Intermediate Filaments part 3

Summary

This transcript discusses the role and importance of neurofilaments and microtubules in the structure and function of neurons, particularly in the axon. It highlights the differences between neurofilaments and microtubules in terms of size and function, and explains how they contribute to nerve impulse conduction. The script also covers the impact of diseases like amyotrophic lateral sclerosis (ALS) on neurofilament accumulation and its effects on neuron function. Additionally, it touches on the structure of intermediate filaments such as keratin in epithelial cells, and how disruptions in these structures can lead to conditions like bullous pemphigoid.

Takeaways

• 😀 Neurofilaments are intermediate filaments found in neurons and play a significant role in the structure and function of axons.
• 😀 Microtubules and neurofilaments differ in diameter, with microtubules being thicker than neurofilaments.
• 😀 The presence and arrangement of neurofilaments determine the diameter of the axon, which influences nerve impulse conduction speed.
• 😀 The expression levels of neurofilaments control the diameter of axons, impacting the speed at which nerve impulses travel.
• 😀 There are three types of neurofilaments (Type L, Type M, and Type N), each with distinct protein compositions.
• 😀 Axon growth involves adding new neurofilaments, which expand the axon diameter once it reaches its target cell.
• 😀 Disease such as Amyotrophic Lateral Sclerosis (ALS) is linked to the accumulation of neurofilaments, disrupting normal nerve function and causing muscle atrophy.
• 😀 Intermediate filaments, such as keratin, provide structural stability to epithelial cells, especially in hair, nails, and skin.
• 😀 Keratin filaments are particularly stable due to their disulfide bond cross-links, making them resistant to destruction even after cell death.
• 😀 Disorders like Bullous Pemphigoid are caused by autoimmune reactions against proteins in the hemidesmosomes, weakening the connection between epithelial cells and the underlying basal membrane.

Q & A

What are neurofilaments, and what is their role in neurons?

Neurofilaments are intermediate filaments found in neurons. They provide structural support and help maintain the shape and stability of axons. They also play a role in the transmission of nerve impulses along the axon by contributing to the diameter of the axon, which impacts its conduction speed.

How do microtubules compare to neurofilaments in terms of size?

Microtubules are larger in diameter compared to neurofilaments. While microtubules have a diameter of around 25 nm, neurofilaments are thinner, with a diameter of approximately 10 nm.

What are the three types of neurofilaments mentioned in the transcript?

The three types of neurofilaments identified are Type L, Type M, and Type N neurofilaments. These different types are made of specific proteins that contribute to the structure and function of the neurons.

How does the presence of neurofilaments affect the axon diameter and nerve impulse conduction?

The number of neurofilaments present in an axon directly influences its diameter. A larger number of neurofilaments leads to an increase in the axon diameter, which enhances the conduction speed of nerve impulses. For example, thicker axons can transmit signals much faster than thinner ones.

What is the role of neurofilaments in diseases like amyotrophic lateral sclerosis (ALS)?

In ALS, a neurodegenerative disease, neurofilament accumulation can occur. This leads to an overexpression of certain neurofilament types, which causes axons and neuron cell bodies to become overwhelmed with neurofilaments. This disruption impairs nerve impulse transmission, contributing to muscle weakness, atrophy, and potentially fatal consequences.

What is the significance of keratin in epithelial cells?

Keratin is a type of intermediate filament found in epithelial cells. It is crucial for providing structural stability and mechanical strength. Keratin filaments form a network that helps cells maintain their shape and resist physical stress. This is evident in structures like hair, nails, and skin, which are rich in keratin.

How do intermediate filaments like keratin contribute to cell-to-cell adhesion?

Intermediate filaments like keratin contribute to cell-to-cell adhesion by forming a dense network that connects with other structural elements like desmosomes and hemidesmosomes. This strengthens the connection between epithelial cells and their underlying tissues, ensuring tissue integrity and resistance to mechanical stress.

What happens when there is an issue with the hemidesmosomes or other structural components in epithelial cells?

When there is a problem with hemidesmosomes or other structural components, the integrity of the epithelium can be compromised. This can lead to conditions like bullous pemphigoid, an autoimmune disorder where the body produces antibodies against components like collagen type 17, leading to detachment of the epithelium from the underlying tissue, causing blistering.

What structural form do neurofilaments take during their assembly in axons?

Neurofilaments are assembled from monomers that form dimers. These dimers then twist together to create tetramers, and eight tetramers form the structural backbone of the neurofilament. This process allows neurofilaments to provide structural support in axons and neurons.

How does the diameter of axons relate to nerve conduction speed?

The diameter of an axon is directly proportional to the speed at which nerve impulses are transmitted. Larger-diameter axons allow for faster conduction of nerve impulses, while smaller-diameter axons have slower conduction speeds. This is influenced by the number of neurofilaments present, which determines the axon’s diameter.