CRANIAL NERVE: MEDIA RESOURCES
Pseudobulbar palsy is caused by bilateral corticobulbar tract disease (UMN disease). The patient will have upper motor neuron signs including a positive jaw jerk and slow side-to-side tongue movements with the jaw frequently moving with the tongue. The patient has incomplete elevation of the palate with excessive nasal air escape when saying "pah" or "kah" (decreased volitional activity of CN 9 & 10) but a hyperactive gag reflex (increased non-voluntary or reflex motor action of CN 9 & 10).
When a patient has weakness of the palatal muscles it is important to determine if this is from UMN vs. LMN disease. Patients with bilateral LMN lesions have both absent voluntary and reflex activity. Patients with bilateral UMN weakness or dysfunction will lack voluntary movement of the palate but will have a hyperactive gag reflex (just like a hyperactive DTR with UMN disease). For UMN disease to cause palatal weakness it must be bilateral because there is bilateral UMN innervation for the nucleus ambiguus.