notes by dr Claudio Italiano
The articulation of the word particularly affects the respiratory system, but it
also involves
1) the specific language centers in the cortex
2) the respiratory centers of the trunk of the brain
3) structures for articulation and resonance of sounds in the mouth and nasal
cavities.
Basically, the spoken language is realized by two distinct mechanical functions:
1) the phonation that is performed by the larynx
2) the joint, which is implemented by the mouth.
The larynx is specially adapted to work like a vibrator. The vibrating structures
are the vocal cords, which are plications arranged along the lateral walls of
the larynx that are stretched and placed in position by specific muscles,
located within the borders of the larynx itself. The basic structure of the
phonation is the larynx and shows that each vocal cord is stretched between the
thyroid cartilage and an arytenoid cartilage.
We can also see the specific, intrinsic muscles of the larynx, which control the
position and the degree of tension of the vocal cords. It can thus be observed
in the figure that the contraction of the posterior cricoaritenoid muscles pulls
the arytenoid cartilages, away from the thyroid cartilage, so as to stretch the
vocal cords. The transverse arytenoid muscle attracts the arytenoid cartilages
to each other and therefore makes the vocal cords close together, which
therefore vibrate when the expired air passes through. In contrast, the
contraction of the lateral cricoaritenoid muscles laterally pulls the arytenoid
cartilages and (abducting the cords) allows normal breathing. The tiarroitenoid
muscles are made up of numerous strands of muscle, controlled separately from
different nerve fibers.
Muscle strips adjacent to the edges of the strings may contract independently of those adjacent to the larynx wall. Moreover, the strips can all contract individually and independently of one another. These contractions control the attitudes of the vocal cords in different types of phonation. Vibration called vocal cords. One might think that the vocal cords vibrate in the direction of the flow of air, but it is not so. In fact, they vibrate in the sense of laterality. The mechanism is as follows: when the vocal cords are injected and air is exhaled, the pressure from below pulls the strings sideways, allowing a rapid flow of air; this causes a depression between the vocal cords, so that the margins of these return to take on each other, interrupting the flow of air again; then, again, the pressure rises and again moves the edges of the strings sideways, and so on in a vibratory way.
The tone of the sounds emitted by the larynx can be varied in two different ways.
With a first modality, variation can be obtained by stretching or releasing the
vocal cords. The mechanisms involved have been partly explained above regarding
the intrinsic laryngeal muscles; but, in addition to the action of the intrinsic
muscles, the muscles that are inserted on the external surfaces of the larynx
can also pull on the cartilages and then collaborate to stretch or loosen the
vocal cords. For example, the whole larynx is moved upward by the extrinsic
muscles, thus making the vocal cords stretch, when a very high frequency sound
must be emitted. While the larynx is moved downward, with consequent loosening
of the vocal cords, when a very low frequency sound must be emitted. The other
modality, to change the frequency of the sound, consists in changing the shape
and the thickness of the margins of the vocal cords. When a very high frequency
sound must be emitted, the different stripes of the thyaritenoid muscles
contract so that the margins of the vocal cords become sharp and thin, while for
the low frequencies the thyaritenoid muscles contract differently, such that the
margins they are flat and thick.
The three main organs for articulating the sounds are the lips, the tongue and the soft palate. This does not require a detailed treatment, since to anyone the movements of these parts are familiar during the articulation of the word or other forms of vocalization. The resonators include the mouth, nose and sinuses, the pharynx and even the same thoracic cavity. Also in this regard everyone has experience of the resonance characteristics of these different structures. For example, the function of the nasal resonator can be easily demonstrated by the change that the voice undergoes in people suffering from a severe cold.
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