sinoatrial node morphology trait sinoatrial node molecular composition trait 2024-04-15T13:00:50Z Trait.ontology SA node molecular composition trait Any measurable or observable characteristic related to the proportions of proteins, minerals, nutrients, gases, or other substances in the small mass of modified cardiac muscle fibers located at the junction of the superior vena cava and the right atrium that is the source of contraction impulses for the heart. VT:0011112 caripark pacemaker molecular composition trait