Biomedical subjects

B B Edin

Publications and source records attributed to B B Edin.

11 recordsLinked to original sources

PubMed1992

Independent control of human finger-tip forces at individual digits during precision lifting.

1. Subjects lifted an object with two parallel vertical grip surfaces and a low centre of gravity using the precision grip between the tips of the thumb and index finger. The friction between the object and the digits was varied independently at each digit by changing the contact surfaces between lifts. 2. With equal frictional conditions at the two grip surfaces, the finger-tip forces were about equal at the two digits, i.e. similar vertical lifting forces and grip forces were used. With different frictions, the digit touching the most slippery surface exerted less vertical lifting force than the digit in contact with the rougher surface. Thus, the safety margins against slips were similar at the two digits whether they made contact with surfaces of similar or different friction. 3. During digital nerve block, large and variable safety margins were employed, i.e. the finger-tip forces did not reflect the surface conditions. Slips occurred more frequently than under normal conditions (14% of all trials with nerve block, <5% during normal conditions), and they only occasionally elicited compensatory adjustments of the finger-tip forces and then at prolonged latencies. 4. The partitioning of the vertical lifting force between the digits was thus dependent on digital afferent inputs and resulted from active automatic regulation and not just from the mechanics of the task. 5. The safety margin employed at a particular digit was mainly determined by the frictional conditions encountered by the digit, and to a lesser degree by the surface condition at the same digit in the previous lift (anticipatory control), but was barely influenced by the surface condition at the other digit. 6. It was concluded that the finger-tip forces were independently controlled for each digit according to a 'non-slip strategy'. The findings suggest that the force distribution among the digits represents a digit-specific lower-level neural control establishing a stable grasp. This control relies on digit-specific afferent inputs and somatosensory memory information. It is apparently subordinated to a higher-level control that is related to the total vertical lifting and normal forces required by the lifting task and the relevant physical properties of the manipulated object.

Adolescent↗

PubMed1992

Quantitative analysis of static strain sensitivity in human mechanoreceptors from hairy skin.

1. Microelectrode recordings from 15 slowly adapting (SA) cutaneous mechanoreceptor afferents originating in hairy skin were obtained from the radial nerve in humans. 2. Controlled skin stretch was applied to the back of the hand that encompassed the physiological range of skin stretch during movements at the metacarpophalangeal (MCP) joints. 3. Both SA Group I and II afferents showed exquisite dynamic and static sensitivity to skin stretch. The median static strain sensitivity was 1.0 imp.s-1 per percent skin stretch for SAI units and 1.8 for SAII units. 4. Translated into sensitivity to movements at the MCP joint, both SAI and SAII afferents in the skin of the back of the hand displayed a positional sensitivity that was comparable with that reported for muscle spindle afferents. 5. These data give quantitative support to suggestions that skin receptors in the human hairy skin provide information on nearby joint configurations and therefore may play a specific role in proprioception, kinesthesia, and motor control.

Adult↗

PubMed1991

The 'initial burst' of human primary muscle spindle afferents has at least two components.

Ten muscle spindle primary afferents from the extensor digitorum communis muscle of man were studied with single unit afferent recordings. Responses to slow test stretches with three different pre-history conditions were assessed to investigate the contribution of rapid stretches to the stretch sensitization phenomenon. In two of the conditions, the slow test ramps were preceded by rapid stretch after which the parent muscle of the receptor was either (a) kept short for 5 seconds or (b) kept long for 3.2 seconds and then returned to the short muscle length for 5 seconds. The third condition (c) consisted of a slow stretch from short to long muscle length followed by a rapid return to the short muscle length, in turn followed by 5 seconds at the short muscle length. Afferent responses were depressed when the muscle had been kept at the long length after the rapid stretches (condition b) and enhanced when the muscle had been kept at the short length (conditions a & c). A prominent 'initial burst' was only present in the afferent discharge when the parent muscles of the primary endings had been kept short (condition a). A second, more prolonged burst was present for conditions (a) and (c) but was lacking or inconspicuous when the muscle had been kept long after rapid stretches (condition b). The rapid stretches in the stretch sensitization paradigm appear to be a primary factor not only for the enhanced responses of sensitized primary afferents but also for the depressed responses of desensitized primary afferents.

