A tumor at the right trigeminal motor nucleus would most likely cause which change in the muscles of mastication?

A tumor at the right trigeminal motor nucleus would most likely cause which change in the muscles of mastication?

• A. Reduced strength on contralateral side
• B. Reduced strength bilaterally
• C. Reduced strength on ipsilateral side
• D. Reduced saliva production on ipsilateral side

Answer: (C)

When a tumor affects the trigeminal motor nucleus on one side, the motor neurons that go to the muscles of mastication (masseter, temporalis, and the pterygoids) on that same side are disrupted. That means the right side muscles of mastication would be weaker, so you’d see reduced bite strength on the right (ipsilateral) side. The jaw would tend to deviate toward the weakened side when trying to bite down. Salivary output is controlled by parasympathetic nuclei, not the trigeminal motor nucleus, so that change wouldn’t be expected. So the deficit is an ipsilateral reduction in mastication strength.

When a tumor affects the trigeminal motor nucleus on one side, the motor neurons that go to the muscles of mastication (masseter, temporalis, and the pterygoids) on that same side are disrupted. That means the right side muscles of mastication would be weaker, so you’d see reduced bite strength on the right (ipsilateral) side. The jaw would tend to deviate toward the weakened side when trying to bite down. Salivary output is controlled by parasympathetic nuclei, not the trigeminal motor nucleus, so that change wouldn’t be expected. So the deficit is an ipsilateral reduction in mastication strength.