Help! Cutting the vagus nerve and force of contraction

[Vangeek]

Cutting the vagus nerve to the heart increases heart rate. What effect would it have in the force of contraction of the heart? Please explain the answer, anyone????????

[mith]

well, what's the force controlled by?

[Vangeek]

If contractile strength is independent of muscle stretch and EDV ,but rather controlled by bloodborne chemicals (epinephrine, excess of Ca,thyroxine) which has little to do with the vagus (parasympathetic division) nerve, even if it's cut; then, yes, HR will increase, reflecting inherent rate of SA note (100beats/min), but the force of contraction will remain the same? Am I on the right path??

[behzad]

Vangeek is right. If we bring out the heart from body and cut its nerves thoroughly you can see that HR will increase. Vagus is a parasympathetic nerve. It shows that heart in normal situation is more affected by parasympathetic nerves. Now I think it's clear why cutting vagus can increase HR