The skull is composed of multiple small bones held together by fibrous joints. Its inferior surface gives rise to a number of projections, and these allow for the attachment of many structures of the neck and face.
The temporal bone is one of the bones of the skull. It is a complex bone, which along with many of its landmarks, features a smooth conical projection called the mastoid process.
The mastoid process is easily palpable just behind the ears. It serves as the insertion site of many muscles in the head and neck region. In addition, it contains air-filled spaces called the mastoid air cells.
This article will discuss the gross and functional anatomy of the mastoid process.
|Definition||The mastoid process is a pyramidal bony projection of the temporal bone at the posterior base of the skull.|
|Muscle attachments||- Occipital belly of occipitofrontalis muscle
- Auricularis posterior muscle
- Sternocleidomastoid muscle
- Splenius capitis muscle
- Posterior belly of the digastric muscle
- Longissimus capitis muscle
Superior border: mastoid angle of the parietal bone via parietomastoid suture.
Anterior border: tympanic part of the temporal bone via tympanomastoid suture.
Posterior border: squamous part of the occipital bone via occipitomastoid suture.
Borders and relations
The mastoid process is a pyramidal bony projection of the temporal bone at the posterior base of the skull.
The mastoid process has the following bony boundaries:
- The superior border of the mastoid portion of the temporal bone articulates with the mastoid angle of the parietal bone via the parietomastoid suture.
- The petrosquamous suture runs vertically from the superior border of the mastoid process, forming a dense ridge also known as Koerner's septum.
- Its anterior border is merged with the tympanic part of the temporal bone via the tympanomastoid suture.
- The posterior border articulates with the squamous part of the occipital bone via the occipitomastoid suture.
It might be a good idea to learn the full anatomy of the skull before zoning in on specific structures like the mastoid process. Our skull bone quizzes and diagrams are ready and waiting for you!
The mastoid process has a rough outer surface that gives rise to the occipital belly of the occipitofrontalis muscle, which covers the skull from the superior nuchal line to the mastoid process. This muscle is innervated by the posterior auricular branch of the facial nerve (cranial nerve VII).
It also gives rise to the auricularis posterior muscle which inserts to the lower part of the cranial surface of the concha (outer ear).
In addition, the mastoid process itself (the pyramidal projection) gives rise to:
- the sternocleidomastoid muscle (which rotates the head to the contralateral side)
- the splenius capitis muscle (which extends, rotates and laterally flexes the head)
- the posterior belly of the digastric muscle (which opens the jaw when the masseter and temporalis muscles are relaxed)
The medial surface of the mastoid portion of the temporal bone has a deep groove called the mastoid notch, which allows the digastric muscle to attach.
The occipital groove can be found medial to the mastoid notch and is traversed by the occipital artery which courses posteriorly, parallel and deep to the posterior belly of the digastric muscle. It continues its course in the occipital groove to run towards the external occipital protuberance at which point it ascends the scalp.
The styloid process lies anterior and medial to the mastoid process, and in between them is the stylomastoid foramen. This foramen allows the muscular branch of the facial nerve to exit the skull and proceed to innervate the muscles of facial expression.
The mastoid bone is normally pneumatised ("air filled") by the mastoid air cells, which are of variable size and extent. The mastoid air cells communicate with the middle ear via the mastoid antrum, an air filled irregular cavity lined by a prolongation of the mucous membrane of the tympanic cavity.
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This is a condition caused by infection of the mastoid air cells. Symptoms include tenderness over the area, fever and swelling. The area may be red, and the patient may have earaches. It is commonly caused by untreated otitis media, where the infection tracks from the middle ear into the mastoid section of the temporal bone. The mastoid process is underdeveloped at birth which leaves the posterior auricular branch of the facial nerve (which ascends anterior to the mastoid process) superficial and unprotected.
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