Adult↗

PubMed1991

Finger movement responses of cutaneous mechanoreceptors in the dorsal skin of the human hand.

1. The movement sensitivity of dorsal skin mechanoreceptors in the human hand was studied by the use of single afferent recording techniques. 2. Units were classified as slowly (SA) and fast adapting (FA) and further characterized by thresholds to vertical indentation and by receptive-field sizes. Whereas SA units were evenly distributed within the supply area of the superficial branch of the radial nerve. FA units were usually situated near joints. 3. The proportion of different receptor types (32% SAI, 32% SAII, 28% FAI, 8% FAII; n = 107) compared favorably with previous electrophysiological and anatomic data, arguing for minimal sampling bias. The majority of the skin mechanoreceptive units were SA, largely due to a relative scarcity of FAII [Pacinian corpuscles (PC)] units. 4. A large majority (92%) of the afferents responded to active hand or finger movements. Responses in all unit types were consistent with observed movement-induced deformations of their receptive fields. 5. FAI units responded bidirectionally, albeit usually with somewhat higher discharge frequencies for finger flexion, which in most cases were associated with skin stretch. FAI units showed meager responses to remote stimuli, typically responding to one or, at the most, two adjacent joints. 6. SA units typically showed simple directional responses to joint movements with an increased discharge during flexion and a reduced discharge during extension. Joint movement that influenced the skin within the receptive field of SA units elicited graded responses even if the field, as assessed by perpendicular indentations, was minute. This finding suggests that definition of cutaneous receptive fields by classical perpendicular indentations may be inappropriate for the receptors in the hairy, nonglabrous skin. 7. The interpretation of the data from these recordings suggests that cutaneous mechanoreceptors in the dorsal skin can provide the CNS with detailed kinematic information, at least for movements of the hand.

Adaptation, Physiological↗

PubMed1990

Finger joint movement sensitivity of non-cutaneous mechanoreceptor afferents in the human radial nerve.

The responses of non-cutaneous receptors in the human hand to normal digit movements were studied using single afferent recordings from the radial nerve. Eight joint-related afferents had thresholds of 50 mN or less. All responded to passive flexion movements within the physiological range of joint rotation and showed predominantly static response sensitivity; none increased its discharge during passive extension. However, only two of these eight afferents showed the same response pattern during active movements; three discharged only during the extension phase whereas the other three discharged both during extension and flexion. No high-threshold, joint-related mechanoreceptive afferents were encountered in a population of 148 afferents recorded from the cutaneous portion of the radial nerve indicating a scarcity of such afferents on the dorsal aspect of finger joints. Seven high-threshold, subcutaneous mechanoreceptive units not related to joints had thresholds for indentations of 50 mN or more and lacked responses to finger movements. Low-threshold mechanoreceptive afferents related to joints in the human hand may thus provide kinematic information in the physiological mid-range of both passive and active movements. Joint position cannot, however, be derived unambiguously from their discharge since the receptor responses may be dramatically altered by muscle activity.

Adult↗

PubMed1990

Dynamic response of human muscle spindle afferents to stretch.

