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Bones of the head and neck

Anatomy and function of the bones of the head and neck.

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Transcript

Hello everyone! It's Megan from Kenhub here, and in today's tutorial, we're going to be looking at the bones of the head and neck. Before we begin, let me first give you a quick overview of what we're going to talk about in this tutorial.

So, first, we'll look at the bones of the head which are divided into two groups – the bones of the neurocranium and the bones of the viscerocranium. Then we'll move on to look at the bones of the neck which are, of course, the cervical vertebrae. So, to start off this tutorial, let's look at the bones of the head or the skull.

The skull is made up of over twenty individual bones that as we know can be divided into two groups – those of the neurocranium and those of the viscerocranium. Let me draw a line on our nice image of the skull here to show you roughly where this division occurs. So, the neurocranial portion of the skull houses and protects the brain whereas the viscerocranial portion forms the face. Now, let's begin by looking at the bones of the neurocranium.

The first bone that we'll look at today is the frontal bone. This unpaired bone which is one of the bones that encases the brain consists of three parts – the squamous part which makes up the largest portion of the frontal bone encompasses the area of the forehead and houses the frontal sinuses, the orbital part which is essentially the part of the frontal bone that contributes to the bony orbit or eye socket and if you look at our skull, you can see that I've now highlighted this part in blue for you, and finally, we have the nasal part which articulates with the frontal processes of the maxilla and the nasal bones. In our image on the right, I've labeled the left nasal bone and I've drawn a line to show you where this articulation occurs.

If we view our skull from the side, we can see the left temporal bone. This paired bone forms part of the base of the cranial vault and is made up of four parts – the squamous part which is then and partly translucent I've highlighted the region for you in blue on our image, the tympanic part which relates to the area I've highlighted around the external acoustic meatus, the styloid process, this spiky process we can see located just below the tympanic part, and the petromastoid part which includes the mastoid process of the skull. Along with forming part of the base of the cranial vault, the temporal bones also participate in the formation of the lateral walls of the skull.

Next, let's have a look at the parietal bones. The parietal bones are bilateral bones found on both sides of the neurocranium and in our image, we can see the left parietal bone. These roughly square-shaped bones are bordered anteriorly by the frontal bone, posteriorly by the occipital bone and laterally by the temporal bone and the sphenoid bone.

If we look at our skull from a posterior perspective, we can see the unpaired occipital bone highlighted in green. This part of the skull houses the cerebellum and is the only cranial bone that articulates with the spine. If we flip our skull to view it from below, we can see that this bone is comprised of four parts namely a basilar part which I've highlighted in blue for you and two condylar parts which contain the occipital condyles that articulate with the first cervical vertebra of the spine. The rest of the occipital bone makes up the squamous part. The four parts of the occipital bone are all arranged around a large opening known as the foramen magnum through which the brainstem, the spinal branch of the accessory nerve, the anterior and posterior spinal arteries, the vertebral artery and the spinal vein all pass. And if you look at our image, you can see that I've outlined this opening for you in blue.

If we cut our skull down the midsagittal plane, we can see the ethmoid bone which is an unpaired bone of the neurocranium. This bone contributes to the formation of the orbit, the nasal cavity, the nasal septum and the floor of the anterior cranial fossa. The ethmoid bone is comprised of a perpendicular plate, two ethmoidal labyrinths which form the superior and middle nasal conchae, the ethmoidal bulla and the uncinate process, as well as the cribriform plate which is the horizontal plate you can see within the blue rectangle on your screen. The cribriform plate contains numerous foramina for the olfactory nerve.

