The Importance of Myelin
Introduction
Myelin, the substance surrounding most nerve fibres, speeds the transmission of nerve impulses to other parts of the body. The loss of myelin can slow or even block these impulses leading to a number of symptoms.
Nerve cells transmit impulses
Nerve cells have long, thin, flexible fibres for impulse transmission. Impulses are electrical signals which are transmitted along the nerve. Their length permits nerve fibres to transmit impulses between distant parts of the body, for instance between the spinal cord and leg muscles.
Myelin accelerates the impulse transmission
Most nerve fibres are surrounded and insulated by a fatty layer called myelin. This substance speeds up the impulse transmission. At certain intervals, the myelin layer is interrupted or constricted at the so-called nodes of Ranvier.
The impulse jumps from node to node, which makes the transmission faster than if the impulse were to travel along the entire length of the nerve fibre. The myelin of nerve fibres can help transmit a signal at a speed of more than 100 metres per second, i.e. as fast as a top racing car.
Loss of myelin leads to a large variety of symptoms
If the myelin sheath surrounding the nerve fibre is damaged or destroyed, the nerve impulses get slower and slower, or are not transmitted at all. The impulse is now transmitted along the entire length of the nerve fibre, which takes a good deal longer than if it were to jump from node to node.
A loss of myelin can also lead to short-circuits or transmission blocks of the nerve impulses. A region demonstrating clearly destroyed myelin is called a lesion or plaque.
The nerve impulses slowed down or completely blocked by lesions lead to a large variety of symptoms, all of which are an expression of the disturbed functional activity of the nervous system. This includes sensory impairments (such as unclear vision), coordination difficulties, gait problems and difficulties with bodily functions (e.g. insufficient bladder control).
