Search PubMed⌕ Search

Biomedical subjects

U Proske

Publications and source records attributed to U Proske.

At least 91 records · Page 5Linked to original sources
PubMed1990

Errors in force estimation can be explained by tendon organ desensitization.

Here we report observations on the sense of muscle tension in human subjects and compare them with responses of tendon organs in cat hindlimb muscles. Human subjects learned under visual guidance to estimate a 4% maximum voluntary contraction (m.v.c.) of elbow flexors of one arm. When they were able to reproduce this force reliably without visual feedback, they repeated the estimation immediately after a 5 second m.v.c. or a 5 second period of relaxation. In a second experiment the 4% m.v.c. was generated under visual control with one arm, and matched with the other, test arm, without visual feedback. The matching task was then repeated after test arm conditioning. In both experiments subjects reported an accurate match using significantly more than the reference force ("overmatched") after an m.v.c. The overmatching was greatest during the first 5 second period following the conditioning contraction, and during the subsequent 20 seconds it gradually declined to near reference levels. The size of the matching error was directly proportional to the duration of the conditioning contraction. In the first experiment extension of the arm immediately following conditioning increased the error, in the second it slightly decreased it, although tension continued to be overmatched. In a series of experiments on the soleus muscle of anaesthetised cats responses of tendon organs to 10% of maximum contraction were seen to drop sharply when preceded by a conditioning maximum contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Effects of muscle history on the stretch reflex in cat and man.

1. This is a report of experiments on cat and man which demonstrate effects of a muscle's previous history of contraction and length changes on the size of the stretch reflex. 2. In adult human subjects the size of the tendon jerk was measured in ankle extensor muscles by tapping the Achilles tendon. Muscle conditioning consisted of a maximum voluntary contraction with the foot dorsiflexed or plantarflexed by 30 deg from the test position, after which the subject was asked to relax while the foot was held still for several seconds before being returned to the test position and a tendon tap given. After a contraction of the lengthened muscle the tendon jerk was smaller than after a contraction of the shortened muscle. 3. The experiment was then repeated, but instead of a tendon jerk an H (Hoffmann) reflex was elicited by transcutaneous electrical stimulation of the tibial nerve in the popliteal fossa. The reflex after a conditioning contraction of the lengthened muscle was larger than after a contraction of the shortened muscle. In other words muscle conditioning produced opposite effects on the tendon jerk and H reflex. 4. These findings were confirmed in cats anaesthetized with chloralose. After a conditioning contraction of triceps surae at a length 5 mm longer than the test length (hold-long) a quick tendon stretch produced a smaller reflex response than following a conditioning contraction with the muscle 5 mm shorter than the test length (hold-short). The reverse trend was seen with a reflex elicited by direct electrical stimulation of the muscle nerve, which stimulates the H reflex. 5. One consequence of a conditioning contraction is that it leads to an alteration of the level of resting discharge of muscle spindles. We propose that the larger tendon jerk after a contraction of the shortened muscle is the result of changes in stretch sensitivity of muscle spindles. The reverse effect on the H reflex we attribute to a rise in the level of resting discharge of muscle spindles, which, we propose, leads to reflex inhibition of motoneurones. 6. We support this conclusion with evidence from an experiment in which the size of the conditioning step was systematically altered. Even quite small hold-short conditioning steps led to depression of the H reflex in man and the monosynaptic reflex in cats. Recordings from single afferents showed that such small steps were also accompanied by a detectable rise in spindle resting discharge.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1989

Tendon organ afferents in the knee joint nerve of the cat.

This article is concerned with the question of whether some of the slowly adapting responses recorded in the mid-range of joint position from the posterior articular nerve (PAN) of the cat hindlimb and which are therefore candidates for joint position sensors, are in fact coming from muscle receptors of the popliteus muscle. Evidence is provided that in addition to afferents of primary endings of spindles, secondary endings of spindles and tendon organs are represented in PAN as well. Removal of the fleshy part of the popliteus muscle does not reliably remove muscle afferent contamination in PAN.

