Skeletal Muscle Tissue

M line

Connects the central portion of each thick filament.

zone of overlap

Thin filaments are arranged in a 6:1 ratio around each thick filament in this.

muscle fiber

any of the elongated cells characteristic of muscle.

thick filaments

composed primarily of myosin

muscle fascicle

is a bundle of muscle fibers. The fibrous perimysium layer separates the fascicles from each other.

sarcolemma

the plasma membrane of a muscle fiber

tropomyosin

cover the active sites on G-actin and prevent actin-myosin interaction. A tropomyosin molecule is a double-stranded protein that is bound to one molecule of troponin midway along its length.

sarcomere

the contractile unit of a myofibril; they are repeating units, delimited by the Z bands, along the length of the myofibril.

A band

the dense region of the sarcomere that contains thick filaments.

sarcoplasmic reticulum

the endoplasmic reticulum of cardiac muscle and skeletal striated muscle that functions especially as a storage and release area for calcium.

Z line

this marks the boundary between adjacent sarcomeres. It consists of proteins called actinins, which interconnect thin filaments of adjacent sarcomeres.

titin

A giant elastic protein with kinase activity that extends over half the length of a sarcomere and serves as a scaffold to which myofibrils and other muscle-related proteins attach.

G actin

Each molecule of this has an active site to which myosin can bind. This is much like a substrate molecule binding to an enzyme's active site.

H band

In a resting sarcomere, it is the lighter region on either side of the M line. The H band contains thick filaments, but no thin filaments.

nebulin

Is a large protein that extends along the F-actin strand in the cleft between the rows of G-actin molecules. It holds the F-actin strand together.

triad

The combination of a pair of terminal cisternae plus a transverse tubule is known as a ___.

I band

contains thin filaments but no thick filaments, extends from the A band of one sarcomere to the A band of the next.

epimysium

a dense layer of collagen fibers, surrounds the entire muscle. It separates the muscle from surrounding tissues and organs. It is connected to the deep fascia, a dense connective tissue layer.

perimysium

a fibrous layer that divides the skeletal muscle into a series of compartments. In addition to possessing collagen and elastic fibers, it contains blood vessels and nerves that maintain blood flow and innervate the muscle fibers within the fascicles.

myosin

a fibrous protein that forms (together with actin) the contractile filaments of muscle cells and is also involved in motion in other types of cells.

aponeurosis

a sheet of pearly-white fibrous tissue that takes the place of a tendon in sheetlike muscles having a wide area of attachment.

myosatellite cells

are stem cells that function in the repair of damages muscle tissue.

myofilaments

are the filaments of myofibrils constructed from proteins. The principal types of muscle are striated muscle, obliquely striated muscle and smooth muscle.

thin filaments

composed primarily of actin

myofibril

is a cylindrical structure. It is very thin and as long as the entire fiber. Any of the elongated contractile threads found in striated muscle cells.

T tubule

is a deep invagination of the sarcolemma, which is the plasma membrane, only found in skeletal and cardiac muscle cells. These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell.

actinin

is a microfilament protein. α-Actinin is necessary for the attachment of actin filaments to the Z-lines in skeletal muscle cells, and to the dense bodies in smooth muscle cells.

endomysium

is a thin layer of areolar connective tissue that surrounds each muscle fiber. It loosely interconnects nearby muscle fibers. Each muscle fiber contains bundles of protein filaments called myofibrils.

F actin

is a twiested strand composed of two rows of 300-400 individual molecules of G-actin.

myoblasts

is a type of embryonic progenitor cell that differentiates to give rise to muscle cells. A muscle fiber is created when multiple of these fuse together. (MULTINUCLEATE)

troponin

molecules which consists of three globular subunits. One subunit binds to tropomyosin, locking them together as a troponin-tropomyosin complex. A second subunit binds to one G-actin, holding the troponin-tropomyosin complex in position. And the third subunit has a receptor that binds two calcium ions.