**Question:** Which of the following types of nerve fibres carry fast pain:

A. Fast-conducting myelinated A-delta fibres
B. Slow-conducting unmyelinated C fibres
C. Fast-conducting myelinated C fibres
D. Slow-conducting myelinated A-delta fibres

**Core Concept:** Different types of nerve fibres are classified based on their conduction velocity, which determines the speed at which they transmit signals. Fast pain is typically mediated by myelinated nerve fibres.

**Why the Correct Answer is Right:** Fast-conducting myelinated A-delta fibres (option A) are responsible for transmitting pain signals at relatively faster rates compared to unmyelinated C fibres (option B, C, and D). Myelination improves the conduction velocity by reducing the electrical resistance along the nerve fibres. A-delta fibres have a faster conduction velocity than C fibres, which are unmyelinated and transmit pain signals at a slower speed.

**Why Each Wrong Option is Incorrect:**

- Slow-conducting unmyelinated C fibres (option B, C, and D) are responsible for transmitting pain signals, but they have a slower conduction velocity compared to A-delta fibres.
- Slow-conducting myelinated C fibres (option C) are also involved in transmitting pain signals but have slower conduction velocity than A-delta fibres.
- Fast-conducting myelinated A-delta fibres (option A) are responsible for transmitting pain signals, but their conduction velocity is faster than both C fibres.

**Clinical Pearl:** Understanding the conduction velocity of different types of nerve fibres helps in interpreting the clinical presentation of pain and choosing appropriate analgesic management strategies based on the type of pain and its characteristics (e.g., burning, sharp, or electric shock-like).

**Correct Answer:** A-delta fibres (option A) transmit fast pain due to their faster conduction velocity.