CSF, Ventricular System and Meninges

• Cerebrospinal fluid

  • clear liquid
  • helps to cushion
  • supplies nutrients
  • helps remove waste products
  • produced continuously by the choroid plexus in the ventricles
  • found in the ventricles, central canal and subarachnoid space
• Cerebrospinal Fluid Pathway

  Lateral ventricles -> foramen of monro -> third ventricle -> cerebral aqueduct (of sylvius) -> fourth ventricle -> foramen of luschka and magendie -> subarachnoid space -> arachnoid villi and then to venous drainage system of brain
• choroid plexus

  • understudied
  • found in ventricles and next to the pia mater
  • highly vascularized
  • made of epithelial cells
  • also contains immune cells
  • makes your CSF
  • develops from the dorsal neural tube
  • first in/with the 4th ventricle, then in the lateral ventricles of the telencephalon, and then in and with the 3rd ventricle
• ventricles

  • two lateral ventricles
  • third ventricle
  • fourth ventricle
  • central canal
• lateral ventricles


  one in each cerebral hemisphere
• third ventricle

  at the midline near the ventral portion of the brain
• fourth ventricle

  within the brainstem, roughly between the pons and medula; connects to the central canal of the spinal cord
• central canal


  not a ventricle per se, but basically a spinal cord ventricle that runs down the middle of it
• connections within the ventricular system

  • foramen of monro
  • cerebral aqueduct
  • foramen of luschka and magendie
  • subarachnoid space
• foramen of monro

  connects lateral and third ventricles
• cerebral aqueduct


  connects third and fourth ventricle
• foramen of luschka and magendie

  connects fourth ventricle to the subarachnoid space
• too much CSF

  • hydrocephaly/hydrocephalus: too much CSF
  • causes include trauma, meningitis, infection, blockage in CSF drainage pathways, and birth defects
  • puts too much pressure on your brain within the skull
• too little CSF

  • usually means you sprung a CSF leak somewhere or are severely dehydrated
  • brain doesn't have enough cushion. can cause brain to sag, stressing nerves and meninges
• choroid plexus pathologies

  • cysts - common with certain disorders
  • hemorrhages - often due to birth trauma/stress/hypoxia
  • tumors and hyperplasia - often lead to hydrocephalus
  • microorganism infiltration - seen in children who have meningitis
  • deficiencies in thyroid hormone carrier protein (thus depriving brain regions of thyroid hormone)
  • perhaps involved in alzheimer's disease - CSF helps to clear the plaques and choroid plexus appears atrophied in those with the disease
• main functions of the meninges

  • provide a supportive framework for the cerebral and cranial vasculature
  • acting with cerebrospinal fluid to protect the CNS from mechanical damage
• dura mater

  • the outermost layer of the meninges
  • directly underneath the bones of the skull and vertebral column
  • thick, tough, and inextensible
  • fits brain like a loose bag
  • also known as the pachymeninx
  • continuous with the periosteum
• connective tissues of the dura mater

  • the dura contains two connective tissue sheets:
  • endosteal (periosteal) layer
  • meningeal layer
  • between these two layers, the dural venous sinuses are located
• endosteal (periosteal) layer


  lines the inner surface of the bones of the cranium; does not extend through the foramen magnum
• meningeal layer

  lines the endosteal layer inside the cranial cavity

  • the only layer present in the vertebral column
• dural venous sinuses

  responsible for the venous vasculature of the cranium, draining into the internal jugular veins
• dural reflections

  in some areas of the skull, where the meningeal layer of the dura mater folds inwards

  • partitions the brain and divides the cranial cavity into several compartments
• the dura mater receives its own vasculature; primarily from the middle meningeal artery and vein
• the dura mater is innervated by the trigeminal nerve (V1, V2 and V3)

  • can feel pain
• meningeal spaces

  • epidural - contains meningeal arteries and veins
  • subdural - traversed by "bridging" veins
  • subarachnoid - communicates with ventricles, includes cisterns, contains CSF, circle of Willis
• dura mater haematomas

  • a haematoma can cause a rapid increase in intra-cranial pressure. death results if untreated
  • two types of haematomas involving the dura mater
  • extradural
  • subdural
• extradural haematoma


  arterial blood collects between the skull and endosteal layer of the dura. the causative vessel is usually the middle meningeal artery, tearing as a consequence of brain trauma
• subdural haematoma

  venous blood collects between the dura and the arachnoid mater. it results from damage to cerebral veins as they empty into the dural venous sinuses
• arachnoid mater/layer

  • middle layer of the meninges, lyind directly underneath the dura mater
  • attached to the dura mater
  • surrounds both the brain and the spinal cord
  • does not line the brain into the sulci, with the exception of the longitudinal fissure
  • avascular
  • does not receive any innervation
• arachnoid mater connective tissue

  • web of collagen
  • consistes of layers of connective tissue
  • dorsal layer
  • ventral layer
• arachnoid mater dorsal layer

  covers internal cerebral veins and fixes them to the surrounding tela choroidea
• arachnoid mater ventral layer


  a direct anterior extension of the arachnoid envelope that the dorsal layer forms over the pineal region
• sub-arachnoid space

  • underneath the arachnoid space
  • contains CSF
  • small projections of arachnoid mater into the dura (known as arachnoid granulations) allow CSF to re-enter the circulation via the dural venous sinuses
• subarachnoid hemorrhage

  • between arachnoid and pia
  • thunderclap headache
  • photophobia
• pia mater

  • located underneath the sub-arachnoid space
  • very thin and tightly adhered to the surface of the brain and spinal cord
  • the only covering to follow the contours of the brain (the gyri and fissures)
  • highly vascularized, with blood vessels perforating through the membrane to supply the underlying neural tissue
• leptomeninges

  • "thin meninges"
  • arachnoid + pia
  • 5% of cancer patients have their cancer spread to the leptomeninges
  • CNS symptoms are divided into 3 anatomic groups:
  • cerebral involvement: headache, lethargy, papilledema, behavioral changes, gait disturbance
  • cranial-nerve involvement: impaired vision, diplopia, hearing loss, sensory deficits (including vertigo); cranial0nerve palsies commonly involve CN III, IV, VI, VII, and VIII
  • spinal-root involvement: nuchal rigidity and neck/back pain, invasion of the spinal roots
• meningitis

  • inflammation of the meninges
  • can be drug induces
  • non-steroidal anti-inflammatory drugs, antimicrobials, intravenous immunoglobulin, intrathecal agents, vaccines
  • usually caused by pathogens
  • bacteria are the most common infective cause
  • the most common organisms are Neisseria meningitidis and Streptococcus pneumoniae
• meningitis immune response

  • can cause cerebral edema, consequently raising intra-cranial pressure
  • two main effects:
  • part of the brain can be forced out of the cranial cavity - this is known as cranial herniation
  • in combination with systematic hypotension, raised intracranial pressure reduces cerebral perfusion
• blood-brain barrier

  • organic barrier between circulating blood and the CNS
  • regulates, in part actively and in part passively, the exchange of substances between blood and brain
  • also acts as a protective shield by preventing the penetration of harmful substances into the CSF
  • few pathogens can overcome the blood-brain-barrier
• blood-brain barrier molecular transport

  • allows passage/transport of small molecules (H2O, O2, CO2), lipophilic molecules (EtOH, heroin), passive transport of glucose, active transport of amino acids/NT precursors
  • prevents passage of larger molecules (dopamine) charged molecules, etc
  • medication can be tailor-made in order that they can overcome the blood-brain barrier