This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
Melatonin is secreted from which cells of pineal gland 
Select and explain. 
A. Glial cells, B. Pinealocytes, C. Oncocytes, D. Zymogen cells
B: Pinealocytes
Answer: B: Pinealocytes 
Explanation: The pineal gland is a Neuroendocrine Transducer as it forms and secretes a hormone called Melatonin in response to sympathetic nerve activity. It consists of parenchymal cells (Pinealocytes), glial cells (neuroglia), secretory cells and numerous post-ganglionic sympathetic nerve fibres from cells in the superior cervical ganglion. It contains high amounts of 5 HT (serotonin), Nor-epinephrine and melatonin. Melatonin is synthesized from 5 HT and norepinephrine by the parenchymal cells (pinealocytes).Ref: Textbook of physiology, Dir. Prof. AK Jain, 5th edition.