41. Taste

What is Being Tested?

Facial weakness can be caused by lesions of upper motor neurons in the contralateral motor cortex or descending CNS pathways, lower motor neurons in the ipsilateral facial nerve nucleus (CN VII) or exiting nerve fibers, the neuromuscular junction, or the face muscles. Note that the upper motor neurons for the upper face (the upper portions of the orbicularis oculi and the frontalis muscles of the forehead) project to the facial nuclei bilaterally (see Neuroanatomy Through Clinical Cases 3e, Figure 12.13). Therefore, upper motor neuron lesions such as a stroke cause contralateral face weakness, sparing the forehead, while lower motor neuron lesions such as a facial nerve injury typically cause weakness involving the whole ipsilateral face.

Unilateral deficits in taste can occur in lesions of the lateral medulla involving the nucleus solitarius or in lesions of the facial nerve.