MEDIAL HEMISPHERIC SURFACE.pptx
- 1. MEDIAL HEMISPHERIC SURFACE Dr B Vinod Mch Neurosurgery Resident Gandhi medical college Hyderabad
- 2. Introduction The frontal, parietal, occipital, and temporal lobes have medial surfaces. The medial surfaces of the frontal, parietal, and occipital lobes are flattened vertically against the falx cerebri, are interconnected below the falx in the floor of the interhemispheric fissure by the corpus callosum, and are separated from the corpus callosum by the callosal sulcus. Temporal lobe is complex and it wraps around the cerebral peduncle and upper brainstem and forms the lateral wall of the cisterns above the tentorial incisura. The gyri of the frontal, parietal, and occipital lobes on the medial surface are arranged in 3 layers roll. Inner layer is represented by corpus callosum intermediate layer by cingulate gyrus, outer layer, from anterior to posterior, by the medial surface of the superior frontal gyrus, the paracentral lobule, precuneus, cuneus, and the lingula
- 4. The cingulate gyrus begins below the rostrum of the corpus callosum, curves around the genu and body of the corpus callosum, and turns downward behind the splenium, where it is connected by a narrow gyral bridge, the isthmus of the cingulate gyrus, to the para-hippocampal gyrus. Separated inferiorly from the corpus callosum by the callosal sulcus. Separated on its outer margin from the remainder of the medial surface of the superior frontal gyrus and the paracentral lobule by the cingulate sulcus and from the precuneus and remainder of the parietal lobe by the subparietal sulcus
- 5. Paracentral ramus ascends from the cingulate sulcus at the level of the midportion of the corpus callosum to separate the superior frontal gyrus anteriorly from the paracentral lobule posteriorly. The marginal or ascending ramus ascends from the cingulate sulcus at the level of the posterior third of the corpus callosum and separates the paracentral lobule anteriorly from the precuneus posteriorly The paracentral lobule, the extension of the pre- and postcentral gyri that wraps around the extension of the central sulcus onto the medial surface, is the site of the motor and sensory areas of the contralateral lower limb and perineal region and the voluntary control areas of defecation and micturition.
- 6. FRONTAL LOBE Formed predominantly by the medial surface of the superior frontal gyrus, the anterior half of the paracentral lobule, and the cingulate gyrus The superior frontal gyrus parallels the superior border and is separated from the cingulate gyrus by the cingulate sulcus. The cingulate sulcus parallels and is situated on the medial surface at the level of the superior frontal sulcus on the lateral surface.
- 7. Anteriorly, the cingulate and the superior frontal gyri wrap around the genu and the rostrum of the corpus callosum and blend into the paraterminal and para-olfactory gyri situated below the rostrum of the corpus callosum and in front of the lamina terminalis. The paraterminal gyrus is separated at its anterior edge from the adjacent para-olfactory gyrus by the shallow posterior paraolfactory sulcus. The anterior para-olfactory sulcus, a short vertical sulcus, separates the para- olfactory gyrus from the anterior part of the frontal pole.
- 8. PARIETAL LOBE Location between anteriorly the line from the upper end of central sulcus to the corpus callosum posteriorly the parieto-occipital sulcus It is formed by paracentral lobule, posterior part of cingulate gyrus and precuneus. Precuneus Quadrangular area Boundaries anteriorly by the ascending ramus of the cingulate sulcus, posteriorly by the parieto-occipital sulcus superiorly the superior hemispheric border, inferiorly from the cingulate gyrus by the subparietal sulcus
- 9. The posterior part of the cingulate gyrus wraps around the splenium and is separate from the precuneus by the subparietal sulcu and from the splenium by the callosal sulcus . The posterior part of the paracentral lobule is a medial extension of the postcentral gyrus, and the precuneus is the medial extension of the superior parietal lobule. The subparietal sulcus is located at approximately the level of the interparietal sulcus on the lateral surface.
