Ventricles of the Brain: Anatomy, Function, CSF Flow
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Ventricles of the Brain - Intro
We will discuss the ventricles of the brain along with their anatomy and function, as well as the flow of cerebrospinal fluid (CSF) through those structures.
By definition, the ventricles are cavities located within the brain that contain cerebrospinal fluid.
The ventricles function to produce, circulate, and reabsorb CSF throughout the brain and spinal cord of the central nervous system.
The ventricular system comprises two lateral ventricles, one third ventricle, and one fourth ventricle that communicate with each other through the interventricular foramina and cerebral aqueduct.
We will use labeled diagrams and lateral views of the brain to learn the anatomy, boundaries, and locations of each ventricle.
We will also learn how cerebrospinal fluid is produced, and how it flows throughout the ventricular system, subarachnoid space, and central canal of the spinal cord.
Every EZmed post contains simple tricks to help you learn the information, and today you will be given the below mnemonic to remember all the structures of the ventricular system as well as the order in which CSF flows through those structures.
Let’s get started!
Ventricles of the Brain - Mnemonic
We will be discussing the anatomy of the ventricular system next, however here is a sneak peak of the mnemonic we will use to remember the structures of the ventricular system along with the order in which CSF flows through those structures:
Image: Simple mnemonic to remember the structures of the ventricular system along with the order in which cerebrospinal fluid flows through those structures.
Ventricular System Anatomy
The ventricular system is a network of communicating cavities within the brain, called ventricles, that function to produce, transport, and reabsorb cerebrospinal fluid (CSF) throughout the central nervous system.
The main structures that make up the ventricular system include:
Lateral Ventricles (2)
Interventricular Foramina (2)
Third Ventricle
Cerebral Aqueduct
Fourth Ventricle
Image (Lateral View): The main structures of the ventricular system include the lateral ventricles (2), interventricular foramina (2), third ventricle, cerebral aqueduct, and fourth ventricle.
The lateral ventricles communicate with the third ventricle through the interventricular foramina (foramina of Monro).
The third ventricle communicates with the fourth ventricle through the cerebral aqueduct (Sylvian aqueduct).
The fourth ventricle narrows caudally to connect with the central canal of the spinal cord.
Let’s walk through each structure of the ventricular system starting with the lateral ventricles.
Image (Lateral View): The lateral ventricles communicate with the third ventricle through the interventricular foramina. The third ventricle communicates with the fourth ventricle through the cerebral aqueduct. The fourth ventricle connects to the central canal of the spinal cord.
Image (Coronal/Frontal View): There are 2 lateral ventricles, one located in each cerebral hemisphere. The third ventricle is located in the midline of the brain, in the diencephalon, below the lateral ventricles. Each lateral ventricle connects to the third ventricle through an interventricular foramen (drawn in to help visualize).
Lateral Ventricles
The brain has 2 lateral ventricles, one located in each cerebral hemisphere.
We will now discuss the anatomical features of the lateral ventricles along with the structures that border them.
Anatomical Features - Lateral Ventricles
The lateral ventricles are a pair of C-shaped cavities with one located in each cerebral hemisphere.
The lateral ventricles are the largest cavities of the ventricular system.
Each lateral ventricle has a central portion called the body, and 3 extensions known as horns.
The 3 extensions are the anterior (frontal) horn, posterior (occipital) horn, and inferior (temporal) horn.
The body extends from the interventricular foramen anteriorly to the splenium of the corpus callosum posteriorly.
The body of the lateral ventricle is located primarily in the parietal lobe with the anterior horn extending anteriorly into the frontal lobe, the posterior horn extending posteriorly into the occipital lobe, and the inferior horn extending inferiorly into the temporal lobe.
The body becomes continuous with the posterior and inferior horns at the atrium (or trigone), a triangular area located behind the body of the lateral ventricle.
The body becomes continuous with the anterior horn at the location of the interventricular foramen.
On the underside of each lateral ventricle is a hole known as the interventricular foramen (foramen of Monro).
