2. DYSARTHRIA: CHANGES IN THE CLINICAL PICTURE OF SPEECH Dysarthria is a syndrome involving bulbar–phonation–articulatory disorders caused by lesions in the motor system or pathways innervating the speech apparatus, with the speech planning component remaining intact (Darley, Aronson, Brown 1969). Other definitions of dysarthria characterize it as a speech articulatory disorder resulting from impairment in the neurological mechanisms of voice production, modulation, intensity, and resonance (Johns 1985). In more recent accounts, dysarthria is described as a group of motor speech disorders due to focalized or diffuse damage to the central nervous system, the peripheral nervous system, or both (Communication Independence for the Neurologically Impaired CINI-1994). Dysarthric speech disorders result from lesions in specific locations of the speech motor system, which includes cortical regions (programming the movements of the tongue, lower jaw, pharynx and larynx), subcortical executive regions, as well respiratory, phonatory, and articulatory systems (cf. e.g. Minczakiewicz 1990). The motor functions of the speech organs are controlled by the cortex of the precentral gyrus and paracentral lobule in both hemispheres. Motor fibers involved in voice initiation and production run from the cortex in the corticobulbar tract to the motor nuclei of the cranial nerves V, VII, IX, X, and XII. Motor fibers running from these nuclei innervate the skeletal muscles of the articulatory and respiratory organs, i.e. the muscles of mastication, the muscles of the lips, tongue, palate, larynx, and respiratory muscles (Minczakiewicz 1990, Pruszewicz 1992). Physiological actions underlying speech production require strict coordination of a number of organs constituting the peripheral part of the speech production system. The airstream necessary for phonation engages the lungs, bronchial tubes, and trachea; the larynx amplifies the fundamental frequency of the voice; whereas the pharynx, nasal cavity, and oral cavity are responsible for producing speech sounds and the voice timbre. Impairments in each of the above-mentioned physiological processes involved in speech production may result in dysarthria-type disorders. Respirational disorders occur due to h y p o - or h y p e r f u n c t i o n of the respiratory system, such as mononeuropathy, myasthenia, other muscle disorders, and
RkJQdWJsaXNoZXIy MTE5NDY5MQ==