Muscle Types: Skeletal vs Cardiac vs Smooth
G protein coupled receptors - highest yield for cell, cv, pulm, renal, endo, Step1
G protein coupled receptors - highest yield for cell, cv, pulm, renal, endo, Step1
In smooth and cardiac muscle. Not skeletal.
Skeletal Muscle - excitation contraction
Excitation-contraction coupling of skeletal muscle. A muscle fiber is excited via the nerve by an endplate potential and generates an action potential, which spreads out along the surface membrane and the transverse tubular
system into the deeper parts of the muscle fiber. The dihydropyridine (DHP)
receptor senses the membrane depolarization, alters its conformation,
and activates the ryanodine receptor, which releases Ca2+ from the SR, a Ca2+ store. Ca2+ binds to troponin and activates the so-called contractile machinery.
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Copyright © 2016 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)
Copyright © 2016 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)
Mechanism of action of succinyl choline:
phase 1 block
phase 1 block
- Binding of suxamethonium to the nicotinic acetylcholine receptor results in opening of the receptor's nicotinic sodium channel; sodium moves into the cell, a disorganised depolarisation of the motor end plate occurs and calcium is released from the sarcoplasmic reticulum. This results in fasciculation.
- In the normal muscle, following depolarisation, acetylcholine is rapidly hydrolysed by acetylcholinesterase and the muscle cell is able to 'reset' ready for the next signal.
- Suxamethonium has a longer duration of effect than acetylcholine and is not hydrolysed by acetylcholinesterase. It does not allow the muscle cell to 'reset' and keeps the 'new' resting membrane potential below threshold. When acetylcholine binds to an already depolarised receptor it cannot cause further depolarisation.
- Calcium is removed from the muscle cell cytosol independent of repolarisation (depolarization signalling and muscle contraction are independent processes). As the calcium is taken up by the sarcoplasmic reticulum, the muscle relaxes. This explains muscle flaccidity rather than tetany following fasciculation.
Cardiac Muscle- signal transduction
Smooth Muscle - signal transduction
Why doesn't the heart cramp? - one reason is the long absolute refractory period of heart muscle cells compared with skeletal muscle cells. Second impulse can't cause contraction if it occurs during absolute refractory period.