The interventricular foramina are bordered by the fornix anteriorly and the thalamus posteriorly, creating channels that connect the lateral ventricle to the third ventricle.
The CSF produced by the lateral ventricles travels to the third ventricle through the interventricular foramina - more on this later in the CSF section!
Image (Lateral View): The lateral ventricles are a pair of C-shaped cavities and are the largest in the ventricular system. The body of the lateral ventricle becomes continuous with the anterior horn at the interventricular foramen (brown rectangle) as indicated by the left red star. The body becomes continuous with the posterior and inferior horns at the atrium (right red star).
Boundaries - Lateral Ventricles
The lateral ventricles are cavities created by surrounding structures that form the walls of the ventricle.
The lateral ventricles have a medial wall, roof, and a floor/lateral wall.
The structures that form these walls vary depending on which segment of the ventricle is being viewed.
Let’s walk through the boundaries of the anterior horn, body, posterior horn, and inferior horn.
We will also look at sagittal views and coronal views of the brain/ventricles to help illustrate the boundaries.
Anterior (Frontal) Horn
Medial Wall: Septum Pellucidum
Roof: Corpus Callosum (Body/Trunk)
Floor/Lateral Wall: Caudate Nucleus (Head) and Corpus Callosum (Rostrum)
Anterior Wall: Corpus Callosum (Genu)
The anterior (frontal) horn extends anteriorly from the body of the lateral ventricle and is located in the frontal lobe.
A thin membrane, called the septum pellucidum, travels between the 2 lateral ventricles from the corpus callosum to the fornix.
As the septum pellucidum separates the anterior horn of the left lateral ventricle from the anterior horn of the right lateral ventricle, it forms the medial wall of the anterior horns as a result.
The roof of the anterior horn is formed by the body (trunk) of the corpus callosum.
The corpus callosum connects the right and left cerebral hemispheres and allows them to communicate with one another.
The floor/lateral wall of the anterior horn is formed by the head of the caudate nucleus (a component of the basal ganglia) and the rostrum of the corpus callosum.
The anterior wall is formed by the genu of the corpus callosum.
Image (Sagittal View): The vertical black line traverses the anterior horn of the lateral ventricle. The roof is formed by the body of the corpus callosum. The anterior wall is formed by the genu of the corpus callosum. The medial wall is formed by the septum pellucidum. The floor/lateral wall is formed by the rostrum of the corpus callosum (along with the head of the caudate nucleus - see next image below).
Image (Sagittal View): The vertical black line traverses the anterior horn of the lateral ventricle. The floor/lateral wall is formed by the head of the caudate nucleus (along with the rostrum of the corpus callosum - see previous image above). The bottom right image is a section through the body of the lateral ventricle, but can be used as a reference to show the lateral ventricle is medial to the caudate.
Image (Sagittal View): Appreciate the relationship between the lateral ventricle and caudate nucleus. The head of the caudate nucleus forms part of the floor/lateral wall of the anterior horn of the lateral ventricle.
Body (Central Portion)
Medial Wall: Septum Pellucidum and Body of the Fornix
Roof: Corpus Callosum (Body/Trunk)
Floor/Lateral Wall: Caudate Nucleus (Body) and Thalamus
The body of the lateral ventricle is located primarily in the parietal lobe.
The body extends from the interventricular foramen anteriorly to the splenium of the corpus callosum posteriorly.
The septum pellucidum will again form part of the medial wall, with the body of the fornix forming the remainder (as we have now moved posterior to the anterior horn).
The body (trunk) of the corpus callosum will again form the roof.
The body of the caudate nucleus forms part of the floor (laterally), however it is not large enough to border the entire floor as the caudate nucleus decreases in size from head to tail.
The remainder of the floor is formed by the thalamus (medially).
Between the caudate nucleus and thalamus are the stria terminalis and thalamostriate vein.
Of note, there is a choroid plexus located medially on the floor of the body, between the upper surface of the thalamus and fornix - more on this later in the CSF section!
