Which way does the tongue deviate if the left hypoglossal nucleus is injured?
Lesioning the nucleus is similar to lesioning the peripheral nerve.
The left hypoglossal nerve innervates the left tongue muscles, which, if acting alone, pushes the tongue to the right.
The right hypoglossal nerve innervates the right tongue muscles, which, if acting alone, pushes the tongue to the left.
Usually, these muscles work together to push the tongue forward without deviation. If the left hypoglossal nucleus is lesioned, the right hypoglossal muscles act unopposed.
The tongue thus deviates to the left, or, in other words, the tongue deviates toward the affected side.
