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W Koehler

Publications and source records attributed to W Koehler.

28 records · Page 2Linked to original sources
PubMed1983

Analysis of nonlinear physiological systems with single or multiple spike inputs and analogue or spike outputs.

This paper outlines an extension of Krausz' (1975) approach to nonlinear analysis of physiological systems with random impulse train inputs. This extension concerns multiple (here two) inputs and spike train outputs in addition to analogue outputs. The respective theoretical formula are given, and the approach is illustrated by experimental data relating to the nonlinear interaction of cat motor units activated with random pulse trains. As outputs are considered muscle tension (as an example for an analogue signal) and discharge frequency of a Ia fibre (as an example for a spike output).

Animals↗
PubMed1982

Analysis of bimodal interspike interval histograms of primary muscle spindle endings in active triceps surae muscles of cats.

A feature frequently observed in interspike interval histograms (IH) derived from stationary Ia fibre discharge patterns was a bimodality suggesting a mixed population composed of two sub-populations of possibly different origins. To verify this hypothesis a separation of these subpopulations was attempted by assuming a Gaussian distribution for the longer intervals. The success of such a separation depended on the distinctness of the histogram peaks and the relative sizes of each mode. Both factors in turn depended on the overall muscle length and, hence, on the mean spindle discharge rate. The smaller intervals were then isolated from the spike trains and submitted to further statistical analysis. By averaging overall muscle tension with respect to the smaller intervals, the latter could often be linked to tension trajectories which were of higher amplitude and faster time course than the trajectories obtained by averaging with respect to the rest of the spikes. In some cases, auto-correlation histograms of isolated small intervals as well as serial correlograms computed for all intervals indicated that some muscle spindle afferents responded sensitively to activity of single motor units. This would confirm recent results of Cameron et al. (1980).

Afferent Pathways↗
PubMed1981

Frequency response characteristics of a multi-loop representation of the segmental muscle stretch reflex.

This paper continues the investigation of a three-loop representation of the segmental muscle stretch reflex system introduced in a preceding communication. Frequency response characteristics were computed for open-loop conditions, control and disturbance signal inputs under a variety of conditions: (i) "in parallel" and "in series" peripheral arrangements of muscle compartments, (ii) various patterns of central connectivity, (iii) various recruitment levels of motor units, (iv) various overall reflex gains, (v) absence or presence of muscle spindle acceleration sensitivity. These computations disclose a number of mechanisms by which the nervous system might improve system stability and behaviour. These mechanisms are discussed with regard to physiological data.

Feedback↗
PubMed1981

Some principles of flexor reflex generation in human leg muscles.

Flexor reflexes, evoked by stimulation of the tibial and deep peroneal nerves at the ankle level, were investigated in several ipsi and contralateral human leg muscles. On both sides, the reflex consist of a stereotyped oscillating sequence of inhibition and facilitation, exhibiting specifity to the stimulated site only in the initial ipsilateral phases. The responsible afferents were identified as belonging to a group of non-nociceptice skin afferents with a maximum conduction velocity of about 40-54 m/sec. Interdependence was observed between both latencies and amplitudes of the individual phases of the reflex sequences in synergistic and antagonistic pairs of muscles. It is concluded that the function of such a conjoint reflex generation in different muscles is to ensure an organized and adequate withdrawal.

Electric Stimulation↗
PubMed1980

Multi-loop representation of the segmental muscle stretch reflex. Its risk of instability.

The multi-channel system of the segmental muscle stretch reflex arc is modelled as an arrangement of two or three parallel "component" loops coupled to each other at spinal and at muscle level. Such a model is thought to be more realistic than the usually adopted representation of the stretch reflex as a single negative feedback loop. Anatomical and physiological data were taken from the literature for an extensive simulation of the compound system with special reference to the problem of its stability. Particular emphasis was put on the question of which kind of central (spinal) connectivity is appropriate to best reduce the risk for instability which arises easily in certain system configurations. This paper describes the system and presents simple introductory computations apt to demonstrate the problems the physiological system has to cope with.

Animals↗