Cerebrospinal Fluid

Cerebrospinal Fluid

A clear, colorless liquid that protects the brain and spinal cord from injuries and carries oxygen, glucose, and necessary chemicals to neurons and neuroglia.

Cerebrospinal Fluid: Composition

CSF primarily consists of water, but also contains small amounts of glucose, proteins, lactic acid, urea, cations (Na⁺, K⁺, Ca²⁺, Mg²⁺), anions (Cl⁻, HCO₃⁻), and some white blood cells.

Ventricular System

The four CSF-filled cavities inside the brain are known collectively as the ventricular system: lateral ventricle, third ventricle, and fourth ventricle

Ventricular System: Lateral Ventricle

Large, C-shaped chambers located in each cerebral hemisphere that produce and hold cerebrospinal fluid

Ventricular System: Septum Pellucidum

A thin, triangular double membrane in the brain that separates the left and right lateral ventricles.

Ventricular System: Third Ventricle

A narrow, midline cavity situated between the right and left halves of the thalamus in the forebrain

Ventricular System: Fourth Ventricle

A tent-like, diamond-shaped cavity positioned at the back of the brainstem between the pons and medulla anteriorly and the cerebellum posteriorly

Cerebrospinal Fluid: Function

• Mechanical protection— serves as a shock-absorbing medium that protects the delicate tissues

• Chemical protection— provides an optimal chemical environment for accurate neuronal signaling

• Circulation— exchanges nutrients and waste products between the blood and adjacent nervous tissue

Choroid Plexus

Choroid plexuses are networks of blood capillaries in the walls of the ventricles mainly produce CSF

Choroid Plexus: Ependymal Cells

Ependymal cells joined by tight junctions cover the blood capillaries of the choroid plexuses.

Cerebrospinal Fluid: Production Process

Substances, mostly water, are filtered from blood plasma through choroid plexus capillaries and then secreted by ependymal cells to form CSF.

Blood-CSF Barrier

A protective barrier formed by tight junctions between ependymal cells that prevents substances from leaking between cells into the CSF and controls which substances can enter the CSF.

Blood-CSF Barrier: Function

The blood-CSF barrier allows selected substances to enter the CSF while excluding potentially harmful substances from the blood.

Blood-CSF Barrier vs. Blood-Brain Barrier: Main Difference

The blood-CSF barrier is formed mainly by tight junctions between ependymal cells, while the blood-brain barrier is formed mainly by tight junctions between brain capillary endothelial cells.

CSF: Circulation: Step 1

CSF is produced by the choroid plexuses of the lateral ventricles and flows into the third ventricle through the interventricular foramina.

CSF: Circulation: Step 2

The CSF then flows through the narrow passage, the aqueduct of the midbrain, which carries it from the third ventricle to the fourth ventricle.

CSF: Circulation: Step 3

CSF leaves the fourth ventricle through one median aperture and two lateral apertures to enter the subarachnoid space

Median Aperture

The single opening in the roof of the fourth ventricle through which CSF enters the subarachnoid space.

Lateral Apertures

The two openings, one on each side of the fourth ventricle, through which CSF enters the subarachnoid space.

CSF: Circulation: Step 4

After leaving the fourth ventricle, CSF circulates through the subarachnoid space around the brain and spinal cord via the central canal

CSF: Circulation: Step 5

CSF is gradually reabsorbed into the blood through arachnoid granulations, villi extensions of the arachnoid mater that project into the dural venous sinuses

CSF: Circulation: Step 5

CSF is gradually reabsorbed into the blood through arachnoid granulations, especially into the superior sagittal sinus, at about 20 mL per hour

CSF: Formation and Reabsorption

Normally, CSF is reabsorbed as rapidly as it is produced by the choroid plexuses, which makes the pressure and volume relatively constant

CSF: Overall Flow

Lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → median/lateral apertures → subarachnoid space and central canal → arachnoid granulations → blood.