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Organization of Muscles

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Northeastern University
BIOL 1117
Christopher Richardson

L15-Organization of Muscle 10/16/13 • myology – the study of the muscular system • about 600 human skeletal muscles • constitute about half of our body weight • three kinds of muscle tissue – skeletal, cardiac, smooth • muscles designed to serve one primary purpose: convert chemical energy inATP phosphate bonds into mechanical energy of motion • An organ specialized to do something • The Functions of Muscles o Movement  move from place to place, movement of body parts and body contents in breathing, circulation, feeding and digestion, defecation, urination, and childbirth  Muscles also support communication: speech, writing and nonverbal communication o Stability  maintain posture by preventing unwanted movements by holding some joints in place by maintaining tension on tendons  antigravity muscles: resist the pull of gravity and prevent us from falling or slumping over o Control of openings and passageways  sphincters: internal muscular rings that control flow of materials in, out, or through the body such as movement of food, bile, blood, and other materials o Heat production by skeletal muscles  as much as 85% of our body heat  Chemical energy becomes mechanical energy and then becomes heat • Connective Tissue of a Muscle o endomysium  thin sleeve of loose connective tissue surrounding each muscle fiber  The endomysium creates room for blood capillaries and nerve fibers to nourish and stimulate the muscle fiber  Ion exchange between the fluid of endomysial tissue and the nerve and muscle fibers generates excitation of nerve and muscle fibers o perimysium  slightly thicker layer of connective tissue  fascicles: bundles of muscle fibers wrapped in perimysium  carry larger nerves and blood vessels, and stretch receptors in muscle spindles as part of somatic reflexes o epimysium  fibrous sheath surrounding the entire muscle  Its outer surface grades into the fascia above it while the inner surface sends projections between fascicles to form perimysium o fascia  sheet of connective tissue that separates neighboring muscles or muscle groups from each other and the subcutaneous tissue  Fascia consists of outer areolar layer and deeper dense fibrous connective tissue layer of dense regular connective tissue which is packed with collagen fibers • Classification of MusclesAccording to Fascicle Orientation o Strength of a muscle and the direction of its pull are determined partly by the orientation of its fascicles. o fusiform muscles  thick in middle and tapered at ends (i.e. biceps) o parallel muscles  have uniform width and parallel fascicles  Span long distances but they have fewer muscle fibers than a fusiform muscle of the same mass and produce less force  Some are elongated straps such as the rectus abdominus o Triangular muscles  fan-shaped, broad at origin and tapering to a narrower insertion  Example is pectoralis major o pennate muscles  fascicles insert obliquely on a tendon (feather shaped) o circular muscles (sphincters)  ring around body opening  Smooth muscle can also form sphincters such as the pyloric valve and the internal urethral and anal sphincters  • MuscleAttachments o indirect attachment to bone  tendons bridge the gap between muscle ends and bony attachment • the collagen fibers of the endo-,
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