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SC EXSC 223 - Chapter 9 Book Notes

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Chapter 9 Book Notes- 3 types of muscles:o Skeletal muscleo Cardiac muscleo Smooth muscle Skeletal and smooth muscle cells are elongated and therefore calledmuscle fibers The plasma membrane of muscle cells is called the sarcolemma andthe muscle cell cytoplasm is called sarcoplasm- Skeletal muscle o Skeletal muscle tissue is packed into the skeletal muscles that attach to and cover the bony skeletono Skeletal muscle fibers are the longest muscle cells and have obvious stripes or striationso Voluntary muscle: subject to conscious controlo Responsible for overall body mobility and can contract rapidly- Cardiac muscle o Seen only in the heart where it constitutes the bulk of the heart wallso Striated muscle but not voluntary o Usually contracts at a steady rate set by the pacemaker, but neural controls allow the heart to speed up for brief periods- Smooth muscleo Found in the walls of hollow visceral organs, such as the stomach, urinary bladder, and respiratory passages o Role is to force fluids and other substances through internal body channelso Consists of elongated cells but have no striations o Is not subject to voluntary control and its contracts are slow and sustained - Special characteristics of muscle tissueo Excitability or responsiveness: is the ability to receive and respond to a stimulus that is any change in the environment either inside or outside the body; stimulus is usually a chemical (ex. neurotransmitter released by a nerve cell, or a local change in pH); the response is to generate an electrical impulse that travels along the plasma membrane of the muscle cell and causes the cell to contract o Contractility: is the ability to shorten forcibly when adequately stimulatedo Extensibility: is the ability to extend or stretch; muscle cells shorten whencontracting, but they can stretch even beyond their resting length when relaxed o Elasticity: is the ability of a muscle cell to recoil and resume its resting length after stretching - Muscle functionso Producing movement Skeletal muscles are responsible for all locomotion and manipulation Enable you to respond quickly to changes in the external environmento Maintaining posture and body position Skeletal muscles function almost continuously making one tiny adjustment after another to counteract the never-ending downward pull of gravity o Stabilizing joints Muscles stabilize and strengthen the joints of the skeleton o Generating heat Muscles generate heat as they contract which is vitally important in maintaining normal body temperature; skeletal muscle is most responsible for generating heat- Skeletal muscleo Each skeletal muscle is a discrete organ, made up of several kinds of tissueso Primarily skeletal muscle fibers, but blood vessels, nerve fibers, and substantial amounts of connective tissue are also present - Skeletal muscle nerve and blood supplyo One nerve, one artery, and one or more veins serve each muscleo Every skeletal muscle is innervated by a nerve that controls its activityo Skeletal muscle has a rich blood supply; muscle capillaries are long and winding and have numerous cross-links, features that accommodate changes in muscle length, they straighten when the muscle stretches and contort when the muscle contracts- Connective tissue sheathso Several connective tissue sheaths wrap individual muscle fibers an together these sheaths support each cell and reinforce and hold together the muscle as a whole, preventing bulging muscles from bursting o 3 layers from the outside in: epimysium: overcoat of dense irregular connective tissue that surrounds the whole muscle perimysium and fascicles: muscle fibers are grouped into fascicles that resemble bundles of sticks; surrounding each fascicle is a layer of fibrous connective tissue called perimysium endomysium: a wispy sheath of connective tissue that surrounds each individual muscle fiber; consists of fine areolar all sheaths are continuous with one another as well as withthe tendons that join muscles to bones when muscle fibers contracts they pull on these sheaths which transmit the pulling force to the bone to be moved- Attachmentso Most skeletal muscles span joints and attach to bones in at least two placeso When a muscle contracts, the movable bone, the muscles insertions, moves toward the immovable or less movable bone, the muscles origin The muscles of the limbs, the origin typically lies proximal to the insertiono Muscle attachments, whether origin or insetion, may be direct or indirect In direct, or fleshy attachments, the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage  In indirect attachments, the muscles connective tissue wrappings extend beyond the muscle either as a ropelike tendon, or as a sheet-like aponeurosis; the tendon or aponeurosis anchors the muscle to the connective tissue covering of a skeletal element (bone or cartilage) or to the fascia of other muscles  Indirect attachments are much more common because of their durability and small size- Microscopic anatomy of a skeletal muscle fibero Each skeletal muscle fiber is a long cyclindrical cell with multiple oval nuclei just beneath its sarcolemma or plasma membraneo Sarcoplasm is the cytoplasm of a muscle cell and contains glycosomes (granules of stored glycogen that provide glucose during muscle cell activity) and myoglobin (a red pigment that stores oxygen)o Muscle cell also contains three modified structures: Myofibrils Sarcoplasmic reticulum  T tubules- Myofibrilso A single muscle fiber contains hundreds to thousands of rod-like myofibrils that run parallel to its lengtho Each myofibril is densely packed in the fiber so mitochondria and other organelles are squeezed between them o Myofibrils contain the contractile elements of skeletal muscle cells, the sarcomeres, which contain even smaller rod-like structures called myofilaments - Striations, sarcomeres, and myofilamentso A repeating series of dark and light bands, are evident along the length of each myofibrilo In an intact muscle fiber, the dark A bands and light I bands are perfectly aligned, giving the cell its striated appearance Each dark A band has a lighter region in its midsection called the Hzone Each H zone is bisected vertically by a dark line called the M line formed by molecules of the protein myomesin Each light I band has a midline interruption, a darker area called the Z disc (or Z line) The region of a


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