Which of the following statements about the stimulation of muscle cells is true? a. neurotransmitters are released into the synapse between two muscle cells. b. calcium ions bind the actin-myosin complex to start the muscle contraction process. c. acetylcholine opens channels that allow calcium ions into the muscle cell. d. an action potential in a muscle cell ultimately results in the release of calcium ions into the cell.

cell division is not regulated in tumor cells.

more words for this could be abiotic and biotic

abiotic: living organisms within an ecosystem

biotic: non-living organisms within an ecosystem

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.