Side by side
| Compared | Gyrus | Sulcus |
|---|---|---|
| Where it is | A gyrus is a raised fold of cortex; the precentral gyrus is the strip at the back edge of the frontal lobe, running from the top of the hemisphere down the side towards the lateral sulcus. [1][6] | A sulcus is a groove; the central sulcus runs from the top of each hemisphere down and forward towards the lateral sulcus, with the frontal lobe in front of it and the parietal lobe behind. [2][4] |
| What it does | A gyrus is cortex, so it does the work of its area: the precentral gyrus holds the primary motor cortex, which sends the commands for voluntary movement. [6][7] | A groove has no job of its own, but its walls are cortex too: much of the primary motor cortex lies in the front wall of the central sulcus and the primary somatosensory cortex in its back wall. [7][8] |
| Connects with | Fibres leave a gyrus through the white matter beneath it; from the precentral gyrus the corticospinal tract runs down through the brainstem to the spinal cord. [9][6] | A sulcus is a landmark rather than a connection: the main ones mark borders between lobes (the central sulcus between the frontal and parietal lobes, the lateral sulcus above the temporal lobe). [2][10] |
| Size measured from the model | Left precentral gyrus (the example gyrus): 66 mm front to back, 66 mm top to bottom, 62 mm side to side [5] | Left postcentral gyrus (the central sulcus’s back bank): 64 mm front to back, 60 mm top to bottom, 67 mm side to side [5] |
Size is the box each part fits in on this one model (left precentral gyrus (the example gyrus); left postcentral gyrus (the central sulcus’s back bank)), not its volume. Real brains vary. A part that comes as a left and a right copy is measured on its left copy; the right one mirrors it.
How far apart are they?
Measured from the model [5], from the left precentral gyrus (the example gyrus) to the left postcentral gyrus (the central sulcus’s back bank):
- Centre to centre: 15 mm in a straight line.
- The centre of the left postcentral gyrus (the central sulcus’s back bank) is 15 mm further back, 1 mm lower and 2 mm further from the midline than the centre of the left precentral gyrus (the example gyrus).
- Nearest points of the two shapes: under 1 mm apart.
A “centre” here is the average position of the points on the part’s 3D surface, so for a curved part such as a C shape it can sit outside the part itself. The nearest-points figure is measured between the corners of the simplified meshes, so a gap of 2 or 3 mm or less is within the model’s coarseness: read it as “touching or nearly so”.
How to tell them apart
- Gyri are often named after the groove beside them: the precentral gyrus lies in front of (pre-) the central sulcus and the postcentral gyrus behind (post-) it. [6][11]
- The plurals are gyri and sulci; a very deep sulcus is often called a fissure, as in the lateral (Sylvian) fissure or the longitudinal fissure between the two hemispheres. [2][12]