The noble gases are left out of the trends in atomic radii because there is great debate over the experimental values of their atomic radii.

The SI units for measuring atomic radii are the nanometer (nm) and the picometer (pm). 1 nm = 1 X 109 m; 1 pm = 1 X 10-12 m.

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#Unit 7. System Physiology – Animal

When the potential reaches a threshold voltage of about −40 millivolts, the L-type calcium channels become “activated,” causing the action potential.

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#Unit 7. System Physiology – Animal

L-type calcium channels become inactivated (i.e., they close) within about 100 to 150 milliseconds after opening

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#Unit 7. System Physiology – Animal

When the L-type calcium channels become inactivated at about the same time, greatly increased numbers of potassium channels open.

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#Unit 7. System Physiology – Animal

Large quantities of positive potassium ions diffuse out of the SA node.

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#Unit 7. System Physiology – Animal

Potassium channels remain open for another few tenths of a second, with resultant excess negativity inside the fiber; this process is called hyperpolarization.

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#Unit 7. System Physiology – Animal