This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Thyroid hormone receptor which is predominantly expressed in CNS/Brain ? 
Select and explain. 
A. a - 1, B. a - 2, C. b-1, D. b-2
C: b-1
Answer: C: b-1 
Explanation: Ans. is'c'i.e., b-1There are three forms of thyroid hormone receptor that are able to bind thyroid hormone.TR - alpha 1+ Widely expressed with high expression in cardiac and skeletal muscle.TR- beta 1-+ Predominantly expressed in brain, liver and kidney.TR- beta 2-+ Expression primarily limited to hypothalamus & pituitary.Fouh isotypes TR- alpha2, is also widely expressed but is unable to bind thyroid hormone.