Cranial Cavity

In many anatomy labs, the brain has been removed so that it can be used by the Neuroscience course. Whether this is true in your case or not, when the calvaria (cranial cap) is removed to expose the cranial cavity, the first structure you see is the fibrous side of the dura mater. This layer was fused to the endosteum covering the inner surfaces of the bones of the skull.
The dura mater has two layers: 1) fibrous outer layer and 2) smooth meningeal inner layer.

Examine the calvaria and note that it varies in thickness in different places. Note also that it is made up of two laminae of compact bone separated by a layer of spongy bone. The spongy bone is called the diploie. Veins run through the diploie and are called diploic veins. Notice the grooves on the inside of the calvaria that have been produced by arachnoid granulations, arteries and venous sinuses. Items to identify in calvaria:
  • 1 grooves formed by arteries
  • 2 arachnoid granulations
  • 3 groove formed by venous sinus
  • 4 diploie (difficult to see on diagram)

Bones and parts of bones of the cranial cavity

  1. frontal bone
  2. crista galli (ethmoid)
  3. body of sphenoid
  4. lesser wing of sphenoid
  5. hypophyseal fossa
  6. dorsum sellae of sphenoid
  7. greater wing of sphenoid
  8. squamous part of temporal
  9. petrous part of temporal
  10. occipital bone
  11. parietal bone
As with the spinal cord, there are three meningeal layers covering the brain: 1) dura, 2) arachnoid and 3) pia, from external to internal. The pia is inseparable from the surface of the brain itself. The arachnoid is normally in touch with the meningeal layer of dura and is connected by many connective trabeculae to the pia. The space between the pia and arachnoid is the subarachnoid space within which the cerebrospinal fluid (CSF) is located. A space may be formed external to the dura, following trauma to the skull. This space is the extradural space. Another potential space can be formed by fluid or blood, and this is the subdural space. So, when examining the skull after trauma, there are three places fluid may collect: 1) extradural, 2) subdural and 3) subarachnoid. The prognosis of the traumatic patient depends on which of these layers is affected.

Another bit of information about the dura. In certain areas, the meningeal layer of the dura splits away from the fibrous layer forming intracranial venous sinuses. When the meningeal layer pulls away, double layers of dura extend into the cranial cavity separating the left and right cerebral hemispheres from one another forming the falx cerebri. Another double layer of meningeal dura is formed between the occipital pole of the brain and the cerebellum and is called the tentorium cerebelli. Now you are ready to identify these various structures within the cranial cavity.

First, identify the various parts of the dura shown below.

Parts of the dura:
  • falx cerebri (1)
  • tentorium cerebelli (2)
  • falx cerebelli (6)
Superior view

Sagittal view

Look for and name the venous sinuses. The superior sagittal sinus is located in the attached margin of the falx cerebri. The inferior sagittal sinus is located in the free margin of the falx cerebri. The transverse sinus is in the attached border of the tentorium cerebelli. The superior petrosal sinus is in the attached margin of the tentorium cerebelli where it attaches to the upper border of the petrous temporal bone.
Cranial intravenous sinuses:

1 sphenoparietal
2 cavernous
3 inferior petrosal
4 transverse
5 sigmoid
6 superior petrosal >br> 7 straight
8 superior sagittal
It might be useful at some point in your education to understand the relationship of the cranial cavity to the base of the brain. This is shown, color coded, in the following images.

Compare the base of the brain with the skull adjacent to it and you can see which parts of the brain are associated with which bones of the skull.
1 frontal
2 ethmoid
3 sphenoid
4 temporal
5 parietal
6 occipital

The images below demonstrate how the cranial nerves appear with the dura intact and then the foramina that the nerves pass through to leave the cranial cavity.


Memorize the cranial nerves;
I Olfactory (cribriform plate)(special sensory)
II Optic (optic foramen)(special sensory)
III Oculomotor (superior orbital fissure)(motor and autonomic)
IV Trochlear (superior orbital fissure)(motor)
V Trigeminal (motor & general sensory)

V1 (superior orbital fissure)(general sensory)

V2 (foramen rotundum)(general sensory)

V3 (foramen ovale)(general sensory and motor)
VI Abducens (motor)
VII Facial (motor, special sensory, and autonomic)
VIII Vestibulocochlear (special sensory)
IX Glossopharyngeal (motor, special & general sensory and autonomic)
X Vagus (motor, general & special sensory and autonomic)
XI Spinal accessory (motor)
XII Hypoglossal (motor)

This diagram points out the structures found within the cavernous sinus and within its walls

In the walls:

  • 1 oculomotor
  • 2 trochlear
  • 4 V1
  • 5 V2
Within:
  • 3 abducens
  • 6 autonomic plexus
  • 7 internal carotid artery
8 pituitary gland
9 body of sphenoid bone

List of Items to be able to identify for this lesson

Calvaria

compact bone
spongy bone
diploie
arachnoid granulations
sulcus for superior sagittal sinus

Bones forming floor and sides of cranial cavity

frontal
ethmoid
sphenoid
lesser wing
anterior clinoid processes
body
hypophyseal fossa
dorsum sellae
greater wings of sphenoid
temporal
squamous part
petrous part
parietal
occipital

Parts of dura mater

falx cerebri
falx cerebelli
tentorium cerebelli
diaphragma selli

Venous sinuses

superior sagittal
inferior sagittal
straight
sphenoparietal
superior petrosal
inferior petrosal
transverse
sigmoid
cavernous

Cranial nerves and foramen of exit from cranial cavity

I olfactory cribriform plate of
ethmoid
II optic optic foramen
III oculomotor superior orbital
fissure
IV trochlear superior orbital
fissure
V trigeminal
V1 ophthalmic division
superior orbital fissure
V2 maxillary division foramen
rotundum
V3 mandibular division
foramen ovale
VI abducens superior orbital
fissure
VII facial internal auditory (or
acoustic) meatus
VIII vestibulocochlear internal
auditory (or acoustic) meatus
IX glossopharyngeal jugular
foramen
X vagus jugular foramen
XI spinal accessory foramen
magnum and jugular foramen
XII hypoglossal hypoglossal
foramen

Cavernous Sinus

Structures in the wall:
oculomotor nerve
trochlear nerve
ophthalmic division of
trigeminal nerve
maxillary division of trigeminal
nerve (sometimes)

Structures within the sinus:
abducens nerve
internal carotid artery
carotid sympathetic plexus

Skull, Scalp & Superficial Face   Orbit and Ear


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