Nerve conductivity

The Nerve conductivity is the ability of nerve fibers to transmit bioelectrical impulses in either direction at a certain speed. The forwarding takes place via action potentials in the severability stimulus line. In diseases such as polyneuropathy, nerve conductivity is disturbed.

What is the nerve conductivity?

Nerve fibers are able to carry bioelectrical impulses through the body. From a physical point of view, each nerve fiber consists of an insulating myelin sheath and a conductive mass inside this sheath.

Signals are transmitted in the nervous system through the transmission of action potentials, which are passed on as bioelectrical voltages. However, since there is a rapid voltage drop along nerve fibers, impulses in the nervous system are only transported over short distances as actual bioelectrical voltages. In addition, there are voltage-dependent ion channels in the membranes of the nerve fibers. These channels of the nerve fibers also serve to transmit tension potentials along individual nerves. Without the ion channels, the nerve conductivity would be significantly less abrupt.

The speed of the nerve pathways can be measured today. In this context, we are talking about the nerve conduction velocity, which in mammals corresponds to between one and 100 m / s. This nerve conduction speed depends on the temperature, since molecular structures are involved in nerve conduction.

Function & task

When certain nerves are irritated, this irritation can be spread thanks to the nerve conductivity. For example, if nerves in the extremities are stimulated, this impulse spreads in both directions of the nerve fiber and changes the body's tension field. The impulse is transmitted to the brain and goes into consciousness there.

Motor impulses that are sent from the central nervous system to the muscles only reach their destination because of the nerve conductivity. The nerve conduction speed determines how long the impulse needs to spread and ultimately to achieve its goal.

The myelin layer of the axons is used for electrical insulation and achieves an extreme amplification of the transmitted signal. The impulse only needs to be amplified on the exposed parts of the nerve fiber. Therefore, ion channels are interposed at these points, which make the signal strong enough to depolarize the membrane of the next nerve fiber and trigger an action potential there too. This system is also known as the severability of the excitation conduction.

A nerve fiber initially has a resting membrane potential. There is thus a potential difference between the extra and intracellular space, but there is no potential difference along the axon. When the nerve fiber is reached in the resting potential by an impulse that depolarizes it beyond the threshold potential, this tension opens the voltage-dependent Na + channels of the fiber. The Na + ions thus flow from the extracellular space into the intracellular space of the nerve fiber. The plasma membrane depolarizes and there is an excess of positive charges compared to the surroundings. This creates an electric field.

As a result, there is a potential difference along the axon. Charge shifts occur that positively affect the membrane potential of the next nerve fiber. In addition to the transmission of action potentials in the peripheral nervous system, the transmission of impulses in the central nervous system also takes place via the processes described.

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Illnesses & ailments

If the peripheral nerve costume and thus the nerve conductivity in the individual nerve tracts is damaged, then numbness and even motor impairments can set in.

Damage to the nerve tracts appears as slowed nerve conduction speeds. One of the most well-known diseases in this context is polyneuropathy. In the context of polyneuropathies, information in the brain and out of the brain into the body is only transferred slowly, not at all or at least incompletely.The reason for this is damaged nerve tracts that inhibit the flow of information.

There are various causes for this phenomenon. In general, medicine differentiates between acquired and congenital polyneuropathies. Acquired forms of the disease can be attributed to toxins or inflammation and harmful metabolic products, for example. Congenital variants, on the other hand, are genetically determined. High alcohol consumption and poor diet are the most common triggers of acquired polyneuropathy. Both blood sugar and metabolic products from the breakdown of alcohol attack the nerves and can damage it.

Infections such as leprosy can also be associated with polyneuropathies. In some infections with a polyneuropathy, the pathogen even goes undetected. This is the case, for example, with Guillain-Barré syndrome. This disease suddenly leads to inflammatory changes in the peripheral nervous system, most of which start from the nerve roots on the spinal cord.

Even more common than polyneuropathy is carpal tunnel syndrome, which is usually caused by pressure damage to the median nerve of the wrist.

Demyelinating diseases of the central nervous system, which impair the nerve conductivity through the breakdown of insulating myelin in control centers such as the brain, must be distinguished from the diseases mentioned. One of the best-known of these diseases is the degenerative disease multiple sclerosis. Neuropathies such as acute motor axonal neuropathy also fall into this area.