<prompt> S.A. node acts as a pacemaker of the hea because of the fact that itIs capable of generating impulses spontaneouslyHas rich sympathetic innervationsHas poor cholinergic innervationsGenerates impulses at the highest rate  <response>: Some cardiac fibers have the capability of self-excitation, a process that can cause automatic rhythmical discharge and contraction. This capability is especially true of the fibers of the hea s specialized conducting system, including the fibers of the sinus node. For this reason, the sinus node ordinarily controls the rate of beat of the entire heaRef: Guyton and Hall textbook of medical physiology 13th edition. Page: 123 