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Epimysium
Fibrous connective tissue covering the skeletal muscles; continuous with tendons at the ends of the muscle.
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Bone Periosteum
A specialized connective tissue covering all bones; tendon is attached here.
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Muscle Fibers
AKA muscle cells; long, cylindrical cells 50-100micrometer diameter; contain several nuclei
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Fasiculi
Bundles of up to 150 muscle fibers; found under the epimysium
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Perimysium
Connective tissue surrounding the fasiculi.
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Endomysium
Connective tissue surrounding each muscle fiber; is continuous with the sarcolemma
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Sarcolemma
Muscle fiber's membrane
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Neuromuscular Junction
The junction between a motor neuron and the muscle fibers it innervates; AKA motor end plate
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Motor Unit
A motor neuron and the muscle fibers it innervates
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Sarcoplasm
The cytoplasm of the muscle fiber; contains contractile components
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Myofibrils
Contain the apparatus that contracts the muscle cell; hunderds of myofibrils dominate the sarcoplasm
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Myosin Filament
Thick filament about 16 nm in diameter that contain up to 200 myosin molecules
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Cross-bridges
Globular heads protruding away from the myosin filament at regular intervals
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Actin Filaments
Thin filaments about 6nm in diameter; consist of 2 strands arranged in a double helix
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Sarcomere
Smallest contractile unit of skeletal muscle; average about 2.2 micrometers in length in a relaxed fiber and are repeated the entire length of the muscle fiber.
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A-band
Dark; corresponds with the alignment of the myosin filaments
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I-band
Light, corresponds with the areas in two adjacent sarcomeres that contain only actin filaments
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Z-line
The middle line of the I-band and appears as a thin, dark line running longitudinally through the I-band
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H-zone
The area in the center of the sarcomere where only myosin filaments are present
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Sarcoplasmic Reticulum
Intricate system of tubules parallel to and surrounding each myofibril that terminates as vesicles in the vicinity of the Z-lines; store calcium ions
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T-tubules
Run perpendicular to the sarcoplasmic reticulum and terminate in the vicinity of the Z-line between two vessicles; AKA transverse tubules
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Triad
Pattern of a T-tubule spaced between and perpendicular to two sarcoplasmic reticulum vessicles
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Action Potential
An electrical nerve impulse
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Sliding Filament Theory
Actin filaments at each end of the sarcomere slide inward on myosin filaments, pulling the Z-lines toward the center of the sarcomere and thus shortening the muscle fiber.
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Troponin
A protein that is situated at reular intervals alond the actin filament and has a high affinity for calcium ions; calcium ions released from the sarcoplasmic reticulum bind with troponin
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Tropomyosin
Protein molecule that runs along the length of the actin filament in the groove of the double helix
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Resting Phase of Sliding-Filament Theroy of Muscular Contration
Little calcium is present in the myofibril, so very few of the myosin cross-bridges are bound to actin; no tension is developed in the muscle
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Excitation-Contraction Coupling Phase of Sliding-Filament Theroy of Muscular Contration
Sarcoplasmic reticulum is stimulated to release calcium ions, which bind with troponin, causing a shift in the tropomyosin. Mysoin cross-bridge head now attaches more reapidly to actin filament
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Contraction Phase of Sliding-Filament Theroy of Muscular Contration
The energy for cross-bridge flexion comes from hydrolysis of ATP to ADP and phosphate, which is catalyzed by ATPase. Another ATP molecule must replace ADP on the myosin cross-bridge head in order for the head to detach from the active actin site and recock.
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Recharge Phase of Sliding-Filament Theroy of Muscular Contration
Measurable muscle shortening transpires only when the binding of calcium to troponin, coupling of the mysoin cross-bridge with actin, cross-bridge fexion, dissociation of actin and myosin, and recocking of the mysosin cross-bridge head is repeated over and over throughout the muscle fiber.
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Relaxation Phase of Sliding-Filament Theroy of Muscular Contration
Occurs when the stimulation of the motor neuron stops. Calcium is pumped back into the sarcoplasmic reticulum, which prevents the link between the actin and myosin filaments. Brought on by the return of actin and myosin filaments to their unbound states
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Acetylcholine
Neurotransmitter released by the arrival of the action potential at the nerve terminal, which diffuses across the neuromuscular junction, causing excitation of the sarcolemma
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All-or-None Principle of Muscle
There is no such thing as a motor neuron stimulus that causes onle some of the fibers to contract. Similarly, a stronger action potential cannot produce a stronger contraction.
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Twitch
The brief contraction that results from an action potential traveling down a motor neuron, activating the muscle fibers
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Tetanus
When stimuli are delivered at so high a frequency that the twitches begin to merge and eventually completely fuse
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Fast-twitch Motor Unit
One that develops force and also relaxes rapidly and thus has a short twitch time.
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Slow-twitch Motor Unit
One that develops force and relaxes slowly and has a long twitch time
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Type I fibers
Slow-twitch; generally fatigue resistant and have a high capacity for aerobic energy supply, but limited potential for raped force development
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Type II Motor Units
Fast-twitch; characterized as inefficient and fatigable and having low aerobic power, rapid force development, high actomyosin myofibrillar ATPase activity, and high anaerobic power.
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Recruitment
Means of vaying skeletal muscle force involving an increase in force through varying the number of motor units activated.
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