Old metronome. Tempos in music: slow, moderate and fast

Hi all. I needed a metronome. There was no big rush, so I bought a metronome on Aliexpress. The metronome is quite functional, quite loud, but there is also a drawback that required studying the waveform oscillograms

This review of a newly purchased metronome was prompted by an extremely unexpected problem, or perhaps its feature, which sharply limited its use.

Many famous musicians do not use a metronome during performances, rehearsals, and even when recording albums, since the metronome forces musicians into strict time frames, depriving them of the freedom to express emotions through music. At the same time, everyone recognizes that a metronome is an absolutely necessary thing for the development of a musician, for developing his sense of time, and training for even playing. For the drummer, who sets the musical pulse of the group and is essentially a metronome for the rest of the musicians, this is especially important.

As it turned out, my sense of rhythm and sense of time were far from ideal, and to control the smoothness of my drumming I needed a metronome. But the volume of the metronome, an Android application that I installed on my mobile phone, turned out to be not enough. Therefore, it was decided to take an “iron” metronome.

There are metronomes on sale that are completely different in functionality. The simplest ones can only make sounds like “pick-peek” with a given periodicity in a given musical time signature. “Advanced” metronomes have several sound options, can be programmed for various rhythmic patterns containing pauses, accented notes, empty measures, speed changes in different parts of the piece, have a memory for storing an n-number of rhythmic patterns, etc. Very advanced models of metronomes (for example, Boss db-90) have built-in realistic drum sounds, a voice counting function, have a midi input for synchronization, an input for a drum pad trigger, an instrument input, allowing, for example, a drummer to hear, in addition to the metronome, also a monitor line from the sound engineer's mixer, etc.

Initially, I wanted to take something serious, so to speak, for the future; I was very attracted to the Boss db-90 metronome (for everything except the price, of course).

But having soberly assessed the situation, realizing that I still have to grow and grow to the level where I really need such a metronome, I abruptly changed my “wants” and bought almost the simplest metronome. If there is a need, we will think about an advanced option. And now there is simply no need to carry such a bandura with you.

In music stores, the prices are much higher than the prices for metronomes on aliexpress that are approximately the same in functionality, but there are no reviews at all for seemingly interesting models, so I settled on one of the simplest and best-selling options. And about 3 weeks later I received a package in the mail.

The metronome is small, very small, from the description and photo on the website I assumed it was larger. But the small size is even good, I attached it to my clothes and it was in order.

There were no batteries included with the metronome, so I couldn’t test it right away. When I bought and inserted a 2032 or 2025 battery, the metronome worked, but periodically the screen went dark and the settings were reset to default. I decided that the battery was not making good contact, and bent the spring contact. Indeed, after this the battery stopped falling off and the settings were not reset.

The kit included instructions in English and Chinese, I’m posting the English one, but in principle you can figure it out without instructions:

The metronome has several settings; you can change the tempo at any time using the “+” and “-” buttons from 30 to 280 beats per minute. Other settings can be changed after pressing the “select” button. The volume has 4 gradations, from the loudest to zero, it is not smoothly adjustable, even at zero volume the red LED flashes in time with the rhythm. There are also two settings “Beat” and “Value” (in the Rhythm types instructions) with which you can set the musical time signature and highlight a strong note. The “On-off” button turns the metronome on and off, the “Play” button, also known as the “Tap” button, is used to turn on/off the metronome signals; in the “Tap” mode, the “Tap” button allows you to enter the tempo of the song into the metronome by successive presses of the “Tap” button. . There is a battery saving function; if the metronome does not beat the rhythm, it turns off after a while.

The metronome is really very loud for its size, the built-in tiny speaker works wonders, for practicing on the practice pad I turn the volume down one unit from the maximum. At maximum volume on a hard surface, the metronome jumps up and down from its own sound, and the sound becomes disgustingly rattling. It’s not for nothing that it has a clothespin, you shouldn’t put it on the table... Also, if you look closely, each sound signal is accompanied by a slight dimming of the LCD screen, apparently the peak load on the battery is quite large. I don’t know how long the battery lasts, in total I used it for 10 hours, and the battery is still alive.

