CHAPTER 6
Chapter Overview
Unilateral upper motor neuron dysarthria is a motor speech disorder caused by damage
to the upper motor neurons on one side of the brain that supply cranial and spinal nerves
involved in speech production. It is characterized by weakness in the lower face, lips,
and tongue on the opposite side of the lesion, resulting in articulation deficits, specifically
imprecise consonants. Because most of the cranial nerves serving the speech muscles
(except the lower face and tongue) receive bilateral innervations from the upper motor
neurons, the speech deficits seen after unilateral upper motor neuron damage almost
Unilateral upper motor neuron dysarthria is primarily a mild-moderate disorder of
articulation, affecting the tongue and lower face much more than it does other speech
production structures. Weakness, reduced range of motion, and decreased fine motor
control of the tongue and lips are noted. Imprecise consonant production is the primary
difficulty, with other deficits being irregular articulatory breakdowns, slow alternate motion
rates, and irregular AMRs. Phonation is characterized by harsh vocal quality. Resonance
can be characterized by hypernasality. Prosody and respiration are generally not
affected.
Study Questions and Answers
1. Define unilateral upper motor neuron dysarthria in your own words.
2. Why does unilateral damage to the upper motor neurons result in such less
severe symptoms as compared with bilateral damage to these neurons?
3. Unilateral upper motor neuron dysarthria is primarily a disorder of what?
4. What is the most common cause of unilateral upper motor neuron dysarthria?
5. Why are traumatic head injuries not a common cause of unilateral upper motor
neuron dysarthria?
6. What is the most common articulation disorder in cases of unilateral upper
motor neuron dysarthria?
7. What did Duffy suggest as the cause of harsh vocal quality in unilateral upper
motor neuron dysarthria?
