When blocking a nerve containing both motor and sensory fibres, the last functional property to be lost is?
## **Core Concept**
The question tests the understanding of nerve physiology, particularly the sequence of functional loss when a nerve is blocked. Nerve blocks affect different types of fibers in a specific order based on their size and myelination.
## **Why the Correct Answer is Right**
The correct answer, , corresponds to the loss of motor function being the last or not the first, implying another option is correct. When a nerve is blocked, the sequence of functional loss generally follows this order:
- **Autonomic (sympathetic) fibers**: These are usually the first to be affected due to their small size and unmyelinated nature.
- **Sensory fibers**: Specifically, the smaller, unmyelinated sensory fibers (carrying pain and temperature) are affected next.
- **Motor fibers**: These are typically larger and myelinated, making them more resistant to local anesthetics.
However, the question asks for the "last functional property to be lost." Given that motor function is often among the last to be affected due to its relatively larger and myelinated fibers, the correct sequence implies that sensory functions (especially those carried by smaller fibers) are lost before motor functions.
## **Why Each Wrong Option is Incorrect**
- **Option A:** If this option suggests an incorrect sequence or property, it would be wrong based on the physiological properties of nerve fibers and the effects of local anesthetics.
- **Option B:** Similarly, this would be incorrect if it does not align with the known physiological effects and sequences.
- **Option C:** This option might suggest an incorrect property or sequence not supported by nerve physiology.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the sequence of recovery from a nerve block is typically the reverse of the sequence of loss. Clinically, this means that as the block wears off, **sensory functions return before motor functions**. This has implications for patient safety and comfort post-procedure.
## **Correct Answer: D. Motor Function**