The transmission of information in primary receptor neurones and second‐order neurones of a phasic system

Responses of the rat dorsal column system to mechanical stimulation of the hind paw

“…As a result of synaptic mechanisms, however, an increase in size of a stimulus may also be signalled by individual cells in the gracile nucleus discharging more impulses. Similar patterns have been shown to occur in primary neurones and in dorsal horn cells in the cat (Armett et al 1962). The repetitive firing of these second-order cells may conceivably serve to reduce the number of post-synaptic channels required for carrying information.…”

“…The results do indicate that some cells in the middle section might be monosynaptically connected to fast-conducting primary units and others could have monosynaptic inputs if they were driven from slower conducting fibres which might have been missed by the extracellular techniques employed. However, there is no certain evidence that slower conducting fibres are excited by mechanical pulses of the sort used in these experiments (see also cat's pad, Armett & Hunsperger, 1961;Armett et al 1962). The view taken by Perl et al (1962) is that primary receptor units responsive to hair movement are connected to cells with small receptive fields and that these cells are found predominantly in the middle section of the nucleus.…”

“…These inputs consisted of activity evoked in a population of primary receptor units which had axons running in the dorsal column; each unit could be excited by mechanical stimulation of a certain area of skin to fire most commonly a single impulse which arrived in the vicinity of the nucleus after a measured delay. A more detailed analysis of the patterns of activity evoked in a population of primary receptor units has been made in the cat (Armett & Hunsperger, 1961;Armett et at. 1962).…”

Projections from Pacinian corpuscles and rapidly adapting mechanoreceptors of glabrous skin to the cat's spinal cord.

“…In addition, according to Janig et al (1968 a) the receptors activated in the studies of Gray and his collaborators (Armett & Hunsperger, 1961;Armett et al 1962) may be positively identified as Pacinian corpuscles. It may be concluded, therefore, that the population of interneurones in the medial part of the dorsal horn studied by Armett et al (1961,1962) …”

“…But it has been shown by Jinig, Schmidt & Zimmermann (1968b) that axons from Pacinian corpuscles activate dorsal horn interneurones responsible for producing presynaptic inhibition of (mainly) axons innervating rapidly adapting mechanoreceptors including the Pacinian corpuscles themselves. Furthermore, it seems likely (see Janig et al 1968 a) that the interneurones studied by Armett, Gray & Palmer (1961) and Armett, Gray, Hunsperger & Lal (1962) were excited by input from Pacinian corpuscles in the central foot pad. It would be expected, therefore, that axons from Pacinian corpuscles should have collaterals at and near their point of entry into the lumbosacral spinal cord.…”