Skeletal Muscle
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Created by:
danyell2489 on March 25, 2010
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55 terms
Terms | Definitions |
|---|---|
 Connective Tissue Layers | Sheets that hold the muscle fibers (cells) together |
| Epimysium | Outermost layer; surrounds the entire muscle |
| Perimysium | Surrounds individual bundles of muscle fibers called fasicles |
| Endomysium | Surrounds individual muscle fibers or cells |
| Cell | Thin, long cylinder that generally extends the length of the muscle |
| Sarcolemma | Muscle cell membrane; selective membrane transport (active & passive) |
| Sarcoplasm | "fluid part"- cytoplasm of the msucle cell; contains cellular proteins, myofibrils, enzymes, nuclei, organelles, glycogen, & myoglobin |
| Myofibrils | Numberous threadlike structures that contain the contractile proteins (myofilaments) |
| Sarcoplasmic Reticulum | System of interconnected tubules surrounding each myofibril like a mesh sleeve |
| Longitudinal Tubules | Run parallel to myofibrils & surround them |
| Terminal Cristernae | (lateral sacs); terminations of the longitudinal that hold calcium; major storage cite of calcium: 10,000x's [cytoplams] |
| Transverse Tubules | Invagination of the surface membrane "dipping" into the muscle between 2 terminal cristernae |
| Sarcomere | Basic functional unit of the muscle cell; individual segment-subdivision of the myofibrial |
| A-Band | Dark colored band due to thick protein myosin and overlap thick & thin filaments; remains the same |
| H-Zone | Lighter Area of A-Band with only myosin; gets shorter may disappear |
| M-Line | Dark line in the center of the H-Zone, hold filaments in place |
| I-Band | Light colored band that contains only actin, thin filament; shortens |
| Z-Line | Boundary of sarcomere, point of attachment of the actin filaments, covers portions of 2 sarcomeres; pulls closer togehter so sarcomere shortens |
| Neuromuscular Junction | Communication site between alpha motor neuron & muscle cell; at this junction, the sarcolemma forms a pocket (motor end plate) |
| Neuromuscular Cleft | Gap between the motor neuron & muscle cell |
| Actin | Thin filament; composed of tropomyosin & troponin |
| Myosin | Thick filament; contains enzyme ATPase |
| Troponin | 3 subunit structure that fastens down the ends of tropomyosin holding it in place |
| Tropomyosin | Thread-like protein that lies in the groove of the actin spiral |
| Sliding Filament Theory | A muscle shortens or lengthens because the thick & thin filaments slide past each other without the filaments themselves changing length |
| Biochemical/Oxidative Capacity | # of mitochondria - provide more ATP; # of capillaries surrounding fiber - deliver O2 to muscle;myoglobin amount - transports O2 from capillary to mitochondria |
| Myosin ATPase | determines speed of ATP breakdown |
| Contractile | Maximal force production: force/CSA; Speed of Contraction (Vmax): rate of crossbridge cycling; Muscle fiber efficiency: less energy per unit of work |
| Slow Oxidative | Type I, slow-twitch |
| Fast Oxidative Glycolytic | Type IIa, intermediate |
| Fast Glycolytic | Type IIb, fast-twitch |
| Average Human | no apparent sex difference; (~50% SF; ~50% FF) |
| Distance runners | 70-80% SF (SO); 20-30% FF (FG, FOG) |
| Track Sprinters | 25-30% SF (SO); 70-75% FF (FG, FOG) |
| Training Adaptations | most research on humans indicates that muscle fibers CANNOT change type |
| Endurance Training | FOG & FG--> SO; 10 wks, 90-min per day |
| Resistance Training | Type FG--> Type FOG |
| Disuse | muscle atrophy, particularly the FG |
| Slow phase | 25-50 years; 10% muscle mass. |
| Rapid phase | >50 years; 40% of muscle mass |
| Isometric | generation of force without change in muscle length (static) |
| Dynamic (isotonic) | muscle action that results in joint movement |
| Concentric | active muscle shortens under tension; force generated by muscle is > than the resistance. |
| Eccentric | active muscle lengthens under tension; force generated by muscle is < than the resistance |
| Twitch | force output of a muscle when given a single stimulus (~100ms); Contraction Time (CT): time from the force onset to peak force; FG Fibers; short CT; SO Fibers: long CT |
| Tetanus | summation (addition) of twitch responses fired rapidly |
| Unfused Tetanus (sawtooth): | submax stimulation causes a decline before returning again to peak force values |
| Fused Tetanus (smooth): | results in a max force production (2-10 x's) > than twitch force. Contraction will continue until the stimuli are stopped or the muscle fatigues (decrease in force due to repeated stimulation). |
| Number & Types of Motor Units (MU) Recruited | All muscle fibers within a motor unit are the same (FG, SO); FG generate > force than SO; The more MU recruited the > the force |
| Initial Length of Muscle | Optimal overlap between actin & myosin for crossbridges; Generally around the muscle's resting length |
| Neural Stimulation of the MU | Repeated stimulation results in summation of twitches = more force output |
| Peak Force | decreases as the speed of the movement increases (both fibers) |
| Golgi Tendon Organs | relay info to CNS about muscle tension; Located in the tendon near the muscle-tendon junction, sensitive to both muscle & tendon tension (much less sensitive than muscle spindle). Large tension in muscle--> GTO stimulation-->sends impulse to CNS--> causes muscle relaxation & activates antagonists (protective mechanism) |
| Muscle Spindles | relay info to CNS about muscle length; Located in the muscle belly; sensitive to stretch & rate of stretch. Stretch Reflex: stretch muscle --> impulse sent to CNS --> CNS activates motor neurons of the muscle--> contraction (ex. patella tendon tap). |
| Chemoreceptors | relay info to CNS about muscle pH, [ions], [O2, CO2] |
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