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L Walløe

Publications and source records attributed to L Walløe.

42 records · Page 3Linked to original sources
PubMed1980

A simulation study of a neuron in a simple muscle control system.

The mechanism underlying signal transmission through the accessory neuron of the muscle receptor organ in the crayfish abdomen was examined experimentally and by computer simulation. The mathematical model of the accessory neuron and its synaptic inputs was based, in part, on previous neuronal models studied by Stein (1965) and Rall (1964). The model predicted with considerable accuracy the behaviour of the experimental system in a number of situations. It was possible to determine in some detail the mechanisms underlying the frequency response characterized by a threshold and an approximately linearly increasing response for stimulus intensities above threshold. Furthermore, we were able to explain the observation that the accessory cell transforms a regular input train from a stretch receptor into an irregular output train. The highly branched structure of the dendritic tree, combined with a firing threshold in the dendrites which prevents action potentials from invading large parts of the dendritic tree, seems essential in determining these properties.

Abdomen↗
PubMed1980

Changes in cerebral blood flow during hyperventilation and CO2-breathing measured transcutaneously in humans by a bidirectional, pulsed, ultrasound Doppler blood velocitymeter.

We have used a bidirectional pulsed ultrasound doppler system which measures the instantaneous mean velocity across the lumen of a blood vessel in order to determine the relationship between alveolar PCO2 (PACO2) and blood flow in the four arteries supplying the brain in humans. Both high and low PACO2-values were explored. Six subjects, 3 males and 3 females (22-40 years) were studied by use of this non-invasive technique. To increase the PACO2 the subjects were breathing 4, 6 and 8% CO2 in air. PACO2 was reduced by voluntary hyperventilation down to a chosen end-expiratory PCO2 value of about 2.2 kPa. We found a linear relationship between arterial blood flow expressed as a percentage of control level and PACO2 in the range from 3.3 to 7.3 kPa. At the very lowest PACO2 values a levelling off of the response, with flow values of 40 to 45%, was observed. The CO2-reactivities in the 6 persons varied between 28.1 and 30.0%/kPa. The time course and the magnitude of the flow response were similar in all four arteries.

Adult↗
PubMed1979

Firing behaviour in a stochastic nerve membrane model based upon the Hodgkin-Huxley equations.

A nerve membrane model with a two-state pore system was investigated by computer simulation in the uniform (space-clamped) case. Both sodium and potassium conducting pores were modelled, each pore having four independent gates which switched randomly between the open and the closed position, governed by the assumed rate constants. Each pore conducted only when all the gates were open. The model was based upon the Hodgkin-Huxley equations for the giant axon in squid, and in the limit of an infinite number of pores it was identical to these. The firing behaviour of this model as a function of the number of pores and the injected current were investigated. The mean firing frequency and the distribution of interspike intervals were mainly used in the presentation of the results. It was found that for pore numbers less than about 20 000 the main effects due to a finite number of pores were a lowering of the current threshold for firing and a more linear frequency current relationship relative to that of the original H-H equations. For higher pore numbers an increase in the current threshold and a pronounced burst firing close to the threshold were found.

Animals↗
PubMedDate not supplied

Menarcheal age in Oslo during the last 140 years.

Data from maternity clinics have been used to study the trend in menarcheal age among girls born in Oslo after 1840. The investigation was based on recordings from approximately 50 women from each year. The women were divided into social categories according to their own or their husband's occupation. The results show a trend toward earlier maturation within the working class, which is characterized by two periods of rapid fall in menarcheal age. The first period covers women born between 1860 and 1880, and shows a fall in menarcheal age from about 15.6 to about 14.6 years. During the second period of rapid fall, which covers women born between 1905 and 1940, the menarcheal age was further reduced from about 14.6 to 13.3 years. The age at menarche has been stable at about 13.3 years for women born after 1940. These results contrast with those of some earlier studies of the menarcheal age in Norway. However, it is shown that the discrepancies between these investigations and our own disappear when the same computational methods and the same interpretation of the age recordings are used.

Adolescent↗
PubMedDate not supplied

Height, weight and menarcheal age of Oslo schoolchildren during the last 60 years.

Every 5th year since 1920 the heights and weights of all Oslo schoolchildren (aged 7 to 18 years) have been measured, and the measurements processed centrally. For ages between 8 and 14 the mean height increased by about 4 cm per decade between 1920 and 1940 for both sexes. A drop of about 1.5 cm occurred during World War II, followed by a rapid catch-up. Since 1950, height has increased only moderately. A weight increase of between 1.5 kg (8 years old) and 3.5 kg (13 years old) per decade before 1940 was followed by a drop during the war equivalent to somewhat less than one decade's gain. A rapid catch-up after the war was followed by a slight decrease since 1950, especially for ages above puberty. A stable difference in the social composition of the eastern and western districts of Oslo allowed comparison of the trends for lower and higher social strata. Before the war, children from higher strata were taller than children from lower strata, but this difference has now practically disappeared. Children from the higher strata weighed more until about 1955, but later those from the lower strata weighed markedly more, especially during adolescence. The difference in menarcheal age between social strata was examined in 1928, 1952, 1970 and 1975. The time trend parallels that for weight: menarcheal age was lowest among higher strata until the 1950s, but after that the lower strata experienced the lowest menarcheal age.

Adolescent↗