There is a headphone jack, if you connect headphones, the volume is quite enough for practicing on a drum kit.

But, a big “but”: I couldn’t use the metronome with headphones. In headphones, each “squeaky” sound of the metronome is accompanied by a powerful, unpleasant shock to the ears, as if a constant voltage pulse is applied to the headphones at the beginning of each tone. Therefore, with headphones, I don’t so much perceive the sound of the signal as I feel the blows on my ears, and this is very unpleasant.

To understand where these percussion effects come from, I recorded the sound from the metronome output on a Zoom H4n recorder to view the sound waveform on the computer.

There was a suspicion that the constant component, so to speak, the low-frequency fluctuation of the “blow,” would not pass into the sound recording channel, and it would not be visible on the “oscillogram.” But the recorder did the job, and this low-frequency transient is very noticeable. True, I was a little mistaken, the “blow” was not before the signal, but after it.

Here's what a "normal" metronome waveform looks like:

As you can see, there are no low-frequency fluctuations here, only a harmonic click sound with human transitions to zero, and no problems arise when playing with headphones under such a click.

Thus, this digital mini-metronome was completely unsuitable for me for playing with headphones. In addition, if you try to broadcast a click from it during a rehearsal, you can easily damage the speaker systems, which will have to work out the low-frequency component of the metronome signal. It doesn’t seem to be enough for the ears either; there is no desire to check it for yourself. I don’t know if this is a mistake in the metronome’s circuitry, or if its microcontroller is wired crookedly... Perhaps it’s enough to connect the headphones to the metronome through small capacitors, which will let the squeak through and cut off the beat, but is it worth making an adapter for headphones larger than the metronome itself... I’ll take it apart I'm not planning it yet.

And finally, a short video with examples of the sound of a metronome in different modes. The sound was taken from the microphone and from the headphone output, I think the “beats” are quite noticeable:

Well, whoever read to the end, a video from a recent rehearsal, from which even a non-professional will notice that a metronome is very necessary. The rehearsal was after a decent break, don’t kick too hard, the vocalist didn’t show up, there’s no bassist yet:

Here is a multifunctional online metronome from the Virartek company, which, among other things, can be used even as a simple drum machine.

How does it work?

A metronome consists of a pendulum with a movable weight and a scale with numbers. If you move the weight along the pendulum, along the scale, the pendulum swings faster or slower and with clicks, similar to the ticking of a clock, marks the desired beat. The higher the weight, the slower the pendulum moves. And if the weight is set in the lowest position, then a quick, as if feverish knock will be heard.

Using the metronome:

Large selection of sizes: click the first button on the left to select a size from the list: 2/4, 3/4, 4/4, etc.
The tempo can be set in different ways: by moving the slider using the “+” and “-” buttons, by moving the weight, by making several presses in a row on the “Set tempo” button
Volume can be adjusted with a slider
You can also turn off the sound and use visual indicators of the beats: orange – “strong” and blue – “weak”
You can choose from 10 sound sets: Wood, Leather, Metal, Raz-tick, E-A Tones, G-C Tones, Chick-Chick, Shaker, Electro, AI Sounds and several drum loops for different dance styles, as well as loops for learning triplets.
To play the drums at the original tempo and size, click the “reset tempo and size” button
The tempo value is indicated for BEATS, i.e. for 4/4 time, 120 would mean 120 quarter notes per minute, and for 3/8 time, 120 eighth notes per minute!
You can force the loop to play in a “non-native” time signature, this will give you additional variations in rhythmic patterns.
Sound sets “Tones E-A”, “Tones G-C” can be useful for tuning a string instrument or for vocal chanting.
A large selection of sounds is convenient when using a metronome to learn pieces in different styles. Sometimes you'll need crisp, punchy sounds like AI Sounds, Metal or Electro, sometimes soft sounds like the Shaker set.

