Skeletal Muscle Structure and Characteristics

Skeletal Muscle Structure and Characteristics

• Skeletal muscle is excitable, meaning motor neurons use action potentials to stimulate contraction.
• It is contractile, meaning it shortens in response to changes in membrane potential.
• Extensible, capable of stretching beyond resting length.
• Elastic, returning to its original length after being stretched.
• Functions include movement production, posture maintenance, joint stabilization, and heat generation.

Muscle Tissue Components

• Epimysium: dense irregular connective tissue surrounding the entire muscle.
• Perimysium: dense irregular connective tissue surrounding fascicles (bundles of muscle fibers).
• Fascicle: bundle of muscle fibers.
• Endomysium: innermost connective tissue layer surrounding individual muscle fibers (cells).
• Myofibril: a group of sarcomeres arranged in a chain.
• Sarcomere: the smallest contractile unit of muscle.
• Z-discs to Z-discs mark the boundary of adjacent sarcomeres.
• Actin (thin) and myosin (thick) myofilaments are proteins interacting within sarcomeres.
• Tropomyosin and troponin regulate actin-myosin binding.
• A band: dark band with overlapping actin and myosin.
• I band: light band with only actin.
• H zone: central region of A band with only myosin.
• M line: center of the H zone.

Motor Units and Fiber Types

• Motor unit: a motor neuron and the muscle fibers it innervates; smallest functional unit.
• Components are motor neuron and muscle fibers.
• Type I (Slow Oxidative): suited for long-distance activities, high mitochondria density, low force production, resistant to fatigue.
• Type IIa (Fast Oxidative Glycolytic): suited for middle-distance activities or activities requiring bursts of energy, moderate mitochondrial density, moderate force production.
• Type IIx (Fast Glycolytic): suited for high-intensity, short-duration activities, low mitochondria density, high force production, fatigable quickly.

Muscle Fiber Properties

• Fiber diameter, hypertrophic potential, mitochondrial density, and capillary density vary among fiber types.
• Type I fibers have a low ratio of fibers to motor neurons, indicating fine motor control.
• Type II fibers have a high ratio of fibers to motor neurons, indicating gross motor control.

Excitation-Contraction Coupling

• Neuromuscular junction: where the nervous system connects with muscles, at the motor end plate.
• Motor end plate is rich in acetylcholine receptors and the junction receives acetylcholine.
• Resting membrane potential (RMP) is -90mV for muscle cells.
• An action potential causes calcium release, which leads to cross-bridge cycling.
• The sarcoplasmic reticulum stores calcium, important for triggering muscle contraction.

Types of Contractions

• Isometric contractions: muscle length does not change.
• Isotonic contractions: muscle length changes.
• Concentric contractions: muscle shortens.
• Eccentric contractions: muscle lengthens.

This quiz explores the structure and properties of skeletal muscle, including its excitability, contractility, extensibility, and elasticity. You'll also learn about the various components of muscle tissue such as epimysium, perimysium, fascicles, myofibrils, and sarcomeres. Test your understanding of how these elements contribute to muscle function.