Answer:
C. calcium ion levels.
Explanation:
Calcium enters the axon terminal during an action potential,
By making his research available to the public
Answer:Valves stop blood flowing backwards
Explanation: Valve are flags of tissue that control the direction of the blood in our heart.,it prevent the backwards flow of blood. valves regulate blood from flowing back into the atria.The right and left atrio-ventricular valves prevent blood from flowing backwards into atria. When the ventricle is full,the valve prevent backwards flow of blood.
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