Image (Coronal/Frontal View): The lateral ventricle bodies are shown in blue. The roof is formed by the body of the corpus callosum. The floor/lateral wall is formed by the body of the caudate nucleus (laterally) and thalamus (medially). The medial wall is formed by the septum pellucidum and body of the fornix.
Image (Sagittal View): The vertical black line traverses the body of the lateral ventricle. The roof is formed by the body of the corpus callosum. The medial wall is formed by the septum pellucidum and the body of the fornix. See next image below for the floor/lateral wall.
Image (Sagittal View): The vertical black line traverses the body of the lateral ventricle. The floor/lateral wall is formed by the body of the caudate nucleus (laterally) and the thalamus (medially). The roof is formed by the body of the corpus callosum. See previous image above for the medial wall.
Image (Sagittal View): Appreciate the relationship between the lateral ventricle, caudate nucleus, and thalamus. The body of the caudate nucleus and the thalamus form the floor/lateral wall of the body of the lateral ventricle.
Image (Sagittal View): Appreciate the relationship between the caudate nucleus and thalamus, and how their anatomy will form the floor/lateral wall of different parts of the lateral ventricle.
Posterior (Occipital) Horn
Roof/Lateral Wall: Corpus Callosum (Tapetum), Optic Radiation, Inferior Longitudinal Fasciculus
Floor/Medial Wall: Forceps Major and Calcar Avis
The posterior (occipital) horn extends posteriorly from the atrium of the lateral ventricle and is located in the occipital lobe.
The roof and lateral wall of the posterior horn are formed by the tapetum of the corpus callosum (fibers from the splenium), the optic radiation, and the inferior longitudinal fasciculus.
Fibers from the splenium of the corpus callosum also travel posteriorly and contribute to the forceps major, providing a connection between the occipital lobes.
The floor/medial wall of the posterior horn has 2 bulges - an upper and a lower indentation.
The upper bulge is formed by the forceps major and is referred to as the bulb of the posterior horn.
The lower bulge is produced by the calcarine fissure/sulcus and is known as the calcar avis.
Image (Sagittal View): The vertical black line traverses the posterior horn of the lateral ventricle. Fibers from the splenium of the corpus callosum form the medial wall, roof, and lateral wall of the posterior horn - see next image below.
Image (Coronal/Frontal View): The roof/lateral wall of the posterior horn is formed by the tapetum of the corpus callosum, optic radiation, and inferior longitudinal fasciculus (I.L.F.). The floor/medial wall is formed by the forceps major superiorly (bulb of the posterior horn) and the calcar avis inferiorly.
Inferior (Temporal) Horn
Roof (Above and Laterally): Stria Terminalis, Caudate Nucleus (Tail), Corpus Callosum (Tapetum)
Floor (Below and Medially): Hippocampus and Collateral Eminence
Anterior Wall/Roof: Amygdaloid Complex
The inferior (temporal) horn extends inferiorly from the atrium of the lateral ventricle and is located in the temporal lobe.
The inferior horn forms a curve around the posterior aspect of the thalamus, and it is the longest and largest of the 3 horns.
The inferior horn is a narrow cavity and is bound above and laterally by the roof, and below and medially by the floor.
The roof of the inferior horn is formed by the stria terminalis and tail of the caudate nucleus medially, and the tapetum of the corpus callosum laterally.
The stria terminalis and tail of the caudate nucleus end anteriorly at the amygdaloid complex.
Therefore, the amygdala is located in the anterior roof/wall of the inferior horn.
The floor of the inferior horn is formed by the hippocampus and associated structures medially, and the collateral eminence produced the by the collateral sulcus laterally.
Of note, there is a choroid plexus located medially on the floor of the inferior horn - more on this later in the CSF section!
Image (Sagittal View): The roof of the inferior horn of the lateral ventricle is formed by by the tail of the caudate nucleus (stria terminalis and tapetum not shown). The floor is formed by the hippocampus (collateral eminence not shown). The amygdala is located at the anterior roof/wall.
