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Smooth - no striations, involuntary visceral organs Skeletal - striated, voluntary, tires easily, powerful Cardiac - striated, involuntary intercalated disks Endomysium - connective tissue that surrounds the muscle fibers Perimysium - fibrous membrane that forms a bundle of fibers called fascicles Epimysium - covers the entire muscle and blends into the strong cord-like tendons Fascia – connective tissue that surrounds the muscle just outside the epimysium and tendon Fig 10-3 p281 Muscle Functions 1. Movement and regulation of body fluids (heart- blood, bladder- urine) 2. Maintains posture 3. Stabilizes joints 4. Generates heat Microscopic Anatomy of Skeletal Muscle Cell membrane cytoplasm Long ribbon like Organelles made up of myofilaments p313 Box 11-1 Microscopic Anatomy of Skeletal Muscle Give striped appearance I band - (light) A band - (dark) Z line - midpoint in the I band H zone - portion of A band where thick and thin filaments don’t overlap myosin actin Sarcomere - tiny contractile units in myofibrils of skeletal muscle between the Z lines. I. Myofilaments -Thick filaments p315 Fig 11-4 Myosin filaments - made mostly of the protein myosin and also contain ATPase enzymes *Make up the length of the Dark A band Myosin heads - small projections or cross bridges that link the thick and thin filaments together during contraction -Thin Filaments p315 Fig 11-4 Actin filaments - contain actin (contractile protein) and regulatory proteins (tropomyosin and troponin)that prevent myosin head from binding to actin. Skeletal Muscle Activity p316 Fig 11-5 Motor unit - a motor neuron and the skeletal muscle cells it stimulates Neuromuscular junction -nerve muscle connection Synaptic cleft - gap between nerve endings and muscle cells Skeletal Muscle Activity What Happens During Muscle Contraction????? 1. Nerve impulse reaches axon terminal and a neurotransmitter acetylcholine ACh is released across synapse 2. ACh attaches to receptors on membrane of muscle (sarcolemma) 3. Causes sarcolemma to become permeable to Na+ ions 4. This creates an action potential or electrical current that travels the cell to cause it to contract Skeletal Muscle Activity p317 Fig 11-7 What Happens During Muscle Contraction????? 5. SR releases Ca+ into the sarcoplasm where it binds to troponin causing the tropomyosin molecules to shift exposing the active sites on actin. 6. Myosin heads bind to actin causing the actin and myosin filaments to slide (ATP) 7. Muscle fibers shorten as it contracts Pearson Muscle Contraction SR - membraneous channels that surround each myofibril, and store Ca+ and release on demand. Skeletal Muscle Activity What Happens During Muscle Relaxation????? 1. Cholinesterase breaks down ACh 2. Ca+ ions diffuse back into SR and tropomyosin returns to its original position. 3. Actin and Myosin filaments are broken and slide apart 4. Muscle relaxes Energy Sources for Muscle Contraction ATP must be regenerated continuously b/c muscles store only 4-6 seconds worth of ATP 1) Creatine Phosphate (CP) - CP & ADP result in a transfer of a phosphate group to make ATP 2) Aerobic respiration - 1 glucose 36 ATP *slow and requires continuous O2 and nutrients 3) Anaerobic - glycolysis *lactic acid buildup 2 ATP w/out O2 Oxygen Debt – is the amt of extra oxygen required by muscle tissue to convert accumulated lactic acid to glucose in the liver and to restore supplies of ATP and creatine phosphate following vigorous exercise. Muscle Fatigue - is due to the accumulation of lactic acid and can cause the muscle to lose its ability to contract (exhaustion produced by strenuous activity) The Muscle Response - Contraction Threshold stimulus - is the minimal stimulus needed to elicit a muscular contraction All or None Response - when a muscle fiber contracts it always contracts to the fullest extent Muscle Twitch Myogram is a recording of a muscle contraction •Latent period - time between when the stimulus is applied and when it responds •Period of contraction •Period of relaxation Sustained Contraction - when a muscle is unable to complete relaxation period before next stimulus •Response to rapid series of stimuli •Tetanic contraction is forceful and sustained, and has partial or lacks partial relaxation (smooth) •Tonic contraction is responsible for muscle tone (response to nerve impulses from spinal cord sending continual, partial stimuli). Responsible for posture. *If sustained contraction is lost body will collapse (loss of consciousness) http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation_ _action_potentials_and_muscle_contraction.html