A metronome can be useful for more than just music practice. You can use it:

For learning dance movements;
To train fast reading (a certain number of strokes on a time limit);
During concentration and meditation.

Additional Information:

Musical tempo indications (Wittner metronome scale)

Beats per minute Italian/Russian
40-60 Largo Largo – wide, very slow.
60-66 Larghetto Larghetto is quite slow.
66-76 Adagio Adagio – slow, calm.
76-108 Andante Andante - slowly.
108-120 Moderato Moderato – moderate.
120-168 Allegro Allegro is lively.
168-200 Presto Presto – fast.
200-208 Prestissimo Prestissimo – very fast.

Anyone who does not play music may consider a metronome to be a useless device, and many do not even know what it is and what its purpose is. The word “metronome” is of Greek origin, and it was formed after the merger of two words “law” and “measure”. The invention of the metronome is associated with the name of the great composer Beethoven, who suffered from deafness. The musician relied on the movements of the pendulum to feel the tempo of the piece. The “parent” of the metronome is the Austrian inventor Melzel I.N. The brilliant creator managed to design a metronome in such a way that it became possible to set the desired tempo of the game.

What is a metronome for?

Metronome- this is a device that plays regular sounds at a certain tempo. By the way, the number of beats per minute can be set independently. Who uses this rhythm machine? For beginners trying to master the guitar, piano, or other instrument, a metronome is a must. After all, when learning a solo part, you can start the metronome to adhere to a certain rhythm. Music lovers, students of music schools and colleges, and professionals cannot do without a metronome. Even though the metronome sounds like a loud ticking clock, the sound is perfectly audible when playing any instrument. The mechanism counts fractions of a beat and it becomes very convenient to play.

Mechanical or electronic?

Arrived before everyone else mechanical metronomes made from plastic or wood. The pendulum beats the beat, and with the help of the slider a certain tempo is set. The movement of the pendulum is clearly perceptible with peripheral vision. It is worth noting that the main “monsters” of musical art prefer mechanical metronomes.

Sometimes they meet metronomes with bell(shown on the left), which emphasizes the downbeat in the measure. The accent can be set according to the size of the piece of music. The clicks of the mechanical pendulum are not particularly annoying and go well with the sound of any instrument, and anyone can set the metronome.

An undeniable advantage of mechanical devices- independence from batteries. Metronomes are often compared to a clock mechanism: in order for the device to work, it must be wound.

A device with the same functions, but with buttons and a display is electronic metronome. Thanks to its compact size, you can take this device with you on the road. You can find models with a headphone input. This mini metronome can be attached to an instrument or clothing.

Artists who play electronic instruments choose electrometronomes. The device has a lot of useful functions: accent shift, tuning fork and others. Unlike its mechanical counterpart, the electronic metronome can be set to a “squeak” or “click” if you don’t like the “thump.”

How many mechanisms and wonders of technology have been invented by man. And how much he borrowed from nature!.. Sometimes you can’t help but marvel that things from different and seemingly unrelated areas obey general laws. In this article we will draw a parallel between the device that sets the rhythm in music - the metronome - and our heart, which has the physiological property of generating and regulating rhythmic activity.

This work is published as part of a competition for popular science articles held at the Biology - Science of the 21st Century conference in 2015.

Metronome... What kind of thing is this? And this is the same device that musicians use to set the rhythm. The metronome taps beats evenly, allowing you to accurately adhere to the required duration of each measure when performing the entire musical piece. It’s the same with nature: it has had both “music” and “metronomes” for a long time. The first thing that comes to mind when trying to remember what in the body can be similar to a metronome is the heart. A real metronome, isn't it? It also taps beats evenly, even if you play music! But in our cardiac metronome, it is not so much the high accuracy of the intervals between beats that is important, but the ability to constantly maintain the rhythm without stopping. It is this property that will be our main topic today.

So where is the spring responsible for everything hidden in our “metronome”?

Day and night without stopping...

