Human Anatomy - Chapter 10 - Skeletal Muscle Tissue PDF

Human Anatomy Chapter 10 Skeletal Muscle Tissue Dr. Kim Muscle Muscle is the primary tissue in the Heart (cardiac muscle tissue) Walls of hollow organs (smooth muscle tissue) Skeletal muscle Makes up nearly half the body’s mass Properties of Muscle Tissu...

Human Anatomy Chapter 10 Skeletal Muscle Tissue Dr. Kim Muscle Muscle is the primary tissue in the Heart (cardiac muscle tissue) Walls of hollow organs (smooth muscle tissue) Skeletal muscle Makes up nearly half the body’s mass Properties of Muscle Tissue Contractility Myofilaments are responsible for shortening of muscles cells o They are comprised of actin and myosin proteins Excitability Nerve signals excite muscle cells, causing electrical impulses to travel along the cell’s plasma membrane Properties of Muscle Tissue Extensibility Contraction of a skeletal muscle stretches the opposing muscle Smooth muscle is stretched by substances within that hollow organ o Food in stomach; urine in urinary bladder Elasticity Recoils after being stretched Terminology Specific to Muscle Tissue Myo and mys—prefixes meaning “muscle” Sarco—prefix meaning “flesh” Sarcolemma—plasma membrane of muscle cells Sarcoplasm—cytoplasm of muscle cells Functions of Muscle Tissue Produce movement Skeletal muscle—attached to skeleton o Moves body by moving the bones Smooth muscle—squeezes fluids and other substances through hollow organs Functions of Muscle Tissue Open and close body passageways Sphincter muscles function as valves o Open to allow passage of a substance o Contract to close the passageway Functions of Muscle Tissue Maintain posture and stabilize joints Enables the body to remain sitting or standing Muscle tone helps stabilize many synovial joints Heat generation Muscle contractions produce heat Helps maintain normal body temperature Types of Muscle Tissue Skeletal muscle tissue Packaged into skeletal muscles Makes up 40% of body weight Cells are striated Skeletal muscle is innervated by voluntary division of the nervous system Types of Muscle Tissue Cardiac muscle tissue Occurs only in the walls of the heart Cells are striated Contraction is involuntary Smooth muscle tissue Occupies the walls of hollow organs Cells lack striations Innervated by involuntary division of the nervous system Skeletal Muscle Each muscle is an organ Consists mostly of skeletal muscle tissue Skeletal muscle also contains o Connective tissue o Blood vessels o Nerves Gross Anatomy of a Skeletal Muscle Connective tissue and fascicles Sheaths of connective tissue bind a skeletal muscle and its fibers together o Epimysium—dense regular connective tissue surrounding entire muscle o Perimysium—fibrous connective tissue that surrounds each fascicle (group of muscle fibers) o Endomysium—a fine sheath of connective tissue wrapping each muscle cell Gross Anatomy of a Skeletal Muscle Connective tissue sheaths are continuous with tendons When muscle fibers contract, pull is exerted on all layers of connective tissue and its tendon Sheaths provide elasticity and carry blood vessels and nerves Connective Tissue Sheaths in Skeletal Muscle: Epimysium, Perimysium, and Endomysium Gross Anatomy of a Skeletal Muscle Nerves and blood vessels Each skeletal muscle supplied by branches of o One nerve o One artery o One or more veins Nerves and vessels branch repeatedly o Smallest branches serve individual muscle fibers Gross Anatomy of a Skeletal Muscle Muscle attachments Most skeletal muscles run from one bone to another One bone will move; other bone remains fixed o Origin—less movable attachment o Insertion—more movable attachment Muscle Attachments (Origin and Insertion) Gross Anatomy of a Skeletal Muscle Muscle attachments Muscles attach to origins and insertions by connective tissue (CT) o Direct attachments—CT fibers are short o Indirect attachments—CT forms a tendon or aponeurosis Bone markings present where tendons