Which one of the following organs will not feel any pain on being pricked by a needle?

The correct answer is B) Brain. Brain tissue has no nociceptors, the receptors that signal tissue damage, so a needle prick into the brain substance itself gives no pain. Headache comes from the meninges, blood vessels and scalp around the brain, not from brain tissue. This is also why neurosurgeons can operate on an awake patient under local anaesthesia of the scalp.

• A) Skin: richly supplied with free nerve endings, so a prick hurts immediately.
• C) Heart: the heart muscle has few pain fibres, which is why cardiac pain is felt as referred pain in the chest or left arm. The pericardium is pain-sensitive, so the heart is not a clean answer.
• D) Eye: the cornea is one of the most pain-sensitive tissues in the body, supplied by the trigeminal nerve.

Core concept: nociception, the difference between tissue sensation and referred pain. For Mains, this links to pain physiology and why headaches and cardiac pain are felt where they are.

Trap: students confuse 'has nerves' with 'has pain receptors'. The brain has plenty of nerve fibres for its own function, but not the pain receptors that would make a prick hurt.