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Results for “Recruitment, Neurophysiological”

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PubMed1977

[A proposition for mutual genesis of hearing loss, recruitment and ear murmurs in the case of acute inner ear alterations (author's transl)].

Pathological changes on the stereocilia of cochlear hair cells observed by Bredberg et al. (1972) after noise exposure and in the early stages of antibiotic intoxication are suggested to cause a mechanical decoupling between the tectorial membrane and the hair cells. During acute episodes of endolymphatic hydrops a similar decoupling is suggested to occur, although for different reasons. Harris (1968) calculated the noise generated at the input to the hair cells on account of the Brownian motion of air particles in front of the tympanic membrane. For tight coupling, he obtained a level of (--)22 dB re auditory threshold. For loose coupling this noise was found to increase to +33 dB, i.e., for 55 dB. These two independent findings are used to account for the combination of hearing loss, recruitment, and tinnitus observed with the inner-ear pathologies mentioned. The proposed hypothesis is in good agreement with clinical observations.

Anti-Bacterial Agents↗
PubMed1981

The influence of temperature on the isometric characteristics of fast and slow muscle in the cat.

The maximum tetanic tension (initial strength) and the length of time, 20, 40 or 60%, of that initial strength could be maintained (endurance) was assessed in 2 fast twitch muscles (the plantaris and the medial gastrocnemius) and a slow twitch muscle (the soleus) of the cat at muscle temperatures ranging between 22 and 38 degrees C. The results of these experiments showed that the strength of the soleus was constant between muscle temperatures of 38 to 28 degrees C, and then gradually decreased as the muscle was cooled further. Plantaris, on the other hand, showed a reduction in strength at all muscle temperatures less than 38 degrees C; the response of the medial gastrocnemius was between these two extremes. The longest endurance for the soleus muscle was found to be at a muscle temperature of 28 degrees C, the endurance being as much as 3 times higher at this temperature than at muscle temperatures of 22 or 38 degrees C. The medial gastrocnemius showed a similar response but the endurance only doubled when comparing the endurance at a muscle temperature of 28 to 38 degrees C. In contrast, the plantaris maintained a constant endurance over the temperature range of 38 to 28 degrees C; below this muscle temperature the endurance decreased markedly. The mechanism for this response appeared to be related to the effect of temperature on the contractile characteristics of the muscles.

Animals↗
PubMed1979

Description of the firing pattern of respiratory neurons by frequency modulated interspike interval distributions.

The description of the firing pattern of respiratory neurons presented here is based on extracellular recordings and directed to the possible influence (facilitating of inhibiting effect) that the neuron might have upon others (output) as well as to the extend of influences that are received from other neurons (input). Developing such a description the spike generating mechanism of the neuron was in a first approach characterized by a frequency modulated gamma distribution. Using this approach an acceptable match between calculated and measured interspike-interval distribution was found although mostly not statistically significant. This non-significancy is most probably due to the choice of the simple gamma distribution as a first approach. However, applying this description it seems possible to retrieve statistical information about the interaction between neurons from extracellular recordings. Based on this description it is proposed to use modal spike frequency as well as the variance of the interspike interval distribution as estimates for the activity and the extent of activation of the neuron.

Action Potentials↗
PubMed1979

The steady state response of brainstem respiratory neuron activity to various levels of PA,CO2 and PA,O2.

Extracellular recordings were made of 52 respiratory neurons in the brainstem of cats, anesthetized (chloralose-urethane), vagotomized and artificially ventilated. Phrenic nerve activity was recorded and quantified as an index of the output of the respiratory neuronal organization in the brainstem. The unit activity was quantified by using the modal spike frequency as a possible indication of the activating effect of one unit on other respiratory neurons (Smolders and Folgering, 1979). Inspiratory neurons showed the strongest reaction to changes in PA,CO2 and/or PA,O2. Expiratory neurons and frequency modulated neurons responded less to changes in chemical drive. Phase spanning neurons did not show any consistent response. Four out of ten continuously firing neurons without any respiratory rhytmicity increased their firing frequency when PA,CO2 was increased. Apart from the increase in modal spike frequency, the respiratory neuronal organization also reacted with an increase in active units (recruitment) when the chemical drive was increased. The relationship between quantified phrenic nerve activity and spike frequency was independent of the stimulus (hypercapnia or hypoxia). A model was developed in which the increase in modal frequency of a unit arouses other units: when the chemical drive increases, progressively more units tend to be recruited into the respiratory neuronal organization in the brainstem.