We all know (even more, we can feel) that our heart works constantly and independently. After all, we don’t think at all about controlling the work of the heart muscle. Moreover, even a heart completely isolated from the body will contract rhythmically if nutrients are provided to it (see video). How does this happen? This is an incredible property - cardiac automatism- provided by the conduction system, which generates regular impulses that spread throughout the heart and control the process. That is why the elements of this system are called pacemakers, or pacemakers(from English pacemaker- setting the rhythm). Normally, the heart orchestra is conducted by the main pacemaker - the sinoatrial node. But the question still remains: how do they do it? Let's figure it out.

Contraction of the rabbit heart without external stimuli.

Impulses are electricity. We know where electricity comes from in us - this is the resting membrane potential (RMP) *, which is an indispensable attribute of any living cell on Earth. The difference in ionic composition on different sides of the selectively permeable cell membrane (called electrochemical gradient) determines the ability to generate impulses. Under certain conditions, channels open in the membrane (representing protein molecules with a hole of variable radius), through which ions pass, trying to equalize the concentration on both sides of the membrane. An action potential (AP) arises - the same electrical impulse that propagates along the nerve fibers and ultimately leads to muscle contraction. After the action potential wave has passed, the ion concentration gradients return to their original positions and the resting membrane potential is restored, allowing impulses to be generated again and again. However, the generation of these impulses requires an external stimulus. How then does it happen that pacemakers on one's own generate rhythm?

* - Figuratively and very clearly about the travel of ions through the membrane of a “relaxing” neuron, the intracellular arrest of negative social elements of ions, the orphan share of sodium, the proud independence of potassium from sodium and the cell’s unrequited love for potassium, striving to quietly leak away - see the article “ Formation of the resting membrane potential» . - Ed.

Be patient. Before answering this question, we will have to recall the details of the mechanism for generating an action potential.

Potential - where do opportunities come from?

We have already noted that there is a charge difference between the inner and outer sides of the cell membrane, that is, the membrane polarized(Fig. 1). Actually, this difference is the membrane potential, the usual value of which is about −70 mV (the minus sign means that there is more negative charge inside the cell). The penetration of charged particles through the membrane does not occur by itself; for this, it contains an impressive assortment of special proteins - ion channels. Their classification is based on the type of ions passed through: sodium , potassium , calcium, chlorine and other channels. The channels are capable of opening and closing, but they do this only under the influence of a certain incentive. After stimulation is completed, the channels, like a door on a spring, automatically close.

Figure 1. Membrane polarization. The inner surface of the nerve cell membrane is negatively charged, and the outer surface is positively charged. The image is schematic; details of the membrane structure and ion channels are not shown. Drawing from the site dic.academic.ru.

Figure 2. Propagation of an action potential along a nerve fiber. The depolarization phase is indicated in blue, and the repolarization phase in green. The arrows show the direction of movement of Na + and K + ions. Figure from cogsci.stackexchange.com.

A stimulus is like the doorbell of a welcome guest: it rings, the door opens and the guest enters. The stimulus can be a mechanical effect, a chemical substance, or an electric current (by changing the membrane potential). Accordingly, the channels are mechano-, chemo- and voltage-sensitive. Like doors with a button that only a select few can press.

So, under the influence of a change in membrane potential, certain channels open and allow ions to pass through. This change can vary depending on the charge and direction of movement of the ions. In case positively charged ions enter the cytoplasm, happens depolarization- short-term change in the sign of charges on opposite sides of the membrane (a negative charge is established on the outside, and a positive charge on the inside) (Fig. 2). The prefix “de-” means “movement down”, “decrease”, that is, the polarization of the membrane decreases, and the numerical expression of the negative potential modulo decreases (for example, from the initial −70 mV to −60 mV). When Negative ions enter the cell or positive ions exit, happens hyperpolarization. The prefix “hyper-” means “excess”, and the polarization, on the contrary, becomes more pronounced, and the MPP becomes even more negative (from −70 mV to −80 mV, for example).

