The term excitation conduction refers to the transmission of excitation in nerve or muscle cells. Excitation conduction is also often referred to as conduction of excitation, but from a medical point of view, this term is not entirely correct.
What is excitation conduction?
The term excitation conduction refers to the transmission of excitation in nerve or muscle cells. Excitation conduction is the basis for the functionality of the nervous system and nerves. In excitation conduction, excitations are transmitted within nerve cells (neurons) or muscle cells. On the other hand, when an excitation is transferred from one cell to another, it is called excitation transmission. This usually occurs in chemical form at synapses. Excitation conduction itself is a bioelectrical process.
Function and task
Basically, excitation conduction is divided into two forms. Electrical excitation conduction is passive. It is designed to cover short distances. Via electrical stimuli at the axon, depolarization is triggered at the specific site. Here, therefore, the charge is more positively charged in contrast to the environment. The difference in charge causes the electric field to form along the nerve fiber. However, the wall of the nerve fibers is rather poorly insulated during electrical excitation conduction. Thus, as the distance increases, the electric field becomes weaker and the depolarization decreases. Therefore, only very short distances can be covered with this form of excitation conduction. Electrical conduction is found, for example, in the outer layers of the retina. The photoreceptors and the bipolar cells of the retina conduct their excitations in this passive way. The other form of excitation conduction is through action potentials. Here, again, a distinction can be made between continuous and saltatory excitation conduction. Continuous excitation conduction is found in markless nerve fibers. In this form of conduction, the nerve impulse is transmitted along the nerve fiber from section to section. This form of excitation conduction is rather slow, with a maximum speed of 30 meters per second. It is found mainly in nerves supplying the internal organs. Nociceptors, i.e. free sensory nerve endings, also transmit their excitations in this way. Saltatory excitation conduction is significantly faster. Most nerve fibers in the human body are sheathed in myelin sheaths. These act as a kind of insulating layer. The layer is interrupted at certain intervals. These are referred to as Ranvier’s lacing rings. Excitation jumps from lacing ring to lacing ring in these nerve fibers. This means that speeds of up to 100 meters per second can be achieved. Excitation can thus be conducted through the entire body to the target organ at lightning speed. A special feature of the body is the conduction of excitation in the heart. Here there is a combination of an excitation conduction system with excitation transmission from cell to cell. The electrical signals that regulate the activity of the heart are transmitted via the excitation conduction system. In this process, the beat is set by the excitation generation system. It is remarkable that these excitation systems of the heart do not consist of nerve cells, but of specialized heart muscle cells. In order for the excitation to spread through the heart, all cardiac muscle cells are connected to each other via so-called gap junctions. It is only through the cooperation of these systems that the heart muscle is able to allow all cells to contract in a coordinated manner.
Diseases and disorders
The term conduction disorders includes all malfunctions of the conduction system in the heart. These malfunctions cause delayed or interrupted transmission of electrical excitations. Excitation conduction disorders include right bundle branch block, left bundle branch block and AV block. In AV block, the AV node of the heart’s excitation conduction system is blocked. This often occurs in the elderly, but can also occur in association with heart disease such as heart attack or myocarditis. When AV block is impaired, there is a drop in heart rate. As a result, the heart’s pumping capacity drops and the body can no longer be adequately supplied with arterial blood.In the case of non-reversible AV block disorders, patients are fitted with a pacemaker. In left bundle branch block, the conduction of excitation in the left side of the heart is impaired, and in right bundle branch block, the conduction of excitation in the right side of the heart is impaired. Causes of these phenomena include coronary artery disease, arterial hypertension or myocardial inflammation. A disease in which saltatory conduction is severely impaired is multiple sclerosis. It is a chronic inflammatory disease. The myelin sheaths of the nerve cells of the central nervous system (CNS) are affected. This is referred to as demyelination. Demyelination foci are found preferentially in the white matter of the spinal cord and brain. The cause of the inflammation is an attack by the body’s own defense cells. However, why the cells attack the body’s own tissue has not yet been clarified. The first symptoms usually appear between the ages of 16 and 40. The disease progresses in relapses. Initially, the symptoms of the relapses usually recede, but later deficits remain. The type of symptoms depends on the localization of the demyelinating lesions. Typical early symptoms are visual disturbances such as double vision or visual blurring. There may also be sensory disturbances, numbness or pain. If the cerebellum and brainstem are affected, symptoms such as dysphagia, dizziness, speech disorders or movement disorders occur. The disease is not curable. Therapeutic measures are designed to enable patients to live as independently as possible.
