Nerve ending sensitive to noxious stimuli are present in all excepta) Stomachb) Intestinec) Mesentryd) Livere) Brain
First, I need to recall where nociceptors (pain receptors) are located. Nociceptors are free nerve endings that respond to harmful stimuli. They're found in most tissues that can experience pain, like skin, muscles, and internal organs. But some areas, like the brain, don't have pain receptors. Wait, the brain itself doesn't have nociceptors, but the meninges do. So if the question is about the brain parenchyma (the actual brain tissue), then it's correct that it doesn't have pain receptors. However, the meninges, which cover the brain, do have pain receptors. So if the option is just "Brain," then it's the correct answer because the brain tissue itself doesn't have nociceptors.
Now looking at the other options: Stomach and Intestine—these are hollow organs with smooth muscle and definitely have pain receptors. The Mesentery, which is the connective tissue that attaches the intestines to the abdominal wall, also has pain receptors. The Liver—well, the liver parenchyma doesn't have pain receptors, but the Glisson's capsule does. Wait, so if the question is about the liver tissue itself, then maybe the answer isn't the liver. But the options here are a) Stomach, b) Intestine, c) Mesentery, d) Liver, e) Brain. So the correct answer would be e) Brain. Because the brain parenchyma lacks nociceptors, while the other organs (except maybe the liver) have them in their structures.
Wait, but the liver's Glisson's capsule does have pain receptors. So the liver as a whole (including the capsule) would have them. So the answer is the Brain. Let me double-check. The brain tissue itself doesn't have pain receptors, so you can't feel pain from a brain tumor pressing on tissue. But if there's inflammation of the meninges (meningitis), that's painful. So the answer is e) Brain. The other options all have parts with pain receptors. So the correct answer is e) Brain.
**Core Concept**
Nociceptors (pain-sensitive nerve endings) detect noxious stimuli in most visceral organs but are absent in the central nervous system's parenchyma. The brain lacks intrinsic nociceptors, though meningeal structures do contain pain receptors.
**Why the Correct Answer is Right**
The **brain parenchyma** (neural tissue) lacks nociceptors, which is why intracranial pathologies like brain tumors or infarcts do not cause pain unless they involve meninges, blood vessels, or cranial nerves. Pain in the brain arises only from structures like the dura mater or blood vessels, not the brain tissue itself.
**Why Each Wrong Option is Incorrect**
**Option A: Stomach** – Contains visceral nociceptors in its wall and serosa, responding to distension or chemical irritation (e.g., peptic ulcers).
**Option B: Intestine** – Pain receptors are present