MRI of a knee. MRIs employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. When a radiofrequency current is then pulsed through the patient, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field.
Noun. 1. aestivation - (zoology) cessation or slowing of activity during the summer; especially slowing of metabolism in some animals during a hot or dry period. estivation. zoological science, zoology-the branch of biology that studies animals.
Inactivation and closure is an intrinsic property of that type of calcium channel, and the channels do not REACTIVATE until the cell returns to being polarized once again. This inactivation is what limits the amount of calcium flux INTO the cell, which as mentioned in the other answer can be toxic to the cell.