Major neurotranmistter released at end organ effectors of the sympathatic division of the autonomic nervous is:
**Core Concept**
The autonomic nervous system (ANS) is a branch of the nervous system that controls involuntary functions of the body. The sympathetic division of the ANS is responsible for the "fight or flight" response, while the parasympathetic division promotes relaxation and restoration. The sympathetic division releases neurotransmitters that act on effector organs to produce various physiological responses.
**Why the Correct Answer is Right**
The correct answer is **Norepinephrine (Noradrenaline)**. Norepinephrine is released at the end organs of the sympathetic division, such as the heart, blood vessels, and adrenal glands. It acts on adrenergic receptors (e.g., alpha-1, beta-1, beta-2) to increase heart rate, blood pressure, and cardiac output, and to dilate airways. Norepinephrine is synthesized from dopamine through the action of dopamine beta-hydroxylase.
**Why Each Wrong Option is Incorrect**
* **Option A:** Acetylcholine is the primary neurotransmitter released at the end organs of the parasympathetic division, not the sympathetic division.
* **Option B:** Dopamine is a neurotransmitter involved in the reward pathway and motor control, but it is not the primary neurotransmitter released at the end organs of the sympathetic division.
* **Option D:** Serotonin is a neurotransmitter involved in mood regulation, appetite, and sleep, but it is not the primary neurotransmitter released at the end organs of the sympathetic division.
**Clinical Pearl / High-Yield Fact**
Remember that the sympathetic division of the ANS is often referred to as the "fight or flight" response, and norepinephrine is the key neurotransmitter that mediates this response. This is why beta-blockers (which block the action of norepinephrine on beta-receptors) are often used to treat conditions such as hypertension and heart failure.
**Correct Answer:** C. Norepinephrine (Noradrenaline)