Image (Sagittal View): Appreciate how the relationship between the caudate nucleus, thalamus, and hippocampus will form the floor and roof of various parts of the lateral ventricle.
Third Ventricle
The lateral ventricles communicate with the third ventricle through the interventricular foramina (foramina of Monro).
We will now discuss the anatomical features of the third ventricle along with the structures that border it.
Anatomical Features - 3rd Ventricle
The third ventricle is a slit-like cavity located in the midline of the brain in the diencephalon between the 2 thalami and hypothalamus.
The interventricular foramina enter the third ventricle at its anterosuperior aspect, allowing the lateral ventricles to communicate with the third ventricle.
The cerebral aqueduct (Sylvian aqueduct or aqueduct of Sylvius) exits the third ventricle at its posteroinferior aspect, allowing the third ventricle to communicate with the fourth ventricle.
The interthalamic adhesion is a mass of grey matter that travels through the third ventricle and connects the 2 thalami (may be absent in some individuals).
The CSF produced by the third ventricle and received by the lateral ventricles (via the interventricular foramina) travels to the fourth ventricle through the cerebral aqueduct - more on this later in the CSF section!
Image (Lateral View): The third ventricle is located in the midline of the brain. It communicates with the lateral ventricles through the interventricular foramina, and with the fourth ventricle through the cerebral aqueduct. The interthalamic adhesion travels through the third ventricle and connects the 2 thalami.
Recesses - 3rd Ventricle
The third ventricle has 5 main recesses that protrude into surrounding structures:
Infundibular Recess: Located on the floor of the third ventricle below the optic chiasm, the infundibular recess protrudes inferiorly into the infundibulum (pituitary stalk) that connects the pituitary gland to the hypothalamus.
Supraoptic Recess: Located on the lower anterior aspect of the third ventricle above the optic chiasm (and infundibular recess) and below the lamina terminalis.
Anterior Recess (Vulva or Bulb of the Ventricle): Recess formed on the anterosuperior aspect of the third ventricle where the interventricular foramina enter the third ventricle laterally.
Pineal Recess: Located on the posterior aspect of the third ventricle and protrudes posteriorly into the stalk of the pineal gland.
Suprapineal Recess: Located on the upper posterior aspect of the third ventricle, protruding above the pineal recess/gland and below the choroid plexus/tela choroidea that make up the roof.
Image (Sagittal View): The 5 main recesses of the third ventricle.
Image (Sagittal View): Location of the third ventricle and its associated recesses.
Image (Sagittal View): The 5 main recesses of the third ventricle. The infundibular recess protrudes inferiorly into the pituitary stalk (infundibulum). The optic chiasm is located above the infundibular recess and below the supraoptic recess (S.O.). The anterior recess is formed near the location of the interventricular foramina entry. The pineal recess protrudes posteriorly into the stalk of the pineal gland. The suprapineal recess (S.P.) is located above the pineal recess and below the tela choroidea/choroid plexus.
Boundaries - 3rd Ventricle
Similar to the lateral ventricles, the third ventricle is a cavity created by surrounding structures that form the walls of the ventricle.
The third ventricle has a roof, floor, and 4 walls (anterior, posterior, and 2 lateral).
Roof: (Anterior to Posterior)
(Interventricular Foramina) - Separates roof and anterior wall
Fornix
Choroid Plexus/Tela Choroidea
(Suprapineal Recess) - Separates roof and posterior wall
The roof of the third ventricle extends from the interventricular foramina anteriorly to the suprapineal recess posteriorly.
The anterior roof is formed by part of the fornix.
The remainder of the roof is formed by the tela choroidea, a highly vascularized membrane formed by a double layer of pia mater that adheres closely to the ependymal layer of the third ventricle.
Two longitudinal vascular fringes project downward from the tela choroidea and give rise to the choroid plexus of the third ventricle.
The choroid plexus is involved in CSF production.
We will discuss the tela choroidea and choroid plexus in more detail in the CSF section below.
The body of the fornix and hippocampal commissure are located above the tela choroidea/choroid plexus.