Afferent Pathways↗
PubMed1989

Measurements of muscle stiffness, the electromyogram and activity in single muscle spindles of human flexor muscles following conditioning by passive stretch or contraction.

In experiments on adult human subjects we examined the effect on passive mechanical properties of a muscle by conditioning it with either an isometric contraction or passive muscle extension. The test measurement was the amount of muscle displacement (stiffness) and the accompanying EMG in response to a brief torque pulse. Two muscles were tested, flexor digitorum profundus (FDP) and brachialis. In FDP the discharge of single muscle spindles was recorded as well. After muscle extension and return to the initial length, passive stiffness was less than after an isometric contraction. The changes in stiffness were accompanied by changes in pattern of EMG and in the responses of muscle spindles. It is suggested that in resting muscle there are stable cross bridges between actin and myosin filaments of muscle fibres which largely determine the passive stiffness. Muscle extension leads to detachment of these cross bridges which then re-form at the longer length. Return of the muscle to its starting length leads to development of slack in muscle fibres because, stiffened by the presence of the stable cross bridges, they are unable to shorten. Slack in muscle fibres lowers their measured stiffness. Muscle contraction, on the other hand, will result in any preexisting slack being taken up by the actively shortening muscle fibres, thereby raising muscle stiffness. Stiffness in intrafusal fibres is likely to follow a similar pattern to that in extrafusal fibres, leading to changes in stretch responsiveness of muscle spindles and consequently in the reflex EMG. It is concluded that the changes in stiffness and accompanying reflexes observed in this study are likely to be seen, at least under some conditions, in normal movements.

Adult↗
PubMed1989

Conduction velocity and fibre diameter of the peroneal nerve in normal and growth retarded fetal sheep.

In this study we have examined structural and functional aspects of nerve fibre development in experimentally growth retarded fetal sheep following restriction of placental growth by carunclectomy in 5 ewes. Measurement of whole-nerve conduction velocity in the peroneal nerve showed, for the most rapidly conducting fibres, a significant slowing from the normal value of 50.3 +/- 1.8 m/s to 33.8 +/- 3.3 m/s (P less than 0.01). Histological examination of nerve sections revealed a deficit of large myelinated fibres in growth retarded fetuses which is consistent with the conduction velocity measurements.

Animals↗
PubMed1989

Responses of electroreceptors in the platypus bill to steady and alternating potentials.

1. This is a report of further observations on the response characteristics of electroreceptors in the bill of the platypus, Ornithorhynchus anatinus, first described by Gregory, Iggo, McIntyre & Proske (1987). 2. The main finding is that, with the bill immersed in water, applying a potential difference between large plate electrodes on either side of the bill, produced detectable responses in a population of electroreceptors to field strengths as low as 4 mV cm-1. Threshold for individual receptors lay between 4 and 25 mV cm-1. 3. An electric dipole placed in the water close to the receptive field could also elicit responses, threshold being lowest when the cathode was near the centre of the field. On several occasions the most sensitive spot was seen, under the microscope, to correspond to the mouth of a mucous sensory gland (Andres & Von Düring, 1984). Response intensity fell when the dipole was moved further away, the drop being less steep in a direction over the top of the bill towards the mid-line. 4. For individual receptors the latency of the first impulse initiated by supramaximal voltage pulses was 1.1-1.8 ms. Latencies tended to be shorter when the site of the receptor lay closer to the recording electrodes. Plotting each latency against conduction path length for eleven receptors gave an approximately linear relation from which was calculated an average axonal conduction velocity of 56 m s-1. The plot yielded an estimate of impulse initiation time of 0.8 ms. It is argued that this is too short to include a synaptic delay. A peripheral synapse is found in all non-mammalian electroreceptors. 5. Electroreceptors responded to both steady and rapidly changing potential gradients. For ramp-shaped gradients of 1-50 V s-1 peak firing rate was approximately proportional to log stimulus velocity. In response to sinusoidal potential changes a 1:1 relation between each afferent impulse and the peak of the stimulating waveform could be obtained over the range 12-300 Hz. Threshold was at its lowest at 50-100 Hz. Tuning curves measured with the bill immersed in water were little different from those obtained by focal stimulation with the bill in air. 6. It is concluded that platypus electroreceptors, supplied by the trigeminal nerve, and which are therefore not part of the acoustico-lateralis system as in non-mammalian electroreceptors, are also unique in not having a peripheral synapse. Furthermore, they are able to respond to both steady and rapidly changing voltage gradients.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1989

Responses of electroreceptors in the snout of the echidna.

