The photograph shows the characteristic features of skeletal muscle fibers in longitudinal section. Skeletal muscle fibers are extremely elongated, unbranched cylindrical cells with multiple flattened nuclei (black arrows) arranged at the cell periphery. The cross-striations, another characteristic feature of longitudinal skeletal muscle fibers , is also observed in the photograph.

The photograph shows the characteristic features of skeletal muscle fibers in longitudinal section: multiple flattened nuclei (black arrows) arranged at the cell periphery and the cross-striations. The striations of a skeletal muscle fiber are composed of alternating broad light I bands (I, yellow lines) and dark A bands (A, green lines). Fine dark lines called Z lines (Z, red arrows) can be seen bisecting the I bands.

The photograph shows the characteristic features of skeletal muscle fibers in longitudinal section: flattened nuclei (black arrows) arranged at the cell periphery and the cross-striations. The striations of a skeletal muscle fiber are composed of alternating broad light I bands (I, yellow lines) and dark A bands (A, green lines). Fine dark lines called Z lines (Z, red arrows) can be seen bisecting the I bands. Numerous mitochondria (Mt) provide a rich energy source in the scanty cytoplasm between the myofibril.

The photograph shows the characteristic features of skeletal muscle fibers in longitudinal section: flattened nuclei (black arrows) arranged at the cell periphery and the cross-striations. The striations of a skeletal muscle fiber are composed of alternating broad light I bands (I, yellow lines) and dark A bands (A, green lines). Fine dark lines called Z lines (Z, red arrows) can be seen bisecting the I bands. The dark A band is bisected by the lighter H band (pink lines), which is further bisected by a more dense M line (M, purple arrows). Numerous mitochondria (Mt) provide a rich energy source in the scanty cytoplasm between the myofibril.

The photograph shows the characteristic feature of skeletal muscle fibers in longitudinal section, the cross-striations. The striations of a skeletal muscle fiber are composed of alternating broad light I bands (I, yellow lines) and dark A bands (A, green lines). Fine dark lines called Z lines (Z, red arrows) can be seen bisecting the I bands. The dark A band is bisected by the lighter H band (pink lines), which is further bisected by a more dense M line (M, purple arrows). T-tubule (blue arrow) located between A-I band junction is also observed. Numerous mitochondria (Mt) provide a rich energy source in the scanty cytoplasm between the myofibril.

A neuromuscular junction shows the axon ending within the synaptic cleft of a skeletal muscle fiber. Numerous mitochondria (Mt) and synaptic vesicles (SV) are visible in the axon ending.

A neuromuscular junction shows the axon ending within the synaptic cleft of a skeletal muscle fiber. Numerous mitochondria (Mt) and synaptic vesicles (SV, black arrows) are visible in the axon ending . The muscle fiber shows the junctional folds (JF, red arrows).

A neuromuscular junction shows the axon ending within the synaptic cleft of a skeletal muscle fiber. Numerous mitochondria (Mt) and synaptic vesicles (SV, black arrows) are visible in the axon ending . The muscle fiber shows the junctional folds (JF, red arrows.

Cardiac muscle consists of fibers that possess the same arrangement of contractile filaments and thus also shows the same cross-striations as skeletal muscle. The histologically differences between cardiac and skeletal muscle fibers are the presence in cardiac muscle of intercalated discs (obscure here, red arrows) and the location of cardiac muscle cell nuclei in the center of the fiber (black arrows).

Cardiac muscle consists of fibers that possess the same arrangement of contractile filaments and thus also shows the same cross-striations as skeletal muscle. The histologically differences between cardiac and skeletal muscle fibers are the presence in cardiac muscle of intercalated discs (obscure here, red arrows) and the location of cardiac muscle cell nuclei in the center of the fiber (black arrows).

The striations of a cardiac muscle display the same arrangement with skeletal muscle fiber: alternating broad light I bands (I, yellow line) and dark A bands (A, green line). Fine dark lines called Z lines (Z, red arrows) can be seen bisecting the I bands. The dark A band is bisected by the lighter H band (pink lines), which is further bisected by a more dense M line (M, purple arrows). An intercalated disc (blue arrows), which represents a highly specialized attachment site between adjacent cardiac muscle cells, is shown at upper left corner. Numerous mitochondria (Mt) are also present in cardiac muscle.

The striations of a cardiac muscle display the same arrangement with skeletal muscle fiber: alternating broad light I bands (I, yellow line) and dark A bands (A, green line). Fine dark lines called Z lines (Z, red arrows) can be seen bisecting the I bands. The dark A band is bisected by the lighter H band (pink lines), which is further bisected by a more dense M line (M, purple arrows. T-tubule (blue arrow) in cardiac muscle is located at Z line. Numerous mitochondria (Mt) are also present in cardiac muscle.

The striations of a cardiac muscle display the same arrangement with skeletal muscle fiber: alternating broad light I bands (I, yellow line) and dark A bands (A, green line). Fine dark lines called Z lines (Z, red arrows) can be seen bisecting the I bands. The dark A band is bisected by the lighter H band (pink lines), which is further bisected by a more dense M line (M, purple arrows. T-tubule (blue arrow) in cardiac muscle is located at Z line. Numerous mitochondria (Mt) are also present in cardiac muscl.

An intercalated disc (red dash-line circle ), which represents a highly specialized attachment site between adjacent cardiac muscle cells, is shown.

The intercalated disc consists of three types of membrane-to-membrane contact, fascia adherens, desmosomes, and gap junctions.

T-tubule (blue arrow) in cardiac muscle is located at Z line.

Numerous mitochondria (Mt) are also present in cardiac muscle.

The intercalated disc consists of three types of membrane-to-membrane contact, fascia adherens (FA, red arrows), desmosomes (D, purple arrow), and gap junctions (G, blue arrow).

Fascia adherens (adhering junction) is the major constituent of the transverse component of the intercalated disc.

Desmosomes reinforce the fascia adherens and are found in both the transverse and lateral components of the intercalated discs.

Gap junctions (communicating junctions) constitute the major structural element of the lateral component of the intercalated disc.