A comparative fiber and numerical analysis of the pyramidal tract

Lassek, A. M.; Rasmussen, Grant L.

doi:10.1002/cne.900720209

Cited by 58 publications

(14 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The incidence of PT cells found in these experiments was 23-4 %; this value may be somewhat higher than the real incidence since the deeper layers of the cortex, in which the PT cells are situated, contain relatively large cells which would therefore tend to be selected by an exploring micro-electrode. It is also conceivable that the percentage of PT cells is unusually high in the rat since the medullary pyramids are particularly well developed in this species (Lassek & Rasmussen, 1940).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

An investigation of pyramidal tract cells in the somatosensory cortex of the rat

McComas¹,

Wilson²

1968

The Journal of Physiology

View full text Add to dashboard Cite

SUMMARY1. An electrophysiological study has been made of pyramidal tract (PT) cells in the somatosensory cortex of the rat; the axons of the cells were shown to project either to the dorsal column nuclei or to the corticospinal tract.2. The corticospinal axons had conduction velocities of 7-6-108 m/sec. and therefore must have belonged to the large population of PT axons with relatively small diameters.3. PT cells constituted almost a quarter of the units encountered; they were distributed throughout the forepaw area within the deeper layers of the cortex.4. The sizes of the receptive fields of PT cells varied widely and did not differ significantly from those of non-PT cells.5. The latencies of PT cell discharges following peripheral stimulation showed less variation than those of non-PT cells though the mean latencies were identical.6. Most PT cells could be driven from the periphery and exhibited spontaneous activity in addition; they therefore function to maintain a continuous control over the somatosensory input to the brain which can be increased whenever the skin is stimulated.

show abstract

Section: Discussionmentioning

confidence: 99%

“…Thus the corticospinal axons issuing from the somatosensory area make a contribution to the large proportion of small diameter axons found in the medullary pyramids (cf. Lassek & Rasmussen, 1940;Goldby & Kacker, 1963).…”

Section: Discussionmentioning

confidence: 99%

An investigation of pyramidal tract cells in the somatosensory cortex of the rat

McComas¹,

Wilson²

1968

The Journal of Physiology

View full text Add to dashboard Cite

show abstract

“…There seems little reason to expect the condition in the rab bit to be different. The rabbit has about 102,000 fibers in its medullary pyramidal tract, all of small diameter [Lassek and Rasmussen, 1940]. If spread uniformly through the cortex that yields an r wave, the density of PT cells bodies would be about 1,300/mm2 (about 3% of the neu rons in that tissue).…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand, its latency and general duration fit reason ably well to what one might expect from reasonable guesses about the fiber spec trum of the rabbit. Lassek and Rasmussen [1940] described the fibers as uniformly small; they showed one histological figure, but made no measurements. By compari son with 22 other mammals, the rabbit has next to the smallest average PT fiber dia meter, being exceeded only by the house mouse.…”

Section: Discussionmentioning

confidence: 99%

Cerebral Response to Medullary Pyramid Stimulation in the Rabbit

Chen¹,

Towe²

1984

Brain Behav Evol

View full text Add to dashboard Cite

The response evoked in the cerebral cortex of the rabbit by stimulation of the medullary pyramid was studied electrophysiologically. The response was everywhere surface-positive and began 2–3 ms after the stimulus. It exceeded 1 mV in amplitude and generally lasted 2–4 ms. Maps of the response showed it to extend throughout the anterior one-third of the cortex (in the ''motor'' cortex) and into adjacent tissue, including the limbic cortex. Although it depended on antidromic conduction in pyramidal tract fibers for its production, it varied in amplitude, configuration and latency at different sites and at the same sites on repeated trials. It was found to reverse polarity deep in the cortex, to become a large, negative wave in layer V and to maintain that polarity into the underlying white matter. The response disappeared during a spreading depression, though it recovered more rapidly than the primary response evoked by skin stimulation. Maps of the primary response showed a strong overlap with the ''antidromic'' response, though the response was largest slightly caudal to the maximal focus of the ''antidromic'' response and extended more caudally through transitional and into limbic cortex. The ''antidromic'' response showed two major foci on the cortex, with an additional minor focus located more laterally. It is argued that the ''antidromic'' response in the rabbit is the same as that found in the opossum, woodchuck, rat and slow loris, and is markedly different from that found in the cat and macaque monkey. It is postulated that this response reflects synaptic action in pyramidal tract axon collaterals, probably onto cell bodies in layer V, rather than being a purely antidromic event.

show abstract

“…The r wave, on the other hand, reverses polarity with depth in the cortex, and depends upon the pyramidal tract discharge for its production. From its timing, the r wave depends upon collateral dis charge from relatively large PT fibers -of which the American opossum has few [46,79] -and involves a single synaptic delay. The r' wave could depend either upon slower PT fibers or involve more synapses (perhaps via the V wave' elements).…”

Section: B Neuron Response Propertiesmentioning

confidence: 99%