Final Exam Review Terminology Belly of the Muscle Refers to the actual working or contracting portion of the muscle Commonly red Some muscles have more than one belly o Bicep is a muscle with two bellies Tendon Tendons are at either end of the belly They are made of dense regular connective tissue They anchor muscle to bone Attach to every muscle to their insertion moving bone and origin non moving bone Anatomy of the Muscle Epimysium dense layer of collagen that surrounds the entire muscle Perimysium divides the skeletal muscle into a series of compartments each compartment is called a fascicle Endomysium within each fascicle there are individual muscle fibers which are surrounded by a third layer of collagen fibers delicate connective tissue called endomysium The endomysium contains capillaries myosatellite cells and nerve fibers Epimysium perimysium endomysium Fascicles muscle fibers Muscle fiber myocytes surrounded by endomysium Multinucleated during development of muscle fibers groups of embryonic cells called myoblasts fuse together forming a muscle fiber Some myoblasts do not fuse with the developing muscle fibers and are called myosatellite cells After injury myosatellite cells enlarge and divide they then fuse with the damaged muscle fibers assisting with repair of the tissue Sarcolemma underneath the endomysium connective tissue that surrounds muscle fibers the plasma membrane of the muscle fiber Sarcoplasm cytoplasm of the muscle fiber surrounded by the sarcolemma T tubules narrow tubes that are continuous with the sarcolemma and extend deep into the sarcoplasm surrounding each myofibril They allow the quick signal distribution of an action potential Tropomyosin cover the active sites on the g actin to prevent myosin interaction Troponin attached midway to the protein Tropomyosin and lies within the groove between the actin filaments Blocks the attachment site for the myosin crosses bridge thus preventing contraction When muscle cell is stimulated to contract by an actin potential calcium channels open in the sarcoplasmic membrane and release calcium into the sarcoplasm Some calcium attaches to the troponin which causes it to change shape exposing binding sites for myosin on the actin filaments Myosin binding to actin forms cross bridges and the contraction of muscle begins Terminal cisternae enlarged areas of the sarcoplasmic reticulum that surround the t tubules o Where calcium is stored o Released the calcium when an action potential stimulates muscle contraction o Because they ensure rapid calcium delivery they are well developed in muscles Triad T tubule 2 terminal cisternae they are connected by a series of proteins that that contract quickly trigger calcium release Myofibrils Smaller fibers within each muscle cell Can actively shorten and are responsible for skeletal muscle fiber contraction Cylindrical structures Each myofibril has a mesh like membrane complex surrounding it called the sarcoplasmic reticulum major calcium storage in muscle cells Myofibrils have two protein filaments o Thin filament primarily composed of myosin G actin are beads which contain a binding site for the myosin heads F actin is a twisted stranded composed of two rows of g actin o Thick filaments primarily composed of myosin Have functional units called sarcomeres which are the actual contractile unit of the muscle each myofibril has thousands of sarcomeres a repeating unit of striated muscle o A band does not change length during muscle contraction and is composed of myosin thick filaments M line the center line connects the thick filaments help with stabilization H band the middle area of myosin where there is no overlap with actin changes size depending on if the muscle is relaxed or contracted o I band changes length during muscle contraction and is composed of only actin thin filaments z line Z lines mark the boundary between adjacent sarcomeres Titin extends from the tips of the thing filaments to attach to sites at the Helps keep thick and thin filaments in proper alignment Aids in restoring resting sarcomere length after contraction Regeneration o Skeletal cells can regenerate because of myosatellite cells o Cardiac muscle can also regenerate Rigor Mortis after death muscles remain contracted because the body no longer releases AChE Types of Muscular Tissue Skeletal muscle tissue o Striated and attached to bones o Voluntary contraction subconsciously to a certain extent o Innervated by somatic nerves Cardiac muscle tissue o Striated and located in heart wall o Involuntary it exhibits autorhythmicity o Innervated by autonomic nervous system ANS o Capable of regeneration more cells Smooth muscle tissue o Non striated o Located in walls of hollow organs structures o Involuntary exhibits autorhythmicity o Innervated by autonomic nervous system ANS o Capable of dividing and making more of itself Muscle Contraction Relaxation Contraction steps Stem cells can come from remote location and enter heart to lay down 1 ACh released by the synaptic terminal at the neuromuscular junction binds to receptors 2 The resulting change in transmembrane potential of the muscle fiber leads to the on the sarcolemma production of an action potential 3 Sarcoplasmic reticulum releases stored calcium Calcium binds to troponin causing the troponin to change shape pulling the Tropomyosin molecule away from the active site on actin and allowing interaction with the energized myosin heads 4 Once the active sites are exposed the energized myosin heads bind to them forming cross bridges 5 The contraction begins as repeated cycles of cross bridge binding pivoting and detachment occurs powered by the hydrolysis of ATP These events produce filament sliding and the muscle fiber shortens Relaxation steps Components 1 ACh is broken down by AChE 2 The Sarcoplasmic reticulum recaptures the calcium 3 Active sites are recovered by Tropomyosin 4 Contraction ends 5 Muscle relaxation occurs muscle returns passively to its resting length Interneuron receives the message and alerts the motor neuron about which specific muscle needs to be moves Effector a peripheral gland or muscle cell stimulated by a neuron Motor unit all of the muscle cells controlled by a single motor neuron Motor neuron hundreds of skeletal fibers are innervated by multiple motor neurons Other Muscle Movements Neuromuscular Junction 1 The cytoplasm of the synaptic terminal contains vesicles filled with Ach 2 Action potential arrives 3 ACh is released by