1. This is a report of experiments which provide evidence in support of the existence of an electric sense in the echidna, or spiny anteater Tachyglossus aculeatus. It is the first known example of electroreception in a terrestrial animal. 2. In each of four animals anaesthetized with alpha-chloralose, afferent responses were recorded in dissected filaments of the infraorbital branch of the trigeminal nerve which supplies skin of the upper jaw. Recordings were obtained from a total of forty-seven units identified as electroreceptors, by their responses to weak voltage pulses using focal stimulation of the moist skin surface. 3. In the absence of a stimulus, some receptors had an irregular resting discharge; others were silent. The receptive field for each receptor consisted of a discrete spot. Receptive fields were restricted to the tip of the snout. Cathodal stimulation over the receptive spot was excitatory for the duration of an applied voltage pulse. Reversal of stimulus polarity silenced any on-going activity and was followed by a post-anodal rebound excitation. 4. Receptor threshold was best measured not in air but with the snout immersed in tap water. An electric field was applied between a pair of large plate electrodes on either side of the snout. Threshold for thirty receptors lay in the range 1.8-73 mV cm-1. Measurements of response latency and of conduction path length gave estimates of axonal conduction velocities for the afferent fibres of 10-18 m Receptors responded to sinusoidally changing voltage gradients over the range 0.5-200 Hz with a maximum sensitivity at 20 Hz. 5. In one experiment a receptor site was marked with fine pins. Serial sections of the piece of underlying skin revealed a large mucus-secreting gland at the marked spot. Similar glands in skin of the platypus have previously been shown to be the sites of electroreceptors. 6. In a behavioural experiment an echidna was trained to choose between two identical tap water-filled troughs, one of which had a weak electric field across it. The animal learned to detect field strengths down to 1.8 mV cm-1 which corresponded to threshold for the most sensitive receptor measured in a subsequent electro-physiological experiment. It is concluded that the echidna, like the other Australian representative of the monotremes, the platypus, has an electric sense. It remains to be determined what kinds of sources of electric fields the animal encounters in its normal habitat.

Air↗
PubMed1989

Corticofugal action on transmission of group I input from the hindlimb to the pericruciate cortex in the cat.

1. In cats anaesthetized with alpha-chloralose, evidence was sought for a corticofugal action on input from muscle group I afferents projecting to the cerebral cortex via the brain stem relay at nucleus Z. 2. Extracellular recordings were made of responses of thirty-four nucleus Z neurones which could be activated by stimuli at group I strength applied to each of a variety of hindlimb muscle nerves. Afferent input to each nucleus Z neurone was restricted to a single muscle. 3. Nucleus Z neurones typically showed a resting discharge which could be increased or decreased by altering the amount of stretch on the muscle which was the source of the afferent input. Ventral root stimulation gave response patterns which showed these neurones to be driven by input from either tendon organs or muscle spindles, but not both. 4. A brief train of focal, cathodal stimuli applied to a discrete region of pericruciate cortex could consistently inhibit the maintained activity evoked by muscle stretch in nucleus Z neurones, or the response evoked by stimulation of the muscle nerve at group I strength. The inhibition was powerful and lasted 50-400 ms. The effective stimulating site corresponded to area 3a, the main cortical receiving area for hindlimb muscle group I input. 5. Since the ascending spinal axons which project to nucleus Z are collaterals of dorsal spinocerebellar tract fibres, it was possible to stimulate the parent axons at their termination in the anterior lobe of the cerebellum. Cortical stimulation was found to have little or no effect on activity in nucleus Z neurones evoked by cerebellar stimulation over conditioning-test intervals in the range 10-200 ms. 6. It is concluded that over the time intervals for which it has been tested, corticofugal inhibitory action appears to be largely operating at the first spinal segmental relay, in Clarke's column. Thus the inhibitory action arising in area 3a of the cerebral cortex will suppress the action of input from hindlimb group I fibres at the level both of the cerebellum and the cerebral cortex.

