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At rest there is a difference in the concentration of sodium ions (Na+) across the membrane of the neurone.

Outside the neurone in the extracellular fluid (ECF) the concentration of Na+ i...

Within the muscle fibre tropomyosin is wrapped around actin filaments and it blocks the binding sites for the myosin-heads.

When calcium ion concentration increases, calciu...

The sequence of bases (a gene) on DNA determines the order of amino acids that come together to form a polypeptide (protein) chain.

The DNA is 'unzipped' by enzymes called Helicases. This...

With a narrowed (stenosed) AV valve it is more difficult (requires more pressure) for the blood to pass from atrium to ventricle. The blood pressure in the atria is increased.

This means ...

An artificial pacemaker would generate regular electrical impulses in the atria.

The regular electical impulses from the pacemaker are stronger than the irregular impulses from the SAN, t...