Heart beat is accelerated by

Options

A. Carbon dioxide
B. Oxygen
C. Vagus nerve
D. All the above

Answer

D

Explanation

Heart beat are affected by
(i) `CO_(2)` level in blood: Increase conc. Of `CO_(2)` the sympathetic nerve stimulate SA node by producing adrenaline and nor adrenaline. This induces impulse generation by entry of `CO^(2+)` into cardiac muscles.
(ii) `O_(2)` amount in blood: Increase conc. of `O_(2)` stimulate parasympathetic nerve inhibits SA node by producing acetylcholine. This compound increases contraction time and hence heart beat is decreased.
(iii) Vagus nerves: Stimulation of vagus nerve decreases the heart rate.