Myelin Function and Importance
- Myelin insulates nerve cell axons to increase the speed of electrical impulses.
- It allows electrical charges to jump along the axon, resulting in faster information transmission.
- The myelin sheath reduces the accumulation of electrical charges by increasing the distance between extracellular and intracellular ions.
- Saltatory conduction occurs as the action potential jumps from one node of Ranvier to the next.
- Myelin is essential for efficient motor function, sensory function, and cognition.
- Myelin allows for the transmission of electrical signals between nerve cell bodies.
- The insulating function of myelin is crucial for various functions, such as movement, sensory perception, and acquiring/recalling knowledge.

Myelin Development and Species Distribution
- Myelination begins in the 3rd trimester of human development.
- Rapid myelination occurs during infancy, corresponding to the development of cognitive and motor skills.
- Myelination continues through adolescence and early adulthood.
- Myelin sheaths can be added in grey matter regions throughout life.
- Language comprehension, speech acquisition, crawling, and walking are associated with myelination.
- Myelin is a defining characteristic of jawed vertebrates (gnathostomes).
- Invertebrates have glial wraps that are functionally equivalent to myelin.
- Non-myelinated axons coexist with myelinated axons in the central nervous system (CNS).
- In the peripheral nervous system (PNS), a large proportion of axons are unmyelinated.
- Invertebrates such as oligochaetes, penaeids, palaemonids, and calanoids have myelin-like sheaths.

Myelin Composition
- Myelin in the central nervous system (CNS) and peripheral nervous system (PNS) performs the same insulating function.
- Myelin is rich in lipid, giving it a white appearance.
- Approximately 40% of myelin is water, while the dry mass consists of 60-75% lipid and 15-25% protein.
- Myelin basic protein (MBP) plays a critical role in the formation of compact myelin.
- Proteolipid protein (PLP) is the most abundant protein in CNS myelin, while myelin protein zero (MPZ or P0) is important in the PNS.

Disorders and Clinical Significance
- Disorders affecting myelination include genetically determined leukodystrophies, multiple sclerosis, and inflammatory demyelinating peripheral neuropathies.
- Multiple sclerosis is the best-known disorder of myelin.
- Demyelination is the loss of the myelin sheath and is associated with neurodegenerative autoimmune diseases.
- Demyelination can lead to impaired conduction of signals along the nerves.
- Symptoms of demyelination vary but can include visual disturbances, weakness, cognitive disruption, and fatigue.
- Dysmyelination is characterised by defective structure and function of myelin sheaths.
- Dysmyelination does not produce lesions like demyelination.
- Genetic mutations affecting myelin biosynthesis can cause dysmyelination.
- Repairing damaged myelin sheaths is an ongoing area of research.

Myelin Plasticity and Future Directions in Research
- Myelin has traditionally been considered a static structure, but recent research has shown that it is dynamic and can undergo remodeling.
- Experience-dependent oligodendrogenesis allows for myelin remodeling in response to environmental stimuli.
- Myelin plasticity is important for learning, memory, and recovery from injury.
- Advances in imaging techniques, such as magnetic resonance imaging (MRI), allow for the visualization and quantification of myelin in vivo.
- The development of animal models and in vitro systems has facilitated the study of myelin biology and pathology.
- Researchers are exploring novel therapeutic approaches to promote myelin repair and regeneration in demyelinating disorders.
- Biomarkers for myelin-related diseases are being investigated to improve diagnosis and monitoring of disease progression.
- Collaborative efforts are being made to better understand the complex interactions between myelin, neurons, and other glial cells in health and disease.