Hi Mar,

I understand the because the SA node independently initiates the AP too fast, the parasympathetic ANS reduces heart rate by sending acetylcholine through the vagus nerve. Is Ach released to the SA node?

Yes, ACh is released to the SA node. However, i would be careful by saying you send acetylcholine through the vagus nerve. To be somewhat pedantic, an action potential will go through the vagus nerve, following by the release of ACh at the neuomuscular juntion between the vagus nerve and the SA node.


And does the sympathetic ANS increase heart rate the same way but with epinephrine/norepinephrine?

Yes, I believe that is correct.

Also, are the SA/AV nodes, bundle of His and purkinje fibres made of neurons?
If so, are the connections between these structures gap junctions?

As far as I know, all of the SA/AV, His and purkinje firbres consist of a specialized set of cardiac muscle cells. There are gap junctions between these cells to allow for the flow of electrical current through the neighboring cells.

I hope this helps!

Katt