Lips & Cheeks
| Muscle/Structure | Innervation | Action |
|---|---|---|
| Orbicularis oris | Buccal branch of facial nerve (CN VII) | Purses or puckers the lips Closes mouth Speech modification |
| Buccinator | Buccal branch of facial nerve (CN VII) | Compresses cheeks against teeth |
| Modiolus | Facial nerve | Important role in chewing and facial expression |
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Orbicularis oris
Orbicularis oris is a circular muscle surrounding the mouth. Its deepest fibres originate from midline slips (incisive and mental slips) that anchor the orbicularis oris to the maxilla superiorly and mandible inferiorly (see below). These deep fibres insert onto the modiolus. More superficial fibres are derived from buccinator and insert into the lips
The orbicularis is sometimes referred to as the 'kissing muscle' due to its action of puckering the lips. It is also useful for whistling, playing instruments and modification of speech
Extra Knowledge
The orbicularis oris can be divided anatomically in a number of ways. This is beyond what is expected by the college but may aid underlying knowledge. As mentioned above it can be divided into superficial and deep layers which helps explain its attachments. It can also be divided into central (marginal) and peripheral parts (pars maginalis and pars peripherals). The division for the marginal and peripheral part is the vermillion border and the functional significance is that the marginal part is adapted for speech
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Buccinator
Buccinator originates from the alveolar processes of the maxilla and mandible (corresponding to the molar teeth) and the TMJ. Its fibres run inferomedially towards the mouth where they blend with orbicularis oris and the lips inserting onto the modiolus.
Buccinator compresses the cheeks against the teeth which is useful for actions such as suckling and keeping food in position for mastication.
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Modiolus
The modiolus is a fibromuscular condensation located just lateral and superior to the angle of the mouth. It is a point of convergence or chiasma of 8 facial muscles. It plays an important role in facial expression, mastication and mouth movement. It derives its motor nerve supply from the facial nerve and arterial supply from labial branches of the facial artery. Contributing muscles are:
- Orbicularis oris
- Buccinator
- Levator anguli oris
- Depressor anguli oris
- Zygomaticus major
- Risorius
- Platysma
- Levator labii superioris