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36 terms

skeletal muscle

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functions of skeletal muscle
force production for locomotion and breathing
fore production for postural support
heat production during cold stress
human body contains over... skeletal muscles which accounts for...% body weight
400, 40-50% total body weight
connective tissue covering skeletal muscle
epimysium, perimysium, endomysium
epimysium
surrounds entire muscle
perimysium
surrounds bundles of muscle fibers (fasicles)
endomysium
surrounds individual muscle fibers
sarcolemma
muscle cell membrane
myofibrils:
threadlike strands within muscle fibers (cells). actin (thin filament), myosin (thick filament)
sarcomere
contractile unit. Z-line, M-line, A-ban and I-band
Titan
connects Z band to M line
spring-like characteristics
passive component force
assists in maintaing shape of cell
Within the sarcoplasm
Sarcoplasmic reticulum: Storage site for calcium
Transverse tubules
Terminal cisternae
Mitochondria
The Neuromuscular Junction
Where motor neuron meets the muscle fiber
Motor end plate
Neuromuscular cleft
Motor unit
motor end plate
Pocket formed around motor neuron by sarcolemma
Neuromuscular cleft
Gap between neuron and sarcolemma
Motor unit:
Motor neuron and all of the fibers it innervates
The sliding filament model
Muscle shortening occurs due to movement of the actin filament over the myosin filament
Formation of cross-bridges between actin and myosin filaments--> "power stroke"
Sarcomere shortens
Actin
Actin (globules), troponin, tropomyosin
Regulatory binding site for Ca++ (troponin)
myosin
Myosin head
Myosin tail
contraction cycle
1. Rest; cross-bridges weakly bound (no Ca++)
2. Ca++ binds; cross-bridges strongly bound (to troponin)
3. Pi released; movement starts
4. ADP released; movement finishes
5. ATP attaches; weak binding state. ATP breakdown-->cross-bridge "energized"
Ca++ removal-->weak binding state (rest)
excitation-contraction coupling
Depolarization of motor end plate (excitation) is linked to contraction: Nerve impulse travels down T-tubles and causes release of Ca** from SR
Ca** binds to troponin and causes position change in tropomyosin, exposing active sites on actin
Permits strong binding state between actin and myosin, and contraction occurs
Continues until Ca** is removed
ATP is required for muscle contraction
1. Myosin ATPase breaks down ATP as fiber contracts
2. Calcium ATPase breaks down ATP for calcium pump in SR
3. Sodium-potassium pump on sarcholemma re-establishes membrane potential
sources of ATP
1. Phosphocratine (PCr)
2. Glycolysis
3. Oxidative phosphorylation
biochemical properties of muscle fibers
oxidative, glycolytic function, type of ATPase
contractile properties of muscle fibers
maximal force production, speed of contraction, muscle fiber efficiency (economy)
isometric muscle contraction
force but no external change in length. used by postural muscles
isotonic (dynamic)
concentric, eccentric
concentric muscle contraction
muscle shortens during force production
eccentric muscle contraction
muscle produces force but length increases
regulation of muscle force is dependent on
1. Size of the muscle
2. Number of motor units recruited (recruitment)
3. Rate at which they are recruited ("rate coding")
muscle weakness
relative lack of strength in an unfatigued muscle. strength is measured as the force of power produced during a maximum voluntary contraction (MVC)
muscle fatigue
acute fall of maximum force generating capacity of the muscle in response to muscular activity. measured as decrease in mvc as a result of contraction(s)
muscular dystrophy
lack of dystrophin (structural protein that helps transmit force developed by actin and myosin to connective tissue to move limb)
amyotrophic lateral sclerosis
loss of motor neurons
myasthenia gravis
Ach Receptors on sarcolemma blocked or destroyed.
McArdle's disease
no glycogen phosphorylase cannot break down glycogen
mitochondrial myopathy
various mutations interferes with ability to make energy from oxidative phosphorylation