**Core Concept:**

The question is testing the understanding of local anaesthetic (LA) action and which types of nerves are less affected by local anaesthetics. Local anaesthetics are drugs that block voltage-gated sodium channels in nerve fibers, preventing the transmission of signals along these fibers. Different types of nerve fibers have varying sensitivities to local anaesthetics due to differences in their properties and distribution.

**Why the Correct Answer is Right:**

The correct answer, **C. Sensory fibers**, is due to several reasons:

1. Sensory fibers are responsible for transmitting sensory information, such as pain and temperature, from the peripheral nerves to the central nervous system (CNS).
2. These fibers have a slower conduction velocity (approximately 1-3 m/s) compared to motor fibers (approximately 20-100 m/s). This slower conduction velocity makes sensory fibers more susceptible to the effects of local anaesthetics.

**Why Each Wrong Option is Incorrect:**

A. **Motor fibers (Aα and Aβ)**: These fibers have a faster conduction velocity and are less affected by local anaesthetics.
B. **Sensory fibers (C and Aδ)**: These fibers have a slower conduction velocity, making them more susceptible to the effects of local anaesthetics.
D. **Autonomic fibers**: These fibers are also less affected due to their fast conduction velocity, similar to motor fibers.

**Clinical Pearl:**

Understanding the differences in the sensitivity of various nerve fibers to local anaesthetics is crucial for safe and effective clinical practice. While motor fibers and autonomic fibers are generally less affected by local anaesthetics, understanding the differential sensitivity of sensory fibers (C and Aδ) can help clinicians choose the appropriate local anaesthetic agent and dosage for specific procedures and patient populations.

For example, in patients with neuropathic pain conditions, using a local anaesthetic agent with a higher potency for sensory fibers (e.g., bupivacaine) might be more effective in providing analgesia while minimizing motor block. Conversely, for procedures where a lower risk of motor block is desired (e.g., ophthalmic surgery), a less potent local anaesthetic agent targeting motor fibers (e.g., lidocaine) may be chosen.