Meninges

• Meninges are 3 membranous layer that surroundes brain and spinal cord and separates them from bony case (skull + vertebral column).

  • they are continuous with each other through foramen magnum (with only 1 only of cranial dura is continuous with spinal dura)
  • Dura matter, arachnoid matter, pia matter.
  • Protects brain + spinal cord from mechanical trauma, supports blood vessels, and form continuous cavity through which CSF passes.

  
• Cranial dura

  • Outermost, thick dense irregular CT layer
  • Consists of outer periosteal and inner meningeal layer.
  • Periosteal layer: periostenum of cranial cavity contains meningeal arteries, firmly attached to skull
  • Meningeal layer: overlies arachnoid matter, continuous with spinal dura.
• The periostenum and meningeal dura layers are normally attached to each other but at some locations they are not forming 2 types of structures:

  • dura sinuses: channels that drain venous blood from brain and drains it into internal jugular (sup sagittal sinus, transverse sinus, sigmoid sinus.)
  • Dura folds: meningeal layer forms inward folds that extend into cranial cavity separating brain into regions (falx cerebri, tentorium cerebelli, falx cerebelli, diaphragma sellae)
• Dura folds

  • Falx cerebri: largest fibrous septa that separates the two cerebral hemisphere. Posterior it blend with tentorium cerebeli.
  • Tentorium cerebelli: horizontal partition that separates cerebrum from cerebellum in posterior cranial fossa.
  • Falx cerebelli: vertical partition that divided hemispheres of cerebellum
  • Diaphragma sellae: covers pituitary gland in sella turcica.

  
• Arterial supply of dura

  • Arterial supply travels in periosteal layer of dura
  • Anterior meningeal arteries in anterior cranial fossa (branch of ethmoidal)
  • Middle + accessory meningeal arteries in middle cranial fossa (branch of maxillary)
  • Posterior meningeal artery in posterior cranial fossa (terminal branch of ascending pharyngeal a.) su
• Innervation of dura matter

  • By small meningeal branches from all three division of trigeminal n, vagus n, ophthalmic and optic cranial nerves
  • glossopharyngeal and hypoglossal n
• Arachnoid matter

  • Thin, avascular membrane that lies beneath dura.
  • Unlike pia it does not enter the grooves or fissure of brain except in longitudinal fissure btw the 2 hemispheres.
  • Outer suf shows mushroom like protusions (archnoid granulation/villi) reabsorbs cfs from subarachnoid into dura where its reabsorbed
  • Inner surface shows arachnoid trabeculae: extends downwards and attaches to out suf of pia
  • Subarachnoid space: filled with csf + all cerebral arteries and veins are located here
• Pia matter


  Thin, delicate mebrane that closely invests surface of brain. Follows all contours of brain, entering all grooves and fissures.

  • Highly vascular blood vessels penetrate pia to supply brain and spinal cord

  
• Meninges and spaces

  • extradural space: potencial space btw dura and bone. Can become actual space filled with fluid in trauma events
  • Subdura space: can be formed in case of hemorages in dura venous sinus resulting in subdural hematoma
  • Subarachnoid space: only natural space, filled woth CSF. surronds brain and spinal cord and in certain location it expands forming subarachnoid cisternae (contains csf + blood vessels). CSF is produced by choroid plexus circulates in subarachnoid space returns to venous system trhough arachnoid villi
• Cerebrospinal fluid (CSF): clear colorless liquid secreted by ependymal cells lining ventricles. It flows through central canal of spinal cord and subarachnoid space surrounding CNS. Its main function is to protect CNS from mechanical injury and maintain homeostasis of intracranial pressure. It also acts as transport medium for nutrients and waste products between blood and CNS
• Ventricular system: consists of four interconnected cavities within the brain. The two lateral ventricles lie deep inside the cerebrum; third ventricle lies in midline of diencephalon; fourth ventricle lies at base of cerebellum. Ventricles communicate with one another via foramina.
• Choroid plexuses: specialized epithelial tissue found in walls of ventricles. They produce most of the CSF. Choroid plexuses consist of capillaries surrounded by cuboidal epithelium which secretes CSF into ventricles. Blood enters choroid plexus via penetrating arteries and leaves via draining veins. Plexuses have fenestrated endothelium allowing free exchange of materials btwn blood and CSF
• CSF is produced mainly in the 2 lateral ventricle→ from there it passes into interentricular foramen of monro into 3 ventricle→cerebral aqueduct of silvius into 4ventricle→ from there it goes into the 2 lateral opening foramen of lushka wich drains into cisterna magna + 1 medial aperture foramen of magendie which drains into cisterna lateralis from these they drain into central canal of spinal cord→ passes into subarachnoid space→subarachnoid granulations→superior sagital sinus→reabsorbed into venous system
• Cerebrospinal fluid circulatiom

  
• Functions of Dura Folds

  • Compartmentalization: They create compartments within the cranial cavity, helping to restrict the movement of brain tissue and maintaining the structure of the brain.
  • Support and Protection: The dura folds support and protect various parts of the brain, providing structural stability and limiting the movement of brain tissues during head movements.
  • Venous Drainage: They contain major dural venous sinuses, which are channels that drain venous blood from the brain and direct it into the internal jugular veins.