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Biomedical subjects

K Malmgren

Publications and source records attributed to K Malmgren.

47 records · Page 3Linked to original sources
PubMed1987

Evidence that low threshold afferents both evoke and depress polysynaptic excitation of wrist flexor motoneurones in man.

The post-stimulus time histogram method was used to measure the time course of the firing probability of voluntarily activated wrist flexors motor units (MUs) after various stimulations. Stimulating the median and the ulnar nerve at an intensity equal to the motor threshold evoked an early increase in firing probability attributed to the monosynaptic Ia EPSP. Reducing the stimulation strength led to the disappearance of this peak and to the appearance of a second peak, whose latency was 3-5 ms longer than that of the monosynaptic peak. It is shown that both group I and cutaneous fibres contribute to the long-latency response but that group I fibres alone are responsible for its onset. Combined stimulation of the same afferents (group I and low threshold cutaneous fibres) reduced the amplitude of the second response. It is argued that this inhibition is exerted onto the interneurones mediating the non-monosynaptic excitation to motoneurones.

Electromyography↗
PubMed1985

Cutaneous facilitation of transmission in Ib reflex pathways in the human upper limb.

Group I effects from wrist extensors to flexors, i.e. an early inhibition followed by a relative facilitation which are thought to be Ia and Ib in origin respectively, were compared in control conditions and when preceded by a weak cutaneous stimulation. Stimulating the skin of the dorsal side of fingers II-III, which did not modify the test reflex size when applied alone, increased Ib facilitation. By contrast this Ib effect was not changed by stimulation of the skin of the palmar side. It has previously been shown that heteronymous Ib inhibition in the lower limb during voluntary contraction is facilitated by cutaneous stimulation from restricted receptive fields. Thus, present results lend support to the idea that cutaneous facilitation of transmission in Ib reflex pathways might be functional in curtailing exploratory movements.

Adult↗
PubMed1979

Histophysiological observations on fast skeleto-fusimotor axons.

In three instances, repetitive stimulation of a single fast skeleto-fusimotor axon supplying cat tenuissimus muscle was observed to activate a secondary ending belonging to a precisely located spindle. Prolonged repetitive stimulation of these beta-axons elicited glycogen depletion in the intrafusal muscle fibres of the located spindles and in extrafusal fibres. The intrafusal depletion affected the longest of the chain fibres in two instances, and the bag1 and bag2 fibres in the third instance. In one experiment, the discharge from the primary ending of the located spindle was also recorded. The fast beta-axon (it supplied the longest chain fibre in the spindle) had a static action on the primary ending. The extrafusal muscle fibres of the 3 fast beta-motor units belonged to the fast oxidative-glycolytic type.

Animals↗
PubMed1978

"Fast" and "slow" skeleto-fusimotor innervation in cat tenuissimus spindles; a study with the glycogen-depletion method.

The glycogen-depletion method was used to investigate the motor supply to tenuissimus with respect to the presence of fast beta axons and to assess the total proportion of both fast and slow beta-innervated spindles in this muscle. In a first series of 5 expts., groups of motor axons with conduction velocities higher than 85 m/s were repetitively stimulated so as to produce glycogen depletion in the muscle fibres they innervated. The whole muscle was then quick-frozen, serially cut, stained to demonstrate glycogen and examined for intrafusal glycogen depletion. Zones of glycogen depletion were found in 16 of the 46 examined spindles; they were most frequently located in the longest of the chain intrafusal muscle fibres. Since it is known that there are no purely fusimotor axons to tenuissimus with conduction velocities above 50 m/s, it was concluded that beta axons are present among the fastest axons to this muscle. In a second series of 5 expts. as many motor axons as possible with conduction velocities above 60 m/s were stimulated. Zones of glycogen depletion were found in 19 of the 47 examined spindles. They affected chain fibres in about half of the instances and bag1 fibers in the others. As this latter location is characteristic of slow dynamic beta axons, it was concluded that both slow and fast beta axons occur regularly in the motor supply to tenuissimus. beta-innervation is present in at least 40% of tenuissimus spindles with almost no convergence of fast and slow beta axons onto the same spindle.

