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.
- The pacemaker sets the heart rate, but can be overridden by neural controls.
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.