What is the neurilemma and what it function?

The neurilemma, also known as the Schwann cell sheath or the myelin sheath, is a specialized cellular layer that surrounds and insulates the axons of peripheral nerves. It plays several important functions crucial for the proper functioning of the nervous system. Here's an overview of the neurilemma and its functions:

1. Myelination: One of the primary functions of the neurilemma is the production of myelin, an insulating layer that wraps around the axons of peripheral nerves. Myelin acts as an electrical insulator, increasing the speed and efficiency of nerve impulses (action potentials) by allowing them to jump from one node of Ranvier to another in a process called saltatory conduction.

2. Axonal Support and Protection: The neurilemma provides structural support and protection for the delicate axons. It helps maintain the integrity of the nerve fibers and prevents damage from physical trauma, compression, or stretching. The myelin sheath acts as a protective barrier, shielding the axons from external chemical or mechanical insults.

3. Nutrient Supply: The neurilemma plays a crucial role in providing nutrients and metabolic support to the neurons. Schwann cells, which form the neurilemma, contain numerous mitochondria that generate energy in the form of ATP. This energy supply is essential for the maintenance and functioning of the neurons, especially during periods of high neuronal activity.

4. Regeneration and Repair: In the event of nerve injury or damage, the neurilemma plays a pivotal role in nerve regeneration and repair. Schwann cells can proliferate and migrate to the site of injury, forming a guiding pathway called the "Bands of Büngner." These bands provide a scaffold along which regenerating axons can grow and reconnect, facilitating the process of nerve regeneration.

5. Electrical Signal Propagation: The neurilemma participates in the propagation of electrical signals along the axons. The nodes of Ranvier, which are small gaps in the myelin sheath, allow the action potentials to "jump" from one node to the next, resulting in the rapid and efficient saltatory conduction of nerve impulses.

6. Control of Axonal Diameter: The neurilemma is involved in regulating the diameter of axons, which affects the speed and efficiency of nerve impulse transmission. Larger axons, which are typically associated with faster conduction velocities, are often found to have thicker myelin sheaths.

In summary, the neurilemma, formed by Schwann cells, serves multiple essential functions in the peripheral nervous system. It provides insulation through myelin, offers structural support and protection to axons, supplies nutrients, facilitates nerve regeneration, participates in electrical signal propagation, and regulates axonal diameter.