Action Potentials↗
PubMed1978

Role of joint afferents in motor control exemplified by effects on reflex pathways from Ib afferents.

1. Intracellular recording from motoneurones to hind limb muscles in the cat was used to investigate the effect of volleys in the posterior nerve to the knee joint on motoneurones and on transmission from Ib afferents. 2. Volleys in the joint nerve facilitate transmission in disynaptic and trisynaptic inhibitory and excitatory reflex pathways from Ib afferents. It is postulated that facilitation, which appears at a strength of 1.5 times threshold, is evoked, not by Ib afferents which 'contaminate' the joint nerve, but by afferents from joints receptors. 3. T;e time course of facilitation of the disynaptic Ib i.p.s.p.s in motoneurones indicates that these joint afferents have disynaptic connexions with the interneurones of the Ib inhibitory pathway. 4. A brief description is given of synaptic effects evoked in motoneurones by graded electrical stimulation of the posterior nerve to the knee joint. At low stimulus strength the effects may be evoked via interneurones of Ib reflex pathways, but some results suggest that other interneuronal paths are utilized as well. Somewhat higher strengths, but occasionally less than 2 times threshold, produce later synaptic effects presumably mediated by reflex paths from the flexor reflex afferents; it does not seem likely that the contributory afferents in the joint nerve have nociceptive function. 5. It is suggested that impulses from impulses from joint receptors can influence tension regulation from Golgi tendon organs; if these receptors are activated in the terminal phase of the movement they may contribute a purposeful decrease of tension. It is pointed out that joint receptors may have an important role in motor regulation by their effects on interneurones of the different neuronal systems controlling motoneurones.

Animals↗
PubMed1977

Cutaneous facilitation of transmission in reflex pathways from Ib afferents to motoneurones.

1. The effect of volleys in low threshold cutaneous afferents upon transmission of synaptic action from Ib afferents to motoneurones has been investigated with intracellular recording from alpha motoneurones to hind limb muscles. 2. There was facilitation from cutaneous afferents of transmission in excitatory and inhibitory reflex pathways from Ib afferents without any evidence for difference in effect on di- and trisynaptic pathways. It is postulated that volleys in cutaneous afferents evoke excitatory action in interneurones of these reflex pathways. 3. The time course of the facilitation suggest that cutaneous afferents have disynaptic excitatory connexions with the interneurones intercalated in the disynaptic Ib inhibitory pathways to motoneurones. 4. Some observations are reported suggesting that interneuronal transmission in Ib inhibitory pathways to motoneurones might be facilitated from Ia afferents. 5. The findings are discussed in relation to the presumed role of Ib reflex action in regulating muscle tension.

Action Potentials↗
PubMedDate not supplied

LD and delinquency: rethinking the "link".

Longitudinal data from a 7-year prospective study was examined to investigate whether the presence of learning disabilities (LD) increases a youth's risk of becoming a juvenile delinquent. The sample included 515 students enrolled in the fifth grade in the fall of 1985, 51 (9.9%) of whom were youth with LD. Self-report data on delinquent activity were collected in the spring of 1993. Official court records were obtained for the years 1985 through 1992. Hierarchical multiple regression analyses were performed using a block of three demographic variables (gender, ethnicity, and socioeconomic status) as predictors in the first step and including LD status in a second step. Seven separate analyses were performed, using different measures of delinquency as criterion variables. In no case did LD status account for a significant portion of unique variance in the delinquency variables when the demographic variables were controlled for. The results of this study did not confirm the presence of a direct relationship between LD and delinquency and suggest that the finding of a direct relationship in other studies may have been due to confounding of the LD status with age, ethnicity, or socioeconomic status.

Adolescent↗