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Muscle - Coggle Diagram
Muscle
Contraction
Ca2+ is released from sarcoplasmic reticulum into sarcoplasm and it binds to troponin causing its conformational change
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This binding causes a conformational change, the head bends and exerts a tiny force which moves actin 5-10nm causing the filaments to slide past one another
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Supplying ATP
Immediate system
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the energy from ATP and CP is limited but ut is availabl eimmediately and it enables fast twitch fibres to generate force quick
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NMJ
Structure
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at rest dihydropyridine receptors are blocked but when depolarisation reaches it opens ryanodine Ca2+ channels and Ca2+ out into the sarcoplasm
Motor unit
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asynchronous recruitment (recruiting motor units alternately or in different combinations) helps to delay or prevent delay
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factors affecting tension development: stimulation frequency, length of fibre, fatigue, fibre thickness
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Action Potential
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APs generated by postsynaptic membrane are conducted along muscle fibre membrane and spread down T tubule
This triggers conformational change of DHP receptor (voltage sensitive)and ryandine receptor (these two proteins are physically connected, DHP changes due to AP and it opens ryanodine)
this releasees Ca2+ stored into sarcoplasmic reticulum and the released Ca2+ diffuses in sarcoplasm stimulating contraction
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Fibre types
Fat twitch
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they have few mitochondria, little or no myoglobin, fewer blood vessels
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fibres cannot repelnish ATP quickly enough to sustain contraction for a long time so used for short-term work that requires maximum strength
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Slow twitch
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they contain large amounts of myoglobin, many mitochondria and well supplied with blood vessels
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Soleus muscle
runs up the back of the leg from the heel and its contraction extends the foot and is used for walking
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Cardiac muscle
structure
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cardiac muscle cells are smaller than skeletal and uninucleate, they branch and adjoining cells interdigitate (and intercalated discs provide stron mechanical adhesions)
action potentials
spontaneous, rapid depolarisation of cells with Na+ influx
Ca2+ enters through calcium channels from extracellular and binds to ryanodine receptors causing Ca2+ channels to open
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pace maker
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K+ channels open causing repolarisation then close, followed by slow depolarisation
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Excitation
T tubules are larger and DHP receprots are Ca2+ channels and aren't physically connected with ryanodine
when an AP spreafs down T tubule it causes voltage gated DHP to open allowing flow of Ca2+ into sarcoplasm which then binds to ryanodine causing their channels to open
The resulting huge rise in sarcoplasmic Ca2+ concentration stimulates fibre contraction and is called Ca2+ induced Ca2+ release
Smooth Muscle
made of 3 filaments
Myosin, which only interacts with actin when light chains are phosphorylated
filaments of medium size, don't play role in contraction but cytoskeleton
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orientation
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contraction results in shorter, fatter diamonds
contraction
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Ca2+ binds to calmodulin which activates a kinase enzyme which phosphorylates myosin activating myosin ATPase so mysoin can act with actin
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When myosin heads in smooth muscle are phosphorylated they undergo cycles of binding and releasing actin
As Ca2+ is removed from the sarcoplasm it dissociates from calmodulon and activity of myosin kinase decreases
2 units
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Single-unit
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no constant resting potential, and always depolarises to threshold
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influencing factors
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extracellular changes (pH, O2)
stretch (example: digestive walls stretched and the membranes of stretched cells depolarise, reach threshold adn dire APs causing contraction
Bone
tendons connect bone and muscle fibre, and transmit mechanical force of contraction to bone
composition
mineralised collagen, which gives flexibility
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function
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store minerals, Ca and phosphorous
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bone cycle
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osteoclasts are resorptive cells, they wear away and then begin to reform and become mineralised
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Reflex
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protective reflex protects the body, like a hot surface
stretch reflex
receptor, a sensory neuron that transmits impulse to spinal cord
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Proteins
fibres
Titin
large (30,000 amino acids) and elastic
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In a relaxes skeletal muscle, resistance to stretch is mostly due to elasticity of the titin molecule
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Myosin
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made of many myosin molecules arranged in parallel with heads projecting sideways at each end of filament
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Regulatory proteins
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Troponin
made of troponin C (binds to Ca), I (inhibits ATPase) and T (binds to tropomyosin)
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