CODI 555  Motor Speech Disorders
Lecture 2: Lower Motor Neuron Disorders:  Flaccid Dysarthria

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 The Final Common Pathway

•  Also referred to as the lower motor neuron system
•  Includes cranial and spinal motor nerve nuclei located in brainstem and spinal cord
•  Axons or peripheral nerves from these nuclei
•  Motor end plates or neuromuscular junctions (synapses with muscles)

 Functions of Lower Motor Neurons

•  Stimulate muscle contraction and subsequent movement of skeletal and other structures
•  Resulting movements may be involuntary (reflexive) or voluntary (skilled learned movements)
•  Other motor divisions have effect on muscles by acting upon LMN

 Input to Lower Motor Neurons

•  Supraspinal - from indirect and direct activation pathways
•  Peripheral - proprioceptive and nonproprioceptive sensory input
•  Feedback from collaterals of LMN itself
•  Multiple inputs allow for convergence of many messages on single motor neuron or divergence of single message to many different motor neurons

 Effects of Damage to LMN

•  Paresis or paralysis
•  Atrophy
•  Fasiculations - spontaneous motor unit discharges
•  Fibrillation - slow repetitive contractions
•  Loss or reduction in reflexive movements

 Final Common Pathways for Speech

•  Cranial nerves: trigeminal (V), facial ( VII), glossopharyngeal (IX), vagus (X), accessory (XI) & hypoglossal (XII)
•  Innervate muscles controlling phonation, resonation, articulation & prosody
•  Spinal nerves involved in respiration

 Flaccid Dysarthria:  Common etiologies

•  Brainstem CVA, TBI affecting bulbar region
•  Infectious diseases
•  Neuromuscular junction diseases
•  Demyelinating diseases
•  Congenital anatomic malformations
•  Degenerative diseases of LMN
•  Muscular Diseases
• Isolated cranial nerve damage

 Speech Musculature Deficits

•  Weakness
•  Hypotonia
•  Reduced reflexes
•  Atrophy
•  Fasiculations& fibrillations
•  Progressive weakness with use

 Nonspeech Oral Mechanism Deficits

•  Normal direction, rhythm, & rate for both individual and repetitive movements
•  Reduced range for individual and repetitive movements
•  Weak force (strength)
•  Reduced muscle tone

 Patient Perceptions &Complaints

•  Vth CN - chewing difficulty, drooling, recognition that jaw is difficult to close or move, decreased sensation to face, cheek, tongue teeth or palate
•  VIIth CN - biting cheek or lip, difficulty keeping food in the mouth, drooling
•  IXth CN - dysphagia, pain on swallowing (glossopharyngeal neuralgia)
•  Xth CN - voice changes, decreased ability to sing, shortness of breath , hypernasality, consonant imprecision
•  XIth CN - Difficulty raising shoulder (side of lesion), weak head-turning (side opposite lesion)
•  XIIth CN - tongue feels heavy or thick, inability to move food around in mouth, drooling

 Deviant Speech Characteristics

• hoarse-breathy, reduced pitch and loudness variations, audible inspirations
• hypernasal, nasal air emissions
• slow-labored, imprecise articulation
• short phrases
• reduced pressure generation, shallow inhalations, reduced exhalation control. slow breaths

 Distinguishing Clusters

•  Phonatory incompetence (breathiness, short phrases, audible inspiration)
•  Resonatory incompetence (hypernasality, imprecise consonants, nasal emission, short phrases)
•  Phonatory-prosodic insufficiency ( harsh voice, monoloudness, monopitch)

 Most Distinctive Speech Deviations

•  Marked hypernasality
•  Nasal air emissions
•  Continuous breathiness
•  Audible inspiration
•  Short phrases