10.2b Microscopic Anatomy of Skeletal Muscle

myoblast

(Under: A Multinucleated Cell) - Skeletal muscle fibers (Myofibers) are formed from embryonic cells called _________ - Undifferentiated muscle cell with the potential of becoming a muscle fiber. - fuse to form single skeletal muscle fibers during development

myofibrils

(Under: Muscle Fibers and Myofibrils) - (also known as a muscle fibril) is a basic rod-like unit of a muscle - also, it contain myofilaments - Approximately 80% of the volume of a muscle fiber is composed of long, cylindrical structures termed _________ - A skeletal muscle fiber contains hundreds to thousands of _____. Each ______ is about 1 to 2 micrometers in diameter and extends the length of the entire skeletal muscle fiber.

sarcomeres

(Under: Organization of a Sarcomere) - Functional unit of skeletal muscle. - or it is a functional unit of myofibril - Myofilaments within myofibrils are arranged in repeating microscopic cylindrical units (2 micrometers in length) called _______ - The number of ________ will vary with the length of the myofibril within the muscle fiber. Each ________ is composed of overlapping thick filaments and thin filaments.

Myoglobin

(Under:Mitochondria and Other Structures Associated with Energy Production) - is a Oxygen-carrying and-storing molecule in muscle. - is a reddish, globular protein that is somewhat similar to hemoglobin. - It binds oxygen when the muscle is at rest and releases it for use during muscular contraction. - This additional source of oxygen provides the means to enhance aerobic cellular respiration and the production of ATP.

Connectin

(Under:Other Structural and Functional Proteins) - also called titin, is a "cablelike" protein that extends from the Z discs to the M line through the core of each thick filamen - It stabilizes the position of the thick filament and maintains thick filament alignment within a sarcomere - Additionally, portions of the connectin molecules are coiled and "springlike" so that during contraction they are compressed to produce passive tension - During relaxation this passive tension is released as the sarcomere is returned to its normal resting length. Thus, _____ contributes to muscle fiber elasticity.

Z discs

(also called Z lines) are composed of specialized proteins that are positioned perpendicular to the myofilaments and serve as anchors for the thin filaments. Although the _____ appears as a flat disc when the myofibril is viewed from its "end," only the edge of the disc is visible in a side view, and it sometimes looks like a zigzagged line.

H zone

(also called the H band) is the most central portion of the A band in a resting sarcomere. - when the muscle is at rest, the _____ is only contain myoson. When it contracts ______disappear and I band disappear - This region does not have thin filament overlap; "only thick filaments are present." During maximal muscle contraction, "this zone disappears" when the thin filaments are pulled past thick filaments.

sarcolemma

(under: Sarolemma and T-tubules) - is a plasma membrane of muscle cells - or the plasma membrane of a skeletal muscle fiber (muscle cell)

Thick filaments

- (or thick myofilaments) - or myosin - have a diameter of about 11 nanometers. - They are assembled from bundles of 200 to 500 myosin protein molecules - Each myosin protein consists of two strands; each strand has a globular head and an elongated tail. The head contains a binding site for actin of the thin filaments

Actin

- Are the thin filaments - 6 _____ surround 1 myosin Thin filaments are primarily composed of two strands of ____ protein that are twisted around each other to form a helical shape - In each strand of actin, many small, spherical molecules (G, or globular, actin) are connected to form a fibrous strand (F, or filamentous, actin). F-actin resembles two beaded necklaces that are twisted and intertwined together, with G-actin as the individual beads.

terminal cisternae

- At either end of individual sections of the sarcoplasmic reticulum are blind sacs called___________ - Store up Calcium ions - which are much like the hem of a sleeve; they serve as the reservoirs for calcium ions

Nebulin

- It appears to be an actin-binding protein that is part of the I band of the sarcomere. - Studies indicate that the length of _______ is proportional to the length of the thin filament—thus, it has been proposed to act as a "ruler," that is responsible for the thin filament length during sarcomere assembly.

I bands

- It only contain actin but not myosin is called _____ - extend from both directions of a Z disc and are bisected by the Z disc. - These end regions contain only thin filaments; this region "appears light when viewed with a microscope." At maximal muscle contraction, the thin filaments are pulled past the thick filaments, causing "the_____ to disappear."

creatine phosphate

- can supply ATP in skeletal muscle only Skeletal muscle fibers also contain another type of molecule unique to muscle tissue called _____ -also, it provides muscle fibers with a means of supplying ATP anaerobically (creatine phosphate is described later in the chapter).

sarcoplasmic reticulum

- is an internal membrane complex that is similar to the smooth endoplasmic reticulum of other cells - Segments of ____________ surround bundles of contractile proteins called myofibrils - The _____fits around the myofibril like a sleeve of membrane netting

M line

- is the protein that hold the myosin in place is a thin transverse protein meshwork structure in the center of the H zone. It serves as an attachment site for the thick filaments and keeps the thick filaments aligned during contraction and relaxation events.

triad

- two terminal cisternae and a centrally placed T-tubule interact to form a structure called_______ that functions during muscle contraction.

Sarcoplasm

- which is the cytoplasm of muscle fibers, - contains the typical cellular structures such as the Golgi apparatus, ribosomes, and vesicles

T-Tubules

A tubules that binds to sarcolemma

calmodulin and calsequestrin

Calcium pumps move Ca2+ into the sarcoplasmic reticulum where it is stored bound to specialized proteins called______ and _________

sarcoplasmic reticulum

Calcium voltage-gated channels open to release Ca2+ from the _______ into the sarcoplasm. Release of Ca2+ from the _________ causes muscle contraction, as described later in detail.

myosin binding site

Each globular G-actin molecule has a significant feature called a __________. The myosin head attaches to the _________ of actin during muscle contraction.

myofilaments

Each myofibril contains bundles of muscle protein filaments called _____________ - ______ bundles contain two types of myofilaments: thick filaments and thin filaments. A ________s not as long as a myofibril; rather it takes many successive units of _____ to extend the entire length of the myofibril.

Satellite cells

If a skeletal muscle is injured, some __________may be stimulated to differentiate and assist to a limited extent in its repair and regeneration.

Myosin and actin

What are contracting proteins?

F-actin

____ resembles two beaded necklaces that are twisted and intertwined together

G-actin

_______act as the individual beads.

Troponin

is a globular or "ball-like" protein attached to tropomyosin. _____ is the binding site for Ca2+.

Tropomyosin

is a short, thin, twisted filament that is a "stringlike" protein. - Consecutive _______ molecules cover small bands of the actin strands, including the myosin binding sites in a noncontracting muscle.

Dystrophin

is part of a protein complex that anchors myofibrils that are adjacent to the sarcolemma to proteins in the sarcolemma. - These proteins of the sarcolemma also extend to the connective tissue of the endomysium. - Thus, ___________ links internal myofilament proteins of a muscle fiber to external proteins. - The genetic disorder of muscular dystrophy is caused by abnormal structure, or amounts, of dystrophin protein.

Yes

is skeletal muscle fibers are multi nucleated cells? (i.e., they have numerous nuclei). Yes or no? - Because During this fusion process, each myoblast nucleus contributes to the eventual total number of nuclei in the fiber.

A band

is the central region of a sarcomere that contains the entire thick filament. - A band is mainly made up of myosin - Thin filaments partially overlap the thick filament on each end of an A band. The A band "appears dark when viewed with a microscope."