- 10. OCCIPITAL LOBE Separated from parietal lobe by parieto-occipital sulcus. Calcarine fissure separates surface into upper(cuneus) and lower part(lingula) Cuneus : wedge shape Anteriorly :parieto-occipital sulcus Inferior :calcarine sulcus Superior : superior border of hemishpere
- 11. Lingula: (tongue like appearance) Bends anteriorly into posterior part of parahippocampal sulcus that extends backward from temporal lobe. The parieto-occipital sulcus is directed downward and forward from the superior border between the cuneus and precuneus at an angle of approximately 45 degrees. It descends to join the anterior part of the calcarine sulcus, giving the region a Y-shaped configuration.
- 12. calcarine sulcus begins just above the occipital pole and courses forward with an upward convexity between the cuneus above and lingual below and joins the parieto-occipital sulcus. It continues anteriorly below the isthmus of the cingulate gyrus, where it may intersect the posterior part of the parahippocampal gyrus before terminating. The primary visual receiving area is located on the upper and lower banks and the depths of the posterior part of the calcarine sulcus
- 13. TEMPORAL LOBE The most complex of the medial cortical areas Formed predominantly by the rounded medial surfaces of the para Hippocampal gyrus and uncus. Medial surface is composed of three longitudinal strips of neural tissue, one located above the other, which are interlocked with the hippocampal formation. Inferior strip is formed by the rounded medial edge of the para- hippocampal gyrus, the site of the subicular zones. Middle strip is formed by the dentate gyrus, a narrow serrated strip of gray matter located on the medial surface of the hippocampal formation. Superior strip is formed by the fimbria of the fornix
- 14. Dentate gyrus blends posteriorly behind the splenium into the fasciolar gyrus, which is continuous with the indusium griseum. The para-hippocampal gyrus deviates medially at the site of the uncus that projects medially above the tentorial edge Also extends around the lower border to form the medial part of the basal surface of the temporal Lobe Posteriorly, the part of the para-hippocampal gyrus below the splenium of the corpus callosum is intersected by the anterior end of the calcarine sulcus.
- 15. UNCUS: Located anterior to para-hippocampus gyrus. Angular shape ,has anterior ,posterior segments and medially directed apex(points 3rd nerve and PCOM). Anterior segment: faces anteromedially,(proximal part of sylvian, carotid cistern,ICA and proximal MCA)has undivided segments, Posterior segment: faces posteriomedial,(cerebral peduncles,anterior choroidal ,medial posterior PCA),divided into upper(formed mainly by head of hippocampus), and lower parts by uncal notch. Optic tract passes above the medial edge.
- 16. The posterior segment is occupied by several small gyri that are continuations of the dentate gyri. The inferior choroidal point, the lower end of the choroidal fissure along which the choroid plexus is attached, is located just behind behind head of hippocampus and lateral to LGB, at the site where the anterior choroidal artery passes through the choroidal fissure to enter the temporal horn.
- 17. The dentate gyrus, named for its characteristic tooth-like elevations, extends posteriorly from the upper part of the posterior segment and has the most prominent denticulations anteriorly. The dentate gyrus is continuous posteriorly below and behind the splenium of the corpus callosum.
- 18. Amygdala can be considered as being entirely located within the boundaries of the uncus It forms the anterior wall of the temporal horn. Superiorly, the amygdala blends into the claustrum and globus pallidus without any clear demarcation. Medially, it is related to the anterior and posterior segments of the uncus. The amygdala gives rise to the stria terminalis, which courses between the thalamus and caudate nucleus deep to the thalamostriate vein.
- 19. HIPPOCAMPUS Blends into and forms the upper part of the posterior uncal segment, is a curved elevation, approximately 5 cm long, in the medial part of the entire length of the floor of the temporal horn It is divided into three parts: head, body , and tail Head: anterior and largest part, directed anterior and medially, forms posterior segment of uncus. Characterized by 3 or 4 shallow hippocampal digitations resembling feline paw, giving the name pes hippocampus. Superiorly head faces posterior part of amygdala. Anterior to head is uncal recess(between head and amygdala)
- 20. BODY: extends along the medial part of the floor of the temporal horn, narrowing into the tail that disappears as a ventricular structure at the anterior margin of the calcar avis The fimbria of the fornix arise on the ventricular surface of the hippocampus behind the head and just behind the choroidal Fissure Temporal horn Extends into medial part of temporal lobe, to just anterior to head of hippocampus and to just behind amygdala It end approx.2.5 cm from temporal lobe.
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