But small shifts in the magnetic field are not enough to generate an impulse that will propagate along the nerve fiber. After all, by definition, action potential- This an excitation wave propagating along the membrane of a living cell in the form of a short-term change in the sign of the potential in a small area(Fig. 2). In essence, this is the same depolarization, but on a larger scale and spreading in waves along the nerve fiber. To achieve this effect, use voltage-sensitive ion channels, which are very widely represented in the membranes of excitable cells - neurons and cardiomyocytes. Sodium (Na+) channels are the first to open when an action potential is triggered, allowing these ions to enter the cell along a concentration gradient: after all, there were significantly more of them outside than inside. Those membrane potential values ​​at which depolarizing channels open are called threshold and act as a trigger (Fig. 3).

The potential spreads in the same way: when threshold values ​​are reached, neighboring voltage-sensitive channels open, generating rapid depolarization that spreads further and further along the membrane. If the depolarization was not strong enough and the threshold was not reached, massive channel opening does not occur, and the shift in membrane potential remains a local event (Fig. 3, symbol 4).

The action potential, like any wave, also has a descending phase (Fig. 3, designation 2), which is called repolarization(“re-” means “restoration”) and consists of restoring the original distribution of ions on different sides of the cell membrane. The first event in this process is the opening of potassium (K+) channels. Although potassium ions are also positively charged, their movement is directed outward (Fig. 2, green area), since the equilibrium distribution of these ions is opposite to Na + - there is a lot of potassium inside the cell, and little in the intercellular space*. Thus, the outflow of positive charges from the cell balances the amount of positive charges entering the cell. But in order to completely return the excitable cell to its initial state, the sodium-potassium pump must be activated, transporting sodium outward and potassium inward.

* - To be fair, it is worth clarifying that sodium and potassium are the main, but not the only ions that take part in the formation of the action potential. The process also involves a flow of negatively charged chloride (Cl−) ions, which, like sodium, are more abundant outside the cell. By the way, in plants and fungi, the action potential is largely based on chlorine, and not on cations. - Ed.

Channels, channels and more channels

The tedious explanation of details is over, so let's get back to the topic! So, we have found out the main thing - impulse really does not arise just like that. It is generated by the opening of ion channels in response to a stimulus in the form of depolarization. Moreover, the depolarization must be of such magnitude as to open a sufficient number of channels to shift the membrane potential to threshold values ​​- such that they will trigger the opening of neighboring channels and the generation of a real action potential. But the pacemakers in the heart do without any external stimuli (watch the video at the beginning of the article!). How do they do this?

Figure 3. Changes in membrane potential during different phases of the action potential. MPP is equal to −70 mV. The threshold potential is −55 mV. 1 - ascending phase (depolarization); 2 - descending phase (repolarization); 3 - trace hyperpolarization; 4 - subthreshold potential shifts that did not lead to the generation of a full-fledged impulse. Drawing from Wikipedia.

Remember when we said there was an impressive variety of channels? You really can’t count them: it’s like having separate doors in a house for each guest, and even controlling the entry and exit of visitors depending on the weather and day of the week. So, there are such “doors” that are called low-threshold channels. Continuing the analogy with a guest entering a house, one can imagine that the bell button is located quite high, and in order to ring the bell, you must first stand on the threshold. The higher this button is, the higher the threshold should be. The threshold is the membrane potential, and for each type of ion channel this threshold has its own value (for example, for sodium channels it is −55 mV; see Fig. 3).

So, low-threshold channels (for example, calcium channels) open with very small shifts in the resting membrane potential. To reach the button of these “doors”, you just need to stand on the rug in front of the door. Another interesting property of low-threshold channels: after the act of opening/closing, they cannot open again immediately, but only after some hyperpolarization, which brings them out of the inactive state. And hyperpolarization, except for those cases that we talked about above, also occurs at the end of the action potential, as its last phase (Fig. 3, designation 3), due to the excessive release of K + ions from the cell.

