Where is optic chiasm located

The ophthalmic artery branches off from a major group of blood vessels in the head and neck known as the internal carotid arteries. The ophthalmic…. The optic nerve is located in the back of the eye. It is also called the second cranial nerve or cranial nerve II.

It is the second of several pairs…. The orbicularis oculi muscle is one of the two major components that form the core of the eyelid, the other being the tarsal plate. The orbicularis…. The vagus nerve is the longest of the 12 cranial nerves. Here, learn about its anatomy, functions, and the kinds of health problems that can occur. The fimbriae of the uterine tube, also known as fimbriae tubae, are small, fingerlike projections at the end of the fallopian tubes, through which….

The bladder, like the stomach, is an expandable saclike organ that contracts when it is empty. The inner lining of the bladder tucks into the folds…. It was also believed that it is the crossing of two vessels that bring tears to the eyes. At that time, it was thought that tears were made in the brain. These misconceptions continue to exist until it was proved that optic chiasm is a structure comprising of nervous tissue.

It was put forward that the optic nerves from the two eyes undergo partial desiccation in optic chiasm. Optic chiasm is located at the bottom or base of the brain. It is present just below the hypothalamus. It is located at the junction of anterior wall and floor of the hypothalamus. The anterolateral angles are continuous with the optic nerves and the posterolateral angles are continuous with the optic tracts.

It is surrounded by the arteries forming the circle of Willis and is present in between the circle. Let us first understand nerve fibers arising from the eyeball. The nerve fibers from the nasal half of eye correspond to the temporal of lateral half of eye field, while the temporal half of nerve fibers correspond to the nasal half or medial half of the eye field.

As discussed earlier, optic chiasm is a nervous structure at which fibers of the optic nerve cross. The fibers are arranged in such a way that the nasal fibers from both sides crossover and pass to the opposite side of the brain.

Thus, the fibers from the temporal half of retina or hemiretina remain on the same side whereas the fibers from the nasal half are crossed. As a result, the left optic tract contains the nasal fibers from the right eye and the temporal fibers from the left eye.

The opposite is true for the right optic tract. As stated earlier, the optic chiasm is surrounded by the circle of Willis. The blood is supplied to optic chiasm by the small branches arising from the arteries forming the circle of Willis.

These include the anterior, middle and posterior meningeal artery. In order to understand why optic chiasm is important, let us first take a look at the visual pathway. The nerve fibers from the temporal and nasal halves of eyeball leave the eyeball as an optic nerve. The fibers in this nerve are present separately. At optic chiasm, the fibers from the nasal half cross while the fibers from the temporal half remain uncrossed.

From the optic chiasm, fibers pass to the optic tract. The left optic tract contains uncrossed temporal fibers from the left eyeball and crossed nasal fibers from the right eyeball.

The optic tracts terminate at the lateral geniculate body. The optic radiations then pass from the lateral geniculate body to the visual cortex, carrying the visual sensation. This crossing over of optic fibers is important in such a way that it allows the same hemispheric visual field to be perceived by visual cortex from both eyes. This can be understood from the example that the left visual cortex receives the temporal visual field from the right eye by crossed right nasal fibers and the nasal visual field from the left eye via uncrossed left temporal fibers.

Quiz questions. Keith L. Moore, Arthur F. Dalley, A. Clinically Oriented Anatomy. Last, R. Last's Anatomy, Regional and Applied. Applied Radiological Anatomy. J Korean Neurosurg Soc. Related articles: Anatomy: Brain. Promoted articles advertising. Figure 1: optic nerve and chiasm Gray's illustration Figure 1: optic nerve and chiasm Gray's illustration. Figure 2: optic nerve and chiasma anatomy Figure 2: optic nerve and chiasma anatomy.

Figure 3: optic chiasm Figure 3: optic chiasm. Figure 4: midsagittal section Figure 4: midsagittal section.