Membrane Potentials in Smooth Muscle || Spike Potential, Plateau, Slow Wave, Junctional Potential
Summary
TLDRThis video explores the diverse membrane potentials in smooth muscles, contrasting them with the uniform action potentials of skeletal muscles. It delves into four main types: spike potentials, plateau action potentials, slow wave potentials, and junctional potentials. Spike potentials are akin to those in skeletal muscles and are common in unitary smooth muscles. Plateau potentials, akin to cardiac muscle, enable prolonged contractions in the gastrointestinal tract and other areas. Slow wave potentials, generated internally, oscillate to elicit rhythmic contractions, particularly in the gut. Junctional potentials, found in small multi-unit muscles like the iris, cause local depolarizations leading to contractions without action potentials. The video also discusses the role of calcium channels in smooth muscle action potentials and the unique characteristics of these potentials.
Takeaways
- đȘ Smooth muscles exhibit a greater variety of membrane potentials compared to skeletal muscles, which primarily contract with action potentials.
- đ Smooth muscle action potentials can be spike potentials or plateau potentials, the latter being similar to those in cardiac muscles and allowing for prolonged contractions.
- đ The resting membrane potential in smooth muscles is between -50 to -60 millivolts, setting the baseline for their electrical activity.
- đ Spike potentials in smooth muscles are like those in skeletal muscles, triggered by external factors or internally by the muscle itself.
- đ Plateau potentials have a prolonged depolarized state, lasting from hundreds of milliseconds to a second, and are seen in the gastrointestinal tract, ureter, uterus, and certain vascular smooth muscle cells.
- đ§ The primary ion channels in smooth muscles are calcium channels, with few sodium channels, leading to a calcium-dominated action potential.
- đŹ L-type voltage-gated calcium channels in smooth muscles are slow to open and close, contributing to the slower depolarization and delayed repolarization compared to skeletal muscles.
- đ Slow wave potentials are self-generated oscillations in the membrane potential, believed to be due to cyclic changes in ion pumping, and can trigger action potentials if the threshold is reached.
- đ¶ Slow wave potentials, also known as pacemaker waves, do not spread or cause contraction by themselves but can elicit rhythmic contractions in muscles like those in the gut.
- đ Junctional potentials occur in small multi-unit smooth muscle fibers, such as in the iris and piloerector muscles, where neurotransmitters cause local depolarizations without an action potential.
Q & A
What types of membrane potentials do smooth muscles exhibit that are different from skeletal muscles?
-Smooth muscles exhibit a variety of membrane potentials unlike skeletal muscles which only contract with action potentials. These include spike potentials, action potentials with plateau, slow wave potentials, and junctional potentials.
What is the resting membrane potential range in smooth muscles?
-The resting membrane potential in smooth muscles is between -50 to -60 millivolts.
How do spike potentials in smooth muscles differ from those in skeletal muscles in terms of duration?
-Spike potentials in smooth muscles have a duration ranging from 10 to 50 milliseconds, which is generally longer than those in skeletal muscles.
What is the significance of the plateau phase in action potentials with plateau seen in smooth muscles?
-The plateau phase in action potentials with plateau allows for a prolonged depolarized state before repolarization, enabling the muscle to contract for an extended period, from hundreds of milliseconds to a second.
In which body structures are action potentials with plateau typically observed?
-Action potentials with plateau are typically observed in the gastrointestinal tract, ureter, uterus under certain conditions, and certain vascular smooth muscle cells.
What type of ion channels predominantly contribute to the action potential in smooth muscles?
-Smooth muscles mainly have calcium channels, with only a few sodium channels, making the contribution of sodium to the action potential not significant.
How do L-type voltage-gated calcium channels contribute to the action potential in smooth muscles?
-L-type voltage-gated calcium channels are slow to open and close, leading to slower depolarization and delayed repolarization, which in turn produces the action potential in smooth muscles.
What is the dual role of calcium in smooth muscle function?
-Calcium in smooth muscles has a dual role: it is involved in the stimulation process by producing action potentials and also plays a part in the contractile process itself.
What are slow wave potentials and how do they contribute to muscle contraction?
-Slow wave potentials are rhythmic oscillations in the membrane potential generated by the fiber itself without external stimulation. They do not spread or cause contraction directly but can elicit action potentials repetitively, leading to rhythmic contractions.
In what type of smooth muscles are junctional potentials observed and what is their role?
