Editing Cerebrospinal fluid (section)

==Development==
At around the fifth week of its [[human embryonic development|development]], the [[embryo]] is a [[Trilaminar embryonic disc|three-layered disc]], covered with [[ectoderm]], [[mesoderm]] and [[endoderm]]. A tube-like formation develops in the midline, called the [[notochord]]. The notochord releases extracellular molecules that affect the transformation of the overlying ectoderm into nervous tissue.<ref name=LARSEN2009/> The [[neural tube]], forming from the ectoderm, contains CSF prior to the development of the choroid plexuses.<ref name="SAKKA2011"/> The open [[neuropore]]s of the neural tube close after the first month of development, and CSF pressure gradually increases.<ref name="SAKKA2011"/>

By the fourth week of embryonic development the [[Brain#Development|brain has begun to develop]]. Three swellings ([[primary brain vesicles]]), have formed within the embryo around the canal, near to where the head will develop. These swellings represent different components of the [[central nervous system]]: the [[prosencephalon]] (forebrain), [[mesencephalon]] (midbrain), and [[rhombencephalon]] (hindbrain).<ref name=LARSEN2009/> Subarachnoid spaces are first evident around the 32nd day of development near the rhombencephalon; circulation is visible from the 41st day.<ref name="SAKKA2011"/> At this time, the first choroid plexus can be seen, found in the fourth ventricle, although the time at which they first secrete CSF is not yet known.<ref name="SAKKA2011"/>

The developing forebrain surrounds the neural cord. As the forebrain develops, the neural cord within it becomes a ventricle, ultimately forming the lateral ventricles. Along the inner surface of both ventricles, the ventricular wall remains thin, and a [[choroid plexus]] develops, producing and releasing CSF.<ref name=LARSEN2009 /> CSF quickly fills the neural canal.<ref name=LARSEN2009>{{cite book |first1=Gary C. |last1=Schoenwolf |first2=William James |last2=Larsen | name-list-style = vanc |title=Larsen's human embryology |year=2009 |publisher=Churchill Livingstone/Elsevier |location=Philadelphia |isbn=978-0-443-06811-9 |chapter=Development of the Brain and Cranial Nerves |edition=4th}}{{page needed|date=July 2014}}</ref> Arachnoid villi are formed around the 35th week of development, with arachnoid granulations noted around the 39th, and continuing developing until 18 months of age.<ref name="SAKKA2011"/>

The [[subcommissural organ]] secretes [[SCO-spondin]], which forms [[Reissner's fiber]] within CSF assisting movement through the cerebral aqueduct. It is present in early intrauterine life but disappears during early development.<ref name="SAKKA2011"/>