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Temporal bone

Structure and landmarks of the temporal bone.

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Hey everyone! This is Nicole from Kenhub, and welcome to our tutorial on the temporal bone. In this tutorial, we'll be covering the borders of the temporal bone which are the parietal border, the occipital margin, and the sphenoidal margin. We'll then have a look at parts of the temporal bone including the squamous part, the petromastoid part, the tympanic part, and the styloid process. We'll then conclude our tutorial by looking at some clinical notes related to the temporal bone.

Okay, let's begin this tutorial by giving you a bit of an introduction about the temporal bone. The temporal bone is a bone located bilaterally on either side of the skull. More, specifically, it is a part of the cranium which is this region of the skull just here. This image shows the skull in a side on or lateral view and the temporal bone is highlighted in green. It is located inferior to the parietal bones, posterior to the zygomatic bone and mandible, and anterior to the occipital bone.

If we have a look at an anterior view of the skull like we see here in this image, we can also see that it articulates with the sphenoid bone. The cranium can be divided into an anterior cranial fossa, a middle cranial fossa, and a posterior cranial fossa. As you can see, the temporal bone is part of the middle cranial fossa.

If we zoom in on the lateral view of the skull and have a look at the temporal bone on its own, we can see that the temporal bone has four parts – the squamous part, the petromastoid part, the tympanic part, and the styloid process. During this tutorial, we will be looking at each of these parts in detail. But, first, let's begin by looking at some of the margins or borders of the temporal bone.

The first border we'll look at is the parietal border of the temporal bone. As you can see, this border is quite irregular or jagged in shape. This is also known as the superior border and overlaps the inferior border on the parietal bone. The area where these two borders overlap is known as the squamous suture. You can see the suture here in green in this lateral view of the skull on the right.

Next, we'll look at the occipital margin of the temporal bone. The occipital margin is where the temporal bone articulates with the occipital bone posteriorly. If we look at the image on the right, we can see the temporal bone here articulating posteriorly with the occipital bone just here. The suture that connects these two bones is known as the occipitomastoid suture.

If we change our viewpoint to look at the anterior surface of the temporal bone, we can see another margin. This margin is known as the sphenoidal margin of the temporal bone. This is where the temporal bone articulates with the sphenoid bone. If we look at the entire skull from the same anterior view, we can see the temporal bone here articulating with the sphenoid bone here.

Now let's move on to look at the different parts of the temporal bone. As you can see in the image on the left, we've gone back to our lateral view. Let's start off by looking at the squamous part of the temporal bone. The squamous part is the most anterosuperior part of the temporal bone. Its external surface is smooth and convex. It forms part of the temporal fossa which is a shallow depression on the lateral surface of the skull that we can see highlighted on the right – just here. The temporalis muscle, one of the muscles of mastication, attaches here.

On the temporal bone, there's a groove for the middle temporal artery. You can see this groove on this image here which shows the temporal bone from a lateral view with this side being the anterior side and this side being the posterior side. The groove is vertical and located on the anterior side of the squamous part of the temporal bone. Within this groove runs the middle temporal artery, which is a branch of the superficial temporal artery, and supplies the temporalis muscle.

Now, we'll look at the anterior surface of the squamous part of the temporal bone. As you can see, the internal surface is concave and contains depressions which correspond to the shape of the temporal lobe. The anterior surface also contains a groove for the middle meningeal artery which you can see here in green. Now as you can see on the image on the right which is looking down on the brain, the middle meningeal artery supplies the meninges. The middle meningeal artery is a branch of the maxillary artery.

The squamous part of the temporal bone contains a zygomatic process. The zygomatic process can be seen in this lateral image of the temporal bone. It juts anteriorly from the inferior aspect of the squamous part of the temporal bone. The superior aspect of the anterior part of the zygomatic process is thin and flat. The temporalis fascia attaches here.

The posterior part of the zygomatic process is triangularly shaped and although it's hard to see from this view has both a superior and inferior surface. The zygomatic process articulates with the temporal process of the zygomatic bone anteriorly which we can see here in this image.

