The ventricles are cavities within the brain filled with CSF. The formation, circulation, and locations of the CSF will be explained with Figure 21.
The ventricles of the brain are the spaces within the brain that remain from the original neural tube, the tube that was present during development. The cells of the nervous system, both neurons and glia, originated from a germinal matrix that was located adjacent to the lining of this tube. The cells multiply and migrate away from the walls of the neural tube, forming the nuclei and cerebral cortex. As the nervous system develops, the mass of tissue grows and the size of the tube diminishes, leaving various spaces in different parts of the nervous system (see Figure OA and Figure OL).
The parts of the tube that remain in the hemispheres are called the cerebral ventricles, also called the lateral ventricles. The lateral ventricle of the hemispheres, shown here from the lateral perspective, is shaped like the letter C (in reverse); it curves posteriorly and then enters into the temporal lobe. Its various parts are: the anterior horn, which lies deep to the frontal lobes; the central portion, or body, which lies deep to the parietal lobes; the atrium or trigone, where it widens and curves and then enters into the temporal lobe as the inferior horn. In addition, there may be an extension into the occipital lobes, the occipital or posterior horn, and its size varies. These lateral ventricles are also called ventricles I and II (assigned arbitrarily).
Each lateral ventricle is connected to the midline third ventricle by an opening, the foramen of Monro (inter-ventricular foramen — seen in the medial view of the brain, Figure 17 and Figure 41B; also Figure 20B and Figure 21). The third ventricle is a narrow slit-like ventricle between the thalamus on either side and could also be called the ventricle of the diencephalon (see Figure
9B). Sectioning through the brain in the midline (as in Figure 17) passes through the third ventricle. Note that the "hole" in the middle of the third ventricle represents the interthalamic adhesion, linking the two thalami across the midline (see Figure 6; discussed with Figure 11; see also Figure 41B).
The ventricular system then narrows considerably as it goes through the midbrain and is now called the aqueduct of the midbrain, the cerebral aqueduct, or the aqueduct of Sylvius (see Figure 17, Figure 18, and Figure 20B; also Figure 41B and Figure 65). In the hindbrain region, the area consisting of pons, medulla, and cerebellum, the ventricle widens again to form the fourth ventricle (see Figure 17, Figure 20B, and Figure 66). The channel continues within the CNS and becomes the very narrow central canal of the spinal cord (see Figure 17, Figure 20B, Figure 21, and Figure 69).
Specialized tissue, the choroid plexus, the tissue responsible for the formation of the CSF, is located within the ventricles. It is made up of the lining cells of the ventricles, the ependyma, and pia with blood vessels (discussed with Figure 21). This diagram shows the choroid plexus in the body and inferior horn of the lateral ventricle; the tissue forms large invaginations into the ventricles in each of these locations (see Figure 27 and Figure 74 for a photographic view of the choroid plexus). The blood vessel supplying this choroid plexus comes from the middle cerebral artery (shown here schematically; see Figure 58). Choroid plexus is also found in the roof of the third ventricle and in the lower half of the roof of the fourth ventricle (see Figure 21).
CSF flows through the ventricular system, from the lateral ventricles, through the interventricular foramina into the third ventricle, then through the narrow aqueduct and into the fourth ventricle (see Figure 21). At the bottom of the fourth ventricle, CSF flows out of the ventricular system via the major exit, the foramen of Magendie, in the midline, and enters the subarachnoid space. There are two additional exits of the CSF laterally from the fourth ventricle — the foramina of Luschka, which will be seen in another perspective (in the next illustration).
F = Frontal lobe T = Temporal lobe P = Parietal lobe O = Occipital lobe
LVa = Anterior horn LVb = Body LVt =Atrium (trigone) LVj = Inferior horn LVo = Occipital horn
3 = 3rd ventricle
Aq = Aqueduct of midbrain
4 = 4th ventricle
C = Cerebellum
Mc = Middle cerebral Ic = Internal carotid
Cp = Choroid plexus
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