**Core Concept**
Spinal anaesthesia involves the injection of local anaesthetic into the subarachnoid space, leading to blockade of nerve fibres in the spinal cord. This affects all types of nerve fibres — sensory, motor, and autonomic — due to the broad distribution of nerve roots and their axons in the subarachnoid space.

**Why the Correct Answer is Right**
Spinal anaesthesia blocks the transmission of signals through all nerve fibres in the affected spinal segments. This includes **sensory nerves** (carrying pain and touch), **motor nerves** (controlling skeletal muscle movement), and **autonomic nerves** (regulating sympathetic and parasympathetic functions). The local anaesthetic diffuses into the cerebrospinal fluid and acts on all nerve fibres, including those that innervate blood vessels, sweat glands, and smooth muscles. This results in loss of sensation, muscle weakness, and autonomic side effects like hypotension or urinary retention.

**Why Each Wrong Option is Incorrect**
Option A: Incorrect because it excludes autonomic and motor nerves, which are indeed blocked.
Option B: Incorrect because it omits motor nerves, which are also affected and cause paralysis.
Option C: Incorrect because it falsely limits the block to sensory nerves only, ignoring the significant motor and autonomic effects.

**Clinical Pearl / High-Yield Fact**
Spinal anaesthesia causes **both motor and autonomic blockade**, leading to hypotension and urinary retention — key clinical signs that must be monitored. Always assess for autonomic effects, especially in patients with cardiovascular instability.

✓ Correct Answer: D. Sensory, autonomic and motor nerves