**Question:** Which among the following is considered as false neurotransmitter?

A. Acetylcholine
B. Norepinephrine
C. Serotonin
D. Gastrin

**Core Concept:** Neurotransmitters are chemical messengers that transmit signals across the synaptic cleft between neurons or between neurons and other target cells, such as muscle or gland cells. They play a crucial role in the transmission of information in the nervous system.

**Why the Correct Answer is Right:** Gastrin is a hormone released by the gastric G cells, mainly responsible for the stimulation of gastric acid secretion. It is not a neurotransmitter, making option D the correct answer.

**Why Each Wrong Option is Incorrect:**

**Option A (Acetylcholine):** Acetylcholine is a well-known neurotransmitter that plays a significant role in the autonomic nervous system, neuromuscular junctions, and the central nervous system. It is involved in various physiological processes, such as muscle contraction, memory, and learning.

**Option B (Norepinephrine):** Norepinephrine is another neurotransmitter found in the sympathetic nervous system, where it regulates blood pressure, heart rate, and the body's "fight or flight" response.

**Option C (Serotonin):** Serotonin is a neurotransmitter involved in regulating mood, appetite, sleep, and gastrointestinal motility. It is also associated with the descending pain inhibition pathway and serotonergic neurons.

**Clinical Pearl:** Understanding the roles of neurotransmitters is essential for understanding various physiological processes, diseases, and treatments. This knowledge is crucial for medical students and practitioners alike, as it helps in understanding the pathophysiology of neurological and psychiatric disorders and the effectiveness of various medications in treating these conditions.