Action Potentials↗
PubMed1976

Structural and functional characteristics of individual phrenic motoneurons.

Intracellular recording and staining techniques were applied to the study of cat phrenic motoneurons. Spontaneously driven phrenic cells possessed individualistic depolarization and spiking patterns that were a function of the conduction velocity in the different motor axons. Staining of phrenic motoneurons with Procion yellow indicated that fast conducting cells with small slow-wave depolarizations were large in size while slow conducting cells with large depolarizations were small in size. This implicated differences in membrane input resistance between large and small cells, although an unequal distribution of inputs to the individual components could not be discounted. On the average, phrenic motoneurons had a smaller dendritic surface area and smaller dendritic dominance than lumbosacral motoneurons. These factors help to explain the higher membrane resistances and longer time constants of phrenic cells. Phrenic dendrites were found to project in all directions away from the cell body and form ellipsoidal receptive fields that overlapped with other phrenic fields. It is speculated that the close approximation of phrenic dendrites with one another could, in part, be responsible for the high degree of synchronization among the different phrenic units.

Animals↗
PubMed1976

The relationship between the rate of rise of isometric tension and motor unit recruitment in a human forearm muscle.

The recruitment properties of single motor units from the human extensor indicis muscle were investigated during voluntary isometric contractions of different rate of rise but equal amplitude. Both the electrical and the contractile events associated with recruitment were analyzed. The threshold force of recruitment (measured as the total muscle force at firing onset) decreased with increasing rate of rise of isometric tension. This was consistently found for all units. Differences between low and high threshold units indicating a preferential tonic or phasic mode of activation were not observed. The contractile events associated with recruitment were analyzed analoguously to the electrical events. For this purpose, muscle force was measured at the time of the first twitch as it was measured at the time of the first spike. This separate measurement of the electrical and mechanical recruitment of a unit is necessary, because during a change of muscle force, force is different at firing onset and during the subsequent twitch contraction. Muscle tension at the time of the peak of the first twitch contraction was calculated from measurements of the twitch concentration time of the single motor units. In contrast to firing onset, the peak of the first twitch of a motor unit occurs at approximately the same muscle tension no matter how fast the contraction is performed. This is the consequence of the result that the average decrease of the threshold force of recruitment at successively faster contraction has the same value as the corresponding increase of total muscle force during the mean contraction time of the motor units. On the basis of this precise matching between these two changes, the mechanical recruitment of motor units occurs at approximately the same force level irrespective of the rate of rise of tension.

Electric Stimulation↗
PubMed1982

Dynamic properties of Renshaw cells: equivalence of responses to step changes in recruitment and discharge frequency of motor axons.

In decerebrate cats, the dynamic responses of Renshaw cells to step changes in input were determined separately both for changes in the number of alpha-axons excited and for changes in the frequency at which they were stimulated. Together, these two input variables to the Renshaw cells describe the level of activity in the motor output from the spinal cord. In either case, the dynamic responses of the interneurons depend only on their static activity before and after an input step occurs, but are otherwise indistinguishable. This favors the interpretation that the two input variables are equivalent under dynamic conditions, i.e., Renshaw cells respond to total motor output.

Animals↗
PubMed1996

Activity of single motor units in attention-demanding tasks: firing pattern in the human trapezius muscle.

