Guyton chapter 8| Membrane potentials and action potentials of smooth muscles, slow wave rhythm |L48
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The membrane potentials of smooth
The membrane potentials of smooth muscles is slightly low as compared to membrane potentials of skeletal muscles. It's about -50 to -60 as compared to -90 of skeletal muscles.
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The action potential occurs only when some external stimulus like nervous stimulation or hormonal stimulation cause, membrane potentials of smooth muscles to reach a threshold at which a rapid wave of depolarization and repolarization occurs.
The action potential of smooth muscles occurs only in VISCERALtype of smooth muscles, because the fibers of MULTI-UNITsmooth muscles is too small to support action potential, there contraction of muscle fibers occurs due depolarization with the help of contact type junctions.
The action potential of smooth muscles is of two types, a spike type which is due to rapid depolarization and repolarization, and action potential with plateau where depolarization occurs quickly, and it is sustained for long time, so that muscle contraction can occur for a long time. Plateau type action potential occurs in viscera like ureter and uterus where prolonged contraction is needed.
The action potentials of smooth muscles depend more on Calcium, as compared to skeletal muscles where it's dependent upon sodium ions.moreover after some external stimulus the calcium ions comes from extracellular fluids as compared to sarcoplasmic reticulum. So calcium ions not only depolarize the membrane but also cause contraction of smooth muscles, so it has two functions. The calcium channels are slow channels so the contraction of smooth muscles is also slow and prolonged.
Another type rhythm in smooth muscles is slow wace, rhythm in which the membrane potential fluctuates, due to the intrinsic property of smooth muscles, rather than due to some external stimulus. This slow wave normally is unable to cause contraction, but if a stimulus occurs on top of this wave e.g stretch of intestines due to food, then contraction can occur on top of slow wave rhythm in smooth muscles of intestines.
https://amzn.to/3hQHHdR
The action potential occurs only when some external stimulus like nervous stimulation or hormonal stimulation cause, membrane potentials of smooth muscles to reach a threshold at which a rapid wave of depolarization and repolarization occurs.
The action potential of smooth muscles occurs only in VISCERALtype of smooth muscles, because the fibers of MULTI-UNITsmooth muscles is too small to support action potential, there contraction of muscle fibers occurs due depolarization with the help of contact type junctions.
The action potential of smooth muscles is of two types, a spike type which is due to rapid depolarization and repolarization, and action potential with plateau where depolarization occurs quickly, and it is sustained for long time, so that muscle contraction can occur for a long time. Plateau type action potential occurs in viscera like ureter and uterus where prolonged contraction is needed.
The action potentials of smooth muscles depend more on Calcium, as compared to skeletal muscles where it's dependent upon sodium ions.moreover after some external stimulus the calcium ions comes from extracellular fluids as compared to sarcoplasmic reticulum. So calcium ions not only depolarize the membrane but also cause contraction of smooth muscles, so it has two functions. The calcium channels are slow channels so the contraction of smooth muscles is also slow and prolonged.
Another type rhythm in smooth muscles is slow wace, rhythm in which the membrane potential fluctuates, due to the intrinsic property of smooth muscles, rather than due to some external stimulus. This slow wave normally is unable to cause contraction, but if a stimulus occurs on top of this wave e.g stretch of intestines due to food, then contraction can occur on top of slow wave rhythm in smooth muscles of intestines.
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