The last bone of the neurocranium we're going to talk about is the sphenoid bone. If we look at the skull from the front, we can see how the anterior surface of the greater wing of the sphenoid bone helps to form part of the orbit. This bone is also known as the "wasp bone" and if we look at it in isolation from an anterior perspective, you can see why with its antenna-like structures and wings. Anyways, this insect-like bone is comprised of four main parts – the body which is essentially the head of our wasp, the lesser wings which are the antennae, the greater wings which are the wings and, finally, the pterygoid processes which are the legs. If we cut our skull down the midsagittal plane, we can see the sella turcica or "Turkish saddle" which is a saddle-shaped depression found on the body of the sphenoid bone. You can see it now contained within the blue circle on your screen and it houses the pituitary gland in the hypophyseal fossa of the sella turcica.

Now, we'll move on to look at the bones of the face or the viscerocranium. We'll start with the maxillae which we can now see highlighted in green. The maxillae is a paired bone consisting of a right and left maxilla, which fuse in the midline here at the intermaxillary suture. It's also known as the upper jaw, and it’s a vital structure of the viscerocranium. It’s involved in the formation of the bony orbit, as well as the nose and palate. This structure holds the upper maxillary teeth, so therefore plays an important role in mastication and communication.

Each maxilla is comprised of a body which is located centrally and is its largest part, a frontal process which articulates with the frontal bone – if you look at the image, you can see I've drawn dotted lines to show you where these articulations occur – and a zygomatic process which articulates with the zygomatic bone of the skull – I've labelled the right zygomatic bone for you in our image.

If we flip our skull to view it from below, we can see the palatine process which is a horizontal extension on the medial side of each maxillary bone and constitutes the roof of the mouth and the floor of the nasal cavity. The palatine process takes part in the formation of the hard palate articulating with the palatine bones. In this image, I've labeled the right palatine bone. Finally, there's the alveolar process which forms the maxillary dental arch that I've roughly drawn around for you in blue.

Next, we have the zygomatic bone which is an irregularly shaped bone found on either side of the viscerocranium as you can see in our image of the skull here. It consists of three processes which we can see better if we view the skull from the side. We can now see the left zygomatic bone highlighted in green. So each zygomatic bone consists of a frontal process which articulates with the frontal bone and forms the anterolateral wall of the orbit, a temporal process which articulates with the zygomatic process of the temporal bone to form the zygomatic arch, and finally, the maxillary process which articulates with the zygomatic process of the maxilla and also helps form part of the orbit. The zygomatic bones protrude laterally forming eminences on the face and it's for this reason that they're commonly known as the cheekbones.

The lacrimal bone is a small bone – the smallest bone of the skull, in fact – and it forms part of the medial wall of the bony orbit. This small paired rectangular-shaped bone also contributes to the lateral wall of the nasal cavity. On its lateral surface which we can see here, it features the lacrimal groove which, together with the lacrimal groove of the maxilla, forms the fossa for the lacrimal sac. At the center of the face, we find two small paired bones known as the nasal bones which form the bridge of the nose. The inferior portion of these two bilateral bones forms the superior margin of the nasal aperture which I've just drawn around for you in blue. Let's zoom in on these tiny bones so we can see them a bit better.

The nasal bones form articulations with the frontal bone, the frontal processes of the maxilla and the perpendicular plate of the ethmoid bone. Now, the mandible, also known as the lower jaw, is the only bone of the head that doesn't articulate with its adjacent bones via sutures. It has a distinctive horseshoe shape, is symmetrical on both sides, and can be divided into five parts. If we look at the mandible in isolation from an anterolateral perspective, we can see these parts a bit more clearly. So, first, we have the ramus of the mandible which includes the coronoid process – this triangular area highlighted in green – and the condylar process which includes the head of the mandible which articulates with the temporal bone of the skull. Next, we have the body of the mandible which includes the alveolar process that houses the lower dentition.

The mandible articulates with the temporal bone forming the temporomandibular joint which is now contained within the blue circle on your screen. The mandible is the movable part of the jaw and several muscles of mastication attach to it.

As we saw earlier, the superior and middle nasal conchae are formed from the ethmoidal labyrinths of the ethmoid bone. In contrast, the inferior nasal concha which is the most inferiorly situated of the three nasal conchae is a bony structure by itself. Located on either side of the nasal septum, the inferior nasal conchae articulate with the frontal processes of the maxilla, the perpendicular plate of the ethmoid bone, the lacrimal bones and the perpendicular plate of each palatine bone.

