Which cranial nerve(s) is/are not involved in “Locked in syndrome”?

**Core Concept**
Locked-in syndrome is a rare neurological disorder characterized by complete paralysis of all voluntary muscles except for the eyes, which are usually able to move. This condition results from damage to the brainstem, specifically the ventral midbrain, leading to the loss of motor function below the level of the brainstem. The cranial nerves involved in this condition are those that control the movement of the eyes, face, and other cranial structures.

**Why the Correct Answer is Right**
The correct answer, C. 11, is because the accessory nerve (cranial nerve XI) is not typically involved in locked-in syndrome. This is because the damage to the brainstem in locked-in syndrome usually spares the spinal accessory nerve nucleus, which is located in the medulla oblongata. The other cranial nerves, such as the oculomotor nerve (cranial nerve III), trochlear nerve (cranial nerve IV), and trigeminal nerve (cranial nerve V), are involved in controlling eye movements and facial expressions, which are typically affected in locked-in syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** Cranial nerve IX, the glossopharyngeal nerve, is often involved in locked-in syndrome due to its proximity to the brainstem and the area affected by the condition.

**Option B:** Cranial nerve X, the vagus nerve, is also commonly affected in locked-in syndrome, particularly in terms of its motor functions.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that locked-in syndrome is a clinical diagnosis that requires careful evaluation of the patient's cranial nerve functions, particularly those controlling eye movements and facial expressions. A thorough neurological examination and imaging studies are necessary to confirm the diagnosis.

**✓ Correct Answer: C. 11. The accessory nerve (cranial nerve XI) is not typically involved in locked-in syndrome.**