Muscle Tissue Types

Skeletal muscle

Skeletal muscle tissue comprises long, parallel cells, which are also called muscle fibers.
Multinucleated
Sarcomeres, which are the contractile units of skeletal muscle, lend a striated, or striped, appearance

The dark stripes are called A-bands
Lighter stripes are called I-bands
Z-discs lie in the middle of the I-bands, and M-lines lie within the A-bands
A single sarcomere comprises the space between two adjacent z-lines. This construction allows the thick and thin filaments to shorten the sarcomeres and contract the skeletal muscles.

Are located throughout the body, and attaches to bones (or other connective tissues) to provide body movement.
Unlike cardiac and smooth muscle, skeletal muscle tissue is under conscious neural control, though it also participates in reflex arcs

Cardiac muscle tissue

Branching cells with 1-2 centrally located nuclei.
Sarcomeres lend striations.
Cardiac muscle cells are connected at intercalated discs, which can appear as light-staining "breaks" or dark-staining lines between cardiac muscle cells.
Intercalated discs comprise interdigitating processes that hold adjacent cells together via complex junctions, including desmosomes and gap junctions.

Gap junctions serve as "electrical synapses" that spread contraction signals from cell to cell.

Cardiac muscle is in the heart, where it contracts involuntarily to provide a rhythmic heartbeat.

Smooth Muscle Tissue

Comprises spindle-, aka, fusiform, shaped elongated cells, with a single central nucleus.
Although they comprise contractile elements, the filaments are not arranged in sarcomeres; therefore, there are no striations.
Intermediate filaments attached to dense bodies form a mesh-like cytoskeleton, which resists tension during contraction

Thin filaments also attach to the dense bodies; during contraction, the cell shortens and takes on a cork-screw appearance.

Smooth muscle tissue is located in the walls of hollow organs, such as urinary and digestive tracts, and in arterial walls.
Involuntary smooth muscle contraction produces peristalsis, a wave-like pattern of movement that propels materials through the body channels (for example, foods through the digestive tract).
Contraction of vascular smooth muscle regulates blood flow.
Involuntary regulation of smooth muscle occurs via autonomic nervous stimulation, hormonal triggers, and local stimuli, including stretch.