Biomedical subjects

D Zilm

Publications and source records attributed to D Zilm.

3 recordsLinked to original sources

PubMed1982

Relationship between EPSP shape and cross-correlation profile explored by computer simulation for studies on human motoneurons.

We used a computer model (making several simplifying assumptions) to explore the relationship between the characteristics of an excitatory postsynaptic potential (EPSP) and the profile of the change in firing probability that occurred when that EPSP was delivered to a rhythmically discharging neuron. In circumstances applicable to studies on human motoneurons we found that the magnitude of the period of increased firing probability in the cross-correlation (produced by the rising phase of the EPSP) was related to the number of stimuli and to the proportion of the interspike interval that the EPSP was within reach of threshold. The interstimulus interval and the statistical distribution of the motoneuron interspike intervals were of little consequence. For this model the subsequent period of reduced firing probability was proportional to the amplitude of the EPSP and not to the duration of its falling phase.

Afferent Pathways↗

PubMed1982

Characteristics of postsynaptic potentials produced in single human motoneurons by homonymous group 1 volleys.

Changes in the firing probability of voluntarily activated human tibialis anterior motor units occurred when the muscle nerve was stimulated below the threshold of motoneuron axons. A prominent period of increased firing probability was considered to result from the group 1 composite EPSP. The rise time of this composite EPSP, estimated from the duration of the period of increased firing probability, was between 2 and 5 ms. One estimate of the relative amplitude of the EPSP was derived from the cross-correlation and tested by inserting synthetic EPSPs into a computer simulation of a rhythmically discharging neuron. A second estimate of the amplitude was obtained by delivering stimuli with various delays within the interspike interval to determine the position (as a percentage of the mean interspike interval) at which the postsynaptic potential was capable of bringing the membrane potential to threshold. The two estimates were in reasonable agreement. The largest of these EPSPs could bring the motoneuron to threshold after 39% of the elapsed interspike interval. The falling phase of the postsynaptic potential was explored by delivering double stimuli within the interspike interval to produce temporal summation. The duration of the falling phase, so tested, was between 5 and 20 ms. An attempt was made to deduce the general form of the trajectory representing the effective distance of an EPSP from threshold during the interspike interval from the alterations in the cross-correlation profile that occurred when motoneuron firing rate was voluntarily altered.

Afferent Pathways↗

PubMed1978

Synaptic connections to individual tibialis anterior motoneurones in man.

The characteristics of post-synaptic potentials in a single human motoneurone can be derived from the profiles of post-stimulus time histograms (PSTH) of that neurone when it is firing rhythmically. We have used this method to explore the synaptic connections to individual tibialis anterior motoneurones in man. Agonist group 1 volleys produced short latency excitation of 85% of tibialis anterior motoneurones probably representing the 1a EPSP. Excitation, at a latency of 70 ms, is attributed to a long loop reflex. Antagonist group 1 volleys produced short latency inhibition of 65% of tibialis anterior motoneurones probably representing the 1a IPSP. Excitation, at a latency of 97 ms, may represent spino-bulbo-spinal reflex. None of these effects are due to the excitation of cutaneous afferent nerve fibres.

Action Potentials↗