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Biomedical subjects

T S Miles

Publications and source records attributed to T S Miles.

At least 73 records · Page 4Linked to original sources
PubMed1986

Climbing fiber lesions disrupt conditioning of the nictitating membrane response in the rabbit.

The pattern of acquisition of the classically conditioned nictitating membrane response was determined in rabbits which had recovered from a surgical lesion of the olivary decussation. In comparison with sham-operated controls, the animals with climbing fiber lesions showed delayed and incomplete conditioning. This observation supports the hypothesis of Marr and Albus that motor learning occurs in the cerebellar cortex when conjunctive inputs arrive along both the mossy and climbing fiber pathways.

Animals↗
PubMed1986

Does reflex inhibition of motor units follow the "size principle"?

The "size principle" is known to dictate the sequence of recruitment of motor neurons during voluntary or reflex activation of muscles. The present study sought to determine whether the size principle also determined the sequence of reflexly-elicited inhibition of motor neurones. It was found that all masseter motor units were about equally inhibited by a mildly-noxious stimulus to the lip, providing that they were tested at the same level of pre-stimulus excitability, i.e., firing frequency. At higher prestimulus firing frequencies, more intense stimuli were required to inhibit motor unit activity. Thus it is the firing frequency of individual motor neurons, rather than their size, which determines their susceptibility to inhibition.

Action Potentials↗
PubMed1986

A simple circuit for producing vertical arrays of analogue signals and dot raster displays of nerve and muscle action potentials.

It is often helpful to display analogue signals such as electromyograms, electroencephalograms, nerve action potentials, etc., in a regular vertical array. A special case of this display is the widely-used dot raster. This paper describes a simple circuit which enables up to 31 analogue signals to be thus displayed on an analogue storage oscilloscope screen or X-Y plotter. A modification permits up to 255 trials to be displayed. The same circuit produces a standard, dot raster display from standard pulses representing nerve or muscle cell action potentials.

Action Potentials↗
PubMed1986

Length-related changes in activation threshold and wave form of motor units in human masseter muscle.

Action potentials of single motor units in the human masseter muscle were recorded during isometric contractions at different muscle lengths over most of the working range of the temporomandibular articulation. The shape of the unit potential wave form changed progressively as the muscle length changed. This was considered to be due principally to a change in the geometric relationship of the electrode to the muscle fibres at various muscle lengths. The recruitment thresholds for all units increased sharply when the jaw opening approached the maximal gape. The pattern of change of unit thresholds with muscle length closely paralleled the curve of length versus passive tension for the combined jaw-closing muscles, temporomandibular articulation and associated soft tissues. It was concluded that the change in unit recruitment thresholds with length is likely to be a consequence of the length-passive tension relationship of the muscles, joint and soft tissues. The results of this study indicate that attempts to assign masseter motor units to one or other of the accepted functional categories on the basis of recruitment force or wave form only are unlikely to give reliable results.

Action Potentials↗
PubMed1985

The effect of stimulus intensity and gape on electrically-evoked jaw reflexes in man.

The changes in masseter EMG and biting force evoked by electrical stimulation of the lip were measured in normal people. Stimulation at noxious intensities elicited a characteristic, biphasic inhibitory response in the masseter EMG and a transient reduction in the biting force. The pattern of masseter inhibition and force change varied both with stimulus intensity and with inter-incisal separation. In general, the decrease in biting force was greater at intermediate jaw positions than in the open and closed positions. The duration of the EMG inhibitory period increased as the stimulus intensity increased but was independent of the jaw separation. Reflex thresholds could not be correlated with pain thresholds because subjects found it difficult to decide at what level an electrical stimulus became painful. Nevertheless this stimulation of high-threshold afferents may be useful in estimating the rate of relaxation of tension in the jaw muscles.

Adolescent↗
PubMed1984

Harmaline disrupts acquisition of conditioned nictitating membrane responses.

A basic tenet of the Marr-Albus theory of motor learning is that the learning process involves concurrent activation of the climbing fibre and mossy fibre inputs to the cerebellum. This theory was tested by administering harmaline, a drug which causes climbing fibres to fire at their maximal rate of 8-12 Hz, to rabbits during a classical conditioning protocol. Harmaline significantly reduced the proportion of conditioned nictitating membrane responses on each of 4 successive training days. When harmaline was given to already-conditioned rabbits, the proportion of conditioned responses fell sharply to the day 1 level: however, this was still a higher proportion of conditioned trials than that which was seen with naive animals trained for 4 days with harmaline. It is therefore concluded that harmaline disrupts the acquisition of classically-conditioned nictitating membrane responses but does not prevent the expression of an already learnt response. These findings are therefore consistent with the proposal in the Marr-Albus theory that the climbing fibres play an essential part in motor learning.

Alkaloids↗
PubMed1983

Programming of antagonist muscle stiffness during masticatory muscle unloading in man.

The activity of the masseter and digastric muscles was monitored carrying out a controlled, isometric biting task. In 7 out of 10 subjects, the level of activity in the digastric muscle, during the phase of isometric biting, was greater when the subjects expected the resistance between their teeth to yield suddenly than when they were confident that the resistance would not yield. It is therefore concluded that the co-activation of the digastric muscle which occurs during forceful isometric bites can be modified in accordance with the subject's expectation of the outcome of the bite.

Adolescent↗
PubMed1982

Axon reflexes in spinal dorsal roots.

The existence of branching of myelinated dorsal root axons has been shown with electrophysiological techniques. The point at which the axons branch is several mm proximal to the ganglion. This observation may be relevant to the interpretation of studies which use spike-triggered averaging to investigate the pattern and the extent of the distribution of sensory information from primary afferent fibers to second-order neurons.