The squamous part of the temporal bone contains a fossa posteroinferior to the zygomatic process. This fossa is known as the mandibular fossa. The mandibular fossa has a smooth concave surface and articulates with the mandible to form the temporomandibular joint. We can see this joint highlighted in green on the image on the right of the screen.

Anterior to the mandibular fossa is the articular tubercle of the temporal bone which we can see here. This tubercle is the anterior portion of the temporomandibular articular surface. Therefore, like the mandibular fossa, it articulates with the mandible to form the temporomandibular joint.

Let's now move on to look at the next section of the temporal bone – the petromastoid part. Once again, we're looking at a lateral view of the temporal bone with the petromastoid part being this area here in green. The petromastoid part is often separated into two distinct parts – the petrous part and the mastoid part. Broadly speaking, the mastoid part is considered the external surface whereas the petrous part is considered the internal part. We'll now have a look at different aspects of the petromastoid part.

The first part we'll look at is the mastoid process which we can see here in green in this lateral image of the temporal bone. The sternocleidomastoid, splenius capitis, and longissimus capitis muscles all attach to this external surface. The internal surface contains a number of hollowed depressions which are known as mastoid air cells. You can see these cells in the cross-section image on the right of our screen. They're referred to as air cells because most of these hollowed spaces contain air within them.

If we zoom in to take a closer look at the mastoid process, we can see that it contains a foramen highlighted here in green. This foramen is located on the posterior aspect of the mastoid process just anterior to the occipitomastoid suture. A branch of the occipital artery passes through this foramen to supply the dura mater as well as a small vein from the sigmoid sinus. The sigmoid sinus is a venous sinus within the skull that we will talk a little bit more about later during the tutorial.

If we continue to look at the lateral view of the temporal bone, we can see that there's a hollowed out area highlighted in green. This is known as the mastoid notch and is sometimes referred to as the digastric groove. The digastric muscle attaches to this structure.

Now we'll switch our view to look at the interior part of the temporal bone. The posterior part of this image is the petrous part inferior to the squamous part. The petrous part contains an apex which is highlighted here in green on the right side of the image.

Located within the petrous part is a hollowed groove in green here. This is the groove for the sigmoid sinus. As we mentioned earlier in the tutorial, the sigmoid sinus is a venous sinus within the skull. The sigmoid sinus receives blood from many veins within the skull as well as from another sinus known as the transverse sinus.

The next part we'll look at is the arcuate eminence seen here in green. The arcuate eminence is a prominence located on the petrous portion of the temporal bone. It's considered to be a bony landmark for the anterior semicircular canal, one of three types of canals that is part of the vestibular system.

The petrous part of the temporal bone contains a depression known as the subarcuate fossa highlighted here. The subarcuate artery and vein both travel through this fossa.

Let's now switch our viewpoint to look at the temporal bone from an inferior view. In other words, we're looking at the underside of the bone. At the top of our image is the anterior part of the temporal bone which consists mostly of the squamous part of the bone. The parts of the bone on the left and at the bottom of our image are showing the petromastoid part of the bone. The depression highlighted in green is known as the jugular fossa. Located within this fossa is the bulb of the internal jugular vein.

Just above the jugular fossa in this image is the carotid canal. The internal carotid artery – the main source of blood supply to the head – travels through this canal to enter the skull. The carotid plexus of nerves also travels through this canal.

The stylomastoid foramen which we can see in this image here is another hole located within the temporal bone. This foramen allows the facial nerve, otherwise known as cranial nerve seven, to exit the skull. The stylomastoid artery, on the other hand, enters the skull through the stylomastoid foramen.

Let's now move on to look at the tympanic part of the temporal bone. Note that we're looking once again at the lateral view of the temporal bone. You can see the tympanic part here in green anterior to the mastoid process and inferior to the squamous part. Between the tympanic part of the temporal bone and the mastoid process is a small groove that separates the two. This is known as the tympanomastoid fissure shown here in green. The auricular branch of the vagus nerve runs within this fissure.