Activity of single motor units in relation to surface electromyography (EMG) was studied in 11 subjects in attention-demanding work tasks with minimal requirement of movement. In 53 verified firing periods, single motor units fired continuously from 30 s to 10 min (duration of the experiment work task) with a stable median firing rate in the range of 8-13 Hz. When the integrated surface EMG were stable, the motor units identified as a rule were continuously active with only small modulations of firing rate corresponding to low-amplitude fluctuations in surface EMG. Marked changes in the surface EMG, either sudden or gradual, were caused by recruitment or derecruitment of motor units, and not by modulations of the motor unit firing rate. Motor unit firing periods (duration 10 s-35 s) in low-level voluntary contractions (approximately 1%-5% EMGmax) performed by the same subjects showed median firing rates (7-12 Hz) similar to the observations in attention-related activation.

Action Potentials↗
PubMed1989

The fatigability of two agonistic muscles in human isometric voluntary submaximal contraction: an EMG study. II. Motor unit firing rate and recruitment.

The recruitment and firing rate of biceps brachii (BB) and brachioradialis (BR) motor units (MUs) were studied in the course of fatiguing isometric contractions at 20%-30% of maximal voluntary contraction (MVC). MU recruitment generally occurred throughout the maintained contraction and was similar for BB and BR muscles. Newly recruited MUs started to discharge in the form of bursts, the duration of which increased until a continuous rhythmical firing was achieved. Within each burst, the first interval between two consecutive discharges was usually the shortest. MU threshold was lowered just after the limit time of the maintained contraction. The MU's firing rate either increased or remained stable as a function of the elapsed time. It is concluded that (1) in fatiguing isometric contractions at 20%-30% MVC contractile failure is mainly compensated for by MU recruitment and a lowered MU threshold and (2) differences between in surface changes in the electromyogram of BB and BR muscles cannot easily be explained by related differences in MU firing rate and recruitment.

Adult↗
PubMed1984

Experimental foundations of EMG biofeedback with the upper extremity: a review of the literature.

This article reviews the experimental foundations of EMG biofeedback with the upper extremity. Considered are investigations on recruitment and training of single and multiple motor units in both normal and nonnormal subjects, on transfer of training effects from trained to untrained muscles, and on the relationship of reduced muscle output to relaxation. Examined are procedures, results, and conclusions of these basic studies. Problems noted in the research are discussed and suggestions are made for further work in the area.

Arm↗
PubMedDate not supplied

Interaction of autorhythmic and reflex mechanisms in the responses of immature cortex of rabbit to rhythmic afferent stimuli.

The evolution of the phenomenon of spindle-shaped change in the amplitude of electric responses of the cortex to rhythmic light and sound stimuli during early ontogenesis of rabbits is described. Results are reported which permit one to consider the amplification and recruitment type responses, as well as the "sleepy spindles," as being due to activation of their ontogenetically primary autorhythmic mechanisms in the cortex and thalamus.

Animals↗
PubMedDate not supplied

Characteristics of the trace reproduction of rhythm by neurons of the sensorimotor cortex of rabbits in the aftermath of periodic stimulation.

The trace recruitment of rhythm (TRR), an analog of the CR to time, which arises in response to prolonged electrodermal stimulation of the forelimb of the awake rabbit at a frequency of 0.5-2 Hz, was studied. The activity of 180 cells of the sensorimotor cortex before (80) and after (100) periodic stimulation for a duration of 10-20 min was recorded. The first series of rhythmical stimulation led to a brief TRR of the stimulation frequency; subsequent series formed a clear TRR which was preserved for several days. The possibility of "retraining" the neurons given a change in the rhythm of stimulation was identified. The capacity of the TRR phenomenon for extinction, prolonged maintenance, and reproduction of traces, as well as "retraining" allies it with processes analogous to the temporary connections.

Animals↗
PubMedDate not supplied

Rhythmic activity of the brain evoked by local injections of carbachol into subcortical nuclei.

The effect of local injections of carbachol into the caudate nucleus and individual nuclei of the thalamus on the electrocorticogram of the anterior portion of the brain was investigated in unanesthetized, immobilized cats. It was shown that chemical stimulation of subcortical structures, like electrical stimulation, can induce spindle-like activity and a recruitment response. The appearance of these reactions after injections of carbachol both into the caudate nucleus and into individual nuclei of the thalamus indicates the existence of a functionally unified caudate-thalamic cholinoreceptive system, responsible for the slow wave rhythmic activity.

Animals↗