Gyri and Sulci of cerebrum

Gyri and Sulci of Cerebrum

1. Lobes of Cerebral Hemisphere its Sulci and Gyri Prepared by: Anish Dhakal MBBS 3 rd Year [email protected]

2. cerebrum Two hemispheres separated by median longitudinal fissure B and of commissural fibres corpus callosum at the bottom of the fissure Median longitudinal fissure occupied by falx cerebri Separated from Cerebellum: tentorium cerebelli

3. Sulcus & gyrus cortex is folded into numerous gyri or convolutions separated by sulci Gyrenchephalic Total surface area – thus increased to 2200 cm square 1/3 exposed as gyri 2/3 hidden in the walls & floor of sulci

4. Sulcus & Gyrus Smooth surface till 3 rd month of IUL Lateral sulcus – appears during 4th month of IUL Other sulci appear during 6 th month - central sulcus, parieto- occipital sulcus, calcarine sulcus, cingulate sulcus All important sulci are laid down by the end of 7th month of IUL

5. 3 poles & six lobes

6. Medial surface Tentorial surface Superolateral surface Inferior surface Orbital

7. Cerebral lobes Frontal: anterior to central sulcus & above the posterior ramus of the lateral sulcus Parietal: behind the central sulcus and in front of the upper part of the first imaginary line. Temporal: lies below the posterior ramus of lateral sulcus and second imaginary line. Occipital: lies behind the vertical line joining the parieto-occipital sulcus and preoccipital notch.

8. Lateral sulcus Stem of the sulci begins as a deep cleft on the inferior surface of the cerebral hemispheres at the anterior perforated substance On reaching the superolateral surface it divides into three rami .

9. S uperolateral surface Begins at the superomedial border just about one cm behind the midpoint between frontal & occipital poles Lower end above the posterior ramus of lateral sulcus Central sulcus of rolando

10. Calcarine sulcus below the posterior end of the corpus callosum and follows an arched course Parieto-occipital sulcus at the midpoint of the calcarine sulcus and courses upwards and backwards to cut the superomedial border in front of the occipital pole

11. Frontal lobe Precentral sulcus – in front and parallel to the central sulcus Superior and inferior frontal sulci – extend forward from precentral sulcus Four gyri – precentral gyrus & superior, middle, inferior frontal gyri Precentral gyrus continues with paracentral lobule at medial surface

12. Inferior frontal gyrus pars orbitalis: below anterior horizontal ramus of lateral sulcus pars triangularis: between anterior horizontal and anterior ascending rami pars posterior: behind anterior ascending ramus

13. Parietal lobe Postcentral sulcus – behind and parallel to the central sulcus Intraparietal sulcus – extends backwards : joins transverse occipital sulcus divides the rest of the parietal lobe into superior and inferior parietal lobule. Postcentral gyrus also continuous with posterior paracentral lobule

14. Parietal lobe Superior Parietal lobule (gyrus) : above the intraparietal sulcus Inferior parietal lobule (gyrus) : below the intraparietal sulcus. In lobule, Supramarginal gyrus arching over posterior ramus of lateral sulcus and Angular gyrus over superior temporal sulcus

15. Temporal lobe superior surface of the superior temporal gyrus presents two transverse temporal gyri The anterior transverse temporal gyrus is called as the Heschl’s gyrus which forms the primary auditory area of the cortex

16. Occipital lobe Lunate sulcus – in front of occipital lobe Lateral occipital sulcus in front of lunate sulcus Superior and inferior occipital gyri Transverse occipital sulcus –behind the parieto-occipital sulcus

17. Cingulate sulcus Cingulate gyrus Callosal sulcus

18. Between the cingulate sulcus and the superomedial border of the hemisphere. Two parts A small part around the upper part of the central sulcus, the paracentral lobule A large medial part, the medial frontal gyrus

19. Cuneus: triangular area between the posterior part of the calcarine sulcus and the parieto- occipital sulcus Isthmus: between the splenium and calcarine sulcus Precuneus: quadrangular area between the parieto-occipital sulcus and paracentral lobule Anteriorly the lingual gyrus is continued as the parahippocampal gyrus

20. On the orbital part of the inferior surface : Anterior end of the PHG gyrus hooks sharply backwards ( limited laterally by a short rhinal sulcus ) This hook like anterior end of the PHG is called uncus. Olfactory sulcus Orbital sulcus : divides the rest of the orbital surface into anterior, posterior, medial and lateral orbital gyri. Inferior surface