In the case of a cranial nerve 12 lesion, where is the deviation typically located?

A cranial nerve 12 lesion, which affects the hypoglossal nerve, leads to weakness in the muscles of the tongue. The typical presentation of this weakness causes the tongue to deviate towards the side of the lesion, which is referred to as ipsilateral. This occurs because the affected side's muscle is weak and can't generate the normal strength needed to keep the tongue in midline when protruded. The healthy contralateral side exerts more force, resulting in the tongue pointing towards the side of the lesion.

Understanding this deviation is crucial in clinical practice as it helps in diagnosing and localizing neurological deficits. In contrast, deviations contralaterally or bilaterally would suggest different types of lesions or conditions affecting both sides of the brain or neuron pathways, while midline positioning of the tongue would indicate normal function, which is not the case when considering a specific lesion of the hypoglossal nerve.