Gyri and Sulci



Gyri and Sulci

Gyri, so also sulci are present in human brain and brain of higher mammals. These are called gyrencephalic brain. Cerebral cortex of lower mammals, birds and reptiles, presents smooth surface called lissencephalic brain.
Sulci of cerebral cortex are of variable length and depth. A suclus separates two adjacent gyri.
It has two adjacent walls and floor which are lined
by layer of gray matter overlying the core of white
matter.
Some important sulci

Sulci of cerebral hemisphere are many. Some are
named and some are unnamed. It is not yet the stage
of this chapter to know the names of all the sulci. But
it is the time to be acquainted with some of the sulci
which are important embryologically and functionally.

  1. Lateral sulcus
    Lateral sulcus is also called fissure of Sylvius. It is most prominent sulcus recognized between temporal pole and orbital surface from where it begins as stem. The stem passes upwards and backwards on the superolateral surface. Immediately then, at a point known as sylvian point, it divides into 3 limbs as follows
    1. Anterior horizontal limb: 2.5 cm in length, passes horizontally forwards.
    2. Anterior ascending limb: Also 2.5 cm in length, passes vertically upwards.
    3. Posterior limb: 7.5 cm long, passes upwards and backwards. Its end is curved and directed upwards.
  2. Central sulcus of Rolando. On the superolateral surface, central sulcus begins by cutting superomedial border 1 cm behind the midpoint between frontal and occipital poles. It runs downwards and forwards on the superolateral surface making an angle of 70° with superomedial border. It ends a little above posterior ramus of lateral sulcus. Upper end of the sulcus extends for 1–2 cm on the medial surface of cerebral hemisphere. A learner may easily identify central sulcus as it is the sulcus cutting superomedial border. Besides, other sulci in front and behind, can easily be identified with its help.
  3. Parietooccipital sulcus. This sulcus is present on the medial surface of cerebral hemisphere. It starts by cutting superomedial border 5 cm in front of occipital pole and runs downwards and forwards. It ends by joining the junction of calcarine sulcus and postcalcarine sulcus (see below). It may extend on the superolateral surface.
  4. Calcarine and postcalcarine sulcus. They are continuous with each other and present on medial surface of cerebral hemisphere. Calca-rine sulcus starts a little behind and below the posterior end of corpus callosum (splenium). It then runs backwards with a convexity upwards and continued as postcalcarine sulcus, where it is joined by parietooccipital sulcus. Postcalcarine sulcus ends at occipital pole and extends slightly on superolateral surface.

Source: Easy and Interesting Approach to Human Neuroanatomy (Clinically Oriented) (2014)