General Structure and Function of Skeletal Muscle PDF

General structure and function of skeletal muscle Dr. Rasha Abuelgasim Babiker MBBS, MSc, PhD Physiology Office 216 Department of Physiology [email protected] Learning objectives:...

General structure and function of skeletal muscle Dr. Rasha Abuelgasim Babiker MBBS, MSc, PhD Physiology Office 216 Department of Physiology [email protected] Learning objectives: Compare and contrast different muscle types Describe the morphology of skeletal muscle Describe the structure & function of sarcotubular system (T- tubules and L- tubules) Functions 1. Locomotion 2. Body defense 3. Shape of the body 4. Skilled activity- writing, speech etc 5. Respiration (inter costal muscles & diaphragm) 6. Pumping action of heart maintains blood supply to different pats of the body 7. Development of BP and blood flow to the tissues 8. Ingestion and digestion of food 9. Storage of urine and micturition 10. Giving birth Muscle Physiology Muscle cells Can be excited Chemically, electrically, and mechanically Action potential Transmitted along their cell membranes Specialized for contracting and to generate force Types  Introduction and contraction Muscle Types 1. Skeletal muscle fiber (10-100 µm diameter), multinucleated syncytium, somatic nervous system. 2. Cardiac muscle fibers (10-15 µm in diameter), cells with one (or two) nuclei, gap junctions, autonomic (parasympathetic and sympathetic) nervous system. 3. Smooth muscle cells (2-15 µm in diameter), cells found as bundles or sheets, gap junctions, autonomic nervous system. Striated Muscle Architecture: Structure of skeletal muscle A muscle belly consist of large number of fasciculi. Each fasciculus consist of large number of muscle fibers. The cell membrane of an individual muscle fiber is called sarcolemma. A single muscle fiber contains numerous myofibrils.  Each myofibril is divided into a number of compartments by Z lines. The portion of myofibril in between any two Z lines is called sarcomere. The sarcomere contain 2 types of filaments 1. Thin : consist of actin, tropomyosin & troponin 2. Thick : consist of myosin molecules The thin & thick filaments are called contractile proteins Structure of Muscle Sarcomere z z z I A Thick filaments Myosin II: consists of two globular heads and long tail. The head contains two binding sites for actin and ATP. It consists of heavy chains and light chains  Myosin II The head consists of 2 light chains and the end of heavy chains While the tail contains only 2 heavy chains The junction between head and tail is flexible (Hinge) Thin filaments Actin is made up of two chains that form double helix. Tropomyosin molecules are long filaments located in the groove between two actin chains Troponin molecules are small globular structures located at intervals along the tropomyosin molecules. Troponin It has three types: T: binds troponin to tropomyosin I : inhibit the interaction of myosin with actin C: binds Calcium and initiates muscle contraction Sliding Filament Theory for Muscle Contraction Muscle Contraction Key Concepts All muscles are composed of two sets of overlapping protein filaments, actin and myosin, the relative sliding of which produces shortening and generates force. This process involves cross bridge formation between actin and myosin and uses ATP. Coupling between the membrane action potentials and contraction is mediated by calcium ions. Skeletal muscle has an actin-based (thin filament) control system. Relaxation occurs with the removal of Ca++.