Anatomy of the Brain: Ventricles

The brain contains four ventricles: two lateral ventricles in each cerebral hemisphere, a third ventricle in the diencephalon, and a fourth ventricle between the pons and cerebellum. The lateral ventricles each have three projections—anterior, inferior, and posterior horns. These hollow cavities are interconnected by channels and filled with cerebrospinal fluid.

The septum pellucidum, a thin membrane, separates the two lateral ventricles. Each lateral ventricle connects to the third ventricle through the interventricular foramen. The third ventricle then connects to the fourth ventricle via the cerebral aqueduct, a canal-like structure posterior to the third ventricle.

Cerebrospinal fluid is produced and filtered from the choroid plexus, a network of blood capillaries located within the ventricles. These capillaries are lined by tightly joined ependymal cells that secrete CSF directly into the ventricles. The fluid then drains into the central canal of the spinal cord and surrounds the brain.

Cerebrospinal fluid provides mechanical protection to the central nervous system, enabling it to cushion the brain and spinal cord. CSF also enables optimal neural signaling by maintaining the chemical environment necessary for neuron function. Additionally, it acts as a medium for nutrient exchange, delivering essential substances to neural tissue.

Each lateral ventricle has three distinct projections visible from the lateral side: the anterior horn, the inferior horn, and the posterior horn. These projections extend into different regions of the cerebral hemisphere, allowing the ventricles to occupy space within the brain's major lobes and structures.

Cerebrospinal fluid produced by the choroid plexus fills the ventricles and flows from the lateral ventricles through the interventricular foramen into the third ventricle. From there, it passes through the cerebral aqueduct into the fourth ventricle, then drains into the central canal of the spinal cord and surrounds the entire brain and spinal cord.

Ependymal cells are tightly joined cells that line the capillaries of the choroid plexus within the ventricles. These specialized cells actively secrete cerebrospinal fluid from the blood into the ventricles. Their tight junctions create a selective barrier that filters blood to produce CSF with the appropriate composition for protecting and nourishing the central nervous system.