heart questions
 

A couple of random wonderings while riding this morning.

First, is the heart’s response to muscular exertion triggered by a chemical or a neurological signal? I know adrenalin can cause the HR to jump, but doesn’t it then stay elevated for a while? If chemical, are there “on and off” signals and are they limited in amount, meaning response gets weaker if used repeatedly in a short time frame? If neurological how does the cell demand for oxygen etc. get translated into a neurological signal?

Second, is the heart muscle susceptible to glycogen depletion like any other muscle? If you are on a no carb diet, for example, can the heart deplete its stored glycogen and if so what effect does this have on the heart’s performance?

You're probably directing this at CardiacCoug, but I'll take a quick shot. In the body, there are chemoreceptors and baroreceptors. Chemoreceptors respond to chemical triggers, such as pH (which would slightly increase as lactic acid is produced through anaerobic metabolism) and CO2 and O2 levels in your blood. Baroreceptors respond to pressure changes (such as would occur with dehydration). These receptors are exquisitely sensitive and respond very quickly by inducing changes in the heart rate and contractility (how hard the contracts). The mechanism for this is both chemical (through the release of adrenaline/epinephrine and the like) and neurologic (through stimulation of the vagus nerve, which runs adjacent to the receptor and connects directly to the heart).

The glycogen stores in the heart are, to my understanding, minimal if existent at all, so it would not be reliant on its own glycogen stores in the same way as other muscles.

CardiacCoug may be able to give you a more detailed explanation. Even better, MudPhud (if you can pull him away from his third year slavery) would be closer to the physiology sections of med school.

Facinating. I was hoping one of you doctor types wold answer. As usual, it is more complicated than Iimagined. I will haveto try to read some more abotu this. Thanks for taking the time.