Myelin And Axon Diameter Effect On Action Potential Conduction Velocity (Schwann Cells) | Clip

Summary

This video explains the key factors influencing the speed of action potential propagation in neurons, focusing on passive propagation through voltage-gated sodium channels and the impact of axon diameter and myelination. Larger axons and myelinated neurons have faster conduction velocities due to reduced resistance and leakage, as well as decreased capacitance. Myelination, provided by Schwann cells or oligodendrocytes, ensures efficient signal transmission through saltatory conduction at the nodes of Ranvier. The video highlights the mechanisms behind these processes and their role in optimizing neural communication.

Takeaways

• 😀 The action potential propagation relies on the passive flow of current, which travels to open adjacent voltage-gated sodium channels.
• 😀 Conduction velocity, or the speed at which an action potential travels, is largely governed by passive propagation and can be increased by two main factors: axon diameter and myelination.
• 😀 Axon diameter affects the conduction velocity by decreasing axial resistance, increasing the space constant, and reducing signal decay over distance.
• 😀 Larger axon diameters allow for faster conduction because the signal can propagate further without significant decay.
• 😀 Myelin is provided by Schwann cells (in the peripheral nervous system) and oligodendrocytes (in the central nervous system), which both insulate axons to increase conduction velocity.
• 😀 Myelination helps maintain current by reducing leakage, which improves the efficiency of action potential propagation.
• 😀 The reduction of capacitance due to myelination helps speed up signal transmission by separating charges more effectively across the axonal membrane.
• 😀 Nodes of Ranvier, the gaps between myelin segments, contain concentrated voltage-gated channels that regenerate the action potential, ensuring efficient signal transmission.
• 😀 Saltatory conduction, which occurs at the nodes of Ranvier, allows the action potential to jump from node to node, making it up to 100 times faster than continuous conduction in unmyelinated axons.
• 😀 The conduction velocity of a neuron is enhanced by both the axon’s larger diameter and its myelination, allowing for quicker transmission of neural signals over long distances.

Q & A

What is the role of passive propagation in the action potential process?

Passive propagation refers to the flow of current that spreads to adjacent voltage-gated sodium channels. This process is essential because it determines the speed at which action potentials travel, making it a key factor in conduction velocity.

How does the diameter of an axon influence conduction velocity?

A larger axon diameter decreases axial resistance, increasing the space constant. This allows the signal to travel further with less decay, which speeds up the conduction velocity.

What are the two main mechanisms that increase conduction velocity?

The two mechanisms are an increase in axon diameter and the presence of myelination along the axon.

How does myelination affect the conduction velocity?

Myelination increases conduction velocity by reducing current leakage (increasing membrane resistance) and decreasing membrane capacitance, which together improve the signal's propagation speed. This results in faster signal transmission through the axon.

What is the significance of the nodes of Ranvier in action potential propagation?

The nodes of Ranvier are crucial because they are rich in voltage-gated sodium channels, which regenerate the action potential as it travels along myelinated axons. This process, known as saltatory conduction, greatly accelerates signal transmission.

What happens to the signal if there are no nodes of Ranvier?

Without the nodes of Ranvier, the signal would decay because there would be no regeneration of the action potential, resulting in slower or incomplete signal transmission.

What are Schwann cells and oligodendrocytes responsible for in the nervous system?

Schwann cells myelinate axons in the peripheral nervous system, while oligodendrocytes myelinate axons in the central nervous system. These cells help improve the speed of signal transmission along neurons.

How is myelin formed around axons?

Myelin forms when Schwann cells (in the peripheral nervous system) or oligodendrocytes (in the central nervous system) wrap around the axon. As they wrap, their cytoplasm is displaced, creating concentric layers of membrane that form the myelin sheath.

What is saltatory conduction, and how does it relate to myelination?

Saltatory conduction is the process where action potentials jump from node to node along a myelinated axon. This process speeds up conduction significantly, sometimes by up to 100 times, compared to unmyelinated axons.

Why does myelination reduce the capacitance of the axonal membrane?

Myelination increases the thickness of the axonal membrane, which reduces the capacitance by increasing the distance between the charges, thus reducing the electric field between them. This helps in faster signal transmission.