MENINGES

• The skull consists of the cranium (vault and base) and the face, with various bones like the frontal, parietal, occipital, temporal, sphenoid, and ethmoid bones
• Facial bones include zygomatic bones, maxillae, nasal bones, lacrimal bones, vomer, palatine bones, inferior conchae, and mandible
• The maxilla is the upper jaw bone that forms the anterior part of the hard palate, lateral walls of the nasal cavities, and floors of the orbital cavities
• The mandible consists of a horizontal body and two vertical rami
• In the lateral view of the skull, structures like the parietal bones, occipital bone, external auditory meatus, and mandible are observed
• The pterion, a thin part of the lateral skull wall, overlies the anterior division of the middle meningeal artery and vein
• The superior and inferior temporal lines, temporal fossa, infratemporal fossa, pterygomaxillary fissure, and inferior orbital fissure are visible in the lateral view of the skull
• The neonatal skull has fontanelles, which are membranous intervals between the bones of the vault that are not closely knit at sutures
• The anterior fontanelle is diamond-shaped and closes by 18 months of age, while the posterior fontanelle is triangular and closes at 1 year
• The brain and spinal cord are covered by three protective meninges: dura mater, arachnoid mater, and pia mater
• The dura mater has two layers in the skull: the endosteal layer and the meningeal layer, which forms inward septa dividing the cranial cavity into spaces
• Dural nerve supply includes branches of the trigeminal, vagus, and the first three cervical spinal nerves innervating the cranial dura
• Dura mater:

  • Falx cerebri separates the two cerebral hemispheres
  • Tentorium cerebelli separates the cerebrum from the cerebellum
  • Falx cerebelli separates the two cerebellar hemispheres
  • Diaphragma sellae is the roof over the sella turcica, which houses the pituitary gland
• Dural nerve supply:

  • Branches of the trigeminal, vagus, and the first three cervical spinal nerves innervate the cranial dura
• Dural arterial supply:

  • Multiple arterial supply
  • The middle meningeal artery is the most important as it is the only arterial vessel found between the meningeal and endosteal layers of dura
• Dural venous sinuses:

  • Superior and inferior sagittal sinuses are located within the falx cerebri
  • Inferior sagittal sinus joins the straight sinus at the junction of the falx cerebri and tentorium cerebelli
  • Occipital sinus is located within the falx cerebelli
• Arachnoid mater:

  • Delicate impermeable membrane between the dura mater and pia mater
  • Separated from the pia mater by the subarachnoid space, which is filled with CSF
  • Arachnoid villi protrude into the dural venous sinuses, allowing CSF diffusion into the bloodstream
• Pia mater:

  • A vascular membrane that closely invests the brain, covering the gyri and descending into the deepest sulci
  • The cerebral arteries entering the substance carry a sheath of pia with them
• Spinal cord meninges:

  • Continuous with the meningeal layer of the cranial dura
  • Arachnoid mater is continuous with cranial arachnoid mater and maintains the same meningeal relationships in the vertebral canal as the cranial cavity
  • Pia mater closely covers the spinal cord and has denticulate ligaments that form a means of suspension for the spinal cord in the dural sheath
• Ventricular system:

  • Ventricles are fluid-filled cavities lined throughout with ependyma
  • Lateral ventricles are the largest and communicate with the third ventricle via the interventricular foramen
  • The third ventricle is found between the two thalami
  • The fourth ventricle is located between the pons/medulla and the cerebellum
• Blood-brain and blood-cerebrospinal fluid barriers:

  • BBB allows gases and water freely, slowly allows glucose and electrolytes, but restricts passage of plasma proteins and other large organic molecules
  • Tight junctions between endothelial cells are responsible for the restriction of large molecules but allow lipophilic molecules to cross the barrier
• Vascular supply of the brain and spinal cord:

  • Internal carotid and vertebral arteries supply the brain
  • The vertebral arteries merge to form the basilar artery
  • The circle of Willis is formed by the anastomosis between the internal carotid and vertebral blood supplies
• Blood supply of the brain:

  • Internal carotid and vertebral arteries supply the brain
  • The basilar artery branches into pontine, labyrinthine, anterior inferior cerebellar, superior cerebellar, and posterior cerebral arteries
• Blood supply of the spinal cord:

  • The spinal cord is supplied by three small arteries: two posterior spinal arteries and the anterior spinal artery
  • The great anterior medullary artery of Adamkiewicz arises from the aorta and is a major source of blood to the lower two-thirds of the spinal cord