"fluid part"- cytoplasm of the msucle cell; contains cellular proteins, myofibrils, enzymes, nuclei, organelles, glycogen, & myoglobin
System of interconnected tubules surrounding each myofibril like a mesh sleeve
(lateral sacs); terminations of the longitudinal that hold calcium; major storage cite of calcium: 10,000x's [cytoplams]
Invagination of the surface membrane "dipping" into the muscle between 2 terminal cristernae
Basic functional unit of the muscle cell; individual segment-subdivision of the myofibrial
Dark colored band due to thick protein myosin and overlap thick & thin filaments; remains the same
Boundary of sarcomere, point of attachment of the actin filaments, covers portions of 2 sarcomeres; pulls closer togehter so sarcomere shortens
Communication site between alpha motor neuron & muscle cell; at this junction, the sarcolemma forms a pocket (motor end plate)
Sliding Filament Theory
A muscle shortens or lengthens because the thick & thin filaments slide past each other without the filaments themselves changing length
# of mitochondria - provide more ATP; # of capillaries surrounding fiber - deliver O2 to muscle;myoglobin amount - transports O2 from capillary to mitochondria
Maximal force production: force/CSA; Speed of Contraction (Vmax): rate of crossbridge cycling; Muscle fiber efficiency: less energy per unit of work
active muscle shortens under tension; force generated by muscle is > than the resistance.
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
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
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)
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).