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Anatomy of the Nervous System

  1. CALVARIA = upper part of cranium enclosing the brain
    1. outer table of resilient compact bone
    2. diploë = trabecular bone containing red bone marrow
    3. inner table of thin and brittle compact bone
  2. EPIDURAL SPACE
    = created when outer layer of dura (periosteum of inner table) becomes detached from calvaria
  3. PACHYMENINGES = DURA MATER
    = thick inelastic membrane composed of 2 layers of fibrous + elastic connective tissue that are fused except for a separation allowing the passage of dural venous sinuses
    1. outer endosteal dural layer
      = highly vascularized periosteum of inner table containing blood vessels that supply the bone
    2. space for venous sinuses
    3. inner meningeal dural layer
      = protective meningeal layer lined on its inner brain surface by layer of mesothelium derived from meninx
      →extensions are reduplications of the meningeal layer projecting into skull cavity to form falx cerebri, tentorium cerebelli, falx cerebelli, diaphragma sellae
  4. SUBDURAL SPACE
    = cleft formed in pathologic states within inner layer of dura
  5. LEPTOMENINGES
    1. Arachnoid mater [arakhnoeides, Greek = like a cobweb]
      = closely applied to inner surface of dura
    2. Subarachnoid space

      Histo: fine connective tissue + cellular septa link pia and arachnoid
      • contains CSF that drains through the valves of arachnoid granulations into venous sinuses
      • forms basal cisterns
    3. Pia mater [pia, Latin = tender]
      = delicate innermost layer of meninges
      Histo: thin fibrous tissue impermeable to fluid with perforations for blood vessels to pass through
  6. SUBPIAL SPACE
    = perivascular space = VR (Virchow-Robin) space
    [Rudolf Virchow (1821–1902), pathologist in Berlin, Germany]
    [Charles P. Robin (1821–1885), anatomist in Paris, France]
    Histo: no communication with subarachnoid space; VR space around intracortical artery continues within subarachnoid space; VR space around cerebral vein is continuous with subpial space
    Function: lymphatic drainage system of the brain
    Sites: Type I = lenticulostriate arteries
    Type II = medullary arteries over high convexities
    Type III = collicular arteries in midbrain
    • smoothly demarcated typically <5 mm fluid-filled cyst; often in clusters
    • SI visually similar to CSF (actually lower when measured as VR spaces are entrapments of interstitial fluid)
    • no restricted diffusion + no enhancement
    • inflow effects on flow-sensitive T1WI
  7. EPENDYMA
    = thin epithelial-like lining of ventricular system + central canal of spinal cord composed of ciliated simple columnar ependymocytes
    Origin: one of four types of neuroglia in CNS
    Function: (1) Production + regulation of CSF, (2) Reservoir for neuroregeneration

Falx Cerebri [falx, Latin = curved blade or scythe]!!navigator!!

= large crescent-shaped inelastic reflection of meningeal layer of dura mater that descends vertically in longitudinal fissure between cerebral hemispheres

Connected to:

  1. anteriorly: crista galli anteriorly in proximity to cribriform plate + frontal and ethmoid sinuses
  2. posteriorly: upper surface of the tentorium cerebelli

Margins:

  1. superior margin attached at midline to internal surface of skull as far back as internal occipital protuberance
    • contains superior sagittal sinus overlying longitudinal cerebral fissure
  2. inferiorly adjacent to corpus callosum + cingulate gyrus + pericallosal arteries
    • contains inferior sagittal sinus arching over corpus callosum deep in longitudinal cerebral fissure

Falx Cerebelli!!navigator!!

= small sickle-shaped fold of dura mater projecting forward into posterior cerebellar notch + into cerebellar vallecula between cerebellar hemispheres

Base: attached to inferoposterior part of tentorium cerebelli

Posterior margin: attached to vertical crest of inner skull surface below internal occipital protuberance

Outline