So what do we have? In the presence of low-threshold calcium (Ca 2+ ) channels (LTCs), it becomes easier to generate an impulse (or action potential) after the previous impulse has passed. A slight change in potential - and the channels are already open, letting Ca 2+ cations in and depolarizing the membrane to such a level that channels with a higher threshold are activated and trigger a large-scale development of the AP wave. At the end of this wave, hyperpolarization again puts the inactivated low-threshold channels into a state of readiness.

What if these low-threshold channels did not exist? Hyperpolarization after each AP wave would reduce the excitability of the cell and its ability to generate impulses, because under such conditions, much more positive ions would need to be released into the cytoplasm to achieve the threshold potential. And in the presence of NCC, only a small shift in the membrane potential is enough to trigger the entire sequence of events. Thanks to the activity of low-threshold channels cell excitability increases and the state of “combat readiness” necessary for generating an energetic rhythm is restored faster.

But that's not all. Although the NCC threshold is small, it does exist. So what pushes MPP even to such a low threshold? We found out that pacemakers don’t need any external incentives?! So the heart has it for this funny channels. No, really. That's what they're called - funny channels (from English. funny- “funny”, “amusing” and channels- channels). Why funny? Yes, because most voltage-sensitive channels open during depolarization, and these weirdos open during hyperpolarization (on the contrary, they close during depolarization). These channels belong to a family of proteins that penetrate the membranes of the cells of the heart and central nervous system and have a very serious name - cyclic nucleotide-gated hyperpolarization-activated channels(HCN - hyperpolarization-activated cyclic nucleotide-gated), since the opening of these channels is facilitated by interaction with cAMP (cyclic adenosine monophosphate). Here we have found the missing piece in this puzzle. HCN channels, open at potential values ​​close to the MPP and allowing Na + and K + to pass in, shift this potential to low threshold values. Continuing our analogy, they lay out the missing rug. So the entire cascade of opening/closing channels is repeated, looped and rhythmically self-sustaining (Fig. 4).

Figure 4. Pacemaker action potential. NPK - low-threshold channels, VPK - high-threshold channels. The dashed line is the threshold potential for the military-industrial complex. Different colors indicate the successive stages of an action potential.

So, the conduction system of the heart consists of pacemaker cells (pacemakers), which are capable of autonomously and rhythmically generating impulses by opening and closing a whole set of ion channels. A feature of pacemaker cells is the presence in them of types of ion channels that shift the resting potential to the threshold immediately after the cell reaches the last phase of excitation, which allows for the continuous generation of action potentials.

Thanks to this, the heart also contracts autonomously and rhythmically under the influence of impulses propagating in the myocardium along the “wires” of the conduction system. Moreover, the actual contraction of the heart (systole) occurs during the phase of rapid depolarization and repolarization of pacemakers, and relaxation (diastole) occurs during slow depolarization (Fig. 4). Well, we see the general picture of all electrical processes in the heart on electrocardiogram- ECG (Fig. 5).

Figure 5. Electrocardiogram diagram. Wave P - propagation of excitation through the muscle cells of the atria; QRS complex - propagation of excitation through the muscle cells of the ventricles; ST segment and T wave - repolarization of the ventricular muscle. Drawing from.

Metronome Calibration

It's no secret that, like a metronome, the frequency of which is in the control of the musician, the heart can beat faster or slower. Our autonomic nervous system is such a musician-tuner, and its regulating wheels are adrenalin(towards an increase in contractions) and acetylcholine(towards decreasing). I wonder what changes in heart rate occur mainly due to shortening or prolongation of diastole. And this is logical, because the firing time of the heart muscle itself is quite difficult to speed up; it is much easier to change its resting time. Since diastole corresponds to the phase of slow depolarization, regulation should be carried out by influencing the mechanism of its occurrence (Fig. 6). In fact, this is what happens. As we discussed earlier, slow depolarization is mediated by the activity of low-threshold calcium and "funny" non-selective (sodium-potassium) channels. The “orders” of the autonomic nervous system are addressed primarily to these performers.

Figure 6. Slow and fast rhythm of changes in pacemaker cell potentials. With increasing duration of slow depolarization ( A) the rhythm slows down (shown by the dashed line, compare with Fig. 4), while its decrease ( B) leads to an increase in discharges.

