How does the sinus node and Purkinje cell autonomic occur? For more details, 3Q la 10

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Bioelectric phenomena of sinus node cells and Purkinje cells:

Sinus node cells and Purkinje cells are both autonomic cells, and their bioelectric phenomena are the most significant compared with non-autonomic cells.

It is characterized by the fact that after the membrane potential at the end of phase 3 repolarization reaches its maximum, it does not remain at a stable level, but is automatically and slowly depolarized in phase 4.

The potential in the membrane gradually decreases, so it is called 4-stage automatic depolarization. The maximum membrane potential at the beginning of phase 4 is called the maximum diastolic potential or maximum repolarization.

Potential. Phase 4 auto-depolarization is the basis for autorhythmic autorhythmicity of autonomic cells. However, the bioelectricity of sinus node cells and Purkinje cells has its own characteristics, which are described as follows

1 Sinus node cells Compared with the action potential of ventricular myocytes, phase 0 depolarization is slow and small, mainly due to the opening of the divalent positive ion channel of slow calcium of the membrane and the divalent positive ion influx of calcium. After phase 0, there was no obvious repolarization phase 1 and plateau stage, and then it was transferred to repolarization phase 3, which was produced by the rapid outflow of potassium cation due to the opening of the potassium cation channel of the membrane. The automatic depolarization of phase 4 is mainly due to the gradual decrease of the positive ion permeability of the membrane to potassium at the end of the third and fourth phases, which causes the positive ion outflow of potassium to be progressively attenuated, coupled with the divalent positive ion influx of sodium and calcium.

2 Purkinje cells have their action potentials that can be divided into five phases. The shape, amplitude and formation mechanism of phase 0 and l are basically the same as those of ventricular myocytes. It is believed that the pacemaker current of phase 4 automatic depolarization of Purkinje cells is mainly a non-specific inward (positive ion of sodium) ion flow, which is different from the positive ion influx of sodium formed by the opening of the positive ion channel of fast sodium.

Phase 4 automatic depolarization is caused by the gradual increase of the permeability of the membrane to the positive ions of sodium, which causes the positive ions of sodium to flow slowly inward. The depolarization rate of Purkinje cells in phase 4 is slower than that of sinus node cells in phase 4, so the automaticity of Purkinje cells is lower than that of sinus node cells.

Answer]: In Purkinje cells, the outward K+ current of membrane repolarization gradually decays as repolarization progresses, while an inward current (IF) that increases over time can be recorded at phase 4 of membrane potential. The IF channel begins to be activated and opened when the repolarization potential reaches about -60mV in the third phase of the action potential, and its activation degree increases with the progress of repolarization and the increase of intramembrane electronegativity, and is fully activated to about -100mV.

As a result, the inward current exhibits increased time adherence, and thus the degree of depolarization of the membrane increases over time, and once the threshold potential level is reached, another action potential is generated, and at the same time, this inward current is terminated by channel deactivation at around -50 mV. It can be seen that the membrane potential itself is the factor that causes the initiation and development of this inward current during the repolarization phase of the action potential, and the generation and enhancement of the inward current leads to the progressive depolarization of the membrane, and the depolarization of the membrane causes another action potential on the one hand, and aborts the inward current on the other hand. This series of processes is initiated by the autonomic cell "self", the "self" develops, and the "self" is focused on the destruction of the family system, so it is understandable why the autonomic cell can automatically and continuously produce rhythmic excitement.

This 4-phase current, commonly referred to as the pacing current, has a predominantly ionic component of Na+, but also K+ is involved. Since the membrane potential that makes it fully activated is -100mV, it is believed that the inward current of the pacing fiber collapse is a non-specific inward (mainly Na+) ion current activated by the hyperpolarization of the membrane, and the channel with the symbol allows Na+ to pass through, but the voltage level activated by the two is different from that of the fast Na+ channel. IF can be blocked by cesium (CS), but puffer fish venom cannot block it.