Chapter 8 Notes

Chapter 8 The Muscular System I. Structure of a Skeletal Muscle A. Each muscle is an organ comprised of a. Skeletal muscle tissue b. Connective tissue (tendons and ligaments) c. Nervous tissue d. Blood II. Connective Tissue Coverings (pg. 178) A. Fascia a. Layers of dense connective tissue that surround and separate each muscle b. Extends beyond the ends of the muscle and gives rise to tendons that are fused to the periosteum of bones B. Aponeuroses a. Tendons that are broad sheets of connective tissue C. Epimysium a. Layers of connective tissue around each whole muscle D. Perimysium a. Surrounds individual muscle bundles (fascicles) within each muscle E. Endomysium a. Connective tissue layer that covers each muscle cell III. Skeletal Muscle Fibers (pg. 179) A. Each muscle fiber is a single long, cylindrical muscle cell B. Sarcolemma a. The cell membrane of a muscle fiber that contains many mitochondria and nuclei b. Also called myofibers c. Myofibrils are contractile fibers within muscle cells d. Thick filaments of myofibrils are made up of the protein actin e. The organization of these filaments produces striations C. Sacromere a. The structural and functional unit of a myofibril D. Extends from z line to z line (pg. 180; fig 8.3) a. I bands (light bands) are made up of actin filaments and are anchored to z lines

b. A bands (dark bands) are made up of overlapping thick (myosin) and thin actin filaments c. In the center of A bands is an H zone consisting of myosin filaments only IV. Neuromuscular Junction A. The site where the motor neutron and muscle fiber meet B. A motor neutron is a fiber from a nerve cell that connects to a skeletal muscle fiber C. The muscle fiber membrane forms a motor and plate in which the Sarcolemma is tightly faded and where nuclei and mitochondria are abundant D. The cytoplasm of the motor neuron contains numerous mitochondria and synaptic vesicles storing neurotransmitters V. Motor Units (Muscles) A. Made up of a motor neutron and the muscle fibers it controls B. When simulated all of the muscle fibers of a motor unit contract simultaneously to form a muscle contraction VI. Skeletal Muscle Contraction A. Muscle contractions involve several components that result in the shortening of sacromeres and the pulling of the muscle against its attachments B. Roles of myosin and actin a. Myosin consists of two twisted strands with globular cross bridges projected outward along the strand b. Actin is a globular protein with myosin binding sites i. Tropomyosin and Troponin are two proteins associated with the surface of the actin filament c. Sliding filament theory of muscle contraction: i. The myosin cross bridge attaches to the binding site on the actin filament and bends ii.This pulls the actin filament iii.It then releases and attaches to eh next binding site on the actin pulling again iv.Energy from the convesion of ATP and ADP is provided to the cross bridges causing the to be in a ‘cocked’ position VII. Stimulus for Contraction

A. The motor neuron must release the neurotransmitter acetylcholine from its synaptic vesicles to the synaptic cleft in the order to initiate a muscle contraction B. Protein receptor in the motor end plate detect the neurotransmitter and a muscle impulse spreads over the surface of the Sarcolemma and into the T tubules, where it reaches the sarcoplasmic reticulum a. The sarcoplasmic reticulum and transverse tubules activate the muscle contraction mechanism when the fiber is stimulated C. Upon receipt of the muscle impulse, the sarcoplasmic reticulum releases its stored calcium to the sarcoplasmic of the muscle fiber D. The high concentration of calcium in the sarcoplasmic interacts with the tropchin and Tropomyosin molecules which move aside, exposing the myosin binding sites on the actin filaments E. Myosin cross-bridges now bind and pull on the actin filaments, causing the saracomeres to shorten F. After the nervous impulse has been received, acetycholinesterase rapidly decomposes the acetylcholine G. Calcium is returned to the sarcoplasmic reticulum and the linkages between myosin and actin are broken VIII. Energy Sources for Concentration A. Energy for contractions comes from molecules of ATP B. Creatine phosphate, which stores excess energy released by the mitochondria, is present to regenerate ATP from ADP and phosphate C. As ATP decomposes, the energy from creatine phosphate can be transferred to ADP molecules, converting them back to ADP IX. Oxygen Supply and Cellular Respiration A. The early phase of cellular respiration yields few molecules of ATP, so muscle has a high requirement for oxygen B. Hemoglobin in red blood cells carries oxygen to muscle C. Myoglobin is a pigment that stores oxygen in muscle tissue X. Oxygen Debt A. During rest or moderate activity, there is enough oxygen to support aerobic respiration (breathing) B. Oxygen deficiency may develop during strenuous exercise, and latic acid accumulates as an end product of an aerobic respiration N. C. Oxygen debt refers to the amount of oxygen that liver cells require to convert the accumulated lactic acid into glucose, plus the amount that

muscle needs to resynthesize ATP and creatine phosphate to their original concentrations D. Repaying oxygen debt may take several hours XI. Muscle Fatigue A. When a muscle loses its ability to contract during strenuous exercise B. Usually arises from the accumulation of lactic acid prevents the muscle from contracting C. A muscle cramp occurs due to a lack of ATP required to return calcium ions back to the sarcoplasmic reticulum so muscle fibers can relax XII. Heat Production A. Muscular contractions represent and important source of heat for the body