Adrenalin, under the influence of which our heart begins to beat like crazy, opens additional calcium and “funny” channels (Fig. 7A). By interacting with β 1 * receptors, adrenaline stimulates the formation of cAMP from ATP ( secondary intermediary), which in turn activates ion channels. As a result, even more positive ions penetrate into the cell, and depolarization develops faster. As a result, the time of slow depolarization is reduced and APs are generated more frequently.

* - The structures and conformational rearrangements of activated G-protein-coupled receptors (including adrenergic receptors), involved in many physiological and pathological processes, are described in the articles: “ A new frontier: the spatial structure of the β 2 -adrenergic receptor has been obtained» , « Receptors in active form» , « β-Adrenergic receptors in active form» . - Ed.

Figure 7. The mechanism of sympathetic (A) and parasympathetic (B) regulation of the activity of ion channels involved in the generation of the action potential of cardiac pacemaker cells. Explanations in the text. Drawing from.

Another type of reaction is observed when interacting acetylcholine with its receptor (also located in the cell membrane). Acetylcholine is an “agent” of the parasympathetic nervous system, which, unlike the sympathetic nervous system, allows us to relax, slow down our heart rate and calmly enjoy life. So, the muscarinic receptor activated by acetylcholine triggers the G-protein conversion reaction, which inhibits the opening of low-threshold calcium channels and stimulates the opening of potassium channels (Fig. 7B). This leads to the fact that fewer positive ions (Ca 2+) enter the cell, and more (K +) exit. All this takes the form of hyperpolarization and slows down the generation of impulses.

It turns out that our pacemakers, although they have autonomy, are not exempt from regulation and adjustment by the body. If necessary, we will mobilize and be fast, and if we don’t need to run anywhere, we will relax.

Breaking is not building

To understand how “dear” certain elements are to the body, scientists have learned to “turn them off.” For example, blocking low-threshold calcium channels immediately leads to noticeable rhythm disturbances: on the ECG recorded on the heart of such experimental animals, there is a noticeable prolongation of the interval between contractions (Fig. 8A), and a decrease in the frequency of pacemaker activity is also observed (Fig. 8B). It is more difficult for pacemakers to shift the membrane potential to threshold values. What if we “turn off” the channels that are activated by hyperpolarization? In this case, mouse embryos will not develop “mature” pacemaker activity (automatism) at all. It’s sad, but such an embryo dies on days 9–11 of its development, as soon as the heart makes its first attempts to contract on its own. It turns out that the described channels play a critical role in the functioning of the heart, and without them, as they say, you can’t go anywhere.

Figure 8. Consequences of blocking low-threshold calcium channels. A- ECG. B- rhythmic activity of pacemaker cells of the atrioventricular node * of a normal mouse heart (WT - wild type) and a mouse of a genetic line lacking the Ca v 3.1 subtype of low-threshold calcium channels. Drawing from.
* - The atrioventricular node controls the conduction of impulses, normally generated by the sinoatrial node, into the ventricles, and with pathology of the sinoatrial node it becomes the main driver of the heart rhythm.

Here is a short story about small screws, springs and weights, which, being elements of one complex mechanism, ensure the coordinated operation of our “metronome” - the pacemaker of the heart. There is only one thing left to do - to applaud Nature for making such a miracle device that serves us faithfully every day and without our efforts!

Literature

1. Ashcroft F. Spark of Life. Electricity in the human body. M.: Alpina Non-fiction, 2015. - 394 pp.;
2. Wikipedia:“Action potential”;Functional roles of Ca v 1.3, Ca v 3.1 and HCN channels in automaticity of mouse atrioventricular cells. Channels. 5 , 251–261;
3. Stieber J., Herrmann S., Feil S., Löster J., Feil R., Biel M. et al. (2003). The hyperpolarization-activated channel HCN4 is required for the generation of pacemaker action potentials in the embryonic heart. Proc. Natl. Acad. Sci. USA. 100 , 15235–15240..