At the anterior aspect of the tympanic part of the temporal bone is another fissure. This fissure is known as the petrotympanic fissure which we can see here. A branch of the seventh cranial nerve – the chorda tympani – travels through this fissure. It allows communication between the middle ear and the temporomandibular joint.

Also located within the tympanic part of the temporal bone is the external auditory pore seen here. The external auditory pore is the opening of the ear canal which is otherwise known as the external auditory meatus.

The fourth and final part of the temporal bone is the styloid process which is this thin and pointed part just here that projects anteroinferiorly from the inferior part of the bone. The styloid process is covered by the parotid gland and is crossed by the internal carotid artery and internal jugular vein.

Okay, let's move on now to the next part of the tutorial and look at some clinical notes. In this part we're going to talk a little bit about temporal bone fractures. Temporal bone fractures occur due to blunt head injuries that normally have to be reasonably severe in nature. They're usually classified into either longitudinal, transverse or oblique fractures. As we've mentioned already during this tutorial, the temporal bone contains many different structures such as the facial nerve and the auditory and vestibular systems. Therefore, the signs and symptoms of a temporal bone fracture often include vertigo, hearing loss, and facial nerve paralysis. Another common symptom is the presence of cerebrospinal fluid or CSF discharging from the ear canal. This is known as otorrhoea.

Diagnosis of a temporal fracture is best done with a high-resolution CT scan. MRIs are very poor at detecting any fractures of the skull. Treatment is usually conservative with most signs and symptoms resolving on their own.

Okay, let's wrap up this tutorial by summarizing what we've talked about today.

First of all, we saw that the temporal bone is the bone located bilaterally on either side of the skull. We then looked at the three borders or margins of the temporal bone – the parietal border, the occipital margin, and the sphenoidal margin. We then looked at its four parts which included the squamous part, the petromastoid part, the tympanic part, and the styloid process.

On the squamous part, we looked at the groove for the middle temporal artery located on the anterior surface and the groove for middle meningeal artery located on the interior surface of the temporal bone. We then looked at the zygomatic process which is this part in green that juts anteriorly from the inferior aspect of the squamous part, posteroinferiorly to the zygomatic process. We looked at the mandibular fossa which articulates with the mandible to form the temporomandibular joint and anterior to the mandibular fossa, we looked at the articular tubercle which forms the anterior portion of the temporomandibular articular surface.

We then looked at some structures seen on the petromastoid part of the temporal bone including the mastoid process which is this part in green which juts inferiorly, the mastoid foramen – a foramen located within the mastoid process – and the mastoid notch – this hollowed out area that is also known as the digastric groove.

From an anterior view of the temporal bone, we also looked at the apex of the petrous part of the temporal bone and this hollowed out groove which is known as the groove for the sigmoid sinus. Next, we looked at the arcuate eminence which is a bony landmark for the anterior semicircular canal and the subarcuate fossa and then we looked at the subarcuate fossa – the depression which we can see here.

We then switched the inferior view of the temporal bone and looked at the jugular fossa, the carotid canal which is located just above the jugular fossa and the stylomastoid foramen which is where cranial nerve seven, otherwise known as the facial nerve, exits the skull.

We then looked at some structures of the tympanic part of the temporal bone including the tympanomastoid fissure – a groove that separates the tympanic part of the temporal bone and the mastoid process – and the petrotympanic fissure – a groove that is located on the anterior aspect of the tympanic part.

Finally, we looked at the external auditory pore which is the opening of the ear canal. We also looked at the styloid process – the thin and pointed part of the temporal bone – that projects anteroinferiorly from the inferior part of the bone.

The final thing we looked at in this tutorial was some clinical notes in the temporal bone on temporal bone fractures. Remember there are three main types – longitudinal, transverse and oblique. They often present with signs and symptoms such as vertigo and otorrhoea and is usually treated conservatively.

So that brings us to the end of our tutorial. Happy studying and thanks for watching!

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