Skull Sutures, Temporomandibular Joint, and Neck Muscles Anatomy
Skull Sutures and the Temporomandibular Joint
Skull sutures are toothed, scaly, harmonica-like (the nose), and esquindélesis (between the underside of the body of the sphenoid and vomer).
Temporomandibular Joint (TMJ)
The temporomandibular joint (TMJ) is located among the temporal fossa, in front of the ear canal, and the condyle of the mandible or lower jaw (synovial condyle). It has a joint capsule and articular surfaces between the two, providing a fibrocartilaginous disc. The joint capsule is reinforced by:
- Ligaments: These reinforce the capsule on the outside and extend from the zygomatic processes of the temporal bone to the mandible. This is the most important reinforcement.
The masticatory muscles act on this joint. These four muscles allow you to raise or lower the jaw, carry it forward or backward (Protraction, Retropulsion), and allow lateral movement of the jaw (grinding food). Chewing muscles are innervated by the fifth cranial or trigeminal nerve, a very thick nerve.
Masticatory Muscles
- Temporalis Muscle: Extends from the temporal fossa where the fibers form a fan that extends down and ends in the coronoid process of the mandible. Functions include occlusion and retraction of the mandible.
- Masseter Muscle: Extends from the zygomatic bone, with fibers directed downward and backward, and ends at the angle of the jaw. Closes the mouth (occlusion, raising the jaw).
- Pterygoid Muscles: Internal and external. The internal pterygoid has the same direction as the masseter but inside the jaw. The external pterygoid allows lateral movement from the outer surface of the mandible.
Facial Expression Muscles
In the skull, we also find a set of muscles: muscles of facial expression or cutaneous muscles of the head or face. They are found around the natural orifices of the face. Unlike the four muscles of mastication, these are innervated by the seventh cranial nerve or facial nerve and have insertions in the skin. They are responsible for expressing emotions. There are transient facial nerve palsies in which mimicry of one side is affected (it usually recovers on its own).
Neck Muscles
Thick neck muscles, from surface to depth:
- The most superficial is the platysma muscle, innervated by the facial nerve. Its attachments run from the jaw to the collarbone, beneath the skin.
- Raising this muscle, we have the sternocleidomastoid muscle, named for its insertions in the manubrium of the sternum, the inner end of the clavicle, and the mastoid process of the temporal bone to the occipital bone. It is a very important muscle.
- Raising this level are the scalene muscles, originating from the transverse processes of the vertebrae of the neck and from there go down and eventually inserted in the first or second rib. There are three: the anterior, middle, and posterior. The most anterior causes the tubercle of Lisfranc.
Inspiratory and Trevertebrales Muscles
- Inspiratory muscles are the scalene muscles, also found in the lateral neck.
- Ahead of the vertebrae is a series of small muscles: prevertebral muscles that help flex the neck.
Muscles Related to the Hyoid Bone
Muscles in relation to the hyoid bone, which is a small bone in the neck below the jaw. It does not articulate with any bone. It is horseshoe-shaped, open in the back, and sets a series of ligaments and muscles. It is attached to the cartilage of the larynx.
- Infrahyoid Muscles: These are inserted into the bones of the shoulder girdle or into the cartilage of the larynx, e.g., in the thyroid cartilage.
- Suprahyoid Muscles: These are above the hyoid bone. They end up in the bones of the skull, and between these muscles, you form the bottom wall of the mouth: mylohyoid. From the hyoid bone to the back of the jaw is the mylohyoid line, shaping each side of the muscle membrane.
Skull Bones
Skull Bones (8 bones) are divided into two parts:
- Superior or vault
- Frontal Bone: Part of the vault and skull base. There are some frontal sinuses lined with mucosa and in communication with the nasal cavity. Also part of the orbital cavity.
- Ethmoid Bone: Sinus home, part of the nasal septum, provides the superior and middle turbinates, and allows connection through its lamina cribrosa between specialized cells in the olfactory sensation of the nasal mucosa and the olfactory bulb of the first pair injury.