CSF is mostly produced by specialized ependymal cells in the choroid plexuses of the ventricles of the brain, and absorbed in the arachnoid granulations.

CSF acts as a shock absorber, cushion or buffer, providing basic mechanical and immunological protection to the brain inside the skull.

There is also a connection from the subarachnoid space to the bony labyrinth of the inner ear via the perilymphatic duct where the perilymph is continuous with the cerebrospinal fluid.

The ependymal cells of the choroid plexus have multiple motile cilia on their apical surfaces that beat to move the CSF through the ventricles.

[1][2] There is a connection from the subarachnoid space to the bony labyrinth of the inner ear making the cerebrospinal fluid continuous with the perilymph in 93% of people.

[7] In general, globular proteins and albumin are in lower concentration in ventricular CSF compared to lumbar or cisternal fluid.

[8] This continuous flow into the venous system dilutes the concentration of larger, lipid-insoluble molecules penetrating the brain and CSF.

[3] The open neuropores of the neural tube close after the first month of development, and CSF pressure gradually increases.

These swellings represent different components of the central nervous system: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).

Along the inner surface of both ventricles, the ventricular wall remains thin, and a choroid plexus develops, producing and releasing CSF.

[3] The subcommissural organ secretes SCO-spondin, which forms Reissner's fiber within CSF assisting movement through the cerebral aqueduct.

[19] Additionally, the larger CSF volume may be one reason as to why children have lower rates of postdural puncture headache.

[3] This fluid then needs to pass through the epithelium cells lining the choroid plexus into the ventricles, an active process requiring the transport of sodium, potassium and chloride that draws water into CSF by creating osmotic pressure.

[24] As a result, to maintain electroneutrality blood plasma has a much lower concentration of chloride anions than sodium cations.

[6] Choroid plexuses also secrete growth factors, iodine,[25] vitamins B1, B12, C, folate, beta-2 microglobulin, arginine vasopressin and nitric oxide into CSF.

[3] A Na-K-Cl cotransporter and Na/K ATPase found on the surface of the choroid endothelium, appears to play a role in regulating CSF secretion and composition.

[26] There are circadian variations in CSF secretion, with the mechanisms not fully understood, but potentially relating to differences in the activation of the autonomic nervous system over the course of the day.

[3] Changes in the pH of the blood can affect the activity of carbonic anhydrase, and some drugs (such as furosemide, acting on the Na-K-Cl cotransporter) have the potential to impact membrane channels.

[31] Symptoms can include problems with gait and coordination, urinary incontinence, nausea and vomiting, and progressively impaired cognition.

[32] In infants, hydrocephalus can cause an enlarged head, as the bones of the skull have not yet fused, seizures, irritability and drowsiness.

[35] CSF can be tested for the diagnosis of a variety of neurological diseases, usually obtained by a procedure called lumbar puncture.

[34] About one third of people experience a headache after lumbar puncture,[34] and pain or discomfort at the needle entry site is common.

[1] A lumbar puncture that drains CSF may also be used as part of treatment for some conditions, including idiopathic intracranial hypertension and normal pressure hydrocephalus.

However, a lumbar puncture should never be performed if increased intracranial pressure is suspected due to certain situations such as a tumour, because it can lead to fatal brain herniation.

[34] Some anesthetics and chemotherapy drugs are injected intrathecally into the subarachnoid space, where they spread around CSF, meaning substances that cannot cross the blood–brain barrier can still be active throughout the central nervous system.

Advances in this field are driven by ongoing research into novel delivery systems and drug formulations, enhancing the precision and efficacy of treatments.

In this approach, the drug interacts with its target within the reservoir, allowing for changing the composition of the CSF without systemic release.

This is perhaps because of the prevailing autopsy technique, which involved cutting off the head, thereby removing evidence of CSF before the brain was examined.

In a manuscript written between 1741 and 1744, unpublished in his lifetime, Swedenborg referred to CSF as "spirituous lymph" secreted from the roof of the fourth ventricle down to the medulla oblongata and spinal cord.

He discovered the foramen Magendie, the opening in the roof of the fourth ventricle, but mistakenly believed that CSF was secreted by the pia mater.