Atlas Musculature: Physiology,I

Out of this embryonic superficial muscle coating later on the muscle tracks are developing in their variety (picture 20, next page). Best discernible as a coating is caudal wards the big plane of  the Platysma, mainly from the mandibular rim downwards. The muscle coating upwards from the rim up to the height of the Os zygomaticum is forming a sort of belt consisting of: Buccinator - Risorius - Orbicularis - Risorius - Buccinator (see also schematic drawing picture 18 next page). This belt part of the coating is playing a specific role in the balance of forces against the interior. Vertically it is kept in its middle position by side braces like the Levator and Depressor labii. This construction lends our "rubber coating“  the inwards pointing, centripetal power.

To these pressure or power resultants arising by muscle actions we have to lend our special mindfulness in respect to the deforming potential in connection with imbalance and dysfunction. For this reason frequently related notes are given within the text being relevant in orthodontic view. These resultants (deformative force directions) do rarely if ever coincide with the actual pulling direction of the single muscle but they feature an angle to these. The pull direction of the muscle may, for example point towards the nose while the resulting vector points centripetally in a right angle to it to the osseous base.

This vectorial variability of the basic force direction is displayed by the orofacial system in an astonishingly high measure. The part of this chapter with its systematical mapping is trying to depict these pull directions leading to a vectorial alteration of the force direction in an analogue draft for each muscle field. For their construction these mappings had been drawn on a clear foil. When we imagine the drawings presented here as a sketch on a foil for each single muscle and then superimposed one upon the other this will make us guess the complexity of variation possibilities. The resulting picture brings to mind a sort of wheel spoke structure (picture 17). In its centre the wheel hub, the muscle ring of the Orbicularis in two ring bows atop and below, in the mouth corners of each side with a tendinous connection. As wheel spokes we imagine the elastic tracks of the radially radiating out muscle tracks being mostly anchored in the bone.

Abb. 17: Wheel spokes (For nomenclature see also Abb. 2. survey, orofacial region, page 3)

Abb. 18: Muscle-”Belt”:

Buccininator – Risorius – Orbicularis – Risorius – Buccinator

Gray’s Anatomy quoted:

”Revelation of emotional state, intentions, and so forth by facial expression serves obvious social functions; but the facial musculature is even more frequently and usefully concerned in speech. There can be no doubt which is the more important form of communication. The niceties of speech immeasurably outstrip the repertoire of even the most expressive face. Nine muscles converge upon the mouth from each side to control the intricate labial movements of speech; occasionally they may curl the lips in irony or a sardonic grin. It is also important not to overlook the contribution of the facial musculature in feeding and drinking, in all their phases. Unfortunately, the individual activity of facial muscles has been little studied by experimental techniques and their participation in different movements is largely a matter of simple observation. Their role in mastication has been the subject of electromyographic study” [58, S. 533].

"Das Offenbaren von emotionalen Zuständen, Absichten und ähnlichem  dient augenfällig sozialen Funktionen; aber die Facialmuskulatur ist noch häufiger und nützlicher beteiligt an der Sprache. Es kann gar kein Zweifel darüber bestehen, welches die wichtigere Form der Kommunikation ist. Die Feinheiten der Sprache übersteigen bei weitem die Fähigkeiten eines noch so ausdrucksvollen Gesichts. Neun Muskeln konvergieren von beiden Seiten über dem Mund und beherrschen die komplizierten Lippenbewegungen beim Sprechen; manchmal können sie auch die Lippen in einem ironischen oder höhnischen Lächeln verziehen. Es ist auch wichtig, die Beteiligung der Facialmuskulatur beim Essen und Trinken  in allen seinen Phasen nicht zu übersehen.  Leider sind bisher die individuellen Aktivitäten der Facialmuskeln wenig durch experimentelle Techniken untersucht worden, wie auch ihre Beteiligung an den unterschiedlichen Bewegungen grossenteils eine Angelegenheit der einfacher Beobachtungen geblieben ist. Ihre Rolle bei der Mastikation war Thema elektromyographischer Untersuchungen."