I always struggled to understand the difference between an Upper Motor Neuron and Lower Motor Neuron Lesion in Cranial Nerves. The following image is a great example of UMN and LMN for Cranial Nerve VII (Facial). It is seen here that the face has bilateral supply for the muscles of facial expression in the upper part of the face, but not in the lower part. Therefore, if the LMN is compressed, such as in the case of Bell’s Palsy, it will affect upper and lower part of the face. But if the compression is occurring on the UMN it will affect only the lower part of the contralateral side, as in the case of a space occupying lesion leading to Central Facial Palsy.

Cranial Nerve VII through facial canal

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