The action of aconitine on the circulation is due to an initial stimulation of the cardio-inhibitory centre in the medulla oblongata (at the root of the vagus nerves), and later to a directly toxic influence on the nerve-ganglia and muscular fibres of the heart itself.
The cerebral convolutions remain unaffected, but the important centres of the medulla oblongata are stimulated.
Similarly the depressant action on the respiratory centre in the medulla oblongata occurs only after the administration of enormous doses.
Morphine exercises its effects chiefly upon the cerebrum and the medulla oblongata in man.
As the vaso-motor centre in the medulla oblongata is also stimulated, as well as the contractions of the heart, there is thus trebly caused a very great rise in the blood-pressure.