Animals↗
PubMed1988

Innervation of muscle receptors in the cross-reinnervated soleus muscle of the cat.

It has recently been reported (Gregory et al., J. Physiol., 331:367-383, 1982) that cutting a muscle nerve and letting it grow back into the muscle or cross-uniting the muscle with a foreign nerve results in major disruption of the normal response patterns of muscle spindles and tendon organs. Here we report observations on the structure of muscle receptors in cross-reinnervated and self-reinnervated soleus muscles in an attempt to detect abnormalities that might account for their disturbed function. Eight soleus muscles were reinnervated with the extensor digitorum longus nerve for periods up to 449 days and two were self-reinnervated. Following the physiological investigation, the muscle was fixed and stained according to the method of Barker and Ip (J. Physiol., 69:73P-74P, 1963). Spindles and tendon organs were teased from the muscle and photographed. In one cross-reinnervated muscle an attempt was made to isolate all receptors. About two-thirds of the normal number of spindles and tendon organs were found. Three categories of receptor were identified: normal, abnormal, and those having no visible nerve endings. There appeared to be little difference in degree of abnormality of receptors in self- and cross-reinnervated muscles. Of the 180 spindles, 3% were normal, 43% had no visible endings, and 54% had abnormal endings. Of 80 tendon organs, 38% were normally innervated, 33% were without visible innervation, and 29% had abnormal endings. We conclude that following long-term cross-reinnervation and self-reinnervation of soleus there is extensive disruption of the normal innervation pattern of both spindles and tendon organs which could account for their functional abnormalities.

Animals↗
PubMed1988

The responses of muscle spindles in the kitten to stretch and vibration.

Discharges of muscle spindle afferents from the soleus muscle were studied in kittens aged 1-21 days and in adult cats. Vibration applied longitudinally to the tendon elicited one impulse for each cycle of vibration over the range 1-200 Hz for the kittens and up to 450 Hz for the adult. Threshold amplitudes were generally higher in the kitten than in the adult. In response to large ramp and hold stretches applied at long muscle lengths kitten spindles showed rate saturation during the length change. Dynamic index, that is the peak rate during the length change minus the rate at the final length became progressively smaller at longer muscle lengths. No sign of saturation was seen at comparable muscle lengths in the adult. It is suggested that in the newborn the bag1 intrafusal fibre is not functional and that the dynamic response is produced only by the afferent terminals on the bag2 fibre. Another difference between kitten and adult was the length sensitivity measured under dynamic conditions. This increased much more steeply with stretch rate in the kitten. One possible explanation for the higher dynamic length sensitivity is a lack of elastic fibres surrounding intrafusal fibres of immature spindles.

Aging↗
PubMed1988

Receptors in the bill of the platypus.