The palatine bone is an L-shaped bone that helps to form part of the nasal cavity and the hard palate. This paired bone is located between the maxilla and the sphenoid bone. The palatine bone consists of a horizontal plate which forms the posterior part of the hard palate as well as a perpendicular plate which is rectangular in shape and contributes to the lateral wall of the nasal cavity. It also forms part of the floor of the bony orbit and part of the wall of the pterygopalatine fossa.

The final bone of the head that we'll look at is the bone we can now see highlighted in green and that is the vomer. The vomer is a small plow-shaped bone that runs vertically within the nasal cavity. As we can see in this image, it forms the posterior inferior part of the nasal septum and it articulates with the maxilla, the palatine bone, the ethmoid bone and the sphenoid bone.

Finally, let's move on to look at the bones of the neck. The bones of the neck are basically made up of the cervical vertebrae and there are seven individual bones that make up the cervical part of the vertebral column. The first, second and seventh cervical vertebrae are unique in shape whereas the rest have a similar structure.

The first cervical vertebra C1, also known as the atlas, supports the skull and articulates with the occipital bones superiorly and the second cervical vertebra inferiorly. The first cervical vertebra doesn't have a body or a spinous process but rather has an anterior and a posterior arch. The second cervical vertebra C2, known as the axis, is also unique in comparison to the other cervical vertebrae. This vertebra has an odontoid process on its superior surface which is also referred to as the dens. The seventh cervical vertebra C7, also known as the vertebra prominens, is the only cervical vertebra whose spinous process is not bifid. It has a long prominent spinous process which protrudes from under the skin and is usually visible on the back of the neck with the naked eye as we can on our nice gentleman here.

The cervical vertebrae C3 to C6 all have a similar structure. They have small bodies, triangularly-shaped vertebral foramina, transverse processes each with a foramen transversarium, and short bifid spinous processes.

Now that we have an understanding of the bones of the head and neck, let's go over some relevant clinical notes. In today's clinical notes, we're going to talk about facial fractures, specifically, Le Fort fractures. There are three classifications of Le Fort fractures – type one which involves the separation of the alveolar part of the maxilla from the rest of the viscerocranium, type two which involves the separation of the mid-face from the rest of the viscerocranium and, finally, type three which involves the separation of the entire viscerocranium from the neurocranium. It's worth noting that this is not a black and white classification system and that there can be some overlap between fracture types.

Before we bring our tutorial to a close, let's quickly summarize what we talked about today.

So, first, we looked at the bones of the head starting with the bones of the neurocranium. First, we saw the frontal bone which is an unpaired bone followed by the temporal bone which is a paired bone then we had the paired parietal bones which are roughly square in shape. Next, we had the unpaired occipital bone which is found at the back of the skull followed by the ethmoid bone which transmits the olfactory nerve. Finally, we had the sphenoid bone which looks more like an insect than part of our anatomy.

We then moved on to the bones of the face or viscerocranium starting with the maxilla or the upper jaw. Next, we saw the zygomatic bones or the cheekbones followed by the tiny lacrimal bones. Up next were the nasal bones which form the bridge of the nose, the mandible or the lower jaw and the inferior nasal concha. We next had the palatine bone which forms part of the roof of the mouth and the vomer which forms the posterior inferior part of the nasal septum.

Thankfully, that brought as to the end of the bones of the head and allowed us to move on to the bones of the neck. First on our list was the atlas also known as C1 then the axis also known as C2 and the vertebra prominens or C7. We then talked about C3 to C6 which exhibit the typical characteristics of cervical vertebrae including a small body, a triangular vertebral foramen, a foramen transversarium in each transverse process and a bifid spinous process.

So that brings us to the end of our tutorial on the bones of the head and neck. I hope you found it useful and thanks for watching.

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