FOURTH VENTRICLE

Fourth Ventricle

• floor
  • rhomboid fossa (diamond shaped)
  • formed by
    • posterior (dorsal surface)
      • lower or closed part of pons
      • open or upper part of medulla oblongata
  • structural layers
    • ependyma
    • thin layer of neuroglia
      • beneath ependyma
    • layer of grey matter forming various nuclei
  • parts
    • upper triangular part
      • dorsal surface of pons
    • lower triangular part
      • dorsal surface of medulla
    • intermediate part
      • junction of pons and medulla
      • prolonged laterally over inferior cerebellar peduncle
        • as floor of lateral recess
        • marked by transverse fibres of striae medullaris
        • arcuate nucleus to cerebellum
  • features
    • dorsal median sulcus
      • sulcus limitans
        • divides each half
          • median eminence
            • wider above
            • narrow below
            • facial colliculus
              • deep to it is genu of facial nerve
                • formed by looping around abducent nucleus
          • lateral vestibular area
        • depression at cranial end
          • superior fovea
        • depression at caudal end
          • inferior fovea
            • sulcus limitans runs obliquely
              • two triangle
                • hypoglossal triangle
                • vagal triangle
        • upper part is locus ceruleus
          • bluish in colour
          • pigmented neurons
            • substantia ferruginea
          • help in paradoxical sleep
            • rich in noradrenaline
    • lowest part resembles tip of writing pen
      • calamus scriptorius
    • between vagal triangle and gracile tubercle
      • area postrema
        • function as chemoreceptor
      • ependymal thickening
        • funiculus separans
          • separates both
• tela choroidea
  • double layer of piamater
  • covered by secretory ependyma
    • forms choroid plexus
• lateral boundaries
  • each side bounded by
    • inferolaterally by
      • tubercles
        • gracile tubercle
        • cuneate tubercle
    • superolaterally by
      • superior cerebellar peduncle
• roof
  • parts
    • superior
      • formed by superior cerebellar peduncle and
      • superior medullary velum
        • fills the gap between superior cerebellar peduncle
        • covered on dorsal syrface by lingula of superior vermiss (cerebellum)
    • inferior
      • very thin
      • devoid of nervous tissue
      • tela choroidea of fourth ventricle covers it posteriorly
      • caudally median aperture
        • communicate with subarachnoid space in
          • cerebello medullary cistern
      • inferior medullar velum
        • forms a part of roof in region of nodule of cerebellum
      • superior to inferior medullar velum
        • tela choroidea
          • reaches floor
            • marked by a ridge tenia
  • opening in roof
    • median aperture or foramen of magendie
      • situated caudal to nodule
      • communication between csf and subarachnoid space
    • foramen of luschka
      • present on lateral recess
        • subarachnoid space
• communication
  • inferiorly with central canal
  • superiorly with cerebral aqueduct