Afferent Pathways↗
PubMed1982

Limitation of jaw movement by antagonist muscle stiffness during unloading of human jaw closing muscles.

The unloading reflex in the jaw closing muscles in man was investigated with a view to correlating the jaw closing movement with the timing of the electrical activity of the agonist and antagonist muscles. When the resistance to the forceful isometric bite was suddenly and unexpectedly withdrawn, the closing movement of the mandible was always arrested before the teeth came together. The rapid arrest of the jaw closing movement was not adequately accounted for by the timing of the inhibition of the jaw closing muscles and reflex excitation of the jaw opening muscles. It was observed that the jaw opening muscles, as well as the jaw closing muscles, were always active during the phase of isometric biting on an object between the teeth. It is therefore concluded that the resulting stiffness of the antagonist muscles is the mechanism which is principally responsible for limiting the jaw closing movement after unloading of the agonist muscles.

Adult↗
PubMed1982

Corticospinal neurones of the supplementary motor area of monkeys. A single unit study.

The direct projection from the supplementary motor area (SMA) to the spinal cord was investigated in six monkeys by means of antidromic identification of single SMA neurones. The exploration concentrated on that portion of medial area 6 from which movements were found to be elicited by stimulation at intensities of less than 30 microA in an earlier study, but also included some of medial area 4. Of 315 identified corticofugal projection neurones, 234 were found to be localized within medial area 6; of these only one third (76 cells) were corticospinal cells and the remaining two thirds were neurones which projected to the brainstem. The conduction velocities of the descending projection neurones of the SMA were slow (modal value: 10 m/s). Corticospinal cells of the SMA were found up to 6 mm rostral to the boundary between areas 4 and 6. Corticospinal neurones activated antidromically from the cervical but not from the lumbar cord ('cervico-thoracic' neurones) were concentrated in the mesial cortex; 'lumbo-sacral' neurones were found both in the dorsal cortex and the dorsal bank of the cingulate sulcus. However, there was considerable intermingling between the two types of projection neurones and there was no separation in the rostro-caudal direction. Similarly, projection neurones receiving orthodromic inputs from the somatotopical subdivisions of the precentral cortex were not segregated, but were intermingled in the entire rostro-caudal extent of the SMA. It is concluded that there is a clustering of corticospinal neurones in the SMA according to their most caudal segmental projection. However, no rostro-caudal differentiation into face, arm and leg areas was established. This observation is consistent with the results of a previous study in which corticospinal neurones in the SMA were labelled with anatomical tracers and efferent zones were investigated with intra-cortical microstimulation (Macpherson et al. 1982).

Animals↗
PubMed1982

Microstimulation of the supplementary motor area (SMA) in the awake monkey.

The supplementary motor area of three Macaca fascicularis was mapped using intracortical microstimulation (ICMS). Both forelimb and hindlimb movements were evoked using currents of 30 microA or less. However, thresholds for evoking movements were higher than those in the primary motor cortex. Proximal motor effects predominated, but distal joint movements were also elicited. Forelimb points were clustered in mesial cortex of area 6, anterior to the precentral hindlimb and tail region. Distal joint effects were located deep in the cortex, intermingled with proximal effects. Hindlimb response which were less spatially localized, were found both ventral to the forelimb area, in the dorsal bank of the cingulate sulcus, and in mesial cortex, well anterior to area 4. No movements of facial muscles were elicited. Injections of HRP were made into the spinal cord at the cervical level in two animals and the lumbar level in the third one. An area of labelled cells was seen in mesial area 6 which corresponded closely to the region from which ICMS effects were elicited. No movements were evoked from the anterior portions of the fundal region of the cingulate sulcus which were also labelled.

Animals↗
PubMed1981

Recovery of function after cryosurgical lesions of peripheral nerves in rats.

Unilateral lesions were made in rat sciatic nerves with a cryoprobe at about -65 degrees C. Three months later, recovery of motor and sensory function of the hindlimb had occurred. The compound action potential from the dorsal root indicated that myelinated and unmyelinated fibre groups had regenerated. Cryosurgery may be useful in the long-term blockade of sensory nerves for pain relief.

Action Potentials↗
PubMed1980

Modulation of the baroreceptor reflex by angiotensin II and other vasoactive drugs in anaesthetized greyhounds.

1. The effects of vascular infusions of acetylcholine, angiotensin II, noradrenaline and prostaglandin F2 alpha on the baroreceptor reflex were studied in the anaesthetized greyhound. 2. Vertebral artery infusions of low doses of angiotensin II, but not of acetylcholine or prostaglandin F2 alpha, resulted in a significant reduction in the depressor response to carotid sinus nerve stimulation. 3. The increases in blood pressure and heart rate in response to bilateral carotid artery occlusion were not significantly changes during vertebral artery infusions of acetylcholine, angiotensin II or prostaglandin F2 alpha. 4. The increases in blood pressure in response to intravenous infusions of noradrenaline were significantly enhanced during vertebral artery infusions of acetylcholine and angiotensin II, but not of prostaglandin F2 alpha. The bradycardia during noradrenaline infusions was significantly enhanced by angiotensin II alone. 5. The depressor response to carotid sinus nerve stimulation was significantly reduced during intravenous infusions of both noradrenaline and angiotensin II. 6. It is considered that although angiotensin II can be shown to have a specific central action to attenuate the response to carotid sinus nerve stimulation, the role of this action in the complete baroreceptor reflex is unproven.

Acetylcholine↗