Prelab Images - Scalp, Cranial Cavity, Meninges & Brain

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

1. Review the osteology of the skull. (Play movie)

Plate N7, TG7-05 identifies the calvaria of the skull and plates N8, N9, N11, TG7-06, TG7-07 show the base of the skull from different angles. The anterior, middle, and posterior cranial fossae are identified in plate N9, TG7-07. Plates N6, TG7-08, N9, TG7-07 label the crista galli, greater and lesser wings of the sphenoid bone, and sella turcica. Plate N9, TG7-07 shows the clivus, petrous ridge of temporal bone (labeled petrous part), and the internal occipital protuberance. Plates N6, TG7-08, N8, TG7-06, and N11, TG7-07 label the foramen magnum. Plates N6, TG7-08, N9, TG7-07 idenitfy the cribriform plate of the ethmoid bone. Plate N2, TG7-57, N11, TG7-07 give views of the optic canal and superior orbital fissure. Plate N11, TG7-07 labels all of the following: foramen rotundum, foramen ovale, foramen spinosum, foramen lacerum, internal acoustic meatus, jugular foramen, hypoglossal canal, and the foramina of condyloid and mastoid emissary veins (labeled mastoid foramen and condylar canal). Plates N6, TG7-08, N7, TG7-05, N8, TG7-06, N9, TG7-07, and N11, TG7-07 review the base of the skull and interior of calvaria.

Step 2. Identify the major features of the brain and its ventricular system. (Play movie)

The frontal, parietal, occipital, and temporal lobes of the cerebrum are identified in plate N105, TG7-53. The longitudinal fissure is identified in plate N107, TG7-54. This fissure divides the cerebrum into right and left halves (plate N99, TG7-49). Plate N115, TG7-53 shows the cerebellum, midbrain, pons, and medulla oblongata. The midbrain is not labeled, but it is the part of the brain with the cerebral aqueduct passing through it in plate N115, TG7-53. Plate N108, TG7-50 identifies the lateral veintricles, interventricular foramina, third ventricle, cerebral aqueduct, and fourth ventricle. The choroid plexus is also identified in plate N109, TG7-50. The CSF is reabsorbed into the venous system into the superior sagittal sinus via arachnoid granulations (also shown in N109, TG7-50).

Step 3. On the right side, remove the brain. (Play movie)

Plates N101, N99, TG7-49 shows the layers of the scalp (remember SCALP - Skin, dense subcutaneous Connective tissue, Aponeurotic layer composed of galea aponeurotica and epicranius muscles, Loose connective tissue, and Pericranium). The scalp itself consists of the first three layers. See plate N26, TG7-30 for the epicranius (occipitalis and frontalis) muscle.

Other than observing and identifying structures, the dissection procedure involves removal of the brain. This can be accomplished by taking a scalpel and cutting around the head just above the brow ridge. Next, take a saw and saw through the bone that is deep to the cut that you just made to remove the top of the skull. Plate N101, TG7-46 shows what it will look like once you have removed the top of the skull. Plates N99, TG7-49, N101, TG7-46 show superior cerebral veins draining the cerebral cortex. The superior cerebral veins drain the blood into the superior sagittal sinus (midline structure seen in plates N99, TG7-49, 101). To remove the right half of the brain you will need to lift it up and cut through the cranial nerves emerging from the brainstem on the inferior side of the brain (plate N113, TG7-55). See plate N11, TG7-07 for where these cranial nerves exit the skull. Next, you will need to cut through the carotid artery, vertebral artery, and spinal cord to remove the brain (see plate N132, TG7-56).

Step 4. Identify the cranial nerves within the cranial cavity. (Play movie)

Plates N114, TG7-55, N118 show where the twelve cranial nerves emerge from the brainstem. Plate N115, TG7-55 also shows the trochlear nerve, the only cranial nerve emerging from the posterior side of the brainstem. Plate N11, TG7-07 shows where each cranial nerve leaves the cranium. Plate N104, TG7-47 shows a view similar to the one you may have in lab after removing the brain. Plate N11, TG7-07 and plate N104, TG7-47 both indicate that the glossopharyngeal, vagus, and accessory cranial nerves exit the skull through the jugular foramen. Plate N126 shows a schema of the accessory nerve receiving fibers from the cervical spinal cord. You can see these fibers traveling near the vertebral artery in plate N104, TG7-47 (the vertebal artery is not labeled, but it is the artery that is deep to the vein labeled great cerebral vein).

