Cerebrospinal fluid is a clear, colorless transcellular fluid, in the ventricular system, and the central canal of the spinal cord. It also fills some gaps in subarachnoid space, known as subarachnoid cisterns. The four ventricles, four lateral, a third, and a fourth ventricle, all contain choroid plexus that produces cerebrospinal fluid. The third ventricle lies in the midline and is connected to the lateral ventricles. A single duct, the cerebral aqueduct between the pons and the cerebellum, connects the third ventricle to the fourth ventricle.
Three separate openings, the middle and the lateral apertures, drain the cerebrospinal fluid from the fourth ventricle to the cisterna magna one of the major cisterns. From here, cerebrospinal fluid circulates around the brain and spinal cord in the subarachnoid space, between the arachnoid mater and pia mater. At any one time, there is about 150mL of cerebrospinal fluid – the bridge within the subarachnoid space. Newer studies (2015) from two laboratories have shown the presence of the cranial nerves.
Cerebrospinal fluid Circulation
At the same time, about 125-150 ml of CSF occur. This CSF circulates in the ventricular system of the brain. The chambers are a series of cavities filled with CSF. Most cerebrospinal fluid is made from two lateral chambers of the heart. From there, CSF passes through the ventricular cell to the third chamber, then to the brain plate into the fourth chamber. From the fourth chamber, the fluid passes into the subarachnoid space through four openings – the central spinal cord channel, the central fissure, and the two lateral openings.
CSF is present in the subarachnoid space, which includes the brain, spinal cord and extends below the end of the spinal cord to the sacrum. There is a connection from the subarachnoid space to the bony labyrinth of the inner ear, which causes the spinal fluid to be continuous with perilima in 93% of people.
CSF moves in one direction outside of the chambers, but in the subarachnoidal space in a multidirectional way. The movement of the liquid is pulsating, adapting to the pressure waves generated in the blood vessels by the heartbeat. Some authors question this by stating that there is no unidirectional circulation of cerebrospinal fluid, but a cycle-dependent two-way systolic-diastolic cerebrospinal-cerebral spinal fluid.
CSF serves several purposes:
Buoyancy: the actual mass of the human brain is about 1400-1500 grams; however, the net weight of the brain suspended in CSF is equivalent to a weight of 25-50 grams. The brain, therefore, exists in a neutral buoyancy that allows the brain to maintain its density without weakening its own weight, which would cut off the blood supply and kill neurons in the lower sections without CSF.
Protection: CSF protects the brain tissue against injury during shock or impact, providing a fluid buffer that acts as a shock absorber from mechanical damage.
Prevention of cerebral ischemia: Prevention of brain ischemia by reducing the amount of CSF in the limited space inside the skull. This reduces the total intracranial pressure and facilitates blood perfusion.
Homeostasis: CSF allows for the regulation of the distribution of substances between brain cells, and neuroendocrine factors, to which small changes may cause problems or damage to the nervous system. For example, the high concentration of glycine interferes with the control of temperature and blood pressure, and high pH in the cerebrospinal fluid causes dizziness and syncope.
Waste disposal: CSF allows the removal of waste from the brain and is crucial in the brain’s lymphatic system.
Cerebrospinal fluid development
Around the third week of development, the embryo is a three-layer disk covered with ectoderm, mesoderm, and endoderm. The tube-like form develops in the middle line, called the dorsal string. Notochord releases extracellular molecules that affect the transformation of ectoderm into neural tissue. The nerve tube, forming from the ectoderm, contains CSF before the development of choroid plexuses. The open nerve tube neuropody closes after the first month of development and the CSF pressure gradually increases.
As the brain develops, in the fourth week of embryonic development in the nip around the canal, near which the head will develop, three swellings have formed. These swellings represent various elements of the central nervous system: midbrains, midbrain, and rhombus. The subarachnoid spaces are visible after the 32th day of development near the romance; the circulation is visible from the 41st day.
Developing forebrain surrounds
The nervous system. As the forebrain develops, the nerve cord becomes a chamber in it, ultimately forming side chambers. Along the inner surface of both chambers, the ventricular wall remains thin. The choroidal plexus develops, producing and releasing CSF. CSF quickly fills the nerve channel. Arachnoid fibers arise around the 35th week of development.
The sublevel organ emits SCO-spondin, which forms the Reissner fiber in CSF, supporting the movement through the brain aqueduct. It occurs in the early period of intrauterine life but disappears during early development.