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Biomedical subjects

P D Neilson

Publications and source records attributed to P D Neilson.

35 records · Page 2Linked to original sources
PubMed1978

The role of action reflexes in the damping of mechanical oscillations.

Reflex responses measured during voluntary contraction of the muscle being stretched are known to differ markedly from reflex responses elicited from passive muscle. The term 'action tonic stretch reflex' or 'action TSR' has been used previously to describe a reflex response to continuous stretch, separated from voluntary activity by means of a cross-correlational and spectrographic analysis. In this paper it is proposed that the action TSR play a functional role during voluntary movement by damping the transient oscillations associated with the natural resonant frequencies of the limbs. It is suggested that oscillations excite an action TSR force response with phase lead ahead of muscle stretch. This force response can be resolved into two force components, one of which has a 90 degree phase lead ahead of muscle stretch and behaves like a viscous friction reaction force causing damping of oscillations. Three experiments which support this proposition are described. (1) Analog computer model stimulation studies of a muscle supporting a mass-spring load reveal that damping only occurs when the force response has a phase lead ahead of muscle stretch. When the force response has a phage lag behind muscle stretch, the system is unstable and the amplitude of oscillation increases with time. (2) It is demonstrated that when a mass-spring load is supported as rigidly as possible by the human arm, reaction forces from the arm damp and mass-spring oscillations more rapidly than when the mass-spring is rigidly supported. Electromyogram (EMG) recordings reveal that mass-spring oscillations excite action TSR responses with phase lead ahead of muscle stretch. (3) Recordings of elbow angle and biceps EMG during rapid forearm flexion or extension movements followed by sudden stops reveal critically damped oscillations in the elbow angle signal (i.e. no more than one or two small overshoots), which are accompanied by EMG action TSR responses with phase lead ahead of muscle stretch.

Arm↗
PubMed1978

A physiological approach to motor disorders.

Spasticity in man is presented as a disinhibition of spinal cord mechanisms, the responses to stretch depending on the interaction of the reflex effects of group Ia with those of group II afferent fibres. The reflex responses to muscle stretch and shortening in Parkinson's disease do not depend on an abnormality of spinal reflex mechanisms. The superimposition of physiological tremor or alternating tremor in rigidity produces the classical cog-wheel sensation. The phase lead of the action tonic stretch reflex was found to be reduced in patients with athetosis and cerebellar disease, thus diminishing damping of unwanted movements. The more complex transmission characteristics of the action tonic stretch reflex of normal man are absent in patients with spasticity and cerebellar lesions, presumably due to interference with long-loop pathways. In normal subjects gain of the reflex loop increases with voluntary contraction but in spasticity gain remains high irrespective of contraction level.

Athetosis↗
PubMed1974

Voluntary control of arm movement in athetotic patients.

Visual tracking tests have been employed to provide a quantitative description of voluntary control of arm movement in a group of patients suffering from athetoid cerebral palsy. Voluntary control was impaired in all patients in a characteristic manner. Maximum velocity and acceleration of arm movement were reduced to about 30-50% of their values in normal subjects and the time lag of the response to a visual stimulus was two or three times greater than in normals. Tracking transmission characteristics indicated a degree of underdamping which was not presnet in normal or spastic patients. This underdamping could be responsible for a low frequency (0·3-0·6 Hz) transient oscillation in elbow-angle movements associated with sudden voluntary movement. The maximum frequency at which patients could produce a coherent tracking response was only 50% of that in normal subjects and the relationship between the electromyogram and muscle contraction indicated that the mechanical load on the biceps muscle was abnormal, possibly due to increased stiffness of joint movement caused by involuntary activity in agonist and antagonist muscles acting across the joint.

Athetosis↗
PubMed1974

Measurement of involuntary arm movement in athetotic patients.

Visual tracking tests have been used to obtain a quantified statistical description of the involuntary movements of the arm about the elbow joint in a group of patients suffering from athetoid cerebral palsy. Three separate components of involuntary activity can be recognized and it is possible that each may be a different physiological mechanism. First there are irregular movements which are represented by a continuous power spectrum which decreases with increasing frequency, reaching a negligible value between 2-3 Hz. The second component is a rhythmical low frequency movement which is indicated by a predominant peak in the power spectrum at a frequency of 0·3-0·6 Hz. The presence of this peak was predicted in a previous paper because of underdamping demonstrated in the closed loop voluntary control of movement in athetosis. The third component is the athetoid action tremor in which both agonist and antagonist muscle groups contract vigorously but asynchronously at a frequency of 1·5-4 Hz.

Athetosis↗
PubMed1973

Effect of procaine infiltration into biceps brachii muscle in man on supraspinal control of reflex transmission.

Sensitivity of the tonic stretch reflex (TSR) of biceps brachii in normal man was measured at different levels of voluntary contraction before and after gamma efferent nerve fibres were selectively blocked by infiltration of dilute procaine. The procaine infiltration reduced TSR sensitivity to one half of its control value. It had no effect, however, on the slope of the relation between TSR gain and level of voluntary contraction. It was concluded that the increase in TSR sensitivity associated with voluntary contraction was not mediated by the gamma efferent fibres and control of reflex transmission is therefore not the main function of the fusimotor system.

