Lab Manual - Scalp, Cranial Cavity, Meninges & Brain

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Define the scalp, its structural layers, muscles, nerves, and vessels. (explanation)
  2. Identify the prominent landmarks on the internal surface of the skull base. (explanation)
  3. Identify the major blood vessels of the brain, the specializations of cranial meninges, and cranial dural modifications. (explanation)
  4. Identify the cranial nerves on the brain and their courses through the skull base.(explanation)
  5. Identify the parts of the ventricular system and trace the flow of cerebrospinal fluid from production to reabsorption. (explanation)

Readings and Modules:

Procedure:

1. Review the osteology of the skull. (Play movie; View images: N 2, 6, 7A, 7B, 8, 9, 11, TG 7-05B, 7-05C, 7-06, 7-07, 7-08, 7-57)

Distinguish between the calvaria and the base of skull. Identify the anterior, middle, and posterior cranial fossae, crista galli, greater and lesser wings of sphenoid, sella turcica, clivus, petrous ridge of temporal bone, internal occipital protuberance, and foramen magnum.

Find the following openings: cribriform plate of ethmoid, optic canal, superior orbital fissure; foramen rotundum, f. ovale, f. spinosum, f. lacerum; internal acoustic meatus, jugular foramen, hypoglossal canal; foramina of condyloid and mastoid emissary veins. Examine the base of the skull and the interior of the calvaria for sulci or grooves produced by various sinuses and arteries.

2. Identify the major features of the brain and its ventricular system. (Play movie; View images: N 99, 105, 107, 108, 109, 115, TG 7-49, 7-50A, 7-50B, 7-53B, 7-53C, 7-54)

Identify the frontal, parietal, occipital and temporal lobes of the cerebrum, and the longitudinal fissure. On the inferior side find the cerebellum, midbrain, pons and medulla oblongata. Compare the brain to the cranial fossae, note how the lobes fit in the fossae and relate to the dural folds.

Brain structures in MRI

On the sectioned brains and plastinated sections of brains provided in the labs, note the cavities of the brain, the ventricles, identifying the lateral ventricles, interventricular foramina, third ventricle, cerebral aqueduct and fourth ventricle. Note the choroid plexus; where is it found and what is its function? Can you trace the flow of cerebrospinal fluid (CSF) from its secretion until it is reabsorbed by the venous system? See Objective 5

Ventricles of the brain

3. On the right side, remove the brain. (Play movie; View images: N 11, 26, 99, 101A, 101B, 113, 132, TG 7-07, 7-30, 7-46, 7-49, 7-55, 7-56)

Five layers of tissue cover the bones of the calvaria: (1) Skin, (2) dense subcutaneous Connective tissue, (3) an Aponeurotic layer, the galea aponeurotica with epicranius muscles (occipitalis and frontalis), (4) Loose connective tissue that allows the skin and galea to move, and (5) Pericranium, the periosteum of the skull (S-C-A-L-P). The scalp itself consists of the first three layers. It will not be dissected, but try to identify the layers on its cut edge. The spread of infection is mainly facilitated through what layer of the scalp?

On the right side, remove the scalp by cutting around the head on a line from above the browridge to the external occipital protuberance. Use the small saw to carefully cut through and remove the calvaria.

On the medial cut surfaces of the brain, identify superior cerebral veins draining the cerebral cortex into the superior sagittal sinus.

Identify and cut the cranial nerves as they enter the skull. Cut the internal carotid artery near the optic nerve. Cut the spinal cord and vertebral artery just below the foramen magnum. Remove the right half of the brain intact.

