**Question:** Which of the following is most susceptible to local anaesthetics?

**Core Concept:** Local anaesthetics are drugs that block the conduction of nerve impulses by reversibly inhibiting voltage-gated sodium channels in neurons, resulting in loss of sensation and motor function. Local anaesthetics are commonly used in clinical practice for pain relief during surgical procedures.

**Why the Correct Answer is Right:** The correct answer is C. Sensitivity to local anaesthetics is greater in unmyelinated C-fibers compared to A-delta and A-alpha fibers. Unmyelinated C-fibers are slower and less excitable, making them more susceptible to the local anaesthetic action.

**Why Each Wrong Option is Incorrect:**

A. Sensitivity to hot in chronic pulpitis indicates stimulation of A-delta fibers, which are less susceptible to local anaesthetics compared to C-fibers.
B. Radiating pain from pulp transmitted by C-fibers implies that C-fibers are involved, not sensitivity to local anaesthetics.
D. Sensitivity to local anaesthetics is less in A-alpha fibers because they are faster and more excitable compared to C-fibers.

**Why C is Right and the Others are Wrong:**

C. Sensitivity to local anaesthetics is greater in unmyelinated C-fibers. This is because C-fibers are less excitable and slower than A-delta and A-alpha fibers. As a result, local anaesthetics have a higher affinity for C-fibers, blocking their conduction and causing loss of sensation.

**Core Concept:** C fibers are unmyelinated and generally slower than A-delta and A-alpha fibers. They are involved in pain transmission and thermoception, particularly cold sensation.

**Why C is Right and the Others are Wrong:**

A-delta and A-alpha fibers are more excitable and faster than C-fibers. They are involved in transmitting information related to touch, pressure, and vibration, respectively. Therefore, they are less susceptible to the effects of local anaesthetics compared to C-fibers.

**Why C is Right and the Others are Wrong:**

B and D: Radiating pain from pulp indicates the involvement of C-fibers, not sensitivity to local anaesthetics. A-delta and A-alpha fibers are responsible for transmitting pain and temperature information, respectively, but they are not the focus of the question.

**Why C is Right and the Others are Wrong:**

C fibers are involved in the transmission of pain and cold sensation, making them more susceptible to the effects of local anaesthetics compared to A-delta and A-alpha fibers, which are involved in transmitting touch, pressure, and vibration, respectively.