1. One hundred and twenty-four muscle afferents from the finger extensor muscles were recorded from the radial nerve in human subjects. 2. The afferents were provisionally classified as muscle spindle primary (78/124) and secondary afferents (25/124), and Golgi tendon organ afferents (21/124), on the basis of their response to 1) maximal twitch contractions, 2) 20- and 50-Hz sinusoids superimposed on ramp-and-hold stretches, 3) stretch sensitization, and 4) isometric contractions and sudden relaxations. 3. Ramp-and-hold stretches at two velocities, 10 and 50 degrees/s, were applied to the appropriate metacarpophalangeal (MCP) joint while the parent muscle remained relaxed. For each unit three discrete parameters were assessed: the presence or absence of 1) an initial burst at the commencement of the ramp stretch, 2) a deceleration response at the beginning of the hold phase, and 3) a prompt silencing at muscle shortening. In addition, two kinds of dynamic indexes were calculated for 79 of the muscle spindle afferents. 4. Most spindle afferents responded readily to stretch, whereas the Golgi tendon organ afferents produced very poor stretch responses. All of them lacked a static response, whereas the dynamic response, when present at all, consisted of only a few impulses. 5. The dynamic index was higher for spindle primaries than for secondaries, and this difference was statistically significant although the distribution was unimodal for spindle afferents as a group. Hence, this parameter was a poor discriminator. 6. Initial bursts, deceleration responses, and silences during imposed shortening were more common in spindle primaries than in secondaries. The differences were significant in all these respects. 7. The three discrete parameters were statistically pairwise independent for the spindle afferents, justifying the combination of the three into a useful battery for discrimination between primary and secondary spindle afferents and the use of this battery as a partial data base for a probability approach towards a solid classification of human muscle afferents.

Adolescent↗

PubMed1990

Muscle afferent responses to isometric contractions and relaxations in humans.

1. One hundred and two single afferents from the finger extensor muscles of humans were studied with the microneurography technique. 2. The afferents were provisionally classified as primary muscle spindle afferents (62/102), secondary spindle afferents (22), and Golgi tendon organ afferents (18) on the basis of their responses to four tests: 1) ramp-and-hold stretch, 2) 20- and 50-Hz small-amplitude sinusoidal stretch superimposed on ramp-and-hold stretch, 3) maximal isometric twitch contraction, and 4) stretch sensitization. 3. The response profiles of the three unit types were analyzed during slowly rising isometric contraction terminating with an abrupt relaxation. About 75% (61/84) of all muscle spindle afferents increased their discharge during isometric contraction, whereas the discharge was reduced for the remaining afferents. All Golgi tendon organs increased their discharge during the contraction. 4. The level of extrafusal contraction at which a spindle afferent increased its discharge rate often varied from trial to trial, speaking against a fixed fusimotor recruitment level of the individual spindle ending. 5. In 70% of the spindle afferents, a distinct burst of impulses appeared when the subject rapidly relaxed after the isometric contraction. The burst was more common and usually much more prominent with primary than secondary afferents, often reaching instantaneous discharge rates well above 100 Hz. 6. Whereas all Golgi tendon organ afferents displayed an increased discharge during the contraction phase, only one of them exhibited a rate acceleration close to the relaxation phase. However, this response could clearly be identified as being of different nature than the spindle bursts.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1990

Classification of human muscle stretch receptor afferents: a Bayesian approach.

1. A sample of 124 human muscle afferents originating from the finger extensor muscles were recorded from the radial nerve in the upper arm. A method is described to formalize the classification of units in muscle spindle primary and secondary afferents and Golgi tendon organ afferents on the basis of a few, nonrigorous assumptions. The classification was based on experimental data that largely have been described in a series of previous papers, although some additional data were collected in the present study. 2. The units were subjected to five tests providing identification data: twitch contraction test, ramp-and-hold stretch, small-amplitude sinusoidal stretches superimposed on ramp stretch, stretch sensitization, and isometric contraction/relaxation. From these five tests the following eight response features were extracted: response to maximal isometric twitch contractions, type of stretch sensitization, correlation between discharge rate and contractile force, response to sudden isometric relaxation, presence or absence of an initial burst, deceleration response, prompt silencing at slow muscle shortening, and driving by small-amplitude sinusoidal stretches. 3. A Bayesian decision procedure was adopted to classify the units on the basis of the eight discriminators. As a first step, units were provisionally classified into muscle spindle primary and secondary afferents, and Golgi tendon organ afferents, by intuitively weighting their responses to the identification tests. Prior probabilities were estimated on the basis of the provisional classification. The eight response features were analyzed and tabulated for all afferents, and the likelihood functions of the tests were directly calculated on the basis of these data.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiology↗

PubMed1988

Single unit retrieval in microneurography: a microprocessor-based device controlled by an operator.

