Membrane Potentials in Smooth Muscle || Spike Potential, Plateau, Slow Wave, Junctional Potential

Summary

This 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

• 💪 Smooth muscles exhibit a greater variety of membrane potentials compared to skeletal muscles, which primarily contract with action potentials.
• 🌟 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.
• 🔋 The resting membrane potential in smooth muscles is between -50 to -60 millivolts, setting the baseline for their electrical activity.
• 🚀 Spike potentials in smooth muscles are like those in skeletal muscles, triggered by external factors or internally by the muscle itself.
• 🕒 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.
• 🚧 The primary ion channels in smooth muscles are calcium channels, with few sodium channels, leading to a calcium-dominated action potential.
• 🔬 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.
• 🌀 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.
• 🎶 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.
• 🔗 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.