Different types of sulci on the brain

Different types of sulci on the  brain

Cranium contain limited space   so for accommodation, the cerebral cortex is folded into numerous gyri separated by sulci . For this region the total surface area of the cortex of human brain is increased to about 2200 cm^2. One third of cortex is exposed as gyri and two third of cortex is hidden in the sulci.

Development of sulci:

Upto the 3^rd months of inter uterine life:  the cerebral cortex remains smooth

During 4^th months of inter uterine life: lateral sulcus appears on the superolateral surface of cerebrum and insular cortex begins to submerge.

During the 6^th months of inter uterine life: central, parieto-occipital, calcarine and cingulate sulci appear.

During the 7^th months of inter uterine life: all sulcus appear

•       Types of sulci  : 

1. Limiting sulcus : central sulcus
2. Axial sulcus : calcarine sulcus
3. Operculated sulcus: lunate sulcus
4. Complete sulcus
5. Primary and secondary sulcus

Limiting sulcus :

It separates agranular  motor cortex  from  granular  sensory cortex  . Agranular cortex contain more pyramidal cell with less granule cell but granular cortex contain more granule cells with less pyramidal cells

Axial sulcus :

Calcarine sulcus presents an axial sulcus because visual cortex grow two side of this sulcus 

Operculated sulcus: 

•       lunate sulcus is operculated sulcus which separates visual area 17  from 19 and

•       floor & wall of lunate sulcus form area 18

Complete sulcus :

Some of the sulcus are called complete sulcus because it extend depth enough to produce elevation in lateral ventricle . The collateral and anterior part of the calcarine sulci are complete because the former produces the collateral eminence in the floor of the inferior horn of lateral ventricle and the later forms the calcar avis of the posterior horn of lateral ventricle

Primary and secondary sulcus :

 Most of the sulcus are primary sulcus since they develop independently but parieto occipital sulcus & lateral sulcus are secondary sulcus because they dependent on other factors. For example,  Shape of lateral sulcus depend on exposure of insular cortex. If insular cortex expose , can see easily from surface the lateral sulcus is wide open and thick .  If insular cortex buried well , cannot see from surface the lateral sulcus remain narrow.

The growth of corpus callosum causes obliteration of small sulci on the medial surface of cerebral hemisphere to form parieto-occipital sulcus .

•       Terminology :

•       Sulcus :  one sulcus 

•       Sulci: more than one sulcus

•       Gyrus : one gyrus

•       Gyri :  more than one gyrus