-Junctional potentials are observed in multi-unit smooth muscles like those in the iris and piloerector muscles of hair. They cause local depolarizations that are equivalent to end plate potentials in skeletal muscles and lead to muscle contraction without the need for action potential spread.
How do slow wave potentials affect the rhythmic contractions of muscles such as those in the gut?
-Slow wave potentials, also known as pacemaker waves, occur at a frequency of several cycles per minute and are responsible for the rhythmic contractions of muscles in the gut by eliciting repetitive action potentials.
Outlines
đĄ Introduction to Smooth Muscle Membrane Potentials
This paragraph introduces the topic of the video, which is the different types of membrane potentials found in smooth muscles, contrasting them with the more uniform action potentials of skeletal muscles. It highlights that smooth muscles exhibit a variety of membrane potentials including action potentials (both spike and plateau types), slow wave potentials, and junctional potentials. The resting membrane potential in smooth muscles is noted to be between -50 to -60 millivolts. The paragraph sets the stage for a detailed exploration of each type of potential, starting with action potentials.
đ Detailed Exploration of Smooth Muscle Membrane Potentials
The second paragraph delves into the specifics of smooth muscle membrane potentials. It begins with a discussion of spike potentials, which are similar to those in skeletal muscles and can be triggered by various external and internal factors. The plateau type of action potential is likened to that in cardiac muscles, characterized by a prolonged depolarized state that facilitates sustained muscle contraction. The paragraph then explains the predominance of calcium channels over sodium channels in smooth muscles, with L-type voltage-gated channels being key to the generation of action potentials. The role of calcium in both stimulation and contraction is emphasized. Moving on, slow wave potentials are described as self-generated oscillations that do not spread or cause contraction but can trigger action potentials if the threshold is reached. Lastly, junctional potentials are discussed as local depolarizations in small multi-unit muscles, such as those in the iris, which can lead to muscle contraction without the need for an action potential. The paragraph concludes with a brief summary of the types of membrane potentials and their functions in smooth muscles.
Mindmap
Keywords
đĄMembrane Potentials
đĄSmooth Muscles
đĄAction Potentials
đĄResting Membrane Potential
đĄSpike Potentials
đĄPlateau
đĄCalcium Channels
đĄSlow Wave Potentials
đĄPacemaker Waves
đĄJunctional Potentials
Highlights
Smooth muscles exhibit more varied membrane potentials compared to skeletal muscles.
Skeletal muscles contract solely with action potentials, unlike smooth muscles.
Smooth muscle membrane potentials include action potentials, slow wave potentials, and junctional potentials.
Resting membrane potential in smooth muscles ranges from -50 to -60 millivolts.
Spike potentials in smooth muscles are similar to those in skeletal muscles and can be triggered by various stimuli.
Action potentials with plateau in smooth muscles are akin to those in cardiac muscles, allowing prolonged contraction.
The plateau phase of action potentials in smooth muscles can last from hundreds of milliseconds to a second.
Smooth muscles primarily utilize calcium channels for action potential generation, with minimal sodium channel involvement.
L-type voltage-gated calcium channels in smooth muscles are slower to open and close, leading to delayed depolarization and repolarization.
Calcium's dual role in smooth muscles includes both stimulation and contraction processes.
Slow wave potentials in smooth muscles are self-generated and do not directly cause muscle contraction.
Slow wave potentials can elicit action potentials if the threshold of approximately -35 millivolts is reached.
Pacemaker waves, or slow waves, are responsible for rhythmic contractions in certain smooth muscles like the gut.
Junctional potentials occur in multi-unit smooth muscles and are akin to end plate potentials in skeletal muscles.
In multi-unit smooth muscles, neurotransmitters cause local depolarizations leading to muscle contraction without action potentials.
Small multi-unit smooth muscle fibers, such as those in the iris and piloerector muscles, utilize junctional potentials for contraction.
A quick summary of the different types of membrane potentials and their roles in smooth muscle function is provided.
