Table 2.2: Laminar origin of corticofugal neurones in primate motor cortex (adapted from Jones and Wise 1977). (Kuypers, 1981)
|
Lamina |
Corticofugal neurones |
|
I |
|
|
II |
|
|
III |
Cortico-cortical Corticocallosal Corticostriate |
|
V-a (upper) |
Corticostriate Corticorubral Corticoreticular Corticopontine Corticobulbar Corticonuclear |
|
V-b (lower) |
Corticospinal (Betz Cells) |
|
VI |
Corticothalamic |
Corticorubral: Magnocellular ( --> Rubrospinal tract) primarily area 4 layer Vb and adjacent (caudal) area 6. Parvocellular from areas 4 and 6 Va, parietal Vb, etc. (Humphrey 1984)
Corticospinal: first approximation
Motorneurons (ventral horn): from M1
Interneurons (central grey matter): from M1, PMd and PMv
Sensory (dorsal horn): from parietal cortex
Table 2.3 Cortical areas giving rise to the corticospinal tract (Porter and Lemon)
| Species | Reference | Technique | Frontal lobe (areas 4, 6) | Parietal lobe (areas 3a, 3b, 1, 2, 5, and SII) | |||||
|
4 |
6 |
3, 1, 2 |
5 |
SII |
|||||
| Man | Jane et al. 1967 | Fibre degeneration | 60% | 40% | |||||
|
Monkey |
Russel and DeMyer (1961) Murray and Coulter (1981) Toyoshima and Sakai (1982) |
Fibre degeneration HRP HRP |
60% 40% 63% |
31% 35% 51% |
29% 5% 12% |
40% 60%1 37% |
13% |
12% |
12% |
|
Cat |
Groos et al. (1978) Keizer and Kuypers (1984) |
HRP HRP, fluorescent tracers |
59%2 80%3 |
41% 20% |
35%
|
4%
|
2%
|
||
1includes 25% of labelled neurones in area 3a 2these authors did not report labelling in area 6; 3includes area 3a
Table 2.4 Distribution of corticospinal neurones in the frontal lobe of the monkey (from Dum and Strick 1991) (as reported in Porter and Lemon).
|
Region |
Area (mm^2) |
WGA-HRP in C4-T2 (n= 42, 912 neurones) (%) | WGA-HRP in C2-T1 (n = 71, 128 neurones) (%) |
| Primary motor cortex (M1) | 84 | 48.5 | 49.7 |
| Sup. precentral sulcus (SPcs) (~PMd) | 20 | 7.0 | 9.9 |
| Arcuate premotor area (APA) (~PMv) | 18 | 4.0 | 9.6 |
| SMA | 44 | 18.5 | 12.2 |
| Cingulate motor areas: | |||
| dorsal (CMAd) | 22 | 10.5 | 8.0 |
| ventral (CMAv) | 14 | 6.8 | 6.1 |
| rostral (CMAr) | 24 | 4.0 | 2.9 |
M1 has more projections to spine than any other single area.
Frontal: Projections from PM areas, SMA, CMA
Parietal: Lots in ambiguous area 3a, but also SII and area 5.
Motor Neurons (lamina IX) dominated by contralateral M1
Interneurons (V-VII) from M1, SMA and CMA
But, some lamina IX from SMA, CMA - corticomotorneurons in SMA, CMA?
Overview
Porter, R. and Lemon, R. Corticospinal Function and Voluntary Movement, Clarendon Press, 1995.
Descending Projections
Jones, E. G. and Wise, S. P. (1977). Size, laminar and columnar distribution of efferent cells in the sensory-motor cortex of monkeys. J Comp. Neurol. 175, 391-437.
Kuypers, H. G. (1981). Anatomy of the descending pathways. In Handbook of Physiology - the nervous system II (eds. J. M. Brookhart and V. B. Mountcastle), pp. 597-666. American Physiological Society, Bethesda, MD.
Corticorubral
Humphrey, D. R., Gold, R., Reed, D. J. (1984). Sizes, laminar and topographic origins of cortical projections to the major divisions of the red nucleus in the monkey. J. Comp. Neurology 225(1): 75-94.
Corticospinal Tract
Toyoshima, K. and Sakai, H. (1982). Exact cortical extent of the origin of the corticospinal tract (CST) and the quantitative contribution to the CST in different cytoarchitechtonic areas. A study with horseradish peroxidase in the monkey. J. Hirnforsh 23, 257-269.
Dum, R. P. and Strick, P. L. (1991). The origin of corticospinal projections from the premotor areas in the frontal lobe. J. Neurosci. 11, 667-689.
Dum, R. P. and Strick, P. L. (1996). Spinal cord terminations of the medial wall motor areas in macaque monkeys. J. Neurosci. 16, 6513-6525.
Ralston, D. D. and Ralston, H. J. (1985). The terminations of corticospinal tract axons in the macaque monkey. J. Comp. Neurology 242, 325-337.