Muscular Tissue Overview

Study Notes

Muscle fiber: The basic structural and functional unit of muscles
Skeletal muscle: Striated, voluntary, found in limbs and other body parts
Cardiac muscle: Striated, involuntary, found in the heart
Smooth muscle: Non-striated, involuntary, found in internal organs and blood vessels

Muscle fiber (cell): Long, cylindrical, multinucleated cells
Sarcomere: Repeating contractile units within myofibrils, defined by Z-lines; they contain thick (myosin) and thin (actin) filaments that slide past each other during contraction
Myofibrils: Thread-like structures within muscle fibers, composed of sarcomeres
Myosin: Thick filaments in the sarcomere; responsible for binding to the thin filaments.
Actin: Thin filaments in the sarcomere; responsible for binding to myosin
A band: Contains the thick filaments (myosin)
I band: Contains the thin filaments (actin)
Z line: Separates sarcomeres; located in the center of the I band
H zone: The center of the A band; contains only thick filaments
Cross-striations: Alternating light and dark bands in skeletal and cardiac muscle fibers due to the overlapping arrangement of actin and myosin filaments
Sarcoplasm: Cytoplasm of muscle fiber
Sarcolemma: The plasma membrane of a muscle fiber
Sarcoplasmic reticulum (SR): Specialized endoplasmic reticulum in muscle cells; stores and releases calcium ions (Ca2+)
T-tubules: Invaginations of the sarcolemma that allow action potentials to quickly penetrate the muscle fiber cell, triggering the release of calcium ions
Triad tubular system: T-tubules and flanking SR structures.

Smooth muscle cells: Spindle-shaped, uninucleated cells. Lack the striations seen in other muscle types,
Smooth Muscle Organization: These cells are arranged in sheets or layers, with their fibers intertwining or interconnecting.
Smooth Muscle Location: Present in walls of internal organs (digestive tract, blood vessels, bladder, etc).

Cardiac muscle cells: Cells are short, branched, and often connected end-to-end at structures called intercalated discs. Intercalated discs play a key role in coordinating heart contractions.
Cardiac Muscle Location: Found in the walls of the heart.

Red muscle fibers: more resistant to fatigue, rely more on oxygen, and contain abundant myoglobin and mitochondria.
White muscle fibers: Contract more quickly and powerfully, but fatigue more rapidly; rely more on glycogen for energy and contain fewer mitochondria.
Intermediate fibers: Have an intermediate speed and resistance to fatigue and have both glycogen reserves and mitochondria

Podcast