Image (Sagittal View): The roof of the third ventricle extends from the interventricular foramina (I.F.) anteriorly to the suprapineal recess (S.P.R.) posteriorly. The roof is formed by the fornix and tela choroidea/choroid plexus (anterior to posterior).
Anterior Wall: (Superior to Inferior)
(Interventricular Foramina) - Separates anterior wall and roof
Anterior Columns of Fornix
Anterior Commissure
Lamina Terminalis
(Optic Chiasm) - Separates anterior wall and floor
The anterior wall of the third ventricle extends from the interventricular foramina superiorly to the optic chiasm inferiorly.
The anterior columns of the fornix form the superior lateral margins of the anterior wall.
The anterior commissure also crosses the upper anterior wall.
Lastly, the lamina terminalis is a thin membrane running from the rostrum of the corpus callosum superiorly to the optic chiasm inferiorly, passing by the anterior commissure, and forms the lower anterior wall.
As mentioned above, the supraoptic recess is located in the lower anterior wall and is formed by the lamina terminalis above it and the optic chiasm below it.
The anterior recess is located at the anterosuperior aspect of the third ventricle near the entry of the interventricular foramina.
Image (Sagittal View): The anterior wall of the third ventricle extends from the interventricular foramina (I.F.) superiorly to the optic chiasm (O.C.) inferiorly. The anterior wall is formed by the fornix, anterior commissure, and lamina terminalis (superior to inferior).
Floor: (Anterior to Posterior)
(Optic Chiasm) - Separates floor and anterior wall
Infundibulum
Tuber Cinereum
Mammillary Bodies
Posterior Perforated Substance
Tegmentum of Midbrain
(Cerebral Aqueduct) - Separates floor and posterior wall
The floor of the third ventricle extends from the optic chiasm anteriorly to the cerebral aqueduct posteriorly.
The floor is formed by (anterior to posterior) the optic chiasm, infundibulum, tuber cinereum, mammillary bodies, posterior perforated substance, and the tegmentum of the midbrain.
As mentioned above, the infundibular recess is located on the floor of the third ventricle and protrudes from the tuber cinereum into the infundibulum (pituitary stalk) of the pituitary gland (between the optic chiasm and mammillary bodies).
Image (Sagittal View): The floor of the third ventricle extends from the optic chiasm (O.C.) anteriorly to the cerebral aqueduct (C.A.) posteriorly. The floor is formed by the optic chiasm, infundibulum, tuber cinereum, mammillary bodies, posterior perforated substance, and the tegmentum of the midbrain (anterior to posterior).
Posterior Wall: (Superior to Inferior)
(Suprapineal Recess) - Separates posterior wall and roof
Habenular Commissure
Pineal Gland and Recess
Posterior Commissure
(Cerebral Aqueduct) - Separates posterior wall and floor
The posterior wall of the third ventricle extends from the suprapineal recess superiorly to the cerebral aqueduct inferiorly.
The posterior wall is formed by (superior to inferior) the habenular commissure, pineal gland, and posterior commissure.
As mentioned above, the suprapineal recess is located in the upper posterior wall above the pineal gland and below the tela choroidea of the roof.
The pineal recess is also located in the posterior wall (below the suprapineal recess) and protrudes into the pineal stalk of the pineal gland.
Image (Sagittal View): The posterior wall of the third ventricle extends from the suprapineal recess (S.P.R.) superiorly to the cerebral aqueduct (C.A.) inferiorly. The posterior wall is formed by the habenular commissure, pineal gland, and posterior commissure (superior to inferior).
Lateral Walls: (Superior to Inferior)
Thalamus - Upper Part
Hypothalamus - Lower Part
As mentioned earlier, the third ventricle is located in the midline of the brain between the right and left thalamus and part of the hypothalamus.
Therefore, the thalamus and hypothalamus form the lateral walls of the third ventricle.
The hypothalamic sulcus is a groove in the lateral wall of the third ventricle marking the boundary between the thalamus and hypothalamus.
