What type of facial muscles does a lesion causing UUMN dysarthria typically affect?

In cases of Upper Motor Neuron (UMN) dysarthria, the primary impact is on the facial muscles due to disruption in the pathways that control these muscles. A lesion in the UMN system typically affects the ability to control facial muscles, leading to weakness or decreased mobility.

The correct choice indicates that a lesion will affect both the upper and lower facial muscles on the opposite side of the lesion. This is because the motor pathways that innervate the muscles of facial expression have a bilateral arrangement for the upper facial muscles (forehead) but primarily contralateral control for the lower facial muscles. Thus, a lesion in the UMN pathway will impair the lower facial muscles on the side opposite to the lesion while maintaining some functionality in the upper facial muscles on both sides due to their bilateral innervation.

This understanding underlines the nuanced nature of facial muscle control and the neurological pathways involved. In the case where a lesion specifically results in deficits in only the lower facial muscles on the same side, it does not reflect how UMN dysarthria typically manifests, as the opposite side is affected due to the anatomy of the motor pathways.