4. Identify the cranial nerves within the cranial cavity. (Play movie; View images: N 11, 104, 114, 115, 118, 126, TG 7-07, 7-47, 7-55A, 7-55B)

On the brain, identify the twelve pairs of cranial nerves: olfactory (I), optic (II), oculomotor (III), trochlear (IV), trigeminal (V), abducens (VI), facial (VII), vestibulocochlear (VIII), glossopharyngeal (IX), vagus (X), spinal accessory (XI), hypoglossal (XII). Identify these nerves at their exit foramina on the base of the skull. What cranial nerves exit the skull through the jugular foramen? Identify cervical fibers of the accessory nerve. Identify the internal carotid artery as it perforates the dura and the vertebral arteries in the foramen magnum.

5. Identify the features of the cranial cavity and meninges. Open the dural sinuses. (Play movie; View images: N 9, 11, 69, 70, 98, 99A, 99B, 101, 102, 103, 104A, TG 104B, 108, 109, 147, 7-07, 7-19, 7-35, 7-46, 7-47, 7-48, 7-49A, 7-49B, 7-50, 7-51, 7-73)

On the right half brain that was removed and plastinated brains in the labs, examine the arachnoid mater, its extent and attachment to the pia mater (via trabeculae). Consider the subarachnoid space, continuities and content. Enlargements of the subarachnoid space at the base of the brain constitute cisterns. Consider the function of cerebellomedullary, pontine and interpeduncular cisterns. Look for arachnoid granulations (villi). What is their function? Note their impressions on the overlying calvaria. Examine the pia mater on the brain. How does it differ from the arachnoid mater in covering the brain?

Subarachnoid space

On both halves of the head, observe the arrangement of the cranial dura mater. Note differences from spinal dura, continuities and layers. Note dural attachment to the calvaria and the base of the skull. Is there any difference? Examine falx cerebri and falx cerebelli (on the left side), tentorium cerebelli, and diaphragma sellae. Are these infoldings periosteal or meningeal? Define attachments and relationship of each and the compartmentalization of the cranial cavity produced by these infoldings. What does each compartment contain? What is the tentorial notch? Observe meningeal arteries in all cranial fossae. Which is the largest? How is it held within the dura? Relation to greater wing of sphenoid? (Significance?) What is the innervation of dura?

Open each of the following venous sinuses by removing part of its wall; remove the coagulated blood and trace completely: superior sagittal sinus, (lacunae, areas of arachnoid granulations, entrance of superior cerebral veins), inferior sagittal sinus, sinus rectus (straight sinus) (is a portion of the great cerebral vein attached to it?), confluens of sinuses (significance, location, pattern and variations), occipital sinus, transverse sinus (inferior cerebral veins), sigmoid sinus, cavernous sinus (ophthalmic vein, middle cerebral veins), superior petrosal sinus (connects what?), inferior petrosal sinus. Define emissary veins and the mastoid, condyloid, parietal, and ophthalmic emissary veins.

Identify the cavernous sinus on either side of the body of the sphenoid bone. Do the two sides communicate? As they enter the lateral wall of the cavernous sinus, locate the oculomotor nerve (III), trochlear nerve (IV), and the trigeminal nerve (V). Identify the severed end of the internal carotid artery (course? ). Identify the abducens nerve (VI) as it pierces the dura covering the inferior petrosal sinus. Enlarge the opening in the diaphragma sellae and remove the hypophysis (pituitary gland). Determine anterior and posterior lobes and stalk. Locate the middle meningeal artery beneath the dura of the middle cranial fossa, noting its position in the dura and its course and entrance through the foramen spinosum.

6. Identify the blood supply to the brain on the sectioned and plastinated brains. (Play movie; View images: N 101, 104, 136, 137, 138, 139, 140, 141, 142, TG 7-19, 7-46, 7-47, 7-56A, 7-56B)

Identify the arterial system at the base of the brain: vertebral, anterior and posterior spinal, posterior inferior cerebellar, basilar, anterior inferior cerebellar, superior cerebellar, posterior cerebral, posterior communicating, middle cerebral, anterior cerebral, anterior communicating, and internal carotid. What is the arterial circle of Willis? Consider the broad distribution of each to the brain. Note veins of the cerebral hemispheres.

Blood vessels of the brain
Vertebral arteries