The hypothalamic sulcus travels from the interventricular foramen to the cerebral aqueduct, and it divides the lateral wall into an upper and lower portion.
The larger upper part is formed by the medial surface of the thalamus, and the smaller lower part is formed by the hypothalamus.
Image (Coronal/Frontal View): The lateral walls of the third ventricle are formed by the 2 thalami (and hypothalamus - see next image below).
Image (Sagittal View): The hypothalamic sulcus is a groove in the lateral wall of third ventricle marking the boundary between the thalamus and hypothalamus. It divides the lateral wall into an upper part formed by the thalamus and a lower part formed by the hypothalamus.
4th Ventricle
The third ventricle communicates with the fourth ventricle through the cerebral aqueduct (Sylvian aqueduct or aqueduct of Sylvius).
We will now discuss the anatomical features of the fourth ventricle along with the structures that border it.
Anatomical Features - 4th Ventricle
The fourth ventricle is a diamond shaped cavity located between the brainstem and cerebellum, with the pons and medulla oblongata located anteriorly and the cerebellum located posteriorly.
The fourth ventricle appears tent-like from the lateral view. The apex of the tent is known as the fastigium and projects posteriorly into the cerebellum.
The third ventricle is connected to the fourth ventricle through the cerebral aqueduct.
The cerebral aqueduct is the narrowest part of the ventricular system and is prone to blockages as a result.
This may cause a condition known as hydrocephalus in which CSF accumulates in the ventricles due to the obstruction.
The fourth ventricle also communicates with the subarachnoid space through 2 lateral apertures (foramina of Luschka) and one median aperture (foramen of Magendie).
The 2 lateral apertures are located in the lateral recesses of the fourth ventricle and communicate with the cerebellopontine angle.
The median aperture is located in the lower roof of the fourth ventricle and communicates with the cisterna magna (cerebellomedullary cistern).
The fourth ventricle narrows caudally to connect with the central canal of the spinal cord. This area of the fourth ventricle is known as the obex.
The obex is located approximately at the level of the foramen magnum of the skull where the spinal cord and brainstem meet.
The CSF produced by the fourth ventricle and received by the third ventricle (via the cerebral aqueduct) travels into the central canal of the spinal cord as well as through the apertures into the subarachnoid space - more on this later in the CSF section!
Image (Lateral View): The fourth ventricle is located between the brainstem and cerebellum. It communicates with the third ventricle through the cerebral aqueduct, and narrows caudally at the obex to connect with the central canal of the spinal cord. The apex of the fourth ventricle is known as the fastigium.
Image (Lateral View): The fourth ventricle communicates with the subarachnoid space through the 2 lateral apertures (foramina of Luschka) and a median aperture (foramen of Magendie). They empty into the cerebellopontine angle and cisterna magna respectively.
Recesses - 4th Ventricle
The fourth ventricle has 5 main recesses:
Lateral Recesses (2) - Extend laterally off the lateral walls of the fourth ventricle. Each lateral recess opens into the subarachnoid space through the lateral aperture (foramen of Luschka)
Median Dorsal Recess - Extends dorsally into the cerebellum
Lateral Dorsal Recesses (2) - Extend dorsally on either side of the median dorsal recess
Image (Lateral View): The fourth ventricle has two lateral recesses, one median dorsal recess, and 2 lateral dorsal recesses. Appreciate the tent-like appearance of the fourth ventricle when viewing the top image from the side (top red arrow). Appreciate the starfish appearance when looking down at the fourth ventricle as seen in the bottom image (down arrow).
Boundaries - 4th Ventricle
Similar to the other ventricles discussed above, the fourth ventricle is a cavity created by surrounding structures that form the walls of the ventricle.
The fourth ventricle has 2 lateral walls, a roof, and a floor.
Floor (Anterior Wall) - Rhomboid Fossa
Superior: Pons
Inferior: Medulla Oblongata
The floor (anterior wall) of the fourth ventricle is formed by the posterior surface of the pons superiorly and the upper medulla inferiorly.
