Biology 11: Muscular System Skeletal Muscle Sarcomeres • Support & movement, blood propulsion, thermoregulation, striated • Voluntary (somatic) control • Multinucelated Red Fibers: Slow twitch. Support (dark meat). Carry out oxidative phosphorylation. White Fibers: Fast-twitch. Active (white meat). Anaerobic metabolism. Smooth Muscle • Respiratory, reproductive, cardiovascular, digestive • Involuntary (autonomic) control • Uninucleated • Can display myogenic activity without neural input • • Sarcomeres attach end-to-end to become myofibrils. Each myocyte contains many myofibrils Sarcolemma: Cell membrane of a myocyte. Contractile tissue of the heart Involuntary (autonomic) control Uninucleated (sometimes binucleated) Can display myogenic activity Cells connected with intercalated discs that contain gap junctions Skeletal System o Z-lines: Define the boundary of each sarcomere o M-line: Middle of sarcomere o I-band: Only actin filaments. o H-zone: Only myosin filaments. o A-band: Contains both actin and myosin. Only part that maintains a constant size during contraction. Sarcoplasmic Reticulum: Ca2+ filled modified endoplasmic reticulum. Cardiac Muscle • • • • • Basic contractile unit of striated muscle • THICK myosin and THIN actin filaments • Troponin & tropomyosin found on the thin filament and regulate actinmyosin interactions T-tubules: Connected to sarcolemma. Carry signals. - Derived from mesoderm Axial Skeleton: Skull, vertebral column, ribcage, hyoid bone. Appendicular Skeleton: Bones of limbs, pectoral girdle, pelvis. Compact Bone: Strength and density. Spongy Bone: Lattice-like structure of bony spicules known as trabeculae. (cancellous) Cavities filled with bone marrow. Bone Marrow: Red: Filled with hematopoietic stem cells. Yellow: Fat Long Bones: Shafts called diaphysis that flare to form metaphyses and that terminate in epiphyses. Epiphyses contain epiphyseal (growth) plate. Periosteum: Connective tissue that surrounds bone. Ligaments: Attach bones to other bones. Tendons: Bone Matrix: Attach bones to muscles. Osteons are the chief structural unit of compact bone, consisting of concentric bone layers called lamellae, which surround a long hollow passageway, the Haversian canal. Between rings are lacunae, where osteocytes reside, which are connected with cancaliculi. Bone Osteoblasts build bone, osteoclasts resorb bone. Remodeling: Parathyroid Hormone: !resorption of bone ![blood Ca2+]. Vitamin D: !resorption of bone, ![blood Ca2+]. Calcitonin: !bone formation, ¯[Ca2+] in blood. Cartilage: Firm & elastic. Matrix is chondrin. Secreted by chondrocytes. Avascular and is NOT innervated. Joints: Immovable: Fused together to form sutures. Movable: Strengthened by ligaments and contain a synovial capsule. Synovial Fluid: Secreted by synovium, lubricates joints. Fetus: Bones form from cartilage through endochondroal ossification. Skull bones form directly from mesenchyme in intramembranous ossification. Contraction / Relaxation • Begins at neuromuscular junction, where the efferent neuron release acetylcholine that binds to receptors on the sarcolemma, causing depolarization • Depolarization spreads down sarcolemma to T-tubules, triggering the release of Ca2+ • Ca2+ binds to troponin, causing a shift in tropomyosin and exposure of the myosin-binding sites on the actin filament • Shortening of the sarcomere occurs as myosin heads bind to the exposed sites on actin, forming cross bridges and pulling the actin filament along the thick filament. “Sliding filament model” • Muscles relax when acetylcholine is degraded by acetylcholinesterase, terminating the signal and allowing Ca2+ to return to the SR. • ATP binds to myosin head, allowing it to release form actin Simple Twitch: Single muscle fiber responds to brief stimulus. Frequency Summation: Addition of multiple simple twitches before the muscle has a chance to fully relax. Oxygen Debt: Difference between O2 needed and O2 present. Creatine Phosphate: Adds a phosphate group to ADP, forming ATP. Myoglobin: Heme-containing protein that is a muscular oxygen reserve.