Excitability measures the ability of some tissues (nerve muscle) to come under the influence of irritation in the engaged state - excitation. What if this complex functional changes in the relevant cells appear next physical, physical-chemical and chemical processes.
Anxiety tissues from different animals vary widely. So, for example, the same muscles in different animals have different anxiety. It is also not the same for different muscles of the same animal, and even the same muscles, depending on its functional state. At pathology anxiety tissues can change in wide limits - from the sharp increase to complete extinction. That is why the study of excitability is not only theoretical but also practical interest, since it allows in many cases to accurately determine the state of the tissue and helps to clarify the diagnosis.
The degree of excitability judged on the strength of irritation, enough to get a response tissue. With this purpose, find the minimum (threshold) the intensity of stimulation, which is capable of producing a minimal effect (for example, the first visible muscles or the first perceptible sensation). The value of threshold of irritation is a measure of anxiety. If the latter is reduced, for excitation of tissue stimulus intensity should be increased accordingly (the threshold is increased). On the contrary, increased excitability threshold is lower, i.e. for excitation of fabric you want a smaller than normal, the intensity of stimulation.
However, not all bitterness, even if it is above the threshold that can cause arousal. A great role is played by the nature of the application irritation. If it is slowly and gradually grows, the institution or may not occur, or occurs at intensities, many times exceeding the threshold. The excitation occurs at minimum power irritation only if it very quickly and steeply rising.
For example, if you take neuromuscular drug frogs, and with enough power to hit a wooden hammer on the nerve, muscle is reduced. But if the same hammer applied to the nerve and very slowly and gradually increase the pressure, it can be the cerebellum, without producing the muscle contraction. The same is observed in case of irritation, tissue electric shock.
The value of the threshold current depends on the steepness of the rise of this power (under the rate of rise or rise, understand the increment current to gain time). A very small rate of rise through the fabric you can skip very strong currents, without causing her excitement. For different fabrics or even for the same fabric, depending on its functional state, slew rate, current, can cause excitation. Experiments show that if for one second to gradually increase the current strength from zero to thresholds, for sciatic nerve frog it is 63 times more than the threshold current at instant inclusion and for nerve toads - 46 times more.
Along with the stimulus intensity and speed of its increase essential to the characteristics of excitability and has the time during which the stimulus. So, irritation, may cause excitation of fabric at a certain duration of exposure can be effective if its duration is reduced. The stronger the irritation, the less time to cause excitation. Conversely, the weaker the stimulus, the longer he must act to bring the fabric in a state of excitement. Between the intensity and duration of irritation there is, thus, an inverse relationship. However, this dependence exists within certain limits. Cannot indefinitely to reduce the duration of the stimulus by increasing its intensity. Gradually reducing the duration of irritation and respectively increasing his power, we finally reach the limit of time, after which a further increase of the intensity of no effect. Similarly, you can not infinitely reduce the intensity by increasing the duration of irritation. When the intensity is below the limit excitation will not happen, as long as neither acted irritation.
The minimum intensity, beyond which an infinite increase in the length of irritation is inefficient, is called reality. The minimum time during which the intensity equal to LeoBase, causes excitation is called a useful time.
Lepik (Lapicque, 1909) proposed to use more easily define the conditional value - ronexiii representing the minimum time during which irritation of double LeoBase that can cause arousal. It is approximately 10 times less of a good time.
Chronometre recognized not only physiologists, but many clinicians who sought to find in it a fairly accurate method of research excitability, and thus the functional state of the fabric. But gradually, as the implementation of the method in the clinic, began to accumulate facts, discrediting all the teachings about chronaki. So, for example, already in the 30's, and then in 40 years we have noted that when determining realizy reduced some muscle fibers, and in determining chronaki (from the same point on the skin) reduced other fibers. Further our observations in this direction showed that the ramifications of the current in the human body largely depends on the applied voltage. Placing active electrode in the middle of the outer surface of the shoulder (approximately on the border between bi - and triceps muscles), you can easily find the point when determining realizy will be reduced fiber biceps muscle of his shoulder, and when determining chronaki - fiber triceps.
Thus, the corruption of chronometrie lies in the very essence of this method, i.e. the need to double Robezu that entails other current distribution in the body, resulting in the determination of realizy irritated some fiber, and when determining chronaki - other. Similar results have led us studies sensitive nerves of the teeth: when determining realizy and chronaki feeling arose in different parts of the tooth.