PhysioEx 8.0 Cardiac Physiology Activity 8

Can anyone help me with these questions from PhysioEx 08 Cardiovascular Activity - Activity 8?? I've posted below along with my attempt at the answers but not sure if I am on the right track at all...
Thanks so much!!


Answer the following questions in the Lab Assignment.

7.9. What was the effect of calcium ions on heart rate?

The heart rate did not stabilize. It was irregular – speeding up and slowing down randomly, mainly remaining below the regular heart rate.

7.10.

Why?

An increase in calcium leads to spastic contractions as calcium induces spasticity.

7.11. What was the effect of sodium ions on heart rate?

The heart rate did not stabilize. It was irregular – speeding up above the heart rate and slowing down below it randomly. Mainly is was irregular below the heart rate though.

7.12. Why?

An increase in sodium increases the resting membrane potential////

7.13. What was the effect of potassium ions on heart rate?

The heart rate did not stabilize. It was irregular – speeding up and slowing down randomly although mainly remaining below normal heart rate.

7.14. Why?

Excessive potassium weakens cardiac contractions and slow the heart rate down as it decreases the resting membrane potential which results in a decrease in the intensity of the action potential.