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= Occipital gyri =


 * The occipital gyri is the ridge located in the occipital lobe of cerebral cortex, it consist of gray matter which contains nerve cell bodies and dendrites.

Brain
The brain is one of the most vital organs of the human body, it is made up of billions of nerves which makes it the center of the nervous system. The brain is divided into hemispheres and lobes. The two hemispheres are: right hemisphere and left hemisphere. And the four lobes are: frontal lobe, parietal lobe, temporal lobe and occipital lobe.

Cerebral cortex
The cerebral cortex is the outer layer of the brain which contains grey matter as a form of ridge folds called gyri and the sulci which is the area between those folds. The cerebral cortex is divided by the interhemispheric fissure into right and left hemispheres.


 * The two hemispheres are divided by different sulci and gyri into four lobes.


 * The gyri and sulci forms the folding of the brain to increase the amount of witch the cerebral cortex can fit in within the skull.
 * The size, location and pattern of the gyri is different between individuals.

Occipital lobe
The occipital lobe is one of the four lobes of the brain and the smallest of them. It is located in the posterior part of the skull underneath the occipital bone. Due to the division of the whole brain to right and left hemispheres the occipital lobe is divided into right two lobes: the left occipital lobe and the right occipital lobe. The occipital lobe consists of three surfaces: the lateral surface, the medial surface and the basal surface. The occipital gyri are sectioned into groups according to their position on the surface of the lobe.

The occipital lobe has three main sulci: the lateral occipital sulcus, the transverse occipital sulcus, the intra-occipital sulcus and the calcarine fissure.

The gyri is divided into three groups :the lateral occipital gyri, the medial occipital gyri and the basal occipital gyri.


 * The lateral occipital gyri is located at the lateral surface of the brain and it contains :the superior occipital gyrus, middle occipital gyrus and inferior occipital gyrus.
 * The medial occipital lobe is located in the inner surface of the brain and it contains: the cuneus gyrus and lingual gyrus.
 * The basal occipital gyri is located at the base of the brain and it contains: the lingual gyrus and the occipitotemporal gyrus.

superior occipital gyrus
the superior occipital gyrus is located at the superior part of the lateral surface of the occipital lobe, it is surrounded anteriorly by the parieto-occipital fissure, laterally by the intra-parietal sulcus and medially by the cuneus. The main function of the superior occipital gyrus is that it is the associative visual area, it contains the regions V3, V4, V5 & V6 of the visual are that are responsible for recognition of shapes, distinguishing of features and attention due to the presence of motion-sensitive neurons.

Middle occipital gyrus
The middle occipital gyrus is located within the calcarine sulcus at the medial part of the occipital lobe, it has two segments : anterior segment and posterior segment, the anterior and posterior segments are surrounded superiorly by the intraparietal sulcus and inferiorly by the inferior occipital sulcus. The main function of the middle occipital gyrus is that it contains the primary visual area V1 that is responsible for reception and perception of the isolated visual impressions. The main visual area is also called the striate cortex, the other visual regions outside the primary visual cortex that are driven by V1 are called extrasriate cortex,  which are associated to different visual tasks.

Inferior occipital gyrus
The inferior occipital gyrus is located on the base of the lateral surface of the occipital lobe, it is surrounded laterally by the inferior occipital sulcus, medially by occipitotemporal sulcus and inferiorly by the calcarine fissure. The main function of the inferior occipital sulcus is that it is the visual association area which responsible for the translation process of the image.

Cuneus gyrus(cuneate)
The cuneus gyrus is considered as a lobe within the occipital lobe. It is surrounded anteriorly by the parieto-occipital sulcus and inferiorly by the calcarine sulcus. The main function of this gyrus is that it is part of the basic visual process by projecting the image of the inferior visual field from the striate cortex to the extrastriate cortex.

Lingual gyrus
The lingual gyrus is located on the medial and basal surface of the occipital lobe. It got its name due to the appearance of the gyrus that is similar to the shape of the tongue. The lingual gyrus that is located medially lays between the calcarine sulcus and the collateral sulcus. While the basal part of the gyrus is connected to the temporal lobe as it continues to joins the parahippocampal gyrus. The main function of the lingual gyrus is that it is associated to dreaming, word processing and the encoding of images.

Occipitotemporal gyrus(fusiform)
The occipitotemporal gyrus is located at the basal surface of the occipital lobe. It is surrounded by the inferior temporal gyrus and the parahippocampal gyrus. The main function of the occipitotemporal gyrus is that it is the area where face, body and word recognition is generated from.

Clinical significance
The occipital gyri has a great impact on the person will being if it get damaged ,as it contains the visual center, the result of the damage will affect vision but depending on the location on which the damage occurred, the degree of visual damage can vary. If the damaged area is:


 * The Superior occipital gyrus & inferior occipital gyrus : the damage to these area can lead to visual agnosia and disability of understanding written language.
 * The middle occipital gyri: the damage to this gyrus will result in Homonymous hemianopia of opposite side with macular sparing.
 * The cuneus  gyrus: damage to this gyrus will result in inferior contralateral quadrantanopia and visual hallucinations in dementia patients.
 * The lingual gyrus: if the damage occurred on the right lingual gyrus the result will be topographagnosia and prosopagnosia, if the damage happened on either side the result is the line bisection error (LBE).
 * The occipito-temporal gyrus: the damage to this gyrus will result in a visual agnosia for objects and prosopagnosia.