Ouabain• A plant alkaloid from Strophantus gratus, that specifically binds
to and inhibits the sodium potassium ATPase• Ouabain Inhibition of Energy Dependent Ion Transport• The difference between the external and internal sodium and
potassium concentrations is important in maintaining the membrane potential and in the generation of the action potential. Without a gradient of sodium and potassium ions there would be no action potential. The maintenance of these gradients are maintained by an ion pump, the Na+/K+
ATPase, that uses the energy from ATP to pump sodium out of the cell and potassium into the cell. This pump can be inhibited by a small amount of the chemical, ouabain.
Skeletal muscle
• Diagram and label the parts of a skeletal muscle fiber
• Sarcolemma, Myofibrils, sarcoplasm, sarcoplasmic reticulum
Anatomy• Sacrolemma- cell membrane of the muscle
cell, fuses with tendon fiber which insert into bones
• MyofibrilsI band, A band , Cross bridges, z disc, sarcomere
Sarcoplasm- salts and mitochondriaSarcoplasmic reticulum-vesicular tubules
containing Ca in high concentration, connects to t-tubules to pass potentials to the SR via junctional feet.
Contractile filaments• Myosin
– Polymer (480,000mw)– 6 chains 4 heavy and
two light– Head = 1 light 1 heavy– 2 lie side by side– Tail– Body – arm– Crossbridges– ATPase activity!
Contractile filamentsActin– Actin– Tropomyosin– Troponin– DS f- actin
backbone– G actin-ADP
activity– 1µm inserts – into z disc
Contractile filamentsTropomyosin– 70,000 MW– Wrapped around f-
actin– Resting- cover
active sites on actin– Troponin– I/T/C subunits– Affinities
Sliding Filament mechanism
• Cross bridges bind with ATP, Hyddolyze extended
• Binding of Calcium and uncovering of active sites on actin. Binding of myosin head.
• Power stroke, tilting of head, movement of actin filament,
• ADP and Pi released, and refreshed
Excitation-contraction coupling
• Muscle action potential– App. –80 mv– 1-5ms– Initiated by myelinated nerve fibers through
the neuromuscular junction– T-tubules spread the current flow to the
sacroplasmic reticulum which release calcium
Twitches, summation and tetany
• Muscle twitches• Motor units
– Control• Summation
– Multiple motor unit– Frequency summation
• Tetany– Critical frequency
• Fatigue– O2, glycogen
Muscle Atrophy
• The polio virus is anenterovirus which in most subjects only causes a non-specific influenza-like illness with or without diarrhoea.
• Damage to lower motor neurons which causes the peripheral nerve fibres or axons supplying the musclefibres to die back. This leaves the muscles fibres 'orphaned'
• The muscle fibres cannot then function and begin to atrophy. Denervation
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