1. The electrical activity
2. Excitation : contraction coupling
Of the cardiac muscle and skeletal muscle
Answer
1. The electrical activity
Cardiac muscle
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Skeletal muscle
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Resting membrane potential
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-90 mV
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-90 mV
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Duration of action potential
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300 mS
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2-4 mS
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Overshoot
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Present
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Present
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Platue
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Present
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Absent
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Duration of absolute refractory period
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200ms
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1-3ms
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Excitation: contraction coupling
The term excitation contraction coupling used to describe the conversion of electrical stimulus into mechanical response in muscle. This excitation contraction coupling is different in cardiac and skeletal muscle.
Outline of excitation contraction coupling of skeletal muscle
The nerve impulse generates action potential in the skeletal muscle. This action potential propagates along sarcolema and T tubules and activates dihydropyridine receptors on T tubules. Activated dihyropyridine receptors mechanically activate the ryanodine receptors in the sarcoplasmic reticulum . Activated ryanodine receptors open their channels and release Ca2+ from the sarcoplasmic reticulum into the cytoplasm. Then Ca+2 ions bind with trophonine C and cause contraction of muscle.
Outline of excitation contraction coupling of cardiac muscle
Unlike skeletal muscle, cardiac muscle action potential produces by pacemaker cells and propagates to contractile cells of the heart. The action potential travels along T- tubules and activate dihyropyridine receptors. Activated dihyropyridine receptors cause influx of extracellular Ca+2 into the cardiac myocyte. Due to increase of intracellular Ca+2 ion ryanodine receptors in the membrane of thesarcoplasmic reticulum get activated. Activated ryanodine receptors release Ca+2 from sarcoplasmic
reticulam into the cytoplasam, and then contraction of cardiac muscle occurs
like in skeletal muscle.
Cardiac muscle
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Skeletal muscle
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Has its own excitability ( SA node , AV node , Bundle of His
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Excited by motor nerve
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Action potential transmits to the contractile muscle via
gap junction
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Acetylcholine binds to muscle membrane and produce an
action potential
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Action potential prorogate along T tubules
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Action potential prorogate along T tubules
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AP activates dihydropyridine receptors on T tubules
and cause an influx of extracellular Ca+2 into the muscle cell
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AP stimulate dihydropyridine receptors on
T tubules and does not cause an influx
of extracellular Ca+2 into the muscle cell
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Increase intracellular Ca+2 ions activate rynodine receptors and
release Ca+2 ions from sarcoplasmic reticulam.
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Activated dihyrdopyrine receptors mechanically stimulate rynodine
receptors and release Ca+2 ions from sarcoplasmic reticulam.
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Ca+2 binds to troponin C and initiate muscle
contraction
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Ca+2 binds to troponin C and initiate muscle
contraction
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