In medical and physiological terms, taking ventricular muscle as an example, the effective refractory period of ventricular muscle refers to the period from zero phase polarization to repolarization and then to membrane potential of -60mV. From depolarization to repolarization -55mV, the Na+ channel changes from activation to inactivation, so no matter how strong the stimulus is given, it will not produce excitement, that is, the excitability is zero. This period is called absolute refractory period.
FMRI: functional magnetic resonance imaging (FMRI, functional? Magnetic? Resonance? Imaging).
The increase in signal observed when stimulation is applied means that the concentration of paramagnetic deoxyhemoglobin is relatively reduced. This proves the results of early PET research. When stimulation is applied, the oxygen uptake is far less than the increase of blood flow.
Early observation of craniotomy also found that the blood leaving the active cortex was bright red, that is, there was more oxygenation, which was the result of imbalance between supply and demand.
Theoretically, signal changes are influenced by arterial oxygenation, blood flow, blood flow, hematocrit, tissue oxygen uptake and blood flow velocity. It increases with the increase of field strength. The change of blood flow is obviously the main factor, which works by diluting deoxyhemoglobin.
PER: Positron emission tomography (PET) is used to measure brain activity, including glucose metabolism, oxygen consumption, blood flow and so on. Among them, blood flow proved to be the most reliable index.
The principle is that a tracer isotope is injected into the human body, and then the positron released by it meets the electron in the tissue, which will produce annihilation and release rays. The position distribution of isotopes can be obtained through the detection of rays by instruments.
Extended data:
Functional magnetic resonance (fMRI) is to measure the attenuation signal by using the inhomogeneity of magnetic field. Because the transverse static magnetic field decays very quickly, the signal can be detected in a very short time, which provides good time resolution.
Echo technology is usually used to measure attenuated signals. Spin echo technology is used to measure T2 signal, and gradient echo technology is used to measure T2* signal.
Baidu encyclopedia -FMRI