Skeletal Muscle Structure and Function Quiz

Skeletal Muscle Structure and Function

• Skeletal muscle is responsible for locomotion, body defense, shaping the body, and skilled activities like writing and speaking.
• Muscles also aid in respiration (intercostal muscles and diaphragm), blood pumping, blood pressure and blood flow regulation, digestion, urine storage and expulsion, and childbirth.
• Muscle cells can be excited chemically, electrically, and mechanically.
• Action potentials are transmitted along muscle cell membranes.
• Muscles are specialized for contraction and generating force.

Muscle Types

• Skeletal muscle fibers (10-100 µm diameter), have multiple nuclei and are part of the somatic nervous system.
• Cardiac muscle fibers (10-15 µm diameter) have one or two nuclei, gap junctions, and are part of the autonomic (parasympathetic and sympathetic) nervous system.
• Smooth muscle cells (2-15 µm in diameter), are arranged in bundles or sheets, have gap junctions, and are part of the autonomic nervous system.

Muscle Classification

• Voluntary muscle (Skeletal)
• Involuntary muscle (Cardiac and Smooth)

Comparison of Muscle Types

Muscle Properties

Muscle Tissue Properties

• Excitability
• Contractility
• Elasticity
• Extensibility

Neuromuscular Junction

• Motor axon terminals contain vesicles containing acetylcholine (ACh).
• Acetylcholinesterase is present on the muscle fiber.
• Nerve impulse arrival at the axon terminal initiates the release of acetylcholine.
• Acetylcholine binds to receptors on the muscle fiber.
• This leads to an end-plate potential (EPP) and then to an action potential along the muscle fiber.

Muscle Contraction Types

• Isometric contraction: Muscle length remains constant; tension increases.
• Isotonic contraction: Muscle shortens; tension remains constant.

Skeletal Muscle Structure

• Muscle belly consists of fascicles.

• Fascicles consist of muscle fibers.

• Sarcolemma: The cell membrane of the muscle fiber.

• Myofibrils are found within each muscle fiber.

• Myofibrils are divided into compartments by Z lines.

• Sarcomere: The portion of the myofibril between two adjacent Z lines.

• Sarcomere contains two types of filaments: Thin filaments (actin, tropomyosin, troponin) and Thick filaments (myosin).

• Thin and thick filaments are contractile proteins.

• Regulatory proteins (tropomyosin and troponin) also play a vital role in muscle contraction.

Thick Filaments

• Myosin II consists of globular heads and a long tail.
• The head has binding sites for actin and ATP.
• Thick filaments are composed of heavy chains and light chains.

Thin Filaments

• Actin filaments form a double helix.
• Tropomyosin molecules lie in the groove between actin chains.
• Troponin molecules are located along tropomyosin at intervals.

Troponin

• This protein has three components (T, I, and C).
• T binds troponin to tropomyosin.
• I inhibits the interaction of myosin with actin.
• C binds calcium and initiates muscle contraction

Sliding Filament Theory

• Actin and myosin filaments slide past each other during muscle contraction.
• This shortening of the sarcomere results in overall muscle contraction.

Sarcotubular System

• Membrane surrounds muscle fibrils

• T-tubules and sarcoplasmic reticulum (L-tubules).

• T-tubules help transmit action potentials to the interior of the muscle fiber.

• L-tubules are involved in calcium ion storage and release.

• Triad: A junction of the T-tubule and two dilated regions of the sarcoplasmic reticulum.

• A triad contains receptors (dihydropyridine receptors and ryanodine receptors) for regulating calcium ion release into the cytoplasm.

Muscle Contraction

• The sliding filament theory and the role of calcium ions regulate muscle contraction, which causes shortening in sarcomeres and overall muscle movement.
• ATP is used during the process.

Key Concepts

• Muscles consist of overlapping actin and myosin protein filaments, which slide to produce force during contraction.
• This process uses ATP and involves cross-bridge formation.
• Calcium ions are essential for mediating the coupling between membrane action potentials and muscle contraction.
• Relaxation occurs when calcium ions are removed.

Test your knowledge on the structure and function of skeletal muscles. This quiz covers various muscle types, their characteristics, and their roles in the body including locomotion and respiration. Challenge yourself with questions that delve into muscle physiology and cellular structure.