The floor is shaped like a rhomboid and is often referred to as the rhomboid fossa for this reason.
Image (Sagittal View): The floor of the fourth ventricle is formed by the pons superiorly and the medulla inferiorly.
Roof (Posterior Wall)
Superior: Superior Cerebellar Peduncles and Superior Medullary Velum
Inferior: Tela Choroidea/Choroid Plexus, Inferior Medullary Velum, Inferior Cerebellar Peduncles
The roof (posterior wall) of the fourth ventricle is shaped like a tent, and the fastigium (apex) of the tent divides the roof into a superior and inferior part.
The superior part is formed by the superior cerebellar peduncles and the superior medullary velum, a thin layer of tissue suspended in the midline between the superior cerebellar peduncles.
The inferior part of the roof is formed by a thin sheet of tissue known as the inferior medullary velum.
Medially, the inferior medullary velum is formed by the ependymal layer of the fourth ventricle and the tela choroidea.
The tela choroidea gives rise to the choroid plexus which is involved in CSF production.
The inferior medullary velum extends laterally to join the inferior cerebellar peduncles.
The median aperture (foramen of Magendie) is located in the lower part of the roof, allowing the fourth ventricle to communicate with the subarachnoid space and deliver CSF into the cisterna magna (cerebellomedullary cistern).
Image (Sagittal View): The fastigium (apex) of the fourth ventricle divides the roof into a superior and inferior part. The superior part (purple) is formed by the superior cerebellar peduncles and superior medullary velum. The inferior part (orange) is formed by the tela choroidea/choroid plexus, inferior medullary velum, and inferior cerebellar peduncles laterally.
Lateral Walls
Superior: Superior Cerebellar Peduncles
Inferior: Inferior Cerebellar Peduncles, Cuneate Tubercles, Gracile Tubercles
The lateral walls of the fourth ventricle can be divided into a superior and inferior part.
The superior part is formed by the superior cerebellar peduncles.
The inferior part is formed by the inferior cerebellar peduncles, and by the gracile and cuneate tubercles of the brainstem.
The lateral recesses project off of each lateral wall, extending laterally and opening into the subarachnoid space as the lateral apertures (foramina of Luschka).
CSF exits the fourth ventricle through the lateral apertures and enters the cerebellopontine angle.
Image: Looking down onto the diamond-shaped floor of the fourth ventricle, we can see the posterior surface of the pons superiorly and the upper medulla inferiorly. The lateral walls of the fourth ventricle are formed by the superior cerebellar peduncles superiorly, and by the inferior cerebellar peduncles, cuneate tubercles, and gracile tubercles inferiorly.
CSF Production and Flow
The main function of the ventricular system is to produce, circulate, and reabsorb CSF.
CSF has several important roles such as providing buoyancy, protection, chemical stability, and waste elimination to the brain.
Buoyancy - The CSF-filled ventricles and surrounding CSF in the subarachnoid space allow the brain to “float” and become buoyant thereby reducing the weight of the brain in the cranium.
Protection - The cerebrospinal fluid acts as a cushion to lubricate and protect the brain and spinal cord.
Chemical Stability - The CSF maintains a stable environment for the brain.
Filtration System - The CSF provides nutrients and removes metabolic waste from the central nervous system as it gets reabsorbed into the vasculature.
We will discuss how CSF is produced and the flow of CSF through the ventricular system.
CSF Production
The ventricles are lined by ependymal cells, and CSF is produced by specialized ependymal cells on the choroid plexus.
What is the choroid plexus?
The choroid plexus is a projection of pia mater (the innermost meningeal layer of the brain) into the ventricle and is lined by specialized ependymal cells.
The choroid plexus contains a network of capillaries, and the capillary plasma is filtered to produce CSF in the ventricles.
The specialized cells of the choroid plexus form tight junctions limiting what can pass from the capillaries into the ventricles.
As a result, the choroid plexus also plays a role in forming the blood-CSF barrier to prevent the passage of large and/or unwanted substances into the CSF.
