interior of the skull

• The interior of the skull is protected by the meninges which are three layers: the dura mater, arachnoid mater, and pia mater.
• The dura mater consists of two layers: the periosteum (endosteum) covering the inner surface of the skull bones and the meningeal layer, a dense, strong, fibrous membrane covering the brain.
• The pia mater is continuous with the dura mater of the spinal cord and provides tubular sheaths for the cranial nerves.
• The falx cerebri is a large, sickle-shaped fold of dura mater that lies in the midline between the two cerebral hemispheres, with a narrow anterior end that attaches to the internal frontal crest and the crista galli, and a broad posterior part that blends in the midline with the upper surface of the tentorium cerebellum.
• Subdural hemorrhage results from the tearing of the superior cerebral veins at their point of entrance into the superior sagittal sinus.
• Cerebral hemorrhage is the rupture of the thin wall lenticulostriate artery, a branch of the middle cerebral artery.
• Intracranial hemorrhage in the infant may occur during birth and may result from excessive molding of the head.
• Subarachnoid hemorrhage results from leakage or rupture of a congenital aneurysm on the cerebral arterial circle (of Willis) or, less commonly, from an angioma.
• The cause of subdural hemorrhage is usually a blow on the front or the back of the head.
• The falx cerebelli is a small, midline, sickle-shaped fold of dura mater that attaches to the internal occipital crest and projects forward between the two cerebellar hemispheres, with its posterior fixed margin containing the occipital sinus.
• The tentorium cerebelli is a crescent-shaped fold of dura mater that roofs over the posterior cranial fossa, covers the upper surface of the cerebellum and supports the occipital lobes of the cerebral hemispheres.
• The tentorial notch is an anterior gap that allows for the passage of the midbrain, producing an inner free border and outer attached or fixed border.
• The fixed border of the tentorium cerebelli attaches to the posterior clinoid processes, superior borders of the petrous bones, and the margins of the grooves for the transverse sinuses on the occipital bone.
• The free border of the tentorium cerebelli runs forward at its two ends, crosses the attached border, and fixes to the anterior clinoid process on each side.
• The falx cerebri and the falx cerebell i attach to the upper and lower surfaces of the tentorium, respectively.
• The diathragma sellae is a small circular fold of dura mater that forms the roof for the sella turcica, with a small opening in its center that allows passage of the stalk of the pituitary gland.
• Three pairs of cerebral arteries branch off the circle and supply the cerebrum.
• The largest mass of gray matter in the cerebellum is the dentate nucleus.
• The cerebellum plays an important role in the control of muscle tone and the coordination of muscle movement on the same side of the body.
• The ventricles of the hindbrain, the two lateral ventricles and the third ventricle, communicate with the fourth ventricle through the interventricular foramen.
• The veins of the brain have no muscular tissue in their thin walls, and they possess no valves.
• The great cerebral vein is formed by the union of the two internal cerebral veins and drains into the straight sinus.
• Intracranial hemorrhage can result from trauma or cerebral vascular lesions.
• The cavity of the hindbrain is the fourth ventricle, bounded in front by the pons and the medulla oblongata and behind by the superior and inferior medullary veins and the cerebellum.
• The blood supply of the brain is provided by two internal carotid and the two vertebral arteries, which anastomose on the inferior surface of the brain and form the cerebral arterial circle (circle of Willis; circulus arteriosus).
• The cortex of the cerebellum is composed of gray matter thrown into folds (folia), separated by closely set transverse fissures.
• The cerebellum is connected to the midbrain by the superior cerebellar peduncles, to the pons by the middle cerebellar peduncles, and to the medulla by the inferior cerebellar peduncles.
• The fourth ventricle is continuous with the narrow central canal of the spinal cord and, through the three foramina in its roof, with the subarachnoid space.
• Extradural (epidural) hemorrhage results from injuries to the meningeal arteries or veins, with the most common artery to be damaged being the anterior division of the middle meningeal artery.
• The ventricles of the hindbrain are filled with cerebrospinal fluid, which is produced by the choroid plexuses of each ventricle.
• The posterior surface of the inferior part of the medulla oblongata contains the gracile and cuneate tubercles, which are produced by the medially placed underlying nucleus gracile and the laterally placed underlying nucleus cuneatus.
• The cerebellum consists of two hemispheres connected by a median portion, the vermis.
• The cerebellum lies within the posterior cranial fossa beneath the tentorium cerebelli, situated posterior to the pons and the medulla oblongata.
• Stimulation of the sensory endings of the trigeminal nerve above the level of the tentorium cerebellum produces referred pain to an area of skin on the same side of the head.
• The middle meningeal artery arises from the maxillary artery in the infratemporal fossa and enters the cranial cavity through the foramen spinosum to lie between the meningeal and endosteal layers of dura.
• Numerous arachnoid villi are located along the superior sagittal sinus.
• For the optic nerve, arachnoid forms a sheath for the nerve that extends into the orbital cavity through the optic canal and fuses with the sclera of the eyeball.
• Stimulation of the dural endings below the level of the tentorium produces referred pain to the back of the neck and back of the scalp along the distribution of the greater occipital nerve.
• The arachnoid fuses with the epineurium of the cranial nerves at their point of exit from the skull.
• The posterior (parietal) branch of the middle meningeal artery curves backward and supplies the posterior part of the dura mater.