Showing papers by "David Burke published in 1988"

Responses to passive movement of receptors in joint, skin and muscle of the human hand.

Abstract: 1. Microneurographic techniques were employed to record unitary activity from afferents associated with digital joints of six conscious human subjects. Of 120 single afferents sampled from the median and ulnar nerves at the wrist, eighteen (15%) were classified as joint afferents; the majority of the sample (72.5%) were of cutaneous origin, and 12.5% were from muscle spindles and tendon organs. 2. Of the eighteen joint afferents six were tonically active in the rest position of the hand. All except two were recruited or accelerated their background discharge during passive joint movement. Three tonically active afferents were responsive to passive movement throughout the physiological range. The majority of the afferents, including the other three tonically active units, responded only towards the limits of joint rotation. 3. As a group, the sample of joint afferents had a limited capacity to signal the direction of joint movement. Nine of the sixteen joint afferents sensitive to movement responded in two axes of angular displacement, and two responded in all three axes. In any one axis of rotation eight afferents were activated in both directions of movement. However, one afferent, associated with the interphalangeal joint of the thumb, responded uni-directionally throughout the physiological range of joint movement and was thereby capable of adequately encoding joint position and movement. 4. Twenty-one of twenty-nine slowly adapting and eleven of eighteen rapidly adapting cutaneous afferents tested were activated by joint movement, but only towards the limits of joint rotation; half of the thirty-two movement-sensitive afferents were bi-directionally responsive. Muscle spindle afferents responded to stresses applied to the joint only if the resulting passive movement stretched the parent muscle. 5. It is concluded that human joint afferents possess a very limited capacity to provide kinaesthetic information, and that this is likely to be of significance only when muscle spindle afferents cannot contribute to kinaesthesia.

Projection to the cerebral cortex from proximal and distal muscles in the human upper limb

Abstract: Motor-point stimulation using insulated microelectrodes has been used to assess the cerebral pro jection from a number of single muscles in the human upper limb. Previous studies with intrafascicular neural stimulation have revealed a short-latency cortical projection from group I muscle afferents of intrinsic muscles of the hand but this technique is unsuitable to study the projection ofafferents from proximal muscles. In 6 subjects, stimuli were delivered to the motor point of the following muscles: anterior deltoid, biceps brachii (short head), flexor carpi radialis, extensor digitorum communis, abductor pollicis brevis and first dorsal interosseous. The mean latency of the early cortical negativity was l5.Oms for deltoid, l6.4ms for biceps, l8.8ms for flexor carpi radialis, 18.8ms for extensor digitorum communis, 21.9ms for abductor pollicis brevis and 25.Oms for first dorsal interosseous. The amplitude of cerebral potentials from individual muscles was smaller than that produced by stimulation of the digital nerves of the index or little finger and did not vary systematically between proximal and distal muscles. This study provides direct evidence for a short-latency cortical projection from proximal muscles of the upper limb. The results are consistent with psychophysical studies which have proposed a role for intramuscular receptors in kinaesthesia at both proximal and distal joints.

Reflex changes in muscle spindle discharge during a voluntary contraction

Abstract: 1. This study was undertaken to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the foot reflexly affect fusimotor neurons innervating the plantar and dorsiflexors of the ankle during voluntary contractions. 2. Recordings were made from 29 identified muscle spindle afferents innervating triceps surae and the pretibial flexors. Trains of electrical stimuli (5 stimuli, 300 impulses per second) were delivered to the sural nerve at the ankle (intensity: 2-4 times sensory threshold) and to the posterior tibial nerve at the ankle (intensity: 1.5-3 times motor threshold for the small muscles of the foot). The stimuli were delivered while the subject maintained an isometric voluntary contraction of the receptor-bearing muscle, sufficient to accelerate the discharge of each spindle ending. This ensured that the fusimotor neurons directed to the ending were active and influencing the spindle discharge. The effects of these stimuli on muscle spindle discharge were assessed using raster displays, frequencygrams, poststimulus time histograms (PSTHs) and cumulative sums ("CUSUMs") of the PSTHs. Reflex effects onto alpha-motoneurons were determined from poststimulus changes in the averaged rectified electromyogram (EMG). Reflex effects of these stimuli onto single-motor units were assessed in separate experiments using PSTHs and CUSUMs. 3. Electrical stimulation of the sural or posterior tibial nerves at nonnoxious levels had no significant effect on the discharge of the 14 spindle endings in the pretibial flexor muscles. The electrical stimuli also produced no significant change in discharge of 11 of 15 spindle endings in triceps surae. With the remaining four endings in triceps surae, the overall change in discharge appeared to be an increase for two endings (at latencies of 60 and 68 ms) and a decrease for two endings (at latencies of 110 and 150 ms). The difference in the incidence of the responses of spindle endings in tibialis anterior and in triceps surae was significant (P less than 0.05, chi 2 test). 4. For both triceps surae and pretibial flexor muscles the electrical stimuli to sural or posterior tibial nerves had clear effects on the alpha-motoneuron pool, whether assessed using surface EMG or the discharge of single-motor units. Based on EMG recordings using intramuscular wire electrodes, the reflex effects differed for the gastrocnemii and soleus. 5. In this study, reflex changes in the discharge of human spindle endings were more difficult to demonstrate than comparable changes in the discharge of alpha-motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)

The optimal recording electrode configuration for compound sensory action potentials.

Abstract: There is no uniformity in the published literature from different laboratories on the optimal electrode configuration for recording nerve action potentials, and a number of standard texts omit any reference to the effects that interelectrode distance and electrode orientation can have on the shape, amplitude and latency of nerve action potentials. The sensory action potential from the digital nerves of the index finger was recorded at wrist and elbow using bipolar electrodes with the "active" electrode over the median nerve and the "reference" placed 4 cm laterally or proximally along the nerve using interelectrode distances of 4, 3 and 2 cm. These potentials were compared with that recorded using a remote reference on the ipsilateral shoulder, the assumption being that this configuration eliminated the contribution of the reference electrode to the compound nerve action potential. With different electrode configurations, there were significant differences in the shape of the potential, the latencies to onset and peak and the rising- and falling-phase amplitudes. The shorter the distance between the electrodes the greater the distortions. Overall, the distortions were least with the 4 cm interelectrode separation, particularly for short conduction distances.

Changes in muscle and cutaneous cerebral potentials during standing.

Abstract: The cerebral potentials produced by electrical stimulation of mechanoreceptive afferents from the foot were recorded in the sitting and standing postures to determine whether transmission to cortex was altered by the postural change. The latencies of the early components of the cerebral potentials produced by muscle afferents (posterior tibial nerve) and cutaneous afferents (sural nerve) did not change with posture. Standing was associated with an approximately 25–35% decline in amplitude of the earliest components of the posterior tibial cerebral potential (N38-P40, P40-N50) for a stimulus intensity associated with a submaximal afferent volley. The amplitude of the equivalent N38-P40 and P40-N50 components produced by sural afferents also declined during quiet stance. In most experiments the subcortical component (P32-N38) was not reduced by stance so that the amplitude attenuation probably occurs in part at cortical level. Qualitatively similar changes in the cerebral potentials were documented for a range of stimulus intensities, including those which evoked a maximal initial component in the nerve volley. For a similar reduction in the initial (N38-P40) component of the cerebral potential, voluntary plantar flexion in the sitting position produced less attenuation in subsequent components than did standing. Thus, attenuation of the cerebral potential during standing may involve specific posture-related factors in addition to those related to volition.