Ions, vitamin, nutrients, and water are among the substances that do get filtered into the CSF.
Furthermore, the specialized ependymal cells of the choroid plexus have microvilli on their apical surface that absorb and remove metabolic waste from the CSF.
Therefore, the choroid plexus assists the brain by providing CSF protection, nourishment, and waste removal.
There is a choroid plexus located in all 4 ventricles and the 2 interventricular foramina, allowing CSF to be produced in each of these structures.
The cerebral aqueduct along with the anterior and posterior horns of the lateral ventricle are the only areas lacking a choroid plexus.
Image (Sagittal View): The ventricles produce, circulate, and reabsorb cerebrospinal fluid (CSF), and are lined by ependymal cells. Certain regions of each ventricle are lined by a vascularized, double layer of pia mater called the tela choroidea. The tela choroidea gives rise to projections lined by specialized ependymal cells, called the choroid plexus (green areas indicated by red stars), which produce most of the CSF.
CSF Flow
The ventricles not only produce their own CSF, but they also receive CSF from the ventricles upstream.
This is especially true since the lateral ventricles produce the most amount of CSF thereby creating a hydrostatic gradient through the rest of the ventricular system.
CSF produced in the lateral ventricles travels to the third ventricle through the interventricular foramina.
The CSF then travels to the fourth ventricle through the cerebral aqueduct.
CSF can then exit the fourth ventricle and enter the subarachnoid space through 2 lateral apertures (foramina of Luschka) or 1 medial aperture (foramen of Magendie).
Therefore, the apertures of the fourth ventricle are the connection between the CSF in the internal ventricular system and the CSF in the external subarachnoid system.
Remember the subarachnoid space is the space between the pia mater and arachnoid mater, 2 of the meningeal layers that surround the central nervous system.
CSF can also exit the fourth ventricle into the central canal of the spinal cord.
There are several factors that contribute to the flow of CSF including: hydrostatic pressure as CSF is being produced, arterial pulsations of the vasculature, and directional beating by the cilia that line the ependymal cells.
Image (Sagittal View): Flow of cerebrospinal fluid (CSF) through the lateral ventricles, interventricular foramina, third ventricle, cerebral aqueduct, fourth ventricle, and subarachnoid space or central canal of the spinal cord.
CSF is reabsorbed from the subarachnoid space into the dural venous sinuses and subsequent venous vasculature.
The arachnoid villi and granulations protrude into the dural venous sinuses and are the site of the reabsorption of the CSF from the subarachnoid space into the venous sinuses.
Image (Sagittal View): Cerebrospinal fluid (CSF) is reabsorbed from the subarachnoid space into the dural venous sinuses through projections of the arachnoid membrane called arachnoid granulations (red circles). The dural venous sinuses drain into the internal jugular vein.
Image: Cerebrospinal fluid (CSF) flows through the subarachnoid space (green arrows) between the arachnoid and pia mater. CSF is reabsorbed into the dural venous sinuses through projections called arachnoid granulations.
Image: Arachnoid granulations (red circles) are projections of the arachnoid membrane through the meningeal layer of the dura mater into the dural venous sinuses. Cerebrospinal fluid (CSF) is reabsorbed from the subarachnoid space into the dural sinuses through these arachnoid granulations.
Ventricular System Mnemonic
Here is a simple mnemonic to remember the CSF flow through the ventricular system:
“Liquid Inside The Cerebrum Flows Around Subarachnoid Space”
Liquid = Lateral Ventricles
Inside = Interventricular Foramina
The = Third Ventricle
Cerebrum = Cerebral Aqueduct
Flows = Fourth Ventricle
Around = Apertures
Subarachnoid = Subarachnoid Space
Space = Sinuses (venous)
This mnemonic is useful because it pertains to the CSF within the cerebrum flowing into the subarachnoid space.
Image: Mnemonic to remember the structures of the ventricular system, along with the order in which cerebrospinal fluid (CSF) flows.
Conclusion
Hopefully this was a good overview of the ventricular system along with the structures, their anatomy, and CSF flow.
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