Step 5. Identify the features of the cranial cavity and meninges. Open the dural sinuses. (Play movie)

Plates N99, TG7-49, N101 show the arachnoid matter and the trabeculae (not labeled) attaching the arachnoid mater to the pia mater. Plate N108, TG7-50 shows the subarachnoid space, and the cerebellomedullary, pontine, and interpeduncular cisterns. Plates N99, TG7-49, N101 label arachnoid granulations (villi) poking into the superior sagittal sinus. Plates N99, TG7-49, N101 both show the dura mater of the skull and its arrangement. Plate N109, TG7-50 also shows the dura mater of the skull and the dura of the spinal cord. Plate N102, TG7-49 labels the falx cerebelli and falx cerebri. Plate N104, TG7-47 labels the tentorum cerebelli. Plate N104, TG7-47 shows the hypophysis (pituitary gland). The stalk of the hypophysis pierces the diaphragma sellae (not labeled). The falx cerebelli, falx cerebri, tentorum cerebelli and diaphragma sellae are all formed by meningeal infoldings. The tentorial notch (not labeled, but can be seen in plate N104, TG7-47) is the large opening in the tentorum cerebelli that allows the brain stem to pass through. The middle meningeal artery is the largest of the meningeal arteries. This artery is a branch of the maxillary artery (N69, TG7-19) and can be seen in plates N98, TG7-35, N99 and TG7-51. Comparing plates N9, TG7-07 and N104, TG7-51 shows that the middle meningeal artery runs right over the greater wing of the sphenoid bone. The innervation of the dura is covered in the dissector answers. Plate N103, TG7-49 shows the superior sagittal sinus. Plates N99, TG7-49, N101 identify lateral lacunae, arachnoid granulations, and superior cerebral veins. Plate N103, TG7-49 shows the inferior sagittal sinus and the great cerebral vein coming together to form the straight sinus. The straight sinus unites with the occipital sinus and superior sagittal sinus at the confluens of sinuses (N103, TG7-49). The blood from the confluens of sinus enters the transverse sinus (N103, TG7-47). The transverse sinus receives inferior cerebral veins (seen in plate N102, TG7-46). Plate N103, TG7-47, TG7-48 shows the transverse sinus and greater petrosal sinus uniting to form the sigmoid sinus. Plate N103, TG7-47, TG7-48 shows the sigmoid sinus receiving the lesser petrosal sinus just before passing through the jugular foramen to become the internal jugular vein. Plate N104, TG7-47 shows the ophthalmic vein and middle cerebral vein coming together to from the cavernous sinus. Several important structures pass through the cavernous sinus and will be discussed soon (plate N104, , TG7-47, TG7-60). Plate N98, TG7-73 shows some of the emissary veins (veins that connect scalp or face with dural sinuses). Plate N70 shows the superior ophthalmic vein which also acts as an emissary vein. Plate N104, , , TG7-47, TG7-60 shows the oculomotor nerve (III), trochlear nerve (IV), trigeminal nerve (V), abducens nerve (VI), and internal carotid artery as they pass through the cavernous sinus. Plate N104, TG7-47 shows the location of the pituitary gland, which you are to remove. Plate N147 shows the pituitary gland with its anterior (pink colored in plate N147) and posterior lobes and stalk (infundibulum). Plate N104, TG7-51 shows the middle meningeal artery coming through the foramen spinosum (foramen spinosum labeled in plate N11 TG7-07).

Step 6. Identify the blood supply to the brain on the sectioned and plastinated brains. (Play movie)

The vertebral artery is shown in plate N136, TG7-19. The two vertebral arteries (see N138, TG7-56) each give off a posterior inferior cerebellar artery (which in turn gives off posterior spinal artery branches) and a contribution to the anterior spinal artery before the vertebral arteries unite to form the basilar artery. The basilar artery gives off anterior inferior cerebellar and superior cerebellar before the basilar artery splits into two posterior cerebral arteries. The internal carotid artery sends a posterior communicating artery to the posterior cerebral artery (N138, TG7-56). The internal carotid also has middle cerebral and anterior cerebral branches (N138, TG7-56). The two anterior cerebral branches are connected together by the anterior communicating artery. This forms the circle of Willis (N139, TG7-56). Plates N140, TG7-56, N141, and N142 show the distribution of the arteries of the brain (you do not have to know them in too much detail). Plate N137 shows a schema of the blood supply to the brain, which may be helpful. Plate N101, TG7-46 shows the veins of the cerebral hemisphere. Plate N104, TG7-47 also shows the carotid artery as it pierces the dura.