How Does Increasing the Extracellular Calcium Concentration Lead to a Decrease

question 26

Multiple Choice

How does increasing the extracellular calcium concentration lead to a decrease in excitability?

• A) Ca²⁺ can block Na⁺ channels, so the extra concentration means fewer channels are available for Na⁺ to move through.
• B) Ca²⁺ increases the voltage threshold required to open the Na⁺ channels, so the extra concentration means channels require more stimulus.
• C) Ca²⁺ decreases the voltage threshold required to open the K⁺ channels, so the extra concentration means K⁺ channels will open sooner, hyperpolarizing the cell.
• D) It makes the outside of the cell more positive, so by comparison the inside is more negative and therefore less likely to depolarize.

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