## **Core Concept**
Spinal anaesthesia involves injecting a local anaesthetic into the subarachnoid space surrounding the spinal cord. This blocks the transmission of signals from the spinal cord to the brain, leading to loss of sensation and motor function below the level of the block. The nerves affected depend on the level of the block and the type of fibres (sensory, motor, or autonomic) targeted by the anaesthetic.

## **Why the Correct Answer is Right**
The correct answer involves understanding which nerves are typically affected by spinal anaesthetic block. Spinal anaesthesia primarily affects the **sensory**, **motor**, and **autonomic** nerve fibres. The block typically starts with the smaller nerve fibres, including **sympathetic** (autonomic) fibres, followed by **sensory** (pain, temperature, touch) and then **motor** fibres. The level of block is usually determined by the dermatomes (skin areas supplied by nerves that arise from specific spinal nerve roots).

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option might suggest a specific type of nerve fibre or a particular level of block that is not universally affected by spinal anaesthesia.
- **Option B:** Similarly, this might imply a selective effect on certain nerve types that does not accurately represent the typical effect of spinal anaesthesia.
- **Option D:** This option could propose an incorrect level of block or type of nerve fibre involvement not characteristic of spinal anaesthesia.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **sympathetic blockade** occurs at a lower concentration of local anaesthetic than motor blockade. This can lead to **hypotension** due to vasodilation of blood vessels. Clinicians often assess the level of sensory block (using pinprick or cold) and motor block (using a scale like the Bromage scale) to gauge the effectiveness and safety of the spinal anaesthetic.

## **Correct Answer:** .