The uniqueness of speech among motor systems.

This paper considers evidence that the speech muscles are unique in their genetic, developmental, functional and phenotypical properties. The literature was reviewed using PubMed, ScienceDirect, ComDisDome and other literature-retrieval systems to identify studies reporting on the craniofacial and laryngeal muscles. Particular emphasis was given to studies of muscle fibre composition. A number of studies on mandibular, lingual, palatal and laryngeal muscles in humans show that these muscles are distinct from limb and other muscles. These speech-related muscles typically contain diverse fibre types and these types can vary regionally within a muscle. In general, the muscles of the speech production system are designed for fast and/or variable contraction and fatigue resistance. The craniofacial and laryngeal muscles are unique among the muscle systems of the human body and the specialized properties of these muscles are relevant to understanding the biomechanics of speech and various speech disorders.