1. Afferent responses were recorded from filaments of the trigeminal nerve in each of two platypuses (Ornithorhynchus anatinus) anaesthetized with alpha-chloralose. All receptive fields were located along the lateral border of the upper bill. Discrete receptive fields could be identified as belonging to two distinct classes of sensory receptor. 2. The most prominent response was an irregular resting discharge which could be increased or decreased by weak electric pulses. These receptors were insensitive to moderately strong mechanical stimulation, and it was concluded that they were electroreceptors. 3. Each electroreceptor had a single spot of maximum sensitivity on the bill surface. When the stimulating electrode over this spot was the cathode it excited the receptor for the duration of the stimulating pulse, using stimulus strengths as low as 20 mV. When it was the anode, it inhibited the discharge. Cathodal excitation was followed by rebound inhibition and anodal inhibition by rebound excitation. 4. Receptors responded to cathodal steps with an initial high-frequency burst of impulses, followed by a lower maintained rate of discharge. Rapidly changing pulses were similarly effective in exciting receptors, adding support to the claim that platypuses are able to detect moving prey by the electrical activity associated with muscle contraction. 5. The centres of the receptive fields of two electroreceptors were marked by the insertion of fine entomological pins. Histological examination established the presence of a large mucus-secreting gland at the marked spot. The epidermal duct of the gland contained an elaborate myelinated innervation, with morphologically distinct axon terminals that we identify as the electroreceptors. 6. As well as electroreceptors, the skin of the bill contained three kinds of mechanoreceptors: slow-adapting receptors, rapidly adapting, vibration-sensitive receptors and receptors with an intermediate adaptation rate. The slowly adapting receptors were characterized by their low threshold to mechanical stimuli, irregular discharge and significant dynamic sensitivity. Vibration receptors showed maintained responses to sinusoidal vibration of the skin up to 600 Hz. 7. These experiments confirm an earlier report that the platypus bill is an electrodetector organ. The presence of electroreceptors of a unique structure and supplied by the trigeminal nerve indicates that electroreception has evolved independently in monotremes. This in turn emphasizes that monotremes are a highly evolved group which split off from the main mammalian stem a long time ago.

Action Potentials↗
PubMed1988

Acute inflammation of the knee joint in the cat alters responses of flexor motoneurons to leg movements.

1. This is a report of changes in reflex excitability of flexor motoneurons in response to innocuous mechanical stimuli following initiation of an acute experimental inflammation of the knee joint in the chloralose-anaesthetized cat spinalized at level T12. 2. Activity of functionally single alpha- or gamma- motoneurons, identified by ventral root stimulation, was recorded in filaments of the nerve to biceps semitendinosus before and after onset of an acute inflammation. The inflammation was evoked by injection into the knee cavity of the compounds kaolin and carrageenan. 3. Measurements were made of resting activity, responses to local pressure applied to parts of the upper or lower limb, and to flexion or extension movements at the knee joint before and after onset of the inflammation. In two experiments, one in which no inflammation was initiated, and another in which recordings were made only after the inflammation had fully developed, a survey of large numbers of neurons (44 alpha and 84 gamma) showed that under control conditions only 14% of alpha-motoneurons showed a response to mechanical stimulation compared with 41% of gamma-motoneurons. In the presence of an inflammation 41% of alpha-cells were responsive compared with 64% of gamma-cells. 4. Inflammation-induced changes in activity of motoneurons including both excitatory and inhibitory effects, took 1-2 h to fully develop. Excitatory effects included a rise in resting discharge, an increase in the response to local pressure, and an increased response to flexion and/or to extension of the knee. Inhibitory effects included falls in resting discharge and/or in the responses to leg movements. 5. For 35 cells identified as alpha-motoneurons and tested both before and after initiation of an inflammation, 20 remained unresponsive throughout the experiment, whereas 4 that had not responded during the control period began after inflammation to respond to local pressure and/or flexion/extension movements. Of 11 units that exhibited some response before inflammation, 8 showed an increase with inflammation, whereas 2 became unresponsive. 6. The inflammation had rather more dramatic effects on gamma-neurons. Many showed control responses to leg movements, and these were measurably modified by inflammation. Of 56 gamma-cells tested under control conditions, 26 were unresponsive to all stimuli, whereas 30 showed some form of response including activity during flexion and extension movements of the leg. Where responses were tested both before and after onset of an inflammation, 11 of 13 unresponsive units remained unresponsive.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute Disease↗
PubMed1988

Aftereffects in the responses of cat muscle spindles and errors of limb position sense in man.

