Ventricles of the Brain PDF

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Ventricles of the Brain...

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Ventricles of the Brain During development, the neural tube within the cerebral hemispheres, diencephalon, metencephalon, and medulla oblongata expands to form chambers called ventricles (VEN-trih-klz). The ventricular system is composed of four ventricles (two lateral ventricles, then the third and fourth ventricles) and their passageways (interventricular foramen and cerebral aqueduct). Each cerebral hemisphere contains a large lateral ventricle (Figure 14–2). The septum pellucidum, a thin plate of brain tissue, separates the two lateral ventricles. Because there are two lateral ventricles, the ventricle in the diencephalon is called the third ventricle. The two lateral ventricles are not directly connected, but each communicates with the third ventricle of the diencephalon through an interventricular foramen. The midbrain has a slender canal known as the cerebral aqueduct. This passageway connects the third ventricle with the fourth ventricle. The superior portion of the fourth ventricle lies between the posterior surface of the pons and the anterior surface of the cerebellum. The fourth ventricle extends into the superior portion of the medulla oblongata. There this ventricle narrows and becomes continuous with the central canal of the spinal cord. Ependymal cells, a type of neuroglia, line the ventricles. These cells produce cerebrospinal fluid (CSF) that fills the ventricles and continuously circulates in the CNS. The CSF passes between the interior and exterior of the CNS through three foramina in the roof of the fourth ventricle. We describe these foramina in Section 14-7. The brain is protected and supported by the cranial meninges, cerebrospinal fluid, and the blood brain barrier The delicate tissues of the brain are protected from physical forces by the bones of the cranium, membranes called the cranial meninges, and cerebrospinal fluid. In addition, the nervous tissue of the brain is biochemically isolated from the general circulation by the blood brain barrier. Refer back to Figures 7–3 and 7–4 (pp. 212–215) for a review of the bones of the cranium. We discuss the other protective factors here The Cranial Meninges The layers that make up the cranial meninges—the cranial dura mater, arachnoid mater, and pia mater—are continuous with the spinal meninges. p. 437 However, the cranial meninges have distinctive anatomical and functional characteristics...