Ventricles and CSF

Ventricles

The ventricles of the brain are open areas that contain cerebrospinal fluid(CSF) – A fluid that cushions and nourishes the brain and spinal cord.. Whenever we do the brain dissection in lab, students will always ask me where is the ventricle. However because these structures are fluid filled they collapse when the brain is pickled or preserved. It is very difficult to visualize these ventricles because they have a diagonal C shape to them. These two sea shaped things here are the lateral ventriclesLarge CSF-filled cavities within the cerebral hemispheres. left and right. These are the first and second ventricles. You can choose whether the left is the first or the right is the second.

These two ventricles are connected by the interventricular foramenThe opening connecting the lateral ventricles to the third ventricle..  This large basin here is the third ventricleA narrow cavity in the diencephalon that contains CSF., which is connected to the fourth ventricleA cavity between the brainstem and cerebellum that contains CSF., another wide open basin.  Unfortunately the 3^rd and 4^th ventricles are connected by a small and fragile tube called the cerebral aqueduct.  This small tube can sometimes become pinched. A shunt is required to keep it open until the brain and skull bone reach full capacity. All of these ventricles drain by gravity into the central canalA hollow canal in an osteon containing blood vessels and nerves. of the spinal cordThe central nervous system structure that relays signals between the brain and body.. Cerebrospinal fluid circulation has no pump like the heart’s circulation. However, there are mechanisms that help cerebrospinal fluid flow through these open spaces.

Choroid Plexuses

Cerebrospinal fluid is made by structures that are called choroid plexuses. There are two choroid plexuses one here in the 4th ventricle and the other one here in the lateralAway from the midline of the body. ventricles. In choroid plexuses blood is filtered by cellsThe basic structural and functional units of life. called ependymal cellsGlial cells that produce and circulate cerebrospinal fluid.. It is these cells that create the cerebrospinal fluid which is essentially filtered blood. These two pictures in black and white are lateral pictures. They show you the choroid plexuses in the lateral ventricles. They also display the 4th ventricle. This picture down here is a transverse picture. You can see the openings of the lateral ventricles. The choroid plexusStructures within the ventricles that produce cerebrospinal fluid (CSF). is visible in those ventricles. Additionally, you can see the choroid plexus in the 4th ventricle.

Cerebrospinal Fluid (CSF)

Ependymal cells were one of the types of neuroglia that are contained only in the central nervous systemComposed of the brain and spinal cord; integrates and processes information. . It is these cells that filter the blood and allow only acceptable substances into the vascular system of the brain. These ependymal cells are technically part of the blood-brain barrierA selective barrier that prevents harmful substances from entering the brain.. They prevent certain toxins from entering the brain circulation. Also functioning as part of the blood brain barrier are astrocytesStar-shaped glial cells in the CNS that support neurons and maintain the blood-brain barrier. pictured here in purple. It is these cells that take specific substances directly from the blood vessels and feed it to the neuronsThe functional cells of the nervous system that transmit signals.. This is different from ependymal cells. They take substances directly from the blood vessels and filter them to make cerebrospinal fluid. All of these ependymal cells have ciliaHair-like projections on the surface of some cells that move fluids or particles. on them and it is the waving of the cilia in unison that in part contributes to the circulation of cerebrospinal fluid through the ventricles and down into the central canal of the spinal cord

CSF Circulation

Every book I’ve taught from usually has a really terrible picture describing the circulation of cerebrospinal fluid. We can make it nice and simple here. All cerebral spinal fluid is created in the choroid plexuses. It eventually flows by gravity down the central canal of the spinal cord. It then diffuses into the subarachnoid space. This space is between the pia materThe thin, innermost layer of the meninges that closely adheres to the spinal cord. and the arachnoid materThe middle layer of the meninges, located between the dura and pia mater., the spinal cord meninges(singular: meninx) – Protective membranes surrounding the spinal cord and brain.. As you move around your skeletal muscles create pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. differences in the subarachnoid space. These pressure differences basically milk your CSF superiorly through the subarachnoid space and back into the brain.

Some of you may know the situation or a condition that requires what is referred to as a neural shunt. Unfortunately, the small central canal that leaves the 4th ventricle can be pinched shut in children. The little tiny canal that connects the 3rd to the 4th ventricle can also close in this way. This happens as their brain and cranium complete their final growthAn increase in size and number of cells.. In these situations, cerebrospinal fluid cannot descend through the 3rd and 4th ventricle. Consequently, it is unable to reach the central canal. Therefore the ventricles start to fill up with CSF asking the brain to swell outward. In adults this is not possible because the skull bones are sutured closed. For adults, the increased pressure in the ventricles is deadly. However, for children whose skulls have not yet reached full capacity this condition is not deadly. As CSF fills the ventricles, it creates pressure on the skull bones. These bones are not yet sutured together. This pressure creates a baby with a really big headRounded proximal end that fits into the acetabulum of the hip bone.. Although this situation is not deadly, a vascular shunt will be put in place. This device keeps open either the cerebral aqueduct or the central canal. It allows the CSF to flow as expected down the central canal.