Superolateral Surface of Brain

SUPEROLATERAL SURFACE

On the superolateral surface, two sulci, the lateral and the central, can be easily identified. The lateral (sylvian) sulcus has a short stem between the orbital surface of the frontal lobe and the temporal pole; in life, the lesser wing of the sphenoid bone projects into it. At its outer end, the stem divides into anterior, ascending, and posterior branches. The anterior and ascending rami are each about 2.5 cm long; the former runs horizontally into the inferior frontal gyrus, and the latter, vertically. The posterior ramus is about 7.5 cm long and inclines upward as it extends backward to end in the supramarginal gyrus, which is part of the inferior parietal lobule. These rami separate triangular areas of cortex called opercula, which cover a buried lobe of cortex, the insula.

The central (rolandic) sulcus proceeds obliquely downward and forward from a point on the superior border almost halfway between the frontal and occipital poles. It is sinuous and ends above the middle of the posterior ramus of the lateral sulcus. Its upper end usually runs onto the medial surface of the cerebrum and terminates in the paracentral lobule.

The parietooccipital sulcus is situated mainly on the medial surface of the cerebrum, but it cuts the superior margin and appears for a short distance on the superolateral surface about 5 cm in front of the occipital pole. At about the same distance from the occipital pole on the inferior margin, there is a shallow indentation, the preoccipital notch, produced by a small ridge on the upper surface of the tentorium cerebelli.

The above features divide the cerebrum into frontal, parietal, occipital, and temporal lobes. The frontal lobe lies in front of the central sulcus and anterosuperior to the lateral sulcus. The parietal lobe lies behind the central sulcus, above the posterior ramus of the lateral sulcus and in front of an imaginary line drawn between the parieto-occipital sulcus and the preoccipital notch. The occipital lobe lies behind this same imaginary line. The temporal lobe lies below the stem and posterior ramus of the lateral sulcus, and is bounded behind by the lower part of the aforementioned imaginary line.

Frontal Lobe. The superolateral surface of the frontal lobe is traversed by three main sulci and thus divided into four gyri. The precentral sulcus runs parallel to the central sulcus, separated from it by the precentral gyrus, the great cortical somatomotor area. The superior and inferior frontal sulci curve across the remaining part of the surface, dividing it into superior, middle, and inferior frontal gyri.

Parietal Lobe. The parietal lobe has two main sulci, which divide it into three gyri. The postcentral sulcus lies parallel to the central sulcus, separated from it by the postcentral gyrus, the great somatic sensory cortical area. The remaining, larger part of the superolateral parietal surface is subdivided into superior and inferior parietal lobules (gyri) by the intraparietal sulcus, which runs backward from near the midpoint of the postcentral sulcus and usually extends into the occipital lobe, where it ends by joining the transverse occipital sulcus.

Only gold members can continue reading. Log In or Register to continue