Anatomy of the Skull (Nursing)

by Darren Salmi, MD, MS

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    00:01 Now let's take a look at the anatomy of the head and neck. We'll start by looking at the bones of the skull.

    00:10 Anteriorly and superiorly we have a wide flat bone called the frontal bone.

    00:17 And then we have a small bone that makes up part of our nose just behind the cartilaginous part called the nasal bones.

    00:24 We also have the small bones called lacrimal bones and when you see the word lacrimal it usually means it has something to do with tears.

    00:33 We have an odd-shaped bone we can see just a little bit up here called the sphenoid bone.

    00:38 In the area of the cheekbones is what we would actually call the maxilla.

    00:44 There's also another bone in that area called the zygomatic bone.

    00:48 Our jaw bone we call the mandible.

    00:52 And we have a very irregular-shaped bone on the side of our head inferiorly called the temporal bone.

    00:58 And most posteriorly is a bone called the occipital.

    01:02 And then on both sides more superiorly we have the parietal bones.

    01:08 We have some interesting features that aren't exactly a bone per se but are features of these bones that are worth noting.

    01:14 One is something called the zygomatic arch which is this arch of bone that's actually composed of pieces of both the zygomatic bone and the temporal bone.

    01:24 And it's important when we talk about the jaw in chewing.

    01:28 We also have small projections of bones that are important landmarks because they're attachments for various muscles such as this pointing one here called the styloid process which is a part of the temporal bone and a more rounded process called the mastoid process, also a part of the temporal bone.

    01:46 We also have a little opening here in the temporal bone that's called the external acoustic meatus and that's the passageway for sound.

    01:55 If we zoom around to an anterior point of view, we can really see the frontal bone in its best view.

    02:02 We can also see the nasal bones a lot better here, a little bit of the lacrimal bones, and we can really see the maxilla and mandible.

    02:13 The zygomatic being more lateral, we see a little bit of a different view but we can still see a fair amount of it here.

    02:18 If we look into the orbit, we can see the sphenoid bone but really only a little bit of the temporal and parietal bones because they are more lateral.

    02:28 And if we really look through the nasal cavity, we can see some of the ethmoid and palatine bones but only a little tiny bit.

    02:38 The bones of the skull with the exception of the mandible, which we'll talk about separately later, don't form the types of joints you see elsewhere in the body that are very movable.

    02:47 Those very movable joints are called synovial joints. Here, the bones are formed by fibrous joints called sutures.

    02:56 And they're very strong and essentially immovable.

    03:01 The first major suture we're going to look at sits in the coronal plane and is therefore called the coronal suture.

    03:09 And we can see it's between the frontal and parietal bones.

    03:13 We also see the suture here laterally between the temporal bone and the parietal bones called the squamous suture and that name might not make sense except that that part of the temporal bone which is flat we call the squamous portion.

    03:27 Squamous means like scales, so whenever you see that means something flat.

    03:34 Posteriorly between the parietal and occipital bones, we have a suture called the lambdoid suture which again doesn't really make sense other than it vaguely resembles the shape of a lambda character.

    03:47 The sagittal suture on the other hand which sits between the 2 parietal bones does make a lot of sense because it actually sits in the sagittal plane.

    03:57 Where the coronal and sagittal sutures meet is a landmark called the bregma and where the lambdoid and sagittal sutures meet is a landmark called the lambda.

    04:06 And early in life, these were the sites of something called the fontanelles, the anterior and posterior fontanelles which are also sometimes called the soft spots on a baby's head.

    04:20 Now, there are other sutures that are smaller but can also be named by their location.

    04:26 So for example there is a small one between the sphenoid and frontal bones which we can just call sphenofrontal.

    04:32 Similar this small one between sphenoid and parietal, we can just call the sphenoparietal.

    04:38 And again, if we remember that the flat part of the temporal bone is called squamous, then sphenosquamous tells us that we're between the temporal and sphenoid bone.

    04:48 Similarly, if we remember that the mastoid process is a part of the temporal bone, we have the parietal mastoid and occipital mastoid sutures as well.

    04:59 Now let's look at the inside of the skull by taking off the top parts of the bone and looking down into what we call the cranial cavity where the brain sits.

    05:11 First, we see the frontal bone anteriorly with a little gap in the middle for another bone called the ethmoid bone.

    05:19 And this little ethmoid bone has a vertical projection called the crista galli that serves as an attachment for the dura.

    05:27 Moving a little bit more posteriorly, we see these small projections of the sphenoid bone called the lesser wings.

    05:35 And then some larger ones called the greater wings. In the middle of the sphenoid bone is a little depression here that we call the sella turcica and that's the little groove in which the pituitary gland is going to sit.

    05:51 Again, moving back a little bit more we see the temporal bone and in particular we see another ridge here and we call that the petrous portion of the temporal bone.

    06:02 And these ridges naturally create little depressions or fossa that we call the cranial fossa.

    06:09 So, all the way back to the lesser wings, we have the anterior fossa and then between them in the petrous portion of the temporal bone is the middle fossa.

    06:20 And then everything behind that is going to be the posterior fossa.

    06:25 And if we're looking closely, you might see a lot of holes but we're going to point out some of the important ones because whenever we see these holes, important structures tend to pass through them.

    06:39 So the first thing we'll look at is that ethmoid bone again and it's actually got tiny tiny holes in it and therefore is called cribriform plate, it means something that has a lot of little holes in it.

    06:52 And all of those little holes are the passageways for the olfactory nerve or cranial nerve I.

    07:00 If we move back to the sphenoid bone, we see these little holes here or foramina and these are the optic canals.

    07:07 And as the name implies, that's a passageway for the optic nerves or cranial nerve II.

    07:14 Then there's a wider opening called a fissure, here we call it the superior orbital fissure.

    07:20 And these are the nerves that are going to control the extraocular muscles.

    07:24 And those were cranial nerves III, IV, and VI.

    07:28 And we also have the passageway for one of the branches of the trigeminal nerve.

    07:35 A little further back, we have this opening here on the petrous portion of the temporal bone called the internal acoustic meatus.

    07:42 We saw the external, now we see the internal and we see that that's the passageway for cranial nerves such as the facial and vestibular cochlear or cranial nerve VII and VIII.

    07:53 And finally, the largest hole back here is the foramen magnum and that is where the brain is going to give yield to the spinal cord as it exits out into the vertebral column.

    About the Lecture

    The lecture Anatomy of the Skull (Nursing) by Darren Salmi, MD, MS is from the course Anatomy of the Musculoskeletal System (Nursing).

    Included Quiz Questions

    1. Parietal
    2. Occipital
    3. Frontal
    4. Temporal
    5. None of the above
    1. Coronal
    2. Squamous
    3. Lambdoid
    4. Ethmoid
    5. Occipital
    1. Ethmoid
    2. Frontal
    3. Sphenoid
    4. Nasal
    5. Temporal
    1. CN I
    2. CN II
    3. CN III
    4. CN IV
    5. CN V

    Author of lecture Anatomy of the Skull (Nursing)

     Darren Salmi, MD, MS

    Darren Salmi, MD, MS

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