Increases in the amount of cytoplasmic calcium required to initiate a muscle contraction are mediated by the coupling between a on the t tubule and a on the membrane of the sarcoplasmic reticulum.

1) Dihydropyridine receptor

2) Rynodine receptor

Explanation:

Rynodine receptor: It is a category of interacellular channels of calcium with different forms like neurons and muscles found in animal tissues.

Dihydropyridine receptor: they are present in muscle tissues and are able to sense voltage in skeleton muscles thus can increase or control the release of calcium.

a electronegativity decreases beacuse the size of nucleus is bigger.