A microprocessor-based device was constructed to retrieve single unit activity from nerve recordings contaminated by other units and EMG activity. The microneurographic signal is sampled at 10 kHz and an algorithm applied to identify impulses from a single nerve fibre. On line, a TTL pulse is delivered when an event, i.e. a provisional nerve impulse, is selected. The wave form and clock time of events are stored. Moreover, the latest selected event and the actual selection criteria are continuously displayed on a standard oscilloscope. Off line, the wave form and clock time of events as well as an instantaneous frequency plot can be displayed on the oscilloscope. The final selection of events is done with a combination of a second algorithm, which essentially is a wave form comparator, and a manual check. The device is controlled either by hardware, with knobs on the front panel, or by software through a data bus connected to a microcomputer. Clock times and wave forms of the events, which are stored in the microprocessor memory, may also be presented on the data bus for later off-line analysis and coordination with other related signals collected during the experiment, e.g. transducer and electromyography records, whether these were stored on analog or digital tape or computer disc. Compared to other available techniques, the device has a superior discriminative power when electromyographic artefacts are present.

Action Potentials↗

PubMed1988

Stretch sensitization of human muscle spindles.

1. Sixty-seven afferents from the finger extensor muscles were consecutively recorded by microneurography. 2. The units were classified as primary or secondary muscle spindle afferents or Golgi tendon organ afferents on the basis of their responses to ramp-and-hold stretches, sinusoidals superimposed on ramp-and-hold stretches, maximal twitch contractions and isometric contractions and relaxations. 3. The muscle was repeatedly stretched and then either kept short or long for a few seconds followed by a slow ramp stretch. The responses of the muscle afferents to the slow stretch were compared under the two conditions. 4. Thirty out of thirty-eight units classified as primary spindle afferents and four out of eleven units classified as secondary afferents showed an enhanced response to the slow ramp when the muscle had been kept short compared to the response when the muscle had been kept long. 5. None of the eighteen Golgi tendon organ afferents showed any difference in this respect. 6. It is concluded that stretch sensitization does occur in human muscle spindles and, when present, constitutes firm evidence of the afferent originating from a muscle spindle rather than a Golgi tendon organ. In addition, due to differences in the response characteristics of primaries and secondaries, the test may aid in separating muscle spindle primary afferents from secondary afferents.

Action Potentials↗

PubMed1987

Twitch contraction for identification of human muscle afferents.

A classical test to differentiate between Golgi tendon organs and muscle spindles is the twitch contraction elicited by electrical stimulation. The possibility of producing maximal twitches in the finger extensor muscles using surface stimulation over the muscle belly was investigated as well as the feasibility of the test in microneurography experiments. Electrical stimuli were applied either over the muscle in the forearm or the radial nerve in the upper arm, while the resulting torque output at single metacarpophalangeal joints was measured. The relationship between current intensity and maximal contraction force was determined and stimulus response plots were constructed over a large range of current intensities. Stimulation of the radial nerve always yielded plots with a steep and monotonous rising limb up to a plateau. It was concluded that the plateau represented maximal twitch contractions. With transcutaneous stimulation over the muscle belly, the stimulus response plots were usually more complex. However, this could be explained by force transmission through the intertendinous connections on the dorsum of the hand and by antagonist activation. It was concluded that maximal twitch contractions can readily be elicited in the human extensor digitorum muscle with nonpainful transcutaneous electrical stimulations. Moreover, maximal twitches are compatible with single unit recording from muscle afferents in microneurography experiments.

Adult↗