Biomedical subjects

J L Veale

Publications and source records attributed to J L Veale.

12 recordsLinked to original sources

PubMed1989

Effect of motor unit firing pattern on twitches obtained by spike-triggered averaging.

The spike-triggered averaging technique (STA) was used to determine the twitch profile of single motor units in human masseter during a voluntary isometric contraction. The effect of the immediate firing pattern of the unit on the twitch was assessed with a computer program which scanned the unit discharge records and selected valid trigger spikes for the averager on the basis of the interspike intervals preceding and following the trigger spike. Successive averages from the same data using different interval parameters revealed progressively more fusion of twitches as the instantaneous firing rate increased. When the data were averaged with interval parameters similar to those used in earlier studies, some fusion of the twitch profile was also evident. It is therefore likely that the degree of fusion of human motor unit twitches obtained by STA has been underestimated in the past. It is further concluded that masseter motor units are sufficiently fast-contracting to allow a relatively unfused twitch profile to be obtained with STA, provided trigger spikes are subjected to appropriate rate control.

Adolescent↗

PubMed1979

Contribution of single motor units to the surface electromyogram.

McComas (1977) has published a method of estimating the number of motor units in human sketal muscle, based on peripheral nerve stimulation and recording of the surface electromyogram (EMG). One assumption of the method is that individual motor units, recruited by peripheral nerve stimulation just above threshold, give discrete observable increments to the surface EMG which are typical of motor units in the muscle. We have investigated this assumption in the thenar muscle. An EMG needle was inserted into the muscle and a series of individual motor units, activated voluntarily, was isolated. The discharge of these units was then used to trigger averaging of the concurrent surface EMG. Our results suggest that motor units activated by peripheral nerve stimulation close to threshold are not representative, in amplitude or timing, in their contribution to the surface EMG, of all motor units in the muscle.

Electromyography↗

PubMed1975

Inferior colliculus. I. Comparison of response properties of neurons in central, pericentral, and external nuclei of adult cat.

The responses of 150 units in the central (ICC), pericentral (ICP), and external nuclei (ICX) of the inferior colliculus of the anesthetized cat were studied in relation to their tuning characteristics and binaural responses to tonal stimuli. Units in ICC were characterized by sharp tuning and binaural responses, while those in ICP and ICX were frequently very broadly tuned with a poorly defined best frequency. Nonetheless, in the latter nuclei a tendency existed for tonotopic organization to occur with high frequencies located externally and low frequencies at the margins of the central nucleus. Tuning measurements were hampered by the common occurrence of habituation in the discharges of single units in ICP and, to a lesser extend, ICX. The majority of units in ICP could be differentiated from those in ICX by their monaural input. Speculations were advanced linking anatomical cell types to physiological responses in the three nuclei and into the possible functional significance of the different behavior of units to tonal stimuli.

Animals↗

PubMed1973

Differential sensitivity of motor and sensory fibres in human ulnar nerve.

The human ulnar nerve has been stimulated with square-wave pulses of various fixed durations. Measurements were made of the growth of hand myograms compared with elbow neurograms and of hand myograms compared with finger neurograms, for fixed durations of pulses and increasing strength. The effect of blocking sensory action potentials with stimuli of various durations has been investigated, as well as the blocking of action potentials in motor nerve fibres by voluntary activity. It is concluded that pulses of long duration (1 msec or more) selectively stimulate sensory fibres at threshold, whereas short duration pulses (less than 200 μsec) selectively stimulate motor fibres.

Action Potentials↗

PubMed1973

Renshaw cell activity in man.

The H-reflex elicited in triceps surae by percutaneous stimulation of the posterior tibial nerve was conditioned by stimuli applied through the same electrode. The differential sensitivity of motor and sensory fibres to duration of the stimulus pulse made it possible to condition the H-reflex with either a motor or a sensory stimulus. With both types of conditioning, the H-reflex was inhibited at conditioning-test intervals of 2-3 msec and was then facilitated, the peak of facilitation occurring at 5-8 msec with motor conditioning and 6-10 msec with sensory conditioning. The phase of facilitation was followed by further inhibition. We have concluded (1) that the effects of motor conditioning on the H-reflex result from the discharge of Renshaw cells activated by the antidromic volley in the motor axons, and (2) that the effects of sensory conditioning (at the times used in these experiments) are largely due to the activation of Renshaw cells secondary to the discharge of alpha motoneurones by the conditioning volley.

Adult↗

PubMed1973