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23 Cards in this Set
- Front
- Back
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Key properties of muscles |
1. Excitability 2. Contractility 3. Extensibility 4. Elasticity
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Connective tissue in muscle cells |
Epimysium: surrounds the whole muscle Perimysium: surrounds fascicles and is a conduit for nerves and blood vessels Endomysium: surrounds each individual muscle fibre. Electrically insulates and seperates muscle cells. |
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Muscle fibres |
Made from myoblast fusion of over 100 mysoblasts They are terminally differentiated and unable to divide (postmitotic) Muscles enlarge due to postnatal growth (hypertrophy) in which sarcomeres are added (lengthen) or increased myofibrils leads to an enlarged myofibre which leads stronger contractions |
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Sarcoplasmic Reticulum |
Specialized smooth ER that surrounds myofibrils (see diagram) It connects across the fibre width but not length (like a sleeve) Stores Ca+ in terminal cisternae and initiates contraction by releasing Ca+ when prompted by t-tubules |
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Satellite cells |
How adult skeletal cells regenerate They are stem-like and persist in mature cells, contained in the epimysium Proliferate, fuse -> regenerate Repairs (growth and hypertrophy) |
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Regular vs relaxed |
Regular: thick and thin filaments only overlap at ends of A band Contracted: I bands shorten, H zones disappears, distance between z discs shortens, m line becomes more compressed, A bands closer together |
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Roles of Atp |
1. ATP hydrolysis puts cross bridges/myosin head in energized state - Provides energy for the power stroke 2. Reattachment of ATP disconnects myosin head from actin, allowing cycle to repeat 3. Active transport of Ca+ back into SR, lowering Ca2+ in the cytoplasm, ending contraction and allowing muscle to relax |
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Rigor Mortis - rigidity of death |
Lasts about 24 hours, 3-4 hours after death ATP hydrolysis is needed for both contraction and relaxation After death, membranes become leaky and Ca2+ leaks into Cytosol, causing myosin heads to bind to actin ATP synthesis has ceased so myosin head cannot detach from actin = constant contraction |
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Transverse Tubules |
Extends into cytoplasm, continuous with ECF, increases SA - surrounds myofibrils - connects with other t-tubules - flanked by terminal cisternae of SR = tried - function: conducts action potentials from surface into myofibrils |
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Neuromuscular Junctions |
Point of contact between somatic motor neutron and muscle finer it innervates. Each muscle fibre only has one NMJ and is only innervates by 1 single motor neuron located midway along the fibre Consists of: Axonal endings: synaptic vessels contain NT acetylcholine Motor end plate: specialize part of the sarcolemma, it is highly folded and contains nicotinic acetylcholine receptors Separated by the synaptic cleft which includes the basal lamina (endonysium) |
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Three Phases of a Muscle Twitch |
1) latent phase: sarcolemna and t-tubules depolarize. Ca2+ released into cytosol, cross bridges begin to cycle, the number of cross bridges are not sufficient to shorten the muscle 2) contraction phase: sarcomeres shorten as a result of myosin cross bridge cycling. Continues until peak tension 3) relaxation phase: ca2+ in cytosol rapidly decreased - actively transported back into terminal cisternae. Cross bridge cycling decreases then stops. Tensions is reduced and muscle restored to original length. |
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Motor units |
Motor neuron and the muscle cells innervates. Motor neuron branches and forms NMJ’s with multiple muscle cells Strength of contraction proportional to the size of the motor unit and the # activated Control precise movements -> small motor unit Control large powerful movements -> large motor unit |
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Recruitment |
Stimulation of additional motor units for an increased strength of contraction Weakest motor units are recruited first, followed by stronger ones Allows for smooth, graded movements of muscles Motor neurone fire asynchronously and this alternate activity delays onset of muscle fatigue. Even during maximal voluntary contraction, not all motor units are activated |
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Muscle tone |
Continuous, passive partial contraction of muscles or resistance to passive stretch at rest Small groups of motor units are active and inactive in constantly shifting pattern Contraction keeps muscles firm but is not strong enough to produce movement No nerve stimulation = no tone = flaccid hyper and hypotonia |
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Extensor and flexor muscles |
Involved in maintenance of muscle tone while at rest and in maintaining posture cramps = changes in muscle tone in extensors or flexors |
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Types of muscles contractions |
1) isotonic (concentric): peak tension > resistance of load. Shortening of muscle and movement of load 2) eccentric: resistance of load > peak tension. Results in muscle lengthening 3) isometric: resistance of load >peak tension. No change in muscle length but it contracts and tenses up. Object is immovable |
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Creatine Phosphate (Direct Phosphorylation) |
Muscle cells use this PCr to store energy = immediate reserve in exercise CP + ADP = ATP + Creatine - takes place in cytoplasm - Energy source: Creatine Phosphate - No use of oxygen; 1 ATP per CP - Duration of energy provision =15 sec **Elevation of CK in blood is an indication of muscle damage |
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Glycolysis (Anaerobic respiration) |
Glucose from glycogen breakdown or delivered from blood → pyruvic acid → lactic acid (through fermentation) which is released into blood - used by muscle cells when insufficient O2 available foraerobic metabolism - takes place in cytoplasm - Energy source: Glucose; 2 ATP per glucose/lactic acid Duration of energy provision = 30-60 sec |
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Kreb's Cycle (Oxidative Phosphorylation) |
glucose → pyruvic acid + fatty acids + amino acids = ATP + CO2 + H20 - high energy electrons are sent to the electron transportsystem which produces the vast majority of the ATP - 36 ATP per 1 glucose, CO2, H20 - Provides energy for hours |
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Muscle Fatigue |
Exact cause of muscle fatigue not found Fatigue may protect muscle cells frompermanent exercise-induced damage dueto the onset of rigor |
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Fast white twitch (Type 2b) |
- large in diameter (lots of myofiliaments) - Light in colour due to reduced myoglobin - Surrounded by few capillaries - few mitochondria - high glycogen Suited for power and speed, short duration activities, mainly used glycolysis |
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Red, slow twitch (Oxidative) (Type 1) |
- half diameter of white - dark red colour due to increased myoglobin - Surrounded by numerous capillaries - increased mitochondria - low glycogen content Suited for endurance and increased contraction, uses oxidative phosphorylation |
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Intermediate, Fast-twitch Fibres (Type 2A) |
Oxidative-glycolytic - properties of bothwhite fast-twitch and red slow-twitch muscle fibres - pinkish in colour - intermediate glycogen storage - intermediate fibre diameter - intermediate fatigue |
