Topography of the Cerebral Hemispheres

1. Topography of the Cerebral Hemispheres

2. Surface structures • The surface of the brain has complicated folding which substantially increases the surface area of the brain. • Gyrus (Gyri, pl) Folds or convulsions • Sulcus (Sulci, pl) Intervening grooves • Fissure: cleft separates large components of the brain. May be used interchangeably with sulcus

3. Major sulci and fissures • 1. Lateral sulcus separates frontal and temporal lobes starts from inferior surface of the hemisphere, stem (beginning segment) of the sulcus extends laterally and divides into three rami on reaching the lateral surface, anterior, ascending, and posterior ramus • 2. Central sulcus separates frontal and parietal lobes. Primary motor area is in front of it and somatosensory area is right behind.

5. Major sulci and fissures • 3. Calcarine sulcus on the medial surface of the hemisphere starts posterior to the corpus callosum, arches down to the occipital pole • 4. Parieto-occipital sulcus separates occipital and parietal lobes extends from calcarine sulcus to the superior border of the hemisphere

7. Fissure • 1. Longitudinal cerebral fissure separates two hemispheres falx cerebri extends into the fissure • 2. Transverse cerebral fissure separates cerebral hemisphere with cerebellum. tentorium cerebeli extends into the fissure. The anterior part of the fissure separates cerebral hemisphere with midbrain and diencephalon

8. Lobes • Frontal lobe • in front of central sulcus and above lateral sulcus, line from central sulcus down to corpus collosum • Parietal lobes • behind central sulcus and above lateral sulcus. A line between parieto-occipital sulcus and preoccipital notch and middle of the line above to the lateral sulcus (See Picture 13-1 on P261) • Temporal lobes • lateral sulcus and line described above, a line from anterior end of calcarine sulcus and preoccipital notch (see Pic 13-2 on P 262) • Occipital lobe • medial surface of the hemisphere, separated from temporal lobe. • Insula • bottom of lateral sulcus.

12. Other gyri and sulci on frontal lobes • precentral sulcus: parallel to central sulcus (see pictures in the book) • precentral gyrus: between central sulcus and precentral sulcus, primary motor area • parallel with longitudinal fissure, two more sulci on the frontal lobe, superior frontal sulcus and inferior frontal sulcus • between longitudinal fissure and superior frontal sulcus: superior frontal gyrus • between superior frontal sulcus and inferior frontal sulcus: middle frontal gyrus • between inferior frontal sulcus and lateral sulcus: inferior frontal gyrus

14. inferior frontal gyrus is further divided into three parts by the anterior and ascending rami of the lateral sulcus • 1). opercular portion: enclosed by precentral sulcus, inferior frontal sulcus, and ascending ramus • 2). triangular portion: enclosed by ascending ramus, anterior ramus, and inferior frontal sulcus • 3). orbital portion: lateral sulcus, anterior ramus, and inferior frontal sulcus

15. Parietal lobe • Parietal lobes: central and lateral sulcus on the lateral surface line between parieto-occipital sulcus and the preoccipital notch, and middle of the line above to lateral sulcus • postcentral sulcus: parallel to the central sulcus sandwiched postcentral gyrus (somatosensory cenetr) with central sulcus • Intraparietal sulcus: extends posteriorly from the postcentral sulcus divide parietal lobe not occupied by postcentral gyrus into superior parietal lobules and inferior parietal lobules • inferior parietal lobules can further be divided into: • supramarginal gyrus: surrounds the upturned ends of lateral sulcus • angular gyrus: surrounds superior temporal sulcus

17. Temporal lobes • superior and inferior temporal sulci divides the temporal lobe into: • superior temporal gyrus • middle temporal gyrus • inferior temporal gyrus

19. Occipital lobe • Primary visual center

20. Insular lobe • Insular lobe covered by frontal, parietal, and temporal opercula • outlined by circular sulcus, central sulcus of insula divides insula into several short gyri, one or two long gyri and limen insulae (over the stem of lateral sulcus)

22. Medial and inferior surfaces • Corpus callosum • splenium: posterior enlarged portion • Genu: anterior portion • Rostrum: thinning out of Genu

24. Medial surfaces • Cingulate gyrus: above the corpus collosum, starts beneath the genu of the corpus collasum goes back to splenium. • Sulcus of the callosum (callosal sulcus) • Cingulate sulcus: above the callosal sulcus • Medial frontal Gyrus: separates from cingulate gyrus by cingulate sulcus

26. Medial surfaces • Cingulate sulcus gives off paracentral sulcus then terminates into marginal and subparietal sulcus • Paracentral lobule: bounded by paracentral and marginal sulci • Precuneus: area above subparietal sulcus • Cuneus: bounded by parieto-occipital and calcarine sulci • Under the corpus collosum, convolution extends from occipital pole

27. Inferior surface • lingual gyrus: between collateral sulcus and calcarine sulcus. The anterior part is called parahippocampal gyrus, which lateral to uncus. • Rhinal sulcus, located at the lateral edge of the parahipocampal gyrus, defines the entorhinal area, which belongs to both limbic system and olfactory system. • occipitotemporal sulcus: intervenes the medial occipitotemporal gyrus and lateral occipitotemporal gyrus • Orbital surface of the frontal lobe: gyrus rectus: medial to the olfactory sulcus

29. Inferior surface • orbital gyri: lateral to the olfactory sulcus • uncus: above the parahippocampal gyrus • isthmus: underneath the splenium of corpus callosum, connects cingulate and parahippocampal gyri

31. Cerebellum • The cerebellum consists of cortex of gray matter (folia), a medullary center of white matter, and four pairs of central nuclei • Primary fissure separates anterior lobe and posterior lobe

33. Cerebellum • The region around the midline is called vermis (superior and inferior vermis) and the reminder is referred as hemispheres. • Three main lobes • Flocculonodular lobe: includes nodule and Flocculus located in between anterior lobe and posterior lobe • Anterior lobe • Posterior lobe