1. This is a report of two series of experiments, one, observations on muscle spindles in the anesthetized cat, the other, based on the animal observations, concerned with limb-position sense in human subjects. 2. When the cat soleus muscle is contracted at a short length and then after a brief period is brought to an intermediate length, the integrated afferent activity recorded in dorsal roots is maintained at a high level. If the contraction is applied while the muscle is held at a long length, the subsequent level of afferent activity back at the intermediate length is much lower. A similar result is obtained if large amplitude vibration of the muscle is used instead of contraction. Recordings from single afferents confirm that these alterations in discharge could be attributed to the primary and secondary endings of muscle spindles. 3. Following the proposal that the resting discharge of muscle spindles contributes to the sense of limb position in man, we have used a sequence of contractions or periods of vibration of biceps and triceps brachii followed by an arm-matching task to look for errors in limb position consistent with the patterns of muscle afferent discharge observed in the animal experiments. 4. Blindfolded subjects were told to contract biceps of one, the test arm, with the arm flexed. After the arm had relaxed, it was placed by the experimenter at an intermediate angle that the subject was asked to match with the other, indicator arm. Then the subject was asked to contract triceps with the arm extended, and the matching task was repeated. 5. The hypothesis was that contracting a muscle while it was short raised the level of afferent discharge coming from it when the arm was moved to an intermediate position so that the muscle would be perceived as more stretched and the arm felt to be displaced further than it really was. Thus, when biceps was contracted with the arm flexed, this would lead the arm in the intermediate position to be perceived as more extended than it really was. When triceps was contracted with the arm extended, this would lead the arm in the intermediate position to be perceived as more flexed than it really was.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1987

Can lactate-evoked cardiovascular responses be used to identify muscle ergoreceptors?

The increase in blood pressure and heart rate which accompanies muscular exercise is in part a reflex mediated by afferent nerve fibres in the group III and IV (small myelinated and unmyelinated) range. It has been reported that perfusion of lactate ions into hind limb muscles is an effective stimulus for these reflex responses. To investigate this hypothesis further, and to test adequacy of the controls used, a solution containing 15 mM lactic acid was perfused through a hind limb of urethane-anaesthetised rats, the leg's circulation being isolated from the rest of the body. During lactate perfusion, increases were seen in arterial blood pressure and heart rate. Denervation of the entire leg abolished the responses. To locate the receptors involved in the reflex, selective denervations of skin or muscle were performed. Clear responses were never seen when the leg was skinned or denervated by section of cutaneous nerves. On the other hand, responses to lactate perfusion were still seen following section of all nerves supplying the muscles of the leg, leaving the cutaneous innervation largely intact. It is concluded that perfusion of a hindlimb with lactate solutions is not an adequate technique to identify ergoreceptors in muscle.

Animals↗
PubMed1987

Responses of muscle receptors in the kitten to succinyl choline.

Responses of soleus muscle afferents were studied in anaesthetised kittens, after intravenous injection of succinyl choline (SCh), a drug which in adult spindles, at low doses, produces a contracture preferentially of bag1 intrafusal muscle fibres and so mimics the effect of dynamic fusimotor stimulation. Following injection of SCh in kittens aged between 1 and 57 days the integrated discharge recorded in large portions of dorsal root during muscle stretch showed a smaller increase than in the adult. Recordings from functionally single afferents of muscle spindles showed that in the youngest animals SCh induced a resting discharge from all spindles, which were normally silent. The response to a ramp-and-hold stretch showed an abrupt rise in firing rate at the start of the stretch followed by a slow decline. The abrupt fall at the end of the ramp, typical of the adult dynamic response, was almost absent in spindles of animals 2-5 days old. In the younger animals SCh allowed primary and secondary spindle endings to be distinguished on the basis of their response to stretch. Conduction velocity of developing Group I nerve fibres was found to increase from 9.5 ms-1 on day 2 to 51.6 ms-1 on day 57, an increase of 0.77 ms-1 per day, while Group II increased from 5.0 ms-1 to 23.2 ms-1 over the same period, an increase of 0.33 ms-1 per day. The two groups appeared to be separate even in the youngest animals. It is concluded that although spindles in the newborn kitten respond vigorously to SCh, the pattern of discharge is quite different from that seen in older animals.

Animals↗