Transcripts
In this video, we will talk about types of membrane potentials, in smooth muscle. Â
Let's get started. First of all, smooth Â
muscles have more varieties of membrane potentials, than skeletal muscles. Â
The skeletal muscles contract only with action potentials. Â
But the smooth muscles show diverse types of membrane potentials. Â
These potentials include action potential, which can be spike potential, Â
or action potential with plateau(), slow wave potential, and junctional potential. Â
And let's not forget that underneath all these, Â
the resting membrane potential in smooth muscles, is -50 to -60 millivolts. Â
Now let's see these types one by one. First, action potentials. Â
Here, the spike potentials, are similar to the action potential that we see in skeletal muscles. Â
They are seen in most unitary smooth muscles. Their duration can be from 10 to 50 milliseconds. Â
They can be elicited by external factors, such as neuronal stimulation, hormones, stretch(), Â
or even internally by the muscle itself, as we will see in slow wave potential. Â
The next type of action potential, Â
the one with plateau, is similar to action potential in cardiac muscles. Â
In this, we have a prolonged depolarized state before repolarization, called a plateau. Â
The duration of such action potential, can be from hundreds of milliseconds to a second. Â
This long plateau, allows prolonged contraction of the muscle. Â
Its seen in gastrointestinal tract, ureter, uterus under some conditions, Â
and certain vascular smooth muscle cells. Â
So these were the types of action potentials, seen in smooth muscles. Â
Now let's talk about the mechanism of these potentials. Â
The smooth muscles mainly have calcium channels. There are only a few sodium channels. Â
So contribution of sodium to smooth muscle action potential is not significant. Â
The action potential is mainly produced by calcium channels. Â
These channels, are L-type of voltage-gated channels. Â
Such channels are slow to open. So the entry of calcium, and therefore, Â
the depolarization, is slower than that in skeletal muscles. Â
Then these channels are slow to close also. So the repolarization is also delayed. Â
In addition, the delayed opening of potassium channels, Â
also contributes to delayed repolarization. In some fibers, the repolarization is so Â
delayed, that a prolonged plateau is seen. So this is how action potentials are produced. Â
The calcium entering during an action potential, contributes to the contractile process also. Â
Thus the calcium in smooth muscles has a dual role. Â
In stimulation(), as well as in contraction. So this was about action potential. Â
The next type of membrane potential seen in smooth muscle, is slow wave potential. Â
These are generated by the fiber itself, without any external stimulation. Â
The exact mechanism is not known, but its believed to be due to Â
cyclic changes in the pumping of positive ions out of the cell. Â
Means for some time, positive ions like sodium or calcium, are pumped rapidly out of the cell. Â
Removal of positive ions, makes the membrane negative. Â
Then for some time, their extrusion is reduced. Â
So their retention in the fiber, makes the potential positive. Â
This way, the potential keeps oscillating. This is called slow wave potential. Â
Such potential changes occur locally and do not spread. Â
Also, they cannot cause muscle contraction. Â
However, during the positive phase of the potential, if the voltage reaches to the Â
threshold of about -35 millivolts, the action potential is generated as usual. Â
And as we know, the action potential can spread along the membrane, and cause muscle contraction. Â
In one peak a slow wave, one or more action potentials may appear. Â
This repetitive sequence of action potentials, causes rhythmic contraction of the muscle. Â
So the slow waves, which are responsible for this rhythm, are also called pacemaker waves. Â
They occur in a frequency of several cycles per minute. Â
They are seen in gut smooth muscles, where they cause rhythmic contractions. Â
So this was about the slow waves. Â
Now let's talk about the junctional potential. They are seen in multi-unit smooth muscles, Â
like those in the iris and piloerector muscles of hair. Â
Fibers in such muscles are very small in size, to generate an action potential. Â
In them, the neurotransmitters are released close to the cell membrane. Â
They cause local depolarizations. This is called junctional potential. Â
They are equivalent to end plate potentials, seen in skeletal muscles. Â
These potentials spread electronically, in nearby areas. Â
This much is enough to excite the entire cell, because of its smaller size. Â
Thus the action potential that spreads in a self-generative Â
manner, is not seen in such fibers. So these were all the types of membrane Â
potentials, seen in smooth muscles. Now let's have a quick summary. Â
Different smooth muscles show different types of membrane potentials. Â
Spike potentials are similar to those seen in skeletal muscles. Â
And they occur in most unitary smooth muscles. Action potential with plateau, allows prolonged Â
contraction, in the gastrointestinal tract, ureter, uterus, etc. Â
Slow wave potentials, are rhythmic oscillations in the membrane potential. Â
They do not spread themselves or cause contraction. Â
But they elicit action potentials repetitively, Â
which causes rhythmic contraction of muscles, as seen in the gut. Â
Finally, the junctional potential is seen in small multi-unit smooth muscle fibers, Â
like those in the iris and piloerector muscles. In this, local depolarizations cause muscle Â
contraction, without action potential. That's it for this video.
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