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