Side by side
| Compared | Precentral gyrus | Postcentral gyrus |
|---|---|---|
| Where it is | On the side of each hemisphere at the back of the frontal lobe, directly in front of the central sulcus; it holds Brodmann area 4. [1][5] | At the front of the parietal lobe, directly behind the central sulcus; it holds Brodmann areas 3, 1 and 2. [2][6] |
| What it does | The primary motor cortex: with the other motor areas it plans and carries out voluntary movement of the opposite side of the body. [5] | The primary somatosensory cortex: the main receiving area for the sense of touch, also for body position (proprioception), from the opposite side of the body. [2][6] |
| Connects with | Its output runs down the corticospinal tract to the spinal cord and the corticobulbar tract to the brainstem; its giant Betz cells are found here. [5][7] | Receives its input from the thalamus, mainly the ventral posterior nucleus, which relays signals that rose from the skin and joints. [6][8] |
| Size measured from the model | 66 mm front to back, 66 mm top to bottom, 62 mm side to side [4] | 64 mm front to back, 60 mm top to bottom, 67 mm side to side [4] |
Size is the box each part fits in on this one model (left precentral gyrus; left postcentral gyrus), 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 [4], from the left precentral gyrus to the left postcentral gyrus:
- Centre to centre: 15 mm in a straight line.
- The centre of the left postcentral gyrus is 15 mm further back, 1 mm lower and 2 mm further from the midline than the centre of the left precentral 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
- Pre- means in front of, post- means behind: both are named for where they sit relative to the central sulcus. [3]
- Each strip holds a map of the body, the cortical homunculus: hands, lips and face take up far more of the strip than the trunk or legs, and the legs are mapped near the top of the head, the face low on the side. [9]
- Motor in front, sensory behind: the precentral gyrus belongs to the frontal lobe, the postcentral gyrus to the parietal lobe. [1][2]