55 terms

Skeletal Muscle

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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]