Total volume: 50 mL in newborn, 150 mL in adult

Composition: inorganic salts like those in plasma, traces of protein + glucose

Production: 0.3–0.4 mL/min resulting in 500 mL/day; secreted into ventricles by choroid plexuses (80–90%), 10–20% from parenchyma of cerebrum and spinal cord

Circulation:

from ventricles through foramina of Magendie + Luschka of 4^th ventricle into cisterna magna + basilar cisterns; 80% of CSF flows initially into suprasellar cistern + cistern of lamina terminalis, ambient / superior cerebellar cisterns → eventually ascending over superolateral aspects of each hemisphere; 20% initially enters spinal subarachnoid space + eventually recirculates into cerebral subarachnoid space

Absorption: into venous system by

1. arachnoid villi of superior sagittal sinus (villi behave as one-way valves with an opening pressure between 20–50 mm of CSF)
2. cranial + spinal nerves with eventual absorption by lymphatics (50%)
3. prelymphatic channels of capillaries within brain parenchyma
4. vertebral venous plexuses, intervertebral veins, posterior intercostal + upper lumbar veins into azygos + hemiazygos veins

Opening pressure: 80–180 mm H₂O