Muscular Tissue

triad

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

Tropomyosin

Regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin.

Dystrophin

Structural protein that links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons

Nebulin

Structural protein that wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development.

actin

The main component of the thin filament is the protein Individual actin molecules join to form an actin filament that is twisted into a helix

sarcolemma

The multiple nuclei of a skeletal muscle fiber are located just beneath

aponeurosis

When the connective tissue elements extend as a broad, flat sheet

filaments

Within myofibrils are smaller protein structures

sarcoplasmic reticulum

a fluid-filled system of membranous sacs

sarcoplasm

cytoplasm of a muscle fiber

H zone

in the center of each A bands contains thick but not thin filaments

Fascia

is a dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscle and othe organs of the body

I band

is a lighter, less dense area that contains the rest of the thin filaments but no thick filaments

Perimysium

is also a layer of dense irregular connective tissue, but it surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles (FAS-i-kuls = little bundles).

Myosin

is the main component of thick filaments and functions as a motor protein in all three types of muscle tissue.

Epimysium

is the outerlyer encircling the enitire muscle. it consists of dense irregular connective tissue

M line

middle of the sarcomere.

Endomysium

penetrates the interior of each fascicle and separates individual muscle fibers from one another. The endomysium is mostly reticular fibers.

Z discs

separate one sarcomere from the next

myofibrils

the contractile organelles of skeletal muscle

terminal cisterns

the contractile organelles of skeletal sarcloplasmic reticulum

transverse tubules

tunnel in from the surface toward the center of each muscle fiber. B

A band

which extends the entire length of the thick filaments (Figure 10.3b). Toward each end is a zone of overlap, where the thick and thin filaments lie side by side.

subcutaneous layer

which separates muscle from the skin is composed of areolar connective tissue and adipose tissue.

Troponin

Regulatory protein that is a component of thin filament; when calcium ions (Ca2+) bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin

Myomesin

Structural protein that forms M line of sarcomere; binds to titin molecules and connects adjacent thick filaments to one another.

α-Actinin

Structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules.

Titin

Structural protein that connects Z disc to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils.