12 Diagnosing Dysarthria in Adults The cerebellum plays an important role in speech production by coordinating the motor functions of the synergistic and antagonistic muscles. Some of the basal nuclei, especially the caudate nucleus, the putamen, the lateral segment of the globus pallidus and subthalamic nucleus (as part of the extrapyramidal system), collaborate with the extrapyramidal system responsible for voice production. In addition, they affect the activity of neurons in the motor nuclei of the cranial nerves. All the above-mentioned structures play a part in speech production and their activity is beyond conscious control. The mechanism of speech production is complicated and even small damage to one of its parts affects the quality of speech in various ways: lesions of parts of the extrapyramidal system can cause increased muscle tension, known as hypertonia; or decreased tension, known as hypotonia. There can also be uncontrolled movements (hyperkinesia) or limited movements and spasticity (hypokinesia). These disorders will be discussed in greater detail below (cf. also Duus 1989; Prusiński 1989).
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