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In humans, the mandible, or lower jaw, is connected to the temporal bone of the skull via the temporomandibular joint. This is an extremely complex joint which permits movement in all planes. The muscles of mastication originate on the skull and insert into the mandible, thereby allowing for jaw movements during contraction.
The orbicularis oris is not a simple sphincter muscle like the orbicularis oculi; it consists of numerous strata of muscular fibers surrounding the orifice of the mouth, but having different direction. It consists partly of fibers derived from the other facial muscles which are inserted into the lips, and partly of fibers proper to the lips.
Underneath skin of lower lip Opening mouth and sliding lower jaw left and right: Lower jaw: Depression, lateral: Depressor angulus oris: Mandible: Underneath skin at corners of mouth Smiling: Corners of mouth: Lateral elevation: Zygomaticus major: Zygomatic bone: Underneath skin at corners of mouth (dimple area), orbicularis oris: Shaping of ...
When the lower jaw is pushed anteriorly as far as possible with some teeth in contact, it is said to be maximum protrusion. In Posselt's border movement diagram, maximum protrusion is the most anterior based on the sagittal view. Condyles are in the most anterior position and determined partly by stylomandibular ligaments. [8]
Muscle Action Risorius: Smirk Buccinator: Aids chewing by holding cheeks flat Levator labii superioris: Elevates upper lip Levator labii superioris alaeque nasi muscle: Snarl Levator anguli oris: Soft smile Nasalis: Flare nostrils Orbicularis oris muscle: Purse Lips Depressor septi nasi: Depresses nasal septum Procerus: Moves skin of forehead
The medial pterygoid muscle has functions including elevating the mandible (closing the mouth), protruding the mandible, mastication (especially for when the maxillary teeth and the mandibular teeth are close together), [1] and excursing the mandible (contralateral excursion occurs with unilateral contraction).
These may include the thick muscle in the cheek that closes the jaw (masseter muscle) and the broad muscle that draws back the lower jaw and closes the mouth (temporalis muscle). Some patients may also experience involuntary contractions of the wide muscle at the side of the neck (platysmal muscle). This muscle draws down the corner of the ...
The jaw jerk reflex is an example; tapping the jaw elicits a reflex closure of the jaw in the same way that tapping the knee elicits a reflex kick of the lower leg. Other incoming fibers from the teeth and jaws go to the main nucleus of V. This information is projected bilaterally to the thalamus and available for conscious perception.