Ventricular System: Flashcards
Describe the functions of cerebrospinal fluid:
Clear colourless liquid found in the ventricles of the brain and the surrounding
subarachnoid space
CSF bathes the external and internal surfaces of the
brain and spinal cord
Pressure 60-150 mm of water
Functions:
- serves as a cushion between the CNS and the surrounding bones protecting it from mechanical trauma
- provides the brain with mechanical buoyancy and
support - serves as a reservoir and assists in the regulation of of the contents of the skull (due to the close relationship of the fluid to the nervous tissue and the blood)
- nourishes CNS as it provides an ideal physiological substrate
- removes excess metabolites from the CNS
- serves as a pathway for pineal secretions to reach the pituitary gland
- chemical stability - CSF creates an environment to allow for proper functioning of the brain, e.g. maintaining low extracellular K+ for synaptic transmission
Describe the lateral ventricles within the ventricular system:
2 large lateral ventricles one present in each cerebral hemisphere
Body:
- occupies the parietal lobe
- extends from inter ventricular foramen to posterior end of thalamus
- contains the choroid plexus which projects through a slit (choroidal fissure) between fornix and superior surface of thalamus
Anterior horn:
- extends forward from the body into frontal lobe
- continuous posteriorly with the body of the ventricle at the interventricular foramen
Posterior horn - extends posteriorly into occipital lobe
Inferior horn - extends inferiorly into temporal lobe
Describe the subarachnoid space:
Space between the arachnoid and pia mater and is present where the meninges envelop the brain and spinal cord
Filled with CSF and and large blood vessels of the brain
Extensions:
- along olfactory nerves to the mucoperiosteum of the nose
- around cranial and spinal nerves until they exit the skull or vertebral canal, where arachnoid and pia mater fuse with the perineurium
- around optic nerve to the back of the eyeball (fuse with sclera)
- along cerebral blood vessels
Inferior extensions:
- surrounds cauda equina
- ends at the interval between the 2nd and 3rd sacral vertebrae
Describe the formation of CSF and choroid plexuses:
CSF is formed by the choroid plexus the lateral, third and fourth ventricles which actively secrete CSF creating a small pressure gradient
The choroid plexuses have a highly folded surface and each fold consists of a core of vascular connective tissue covered with cuboidal epithelium of the ependyma
CSF production isn’t pressure regulated and will continually be produced even if reabsorption mechanisms are obstructed = hydrocephalus
Choroid plexuses:
Lateral ventricles - chord plexus projects into the ventricle medially and is continued into the inferior horn projecting through choroidal fissure
3rd ventricle - forms two ridges that hang from the roof of the ventricle
4th ventricle - T shaped suspended from inferior half of ventricle roof
Describe the Subarachnoid cisterns:
Cerebomedullary cistern - space between the inf. surface of the cerebellum and the post. surface of the medulla oblongata
Pontine cistern - located around ant. surface of pons and medulla
Interpeduncular cistern - between cerebral peduncles
Superior / quadrigeminal / cistern of great cerebral vein - a finger like extension of the subarachnoid space between the fornix and the roof of the 3rd ventricle
Chiasmatic/ suprasellar cistern - located above sella turcica + below hypothalamus, contains optic chasm and pituitary stalk
Describe the absorption of CSF:
Main absorption sites - arachnoid villi projecting into dural venous sinuses, especially the superior sagittal sinus
Villi group to form arachnoid granulations
Absorption mechanism:
- occurs when CSF pressure > venous pressure in the sinus
- fine epithelial-lined tubules allow direct CSF flow into venous sinuses
- if venous pressure > CSF pressure, villi compress, closing tubules to prevent blood entry into subarachnoid space
Absorption rate controls CSF pressure, as CSF production remains constant
Additional absorption pathways include direct absorption into veins of the subarachnoid space
Describe hydrocephalus and its causes:
Excessive accumulation of CSF due to blockage or absorption failure, leading to increased CSF pressure and ventricular expansion, compressing brain tissue
causes:
- blockage in CSF circulation
- overproduction of CSF (choroid plexus tumours, papillomas)
- failure of CSF absorption ( obstruction of superior sagittal sinus, subarachnoid bleeding
Describe the Third Ventricle as part of the ventricular system:
Slit like cleft between the 2 thalami
Communicates anteriorly with lateral ventricles through the interventricular foramina (foramina of Munro)
Communicates posteriorly with 4th ventricle via cerebral aqueduct
Superior wall has a two layered fold of pia matter called the tela choroidea where internal cerebral veins lie
The anterior surface of the ventricle contains two protrusions;
supra optic recess - located above the optic chiasm
infundibular recess - located above the optic stalk
Describe the Fourth Ventricle as part of the ventricular system:
Tent shaped cavity (triangular in anatomy)
Ant. to cerebellum and post. to pons and medulla oblongata
Continuous superiorly with cerebral aqueduct and inferiorly with central canal
Roof projects into the cerebellum
Inferior aspect of roof pierced by median aperture (foramen of Magendie)
There are also two lateral apertures in the 4th ventricle, the foramina of Luschka
These openings permit the CSF to flow from the ventricular system into the subarachnoid space
Describe the terminal ventricle as part of the ventricular system:
Located at the inferior end of the spinal cord
The ventricles are lined throughout with ependyma and are filled with cerebrospinal fluid
ventriculus terminalis present in children but usually absent in adults
Describe the circulation of CFS:
Ventricular flow:
- moves from lateral ventricles → third ventricle via interventricular foramina
- travels from third ventricle → fourth ventricle via cerebral aqueduct
- circulation is assisted by arterial pulsations of the choroid plexuses and cilia on ependymal cells
Exit to subarachnoid space:
- CSF leaves 4th ventricle via median aperture and lateral foramina
- enters subarachnoid space via the cerebellomedullary and pontine cisterns
Superior circulation:
- moves upward through the tentorial notch to the inferior cerebrum
- continues superiorly over the cerebral hemispheres, aided by cerebral arterial pulsations
Spinal circulation:
- some CSF moves inferiorly around spinal cord and cauda equina
- this region is a dead end and further circulation requires spinal arterial pulsations or vertebral column movements
describe the different types of hydrocephalus:
Communicating (non obstructive):
- no blockage in CSF flow
- caused by failure of CFS reabsorption
Causes:
- raised venous pressure due to superior sagittal sinus obstruction
- subarachnoid bleeding
Non-communicating (obstructive):
- caused by a physical blockage in the ventricular system
- Tumours blocking interventricular foramina, causing lateral ventricle hydrocephalus
- congenital failure of 4th ventricle apertures developing
- pineal gland tumours
