How does cerebrospinal fluid flow through the brain?
Cerebrospinal fluid (CSF) is made mostly by the choroid plexus and flows one way: from each lateral ventricle through an interventricular foramen into the third ventricle, down the cerebral aqueduct into the fourth, then out through three apertures into the subarachnoid space. [1][2]
Fluid has no shape in this atlas, but the spaces it fills do; lit: the parts it runs through, in order.
The 3D brain needs JavaScript. The steps below still say where the cerebrospinal fluid runs, in order.
The brain starts seen from the left, a little from the front and above; the ventricles lie deep inside it and are lit through the faint cortex. Step through lights one step at a time, about 1.2 s each, along the flow; tap a step below to light it. The lit step is in the bright highlight colour, the steps before it stay lit in a paler tint of it and the steps still ahead are grey. Drag to turn, pinch or scroll to zoom. Step through is off because your device asks for reduced motion; tap each step instead.
A pathway through spaces, not tissue: the atlas draws each ventricle as the shape of the cavity itself, so what lights up is where the fluid sits. Only the choroid plexus inside the lateral ventricles has a shape (none in the third and fourth), and the apertures, the subarachnoid space and the arachnoid granulations are not drawn at all. [3][4][5]
The route, in 7 steps
Most CSF is made by the choroid plexus: tufts of leaky capillaries wrapped in a layer of modified ependymal cells, which take water and salts from the blood plasma and secrete them as clear fluid. Tight junctions between those cells form the blood–CSF barrier. Choroid plexus lies in all four ventricles; the atlas draws only the strip inside each lateral ventricle. [4][1][2]Where is the choroid plexus (lateral ventricles)?
The fluid first fills the two lateral ventricles, the largest of the four, one C-shaped cavity inside each cerebral hemisphere that curves from the frontal lobe back over the thalamus and down into the temporal lobe. [6][5]Where are the lateral ventricles?
Near the front of each lateral ventricle a short opening, the interventricular foramen (foramen of Monro), with the fornix in front of it and the thalamus behind, lets the fluid pass down and inward to the midline. [7][2]Where are the interventricular foramina?
The fluid from both sides meets in the third ventricle, a thin slit on the midline between the left and right thalamus with the hypothalamus as its floor; choroid plexus in its roof adds more fluid. [8][4]Where is the third ventricle?
From the back of the third ventricle the fluid runs down the cerebral aqueduct (aqueduct of Sylvius), a channel about 15 mm long and 1–2 mm across through the midbrain. [9][2]Where is the cerebral aqueduct?
The aqueduct opens into the fourth ventricle, a tent-shaped space with the back of the pons and upper medulla as its floor and the cerebellum behind it; more choroid plexus hangs from its roof. [10][2]Where is the fourth ventricle?
Out of the ventricles, not drawn: the fluid leaves the fourth ventricle through the median aperture (foramen of Magendie), at the lower end of its roof, into the cisterna magna behind the medulla, and through the two lateral apertures (foramina of Luschka), one at the end of each lateral recess, into the cistern at the angle between the cerebellum and the pons. From there it spreads through the subarachnoid space, between the arachnoid and pia mater, over the brain and spinal cord. The atlas has no shape for the apertures or the subarachnoid space, so nothing is lit for them. [11][12][13][2]
At its lower tip the fourth ventricle narrows into the central canal, the thin ependyma-lined channel down the middle of the spinal cord, a fourth way out besides the three apertures. In many adults parts of the canal close off with age. The atlas draws only its top, just below the medulla. [14][1]Where is the spinal cord?
More about the cerebrospinal fluid
Other names: CSF flow, CSF circulation, circulation of cerebrospinal fluid, CSF pathway [1][2]
An adult holds about 125–150 mL of CSF at any one time and makes about 500 mL a day, so the whole volume is replaced roughly three to four times a day. [1]
Inside the ventricles the fluid moves one way, outward from the lateral ventricles to the fourth; in the subarachnoid space it moves in many directions, and the flow pulses with each heartbeat. [1]
The ependymal cells lining the ventricles carry cilia whose beating helps move the fluid along. [15]
The fluid returns to the blood mainly through the arachnoid granulations, small outpouchings of the arachnoid that push into the dural venous sinuses such as the superior sagittal sinus. [16][2]
Floating in CSF, a brain of about 1,400–1,500 g has a net weight of only about 25–50 g, so its lower parts do not bear the weight of the rest. [1]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); it draws the ventricles as the shapes of the spaces themselves, not the fluid in them, so this route is shown by the spaces the fluid runs through; openings and spaces it has no shape for are named in text and never lit.