Cranial Cavity

by Darren Salmi, MD, MS

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    00:01 Now we're going to take a look inside the skull at the space called the cranial cavity.

    00:08 Here's a superior view with some of those skull bones removed to give us a view of the cavity.

    00:15 Here we see the frontal bone.

    00:17 And again, in that middle portion, we have a gap for the ethmoid bone with its vertically oriented plate, the crista gali.

    00:25 And then moving posteriorly, we have the lesser wing of the sphenoid followed by the larger greater wing of the sphenoid.

    00:34 More centrally, we have the sella turcica, which is that little groove for the pituitary gland.

    00:40 As we move backwards, we still have the temporal bone with a groove here internally called the petrous portion of the temporal bone.

    00:50 And then these landmarks give us three separate cavities or spaces that we call fossa.

    00:58 Anteriorly, in front of the lesser wing, we have the anterior fossa.

    01:03 Behind them, and in front of the petrous portion of the temporal bone, we have the middle fossa, and then posterior to that petrous portion of the temporal bone, we have the posterior fossa.

    01:15 We also have a lot of holes or foramina in the skull through which a lot of important structures are going to pass.

    01:22 Working our way from anterior to posterior, we see the cribriform plate of the ethmoid bone.

    01:30 In the sphenoid bone, we have a little opening called the optic canal sitting right here at the posterior aspect of the lesser wings.

    01:39 And then just underneath these lesser wings, we have the superior orbital fissure.

    01:46 Followed by that we have a round opening called the foramen rotundem, which is followed by a more oval opening called the foramen ovale.

    01:56 And then a smaller one called the foramen spinosum.

    02:02 There's a more linear shaped one called the foramen lacerum.

    02:07 One in the petrous portion of the temporal bone called the internal acoustic meatus.

    02:13 And then as we're moving more inferiorly, we have the jugular foramen, and hypoglossal canal.

    02:21 And then finally the largest one where the spinal cord is going to connect, the foramen magnum.

    02:28 So let's look at some of the nerves that travel through these foramena.

    02:32 Going back to that cribriform plate, the cribriform plate is where many, many, many tiny olfactory nerves are going to pass from the nasal cavity through the bone and into the cranial cavity.

    02:47 And so those are collectively going to be our cranial nerve one or olfactory nerve.

    02:53 The optic canals are going to hold the optic nerves or cranial nerve II.

    03:00 The superior orbital fissure being a larger opening is going to have a lot of things going through there.

    03:07 It's going to be the oculomotor nerve or cranial nerve III, trochlear or cranial nerve IV, the abducens nerve or cranial nerve VI, as well as the ophthalmic division of the trigeminal nerve or cranial nerve V1.

    03:25 Next, the foramen rotundum has the other branch of the trigeminal, the maxillary nerve and foramen ovale has the third branch, the mandibular nerve or cranial nerve V3.

    03:40 Working our way posteriorly, we then have the internal acoustic meatus in the petrous portion of the temporal bone where we have cranial nerve VII or the facial nerve and the vestibulocochlear nerve cranial nerve VIII.

    03:54 Next with the jugular foramen, we have cranial nerve IX glossopharyngeal, cranial nerve X, vagus, and cranial nerve XI, the accessory nerve, which is the weird cranial nerve in the sense that it's actually coming up from the spinal cord but yet still exiting the skull via this foramen.

    04:15 Then we have the hypoglossal canal, which is where we find the hypoglossal nerve or cranial nerve XII.

    04:25 We also have some vessels that travel through some of these foramena.

    04:30 Here we see the foramen lacerum.

    04:33 And we see in this area emerging the internal carotid artery, it's actually emerging from the carotid canal.

    04:41 It's a bit complicated, but in this area of the foramen lacerum is where we're going to see the internal carotid artery enter the cranial cavity.

    04:51 We also have the smaller foramen, the foramen and spinosum and that's where we're going to have the middle meningeal artery, a branch of the mouth axillary artery that's going up to supply that portion of the meninges.