meet bones o Tubercles, trochanters, and crests Microscopic and Functional Anatomy of Skeletal Muscle Tissue The skeletal muscle fiber Fibers are long and cylindrical o Are huge cells—diameter is 10–100 µ m o Length—several centimeters to dozens of centimeters Each cell formed by fusion of embryonic cells Cells are multinucleate Nuclei are peripherally located Microscopic Anatomy of the Skeletal Muscle Fiber (Cell) Myofibrils and Sarcomeres Striations result from internal structure of myofibrils Myofibrils Are long rods within cytoplasm Make up 80% of the cytoplasm Are a specialized contractile organelle found in muscle tissue Are a long row of repeating segments called sarcomeres (functional unit of skeletal muscle tissue) Myofibrils and Sarcomeres Basic unit of contraction of skeletal muscle Z disc (Z line)—boundaries of each sarcomere Thin (actin) filaments—extend from Z disc toward the center of the sarcomere Thick (myosin) filaments—located in the center of the sarcomere o Overlap inner ends of the thin filaments Myofibrils and Sarcomeres A bands—full length of the thick filament Includes inner end of thin filaments H zone—center part of A band where no thin filaments occur A bands and I bands refract polarized light differently A bands—anisotropic I bands—isotropic Myofibrils and Sarcomeres M line—in center of H zone Contains tiny rods that hold thick filaments together I band—region with only thin filaments Is part of two adjacent sarcomeres Microscopic Anatomy of the Skeletal Muscle Fiber (Cell) Microscopic Anatomy of the Skeletal Muscle Fiber (Cell) Titin and Other Myofibrils Titin is a springlike molecule that resists overstretching Titin molecules extend from the Z disc to thick filaments to the M line o Two functions ▪ Holds thick filaments in place ▪ Unfolds when muscle is stretched Sarcoplasmic Reticulum and T Tubules Sarcoplasmic reticulum A specialized smooth endoplasmic reticulum (ER) Interconnecting tubules surround each myofibril o Some tubules form cross-channels called terminal cisterns o Cisterns occur in pairs on either side of a T tubule Sarcoplasmic Reticulum and T Tubules Sarcoplasmic reticulum Contains calcium ions—released when muscle is stimulated to contract Calcium ions diffuse through cytoplasm o Trigger the sliding filament mechanism T tubules—deep invaginations of sarcolemma Triad—T tubule flanked by two terminal cisterns Sarcoplasmic Reticulum and T Tubules in the Skeletal Muscle Fiber Mechanism of Contraction Two major types of contraction Concentric contraction—muscle shortens to do work Eccentric contraction—muscle generates force as it lengthens o Muscle acts as a “brake” to resist gravity o “Down” portion of a pushup is an example Mechanism of Contraction Sliding filament mechanism Explains concentric contraction o Myosin head attach to thin filaments at both ends of a sarcomere ▪ Then pull thin filaments toward the center of the sarcomere o Thin and thick filaments do not shorten Initiated by release of calcium ions from the sarcoplasmic reticulum Powered by ATP Sliding Filament Mechanism for Concentric Contraction in a Skeletal Muscle Sliding Filament Mechanism Contraction changes the striation pattern Fully relaxed—thin filaments partially overlap thin filaments Contraction—Z discs move closer together o Sarcomere shortens o I bands shorten; H zone disappears o A band remains the same length Changes in Striations as Skeletal Muscle Contracts Structure and Organizational Levels of Skeletal Muscle Structure and Organizational Levels of Skeletal Muscle Structure and Organizational Levels of Skeletal Muscle Innervation of Skeletal Muscle Motor neurons innervate skeletal muscle tissue Neuromuscular junction is the point where nerve ending and muscle fiber meet Terminal boutons (axon terminals) o Located at ends of axons o Store neurotransmitters Synaptic cleft o Space between axon terminal and sarcolemma Neuromuscular Junction Motor Units