Skeletal Muscle Structure and Function

A thin membrane surrounding a skeletal muscle fiber, consisting of a plasma membrane and a thin layer of polysaccharide material with collagen fibrils. It fuses with tendon fibers at each end of the muscle fiber.

Large protein molecules that are responsible for muscle contraction, found within myofibrils. There are two types: thick filaments are myosin, and thin filaments are actin.

Bundles of protein filaments (myosin and actin) found within muscle fibers. Their arrangement causes light and dark bands, giving skeletal muscle a striated appearance.

A single, cylindrical muscle fiber that extends the length of the muscle, generally innervated by a single nerve ending.

The darker bands in a myofibril, composed of overlapping myosin and actin filaments, which are responsible for the striated appearance of skeletal muscle.

The lighter bands in a myofibril, composed only of actin filaments. This is because the myosin filaments do not extend into this region.

The junction between two sarcomeres, characterized by a thin, dark line that represents the attachment point for actin filaments.

The basic repeating unit of a myofibril, extending from one Z-line to the next. Each sarcomere contains both thick and thin filaments and is responsible for muscle contraction.

Small projections extending from the sides of myosin filaments responsible for interacting with actin filaments during muscle contraction.

The basic mechanism of muscle contraction where actin filaments slide along myosin filaments.

Protein responsible for holding the myosin and actin filaments in place within the sarcomere.

The intracellular fluid within a muscle fiber, surrounding the myofibrils and containing essential ions and enzymes.

A specialized endoplasmic reticulum in muscle fibers responsible for storing, releasing, and reabsorbing calcium ions for muscle contraction.

A neurotransmitter released at the neuromuscular junction, initiating muscle contraction.

Specialized channels in the muscle fiber membrane that open in response to acetylcholine binding, allowing sodium ions to enter.

Channels in the muscle fiber membrane that open in response to membrane depolarization, allowing sodium ions to enter and propagating the action potential.

The process of the muscle fiber membrane becoming less negative, triggered by the influx of sodium ions.

Calcium ions released from the sarcoplasmic reticulum bind to troponin, initiating the sliding filament mechanism.

The process of calcium ions being actively pumped back into the sarcoplasmic reticulum, stopping muscle contraction.

Thin filaments in muscle fibers composed of actin, tropomyosin, and troponin.

Thick filaments in muscle fibers composed of myosin, responsible for binding to actin during contraction.

When a new ATP molecule attaches to the myosin head, it detaches from the actin filament.

The breakdown of ATP provides energy that "cocks" the myosin head back to its perpendicular position, ready for another power stroke.

The cocked myosin head binds to a new active site on the actin filament, releasing energy and initiating another power stroke.

The amount of overlap between actin and myosin filaments determines the tension a muscle fiber can generate.

The point at which maximum tension is achieved in a sarcomere, where actin filaments fully overlap myosin filaments but haven't reached the center.

The point where the two ends of the actin filaments begin to overlap each other, causing a decrease in contraction strength.

The force generated by a contracting muscle increases progressively as the sarcomere shortens, reaching maximum tension at a specific length.

The amount of tension generated by a whole muscle during contraction is influenced by the combined activity of its individual sarcomeres.

Active tension is the increase in force generated by a muscle during contraction, and it decreases as the muscle is stretched beyond its optimal length.

The velocity of muscle contraction decreases as the load applied to the muscle increases, reaching zero velocity when the load equals the maximum force the muscle can generate.

The overlapping arrangement of actin and myosin filaments within a sarcomere, where the filaments slide past each other during muscle contraction.

The globular head of a myosin molecule, responsible for binding to actin and generating the force for muscle contraction.

The process by which the myosin head attaches to and detaches from actin, powered by the hydrolysis of ATP. This cycle drives the sliding of filaments during muscle contraction.

The enzyme that breaks down ATP, releasing energy that powers the cross-bridge cycle and muscle contraction.

A protein that wraps around the actin filament, blocking the myosin binding sites in a relaxed muscle.

A protein complex that regulates muscle contraction by controlling the position of tropomyosin on the actin filament.

The release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm, initiating muscle contraction.

The electrical signal that travels along the muscle fiber membrane, triggering the release of calcium from the sarcoplasmic reticulum.

A state where the myosin binding sites on actin are blocked by tropomyosin, preventing muscle contraction.

A state where the myosin binding sites on actin are exposed due to the movement of tropomyosin, allowing myosin to bind and initiate contraction.

The region where actin filaments attach to the Z disk. This is where the force of muscle contraction is transmitted to the connective tissue surrounding the muscle fiber.

The region in the middle of the sarcomere, where only the tails of the thick filaments are present. It does not have any myosin heads.

A protein complex made of three subunits: troponin I, troponin T, and troponin C. This complex plays a crucial role in controlling muscle contraction by attaching to actin and tropomyosin.

The mechanism by which muscle contraction occurs, involving the repeated attachment and detachment of myosin cross-bridges to actin filaments. It resembles a walking motion.

The active sites on the actin filament that bind to the myosin cross-bridge heads, initiating muscle contraction.

The specific part of the myosin molecule that projects from the myosin filament and interacts with actin during contraction.

A chemical reaction that releases energy for muscle contraction. Myosin heads cleave ATP into ADP and phosphate.

The process by which calcium ions bind to troponin C, causing a conformational change in the troponin complex, which then uncovers the active sites on actin.

Troponin C's strong binding affinity for Calcium ions initiates the contraction process.

Refers to how a muscle contracts more strongly when more cross-bridges are in contact with the actin filament. This is due to the independent operation of each cross-bridge.

The energy source for muscle contraction. It is cleaved to ADP and phosphate, releasing energy that fuels the myosin heads.

The state of a muscle fiber during active contraction, where the myosin cross-bridges are attached to the active sites on actin and pulling the actin filaments.

The force generated by a muscle during contraction that causes the movement of a load.

The process by which the troponin-tropomyosin complex inhibits the interaction between actin and myosin, preventing the myosin cross-bridges from binding.