Systole heart beats—is cued by messages from the brain, reflecting the brain's responses to conditions of the body, such as pain, emotional stress, level of activity, and to ambient conditions including external temperature, time of day, etc. Electrical systole opens voltage-gated sodium, potassium and calcium channels in cells of myocardium tissue. Subsequently, a rise in intracellular calcium triggers the interaction of actin and myosin in the presence of ATP which generates mechanical force in the cells in the form of muscular contraction, or mechanical systole. The contractions generate intra-ventricular pressure, which is increased until it exceeds the external, residual pressures in
Edmund Alexander Parkes Exercise on the Elimination of Nitrogen". He confirmed independently the observations of Adolf Eugen Fick and Johannes Wislicenus, against Justus Liebig's theory that muscular work implies the destruction of muscular tissue by oxidation. Parkes suggested that the elimination of urea is not dependent on the amount of muscular exercise, but on the consumption of nitrogenous food; and that muscular tissue does not consume itself as a fuel doing work. His experiments on the effects of alcohol on the human body (in which he was assisted by Cyprian Wollowicz) were in three papers (in 1870, 1872, and 1874), on the "Effects