Noradrenaline is major neurotransmitter in –
**Core Concept**
Noradrenaline, also known as norepinephrine, is a catecholamine neurotransmitter that plays a crucial role in the body's fight-or-flight response. It is involved in various physiological processes, including increasing heart rate, blood pressure, and energy mobilization.
**Why the Correct Answer is Right**
Noradrenaline acts on adrenergic receptors, particularly alpha-1 and beta-1 adrenergic receptors, to increase sympathetic nervous system activity. This leads to vasoconstriction, increased heart rate, and increased cardiac contractility. Noradrenaline is also involved in the regulation of blood pressure and is released from the postganglionic neurons of the sympathetic nervous system. It is a major neurotransmitter in the locus coeruleus, a region of the brain involved in stress response and arousal.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the question, as noradrenaline is not primarily associated with this neurotransmitter system.
**Option B:** While serotonin is an important neurotransmitter, it is not the major neurotransmitter associated with noradrenaline.
**Option C:** GABA is an inhibitory neurotransmitter that is not directly related to noradrenaline's primary functions.
**Clinical Pearl / High-Yield Fact**
Noradrenaline is often used as a medication to treat hypotension and shock, particularly in critical care settings. It works by increasing vascular tone and cardiac contractility.
**Correct Answer: D. Brainstem, particularly the locus coeruleus.**