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Ventricular system

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Ventricles.jpg

The ventricular system is a group of four cavities in the brain. It includes the lateral ventricles, the third ventricle, and the fourth ventricle. Ependymal cells in the ventricles are responsible for the production of cerebrospinal fluid. This is an important function because cerebrospinal fluid prevents injury to the brain, decreases the total weight of the brain so it experiences less pressure, and maintains chemical balance. The lateral ventricles are larger than the other ventricles and form most of the cerebrospinal fluid. Interventricular foramina lead from the lateral ventricles to the third ventricle, and the cerebral aqueduct connects the third and fourth ventricles.

Anatomy

Chart depicting the major structures of the ventricular system

The ventricles appear as hollow cavities in the brain. They are surrounded by ependymal cells, which form and distribute cerebrospinal fluid, blood vessels, which provide nutrients, and supporting cells. Together, these form the choroid plexuses. The brain contains four ventricles. These include two lateral ventricles, located in the hemispheres of the brain, and the third and fourth ventricles.[1]

Interventricular foramina, or holes, allow the lateral ventricles to send messages to the third ventricle, and the cerebral aqueduct forms the connection between the third and fourth ventricles.[1] In embryos, the ventricles form as part of the neural tube.[2] The lateral ventricles start out as lobes on the top of the tube. On the other side of the tube, the third and fourth ventricles develop as part of the diencephalon and the midbrain.[1]

Function

Tubes filled with cerebrospinal fluid

The ependymal cells in the ventricles create and distribute cerebrospinal fluid.[1] Cerebrospinal fluid has several important functions. First, it protects the brain against damage and injury. Being suspended in cerebrospinal fluid also decreases the brain's total weight, reducing the pressure put on it. Also, cerebrospinal fluid maintains the proper level of chemicals for the brain to work at its maximum potential. By producing cerebrospinal fluid, the ventricles are instrumental in all of these functions[3]

The choroid plexus, especially in the lateral ventricles, is responsible for the making of most cerebrospinal fluid in the body. This liquid travels through the interventricular foramina to the third ventricle and from the cerebral aqueduct to the fourth ventricle. This occurs because of the hydrostatic pressure that builds up when cerebrospinal fluid, the pulsating of arteries, and the movement of cilia on ependymal cells. Eventually, the cerebrospinal fluid enters the arachnoid space and goes into the bloodstream through arachnoid villi[4]

Lateral Ventricles

Main structures of the lateral ventricles

The lateral ventricles are larger than the third and fourth ventricles and are located in the right and left hemispheres of the brain. Together, they create approximately eighty percent of the cerebrospinal fluid.[1] They each consist of a central body, which can be found in the parietal lobe, and three horns. A grouping of nerve fibers called the corpus callosum makes up the top of each lateral ventricle and the choroid plexus, the front part of the fornix, the dorsal surface of the thalamus, the striater terminalis, and the caudate nucleus are on the bottom.[5][4] On the side of each lateral ventricle is the septum pellucidum, a membrane that serves as a barrier between the two lateral ventricles.[6][4]

In between the fornix and the thalamus, one can find the interventricular foramina, which lead to the third ventricle. The frontal horn sits in front of the interventricular foramina. The posterior and inferior horns can be found in the occipital and temporal lobes, respectively. Capillaries extend into the choroid plexus of each lateral ventricle from the pia mater, which is the inner membrane surrounding the brain, and the tela choroidia, a double layer of pia mater, connects the choroid plexus to nearby parts of the brain.[4][7]

Third and Fourth Ventricles

The third ventricle is located in the diencephalon. The foramina of Monro (an interventricular foramina)leads into it from the lateral ventricles. In the top of the third ventricle is a tela choroidea that contains arteries. The hypothalamus and medial thalamus make up its lateral sides. In the front it has a collection of fibers known as the anterior commissure, a plate called the lamina terminalis, and the optic chiasm.[4] [8][9]Its posterior side consists of the pineal gland and the habenular commissure. Strips of gray matter called interthalamic adhesions are on the ventricle's outside walls.[4] It has two processes on the front called the supra-optic recess and the infundibular recess.[3]

The fourth ventricle is shaped like a diamond can be found between the pons and upper medulla oblongata and in front of the cerebellum. A cerebral aqueduct attaches it to the third ventricle. The top of the fourth ventricle consists of the superior cerebellar peduncles, which are strips of nerve fibers made of white matter used for connection, and the medullary velas, which have a tela choroidea.[4][10] The rhomboid fossa makes up its floor. The foramen of Luschka and the foramen of Magendie connect the fourth ventricle to the subarachnoid space.[4]

References

  1. 1.0 1.1 1.2 1.3 1.4 Wile, Jay L., and Shannon, Marilyn M. The Human Body: Fearfully and Wonderfully Made!. Cincinnati: Apologia Educational Ministries, Inc., 2001. 230-231. Print.
  2. Bora, Chandramita. Ventricles of the Brain Buzzle. Web. Last modified March 22, 2013.
  3. 3.0 3.1 The Ventricles of the Brain Teach Me Anatomy. Web. Last modified March 9, 2016.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Crisan, Elena . Ventricles of the Brain Medscape. Web. Last modified September 4, 2013
  5. Corpus callosum Encyclopedia Britannica . Web. Accessed on March 29, 2016. Author unknown.
  6. What is the Septum Pellucidum? wiseGEEK. Web. Accessed March 29, 2016.
  7. pia mater The Free Dictionary. Web. Accessed March 29, 2016. Author unknown.
  8. commissure The Free Dictionary. Web. Accessed on April 8, 2016. Author unknown.
  9. lamina terminalis The Free Dictionary. Web. Accessed on April 8, 2016. Author unknown.
  10. peduncle The Free Dictionary. Web. Accessed on April 8,2016. Author unknown.