Muscular Tissue Overview

A network of smooth endoplasmic reticulum surrounding myofibrils in muscle cells. It plays a crucial role in storing and releasing calcium ions (Ca++) for muscle contraction.

Cylindrical protein structures that make up muscle fibers. They are responsible for muscle contraction and are arranged in parallel bundles within each muscle cell.

The functional unit of a myofibril, responsible for muscle contraction. It is characterized by alternating dark (A) and light (I) bands.

The darker band in a sarcomere, containing both thick (myosin) and thin (actin) filaments.

The lighter band in a sarcomere, composed solely of thin (actin) filaments.

A dark line that bisects the I-band and serves as the attachment point for thin (actin) filaments.

The central region of the A-band where only thick (myosin) filaments are present.

A thin line in the center of the H-zone, where the thick (myosin) filaments are linked together.

Red muscle fibers are characterized by their dark color due to abundant myoglobin, mitochondria, and vascularization. They utilize aerobic respiration to produce energy, allowing them to contract slowly and resist fatigue for extended periods.

White muscle fibers are pale in color due to less myoglobin and higher glycogen levels. They rely on anaerobic glycolysis for energy, leading to rapid and powerful contractions but rapid fatigue.

Intermediate fibers possess characteristics of both red and white fibers, exhibiting a blend of aerobic and anaerobic capabilities.

Satellite cells are inactive myoblasts found in adult muscle fibers, nestled between the sarcolemma and basal lamina. They are responsible for regenerating muscle fibers after injury.

The musculotendinous junction is where muscle fibers merge with tendons. The muscle fiber gradually tapers off, while the connective tissue components of the muscle continue into the tendon.

Skeletal muscle hypertrophy refers to an increase in muscle fiber size, typically caused by exercise or physical training.

Muscular dystrophy involves a progressive degeneration of skeletal muscle fibers. A key feature is the absence of dystrophin, a protein crucial for muscle function.

Invaginations of the sarcolemma into the muscle fiber's interior, encircling myofibrils and aiding in the transmission of nerve impulses.

The process by which a nerve impulse triggers calcium release from the sarcoplasmic reticulum, leading to muscle contraction.

The process by which calcium is actively pumped back into the sarcoplasmic reticulum after contraction, resulting in muscle relaxation.

Sudden, painful muscle contractions caused by factors like reduced blood flow, low potassium levels, or intense exercise without proper warm-up.

An autoimmune disease where the body's immune system attacks acetylcholine receptors in skeletal muscles, causing weakness. This starts with facial, eye, and tongue muscles and progresses to respiratory muscles, potentially leading to respiratory failure.

The specialized muscle tissue that makes up the heart's middle layer.

The outer layer of the heart, surrounding the myocardium.

The inner layer of the heart, lining the chambers.

The interconnected, branched muscle fibers that make up cardiac muscle.

The junctions between individual cardiac muscle cells (myocytes) within a fiber.

Single, oval-shaped nuclei found in each cardiac myocyte.

These are specialized cardiac muscle fibers found in the moderator band, atrioventricular bundle, and its branches. They transmit impulses faster than ordinary myocardium, ensuring synchronized ventricle contractions.

Irreversible injury and death of cardiac muscle cells, commonly caused by a complete blockage of a coronary artery.

These junctions allow for direct communication between adjacent cardiac muscle cells, facilitating the rapid spread of electrical impulses.

Involuntary rhythmic contraction of cardiac muscle fibers, regulated by the autonomic nervous system and hormones.

A narrowing of the coronary artery lumen due to atheroma buildup, leading to reduced oxygen supply to ventricular muscle and chest pain upon exertion.

A condition where the ventricular muscle is inadequately oxygenated due to a slowly progressive narrowing of the coronary artery lumen.

Smooth muscle, a type of muscle tissue found in the walls of hollow organs like the digestive, urinary, and respiratory tracts, as well as blood vessels, skin, and the eye. It contracts slowly and involuntarily, helping to move substances through organs and regulate blood flow.

Smooth muscle fibers, unlike skeletal muscle fibers, are connected together by gap junctions. This allows for coordinated contraction of the muscle fibers, facilitating smooth muscle movement.

Smooth muscle fibers are surrounded by a thin layer of reticular fibers called endomysium. This provides structural support and helps to organize the muscle fibers.

Smooth muscle fibers are arranged in sheets, layers, or bundles, which are in turn surrounded by a thin collagenous connective tissue called perimysium. This perimysium also contains blood vessels and nerves, providing the muscle with necessary resources and control.

Oxytocin, a hormone, can directly influence smooth muscle contraction. It plays a crucial role in uterine contraction during childbirth, making it a valuable tool for inducing or enhancing labor.

Caveolae are invaginations on the smooth muscle cell surface, functioning in controlling calcium release and regulating muscle contraction. Unlike skeletal muscle, smooth muscle lacks T-tubules.

Smooth muscle cells are spindle-shaped, meaning they are wider in the center and taper at both ends, which allows them to fit together tightly. The tapered ends lie next to the broader parts of neighboring cells, forming sheets.

Dense bodies, analogous to Z-lines in striated muscle, serve as attachment points for actin filaments. They transmit the contractile force throughout the smooth muscle, enabling coordinated movement.