    05:06 The foramen magnum is where the vertebral arteries are going to come up from the neck and eventually merged to form the basilar artery.

    05:17 And the jugular foramen was where we're going to see the sigmoid sinus, draining much of the dural venous sinuses of the meninges.

    05:29 If we swing around to an inferior point of view, we can see some familiar features such as the zygomatic arch, the styloid process, followed by the mastoid process more posteriorly.

    05:44 And the occipital condyles, which rests on top of Atlas or C1.

    05:50 We also see in the hard palate, a little opening here called the incisive foramen.

    05:57 And that's where we're going to have the nasal palatine nerve, a branch of the maxillary division of trigeminal or cranial nerve V2.

    06:06 There's also the greater palatine foramen for the greater palatine nerve, and the lesser palatine foramen for the lesser palatine nerve.

    06:16 Also branches of cranial nerve V2.

    06:20 We see the foramen and ovale here, where the mandibular nerve or the third branch of trigeminal.

    06:28 The foramen spinosum, again, where the middle meningeal artery will enter after it's branched off of the maxillary artery, the foramen lacerum, which is actually not receiving the internal carotid, but actually the carotid canal, which is where the internal carotid is entering.

    06:47 If we zoom in a little bit more, we see the stylohyoid mastoid foramen between the styloid process and the mastoid process.

    06:55 That's where the facial nerve or cranial nerve VII is going to emerge.

    06:59 We see the jugular foramen, which again has cranial nerves IX, X and XI.

    07:05 The hypoglossal canal, which again has the hypoglossal nerve or cranial nerve XII.

    07:10 So to explain that a little weird thing about the foramen lacerum and the internal carotid, here's sort of a diagrammatic representation of what's happening as the internal carotid is entering the cranial cavity.

    07:23 So the foramen lacerum inferiorly is actually covered by a little fibrocartilaginous plug, and nothing is actually passing through the foramen lacerum.

    07:32 Instead, the internal carotid artery is passing through the carotid canal, and really emerging above this plug of fibrocartilaginous tissue that seals off the foramen lacerum.

    07:46 So it doesn't actually pass through it, but it does kind of pass over it on its way into the cranial cavity.

    07:52 From an anterior point of view, we can see a few more foramina starting with one that sits just on the superior aspect of the orbit called the supraorbital foramen.

    08:04 Sometimes it's not a complete hole, rather, it's just a notch, in which case we would call it the super orbital notch.

    08:11 But whether it's foramen or notch, that's where we're going to find the super orbital artery and nerve.

    08:18 We also have a small foramen called the zygomaticoficial foramen, which is where we're going to have the appropriately named zygomatic facial nerve.

    08:30 Just below the orbit, we're going to have the infraorbital foramen, and this is where we're going to find the infra orbital artery and nerve.

    08:40 Then finally, we have the mental foramen on the mandible.

    08:44 And this is where we're going to have the mental nerve, which is really just a continuation of the inferior alveolar nerve that's passing through the mandibular canal.

    About the Lecture

    The lecture Cranial Cavity by Darren Salmi, MD, MS is from the course Skull.

    Included Quiz Questions

    1. Sella turcica
    2. Frontal bone
    3. Ethmoid bone
    4. Greater wing
    5. Lesser wing
    1. Foramen magnum
    2. Superior orbital fissure
    3. Optic canal
    4. Internal acoustic meatus
    5. Foramen spinosum
    1. Maxillary nerve
    2. Mandibular nerve
    3. Trochlear nerve
    4. Ophthalmic nerve
    5. Abducens nerve
    1. Vertebral artery
    2. Basilar artery
    3. Middle meningeal artery
    4. Internal carotid artery
    5. External carotid artery

    Author of lecture Cranial Cavity

     Darren Salmi, MD, MS

    Darren Salmi, MD, MS

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