oxygen

Myofibrils

Structural unit of a muscle fiber

Sarcoplasmic Reticulum/SR

Encircles each myofibril

Terminal cisterns

Enlarged area of sarcoplasmic reticulume that butts against a t-tubule and stores calcium

Triad

A transverse tubule and two terminal cisterns on either side of it

Filaments/Myofilaments

Smaller protein structures within myofibrils

Sarcomere

Functional Unit of a myofibril

Thin filaments

composed mostly of actin

Thick filaments

composed mostly of myosin

Z disc

separate one sarcomere from the next

A band

Extends the entire length of the thick filaments

Zone of Overlap

Where thick and thin filaments lie side by side

I Band

Contains thin filaments but no thick filaments; Z disc passes through the center

H Zone

Contains thick filaments but no thin filaments

M Line

In the center of the sarcomere

Delayed Onset Muscle Soreness (DOMS)

Microscopic muscle damage occuring 12-48 hours after strenuous exercise

Contractile Proteins

Generate force during contraction; myosin and actin

Myosin

Main component of thick filaments

Actin

Main component of thin filaments

Regulatory Proteins

Help switch the contraction process on and off, Tropomyosin and Troponin

Tropomyosin

Covers myosin binding site on actin

Troponin

Holds Tropomyosin in place

Structural Proteins

Keep thick and thin filaments in proper alignment (Titin, alpha-actinin, myosin, nebulin, dystrophin)

Titin

Helps stabilize thick filaments