Electromyography↗
PubMed1973

Comparison of stretch reflexes and shortening reactions in activated normal subjects with those in Parkinson's disease.

The stretch reflexes and shortening reactions evoked in six normal subjects during reinforcement were compared with those recorded from patients with Parkinson's disease. Although the responses to stretch and shortening of triceps were similar in both groups, they differed in the biceps muscle. In Parkinson's disease increasing muscle stretch of biceps was associated with increasing reflex activity, whereas the reverse relationship occurred in the activated normal subjects. The biceps EMG during sinusoidal stretching comprised two peaks in the activated normal group, a phenomenon not seen in Parkinson's disease. It is postulated that this response in the activated normal group is due to activation or reinforcement engaging long-loop reflexes. It is concluded that the rigidity of Parkinson's disease is not simply an exaggeration of the stretch reflexes found in normal man but differs in that the effects of flexor reflex afferent nerve fibres are submerged by group Ia afferent activity, and that some long-loop reflex pathways are no longer operative in Parkinson's disease.

Electromyography↗
PubMed1973

Comparison of the tonic stretch reflex in athetotic patients during rest and voluntary activity.

An electromyographic technique was used to record the tonic stretch reflex (TSR) responses to passive sinusoidal stretching of biceps brachii muscle in athetotic patients. The TSR transmission characteristics measured while the patient was in a relaxed state were compared with those measured while the patient was voluntarily active. The resting TSR and action TSR were found to differ markedly. Sensitivity, pattern, duration, and timing of the TSR responses were all changed during voluntary activity. The results suggest that the TSR in athetosis is functionally reorganized by supraspinal influences during voluntary activity. It is proposed that athetoid movements and action tremor may be a manifestation of abnormal action TSR caused by faulty supra-spinal control during activity.

Adult↗
PubMed1972

Voluntary and reflex control of the biceps brachii muscle in spastic-athetotic patients.

A cross-correlation technique of analysis was used to measure the transmission characteristics of tonic stretch reflex (TSR) pathways in spastic-athetoid subjects sustaining a voluntary contraction in the biceps brachii muscle. A comparison was made with the transmission characteristics of normal subjects measured by the same technique. It was found that gain and phase characteristics of spastic patients did not display the large resonant peaks present in normals. It is proposed that the resonant peaks in the TSR transmission of normal subjects were caused by long loop pathways. The absence of these peaks in the spastic patients supports the hypothesis that short-circuiting of long loop pathways by hyperactive spinal reflexes is part of the mechanism of spasticity.

Arm↗
PubMed1972

Interaction between voluntary contraction and tonic stretch reflex transmission in normal and spastic patients.

Transmission characteristics of tonic stretch reflex (TSR) pathways in both normal and spastic patients have been measured during different levels of sustained voluntary contraction of the biceps brachii muscle. A cross-correlation technique of analysis was used to separate reflex responses from the total electromyographic activity. TSR transmission in normal subjects was observed to change with the level of voluntary contraction; sensitivity to stretch increased approximately three-fold as the subject stiffened the arm by simultaneously contracting flexor and extensor muscles. In contrast, TSR transmission did not alter during voluntary contraction in spastic patients. It is proposed that in spastic patients supraspinal modulation of reflex transmission is impaired because hypersensitive spinal reflexes short-circuit long loop pathways.

Cerebral Palsy↗
PubMed1969

Presynaptic inhibition of the monosynaptic reflex by vibration.

In cats, the monosynaptic reflex (MSR) elicited from L7 or S1 dorsal roots, or from the tibial nerve (H reflex) was suppressed by vibration at 50-500 c/s of the hind limb with innervation intact. The MSR was not suppressed by selective vibration of cutaneous receptors, and suppression was still observed after the hind limb was skinned. In contrast, the phenomenon disappeared when all muscle nerves were crushed. SUPPRESSION OF THE MSR BY VIBRATION WAS SHOWN TO BE MEDIATED BY PRESYNAPTIC INHIBITION BY THE FOLLOWING METHODS: correlation with onset of the dorsal root potential (DRP) evoked by vibration, and abolition of both DRP and reflex suppression by picrotoxin; demonstration of primary afferent depolarization and normal excitability of motoneurones to direct stimulation. Reasons are given for deducing that the muscle afferent fibres responsible for the presynaptic inhibition induced by vibration are group Ia rather than groups Ib or II, or afferent fibres from Pacinian corpuscles.

Animals↗
PubMedDate not supplied

Tonic stretch reflexes in older able-bodied people.

It is a general assumption that, in able-bodied persons, tonic stretch reflex (TSR) activity is not elicited during stretching of relaxed muscles and that the presence of TSR activity following brain damage is, therefore, indicative of spasticity. However, a variety of studies have reported age-related changes in reflex activity, raising the question of whether this assumption is justified in older subjects. The aim of this study was to determine if TSRs were activated in the relaxed elbow flexors of able-bodied people in an age-group at risk of stroke. Electromyographic (EMG) activity was recorded in 30 able-bodied subjects aged 46 to 78 years when their relaxed elbow flexors were subjected to ramp and sinusoidal stretches of different amplitudes and velocities. It was found that these subjects did not exhibit TSR activity under these conditions. Therefore, the practice of measuring TSR activity as a means of quantifying spasticity in stroke patients appears justified.

Aged↗