This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'False about smooth muscle \nSelect and explain. \nA. Ca2+ is the excitation-contraction coupler, B. The "latch" mechanism facilitates prolonged holding of contractions of smooth muscle, C. Shows the propey of plasticity, D. Musculature of uterus is made of multi unit smooth muscle', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Unitary smooth muscle is found primarily in the walls of hollow viscera like uterus, intestine, ureters. Multiunit smooth muscle is made up of individual units with few (or no) gap junctional bridges. It is found in structures such as the iris of the eye, in which fine, graded contractions occur. Depending on the activating stimulus, the Ca2+ increase can be due to influx through voltage- or ligand-gated plasma membrane channels, efflux from intracellular stores through the RyR, efflux from intracellular stores through the inositol trisphosphate receptor (IP3R) Ca2+ channel, or a combination of these channels. Smooth muscle behaves more like a viscous mass than a rigidly structured tissue, and it is this propey that is referred to as the plasticity of smooth muscle. .The "latch" mechanism facilitates prolonged holding of contractions of the smooth muscle.', 'role': 'assistant'}]