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Biomedical subjects

J A Stephens

Publications and source records attributed to J A Stephens.

At least 55 records · Page 3Linked to original sources
PubMed1990

Mirror movements studied in a patient with Klippel-Feil syndrome.

1. Electromyographic (EMG) recordings have been made from upper limb muscles in a patient with well-defined congenital mirror movements occurring in association with Klippel-Feil syndrome and the results compared to those obtained in normal control subjects. 2. In the patient, liminal percutaneous electrical or magnetic brain stimulation applied over either hemisphere elicited bilateral and symmetrical short-latency muscle responses in relaxed intrinsic hand muscles. In the normal subjects unilateral brain stimulation only elicited contralateral muscle responses. 3. F response and H reflex studies for the patient's ulnar-supplied intrinsic hand muscles were normal. No crossed responses were recorded in the homologous muscles of the contralateral hand. 4. Scalp-recorded somatosensory-evoked responses following ulnar or median nerve stimulation were of normal latency and distribution in the patient. 5. In the patient, cross-correlation analysis of on-going single and multiunit needle EMGs recorded between muscles of left and right hands revealed a central peak in the cross-correlogram. No cross-correlogram peaks were found between left- and right-hand muscles in normal subjects. The magnitude and time course of the central peaks in the cross-correlograms constructed between the firing of motor units on opposite sides of the body in the patient were similar to those found in cross-correlograms constructed between the firing of motor units from muscles on the same side of the body in the patient and in normal subjects. 6. The magnitude of cross-correlogram peaks detected within a muscle and those detected between left and right homologous muscles showed a gradient in which the largest peaks were found in the intrinsic hand and forearm extensor muscles. The smallest peaks were observed in the forearm flexor muscles. No peaks were detected between left and right biceps brachii muscles. In intrinsic hand muscles, the size of the cross-correlogram peak detected between the EMGs of homologous muscle pairs was greater than that found for non-homologous muscle pairs. 7. Cutaneous reflex responses were recorded from first dorsal interosseous muscle following unilateral electrical stimulation of the digital nerves of the index finger. In the patient, this produced an early excitatory (E1) response on the stimulated side. Later excitatory (E2 and E3) responses, of approximately equal size and latency, were distributed bilaterally. In the normal subjects, reflex responses were confined to the stimulated side.(ABSTRACT TRUNCATED AT 400 WORDS)

Arm↗
PubMed1989

Task-dependent changes in cutaneous reflexes recorded from various muscles controlling finger movement in man.

1. Cutaneous reflex responses have been recorded from muscles involved in the control of finger movement following electrical stimulation of the digital nerves of the fingers in man. 2. Recordings have been made while subjects performed various manual tasks. 3. Reflexes recorded while subjects performed a relatively isolated finger movement consisted of an initial short-latency increase in muscle electrical activity, followed by a decrease, followed by a prominent longer-latency increase. The long-latency excitatory component was smaller or absent during those grips used in the present study. 4. The short-latency excitatory (E1) and inhibitory (I1) components of the cutaneomuscular reflex response are mediated via spinal pathways. The second longer-latency excitatory component (E2) is of supraspinal origin, requiring the integrity of the dorsal columns, sensorimotor cortex and corticospinal tract (Jenner & Stephens, 1982). The results of the present study suggest that one or more of these supraspinal pathways is more active when a finger is used in a relatively isolated manner than when the same finger participates in any of the gripping manoeuvres used in the present experiments.

Adolescent↗
PubMed1989

Task-dependent changes in the size of response to magnetic brain stimulation in human first dorsal interosseous muscle.

1. Electromyographic responses have been recorded from human first dorsal interosseous muscle (FDI) in response to magnetic and transcutaneous electrical stimulation of the brain. 2. Following magnetic but not electrical stimulation of the brain, the recorded EMG response was larger when FDI was active during voluntary isometric index finger abduction than during a power grip. 3. In the same experiment, cutaneous reflex responses have been recorded from FDI following electrical stimulation of the digital nerves. The long-latency excitatory component at about 60 ms (E2) was larger when recorded during voluntary finger abduction than during a power grip. This difference in size of E2 with task bore no simple relationship to the difference in size with task of the motor response to magnetic brain stimulation. 4. The results are discussed in relation to the presumed site of action of magnetic and electrical brain stimulation. It is concluded that the results may best be interpreted by assuming a higher level of cortical activity during a voluntary index finger abduction than during a grip and that this could in part explain the task-dependent changes in the long-latency response to cutaneous stimulation.

Adult↗
PubMed1985

Maturation of cutaneous reflex responses recorded in the lower limb in man.

Cutaneous reflex responses from tibialis anterior muscle following electrical stimulation were recorded for 39 normal children between the ages of one and 16 years. In the first year of life stimulation produces a monophasic excitatory reflex response at short latency; in the second year it produces long- as well as short-latency increases in activity. Maturation of reflex function continues during the school years, with progressive emphasis on long- rather than short-latency components. These results are discussed in relation to mechanisms underlying the acquisition of motor skills during childhood.

Adolescent↗
PubMed1985

Cutaneous reflex responses recorded in children with various neurological disorders.

Cutaneous reflex responses were recorded from tibialis anterior or first dorsal interosseous muscles of children with hemiplegia, spinal-cord compression, necrotizing sacroid granulomatosis, acute encephalomyelitis, myalgic encephalomyelitis, and a group of children attending the Learning Difficulties Clinic. Abnormalities of response are reported and are compared with the different reports in the literature of abnormal reflex EMG responses recorded by various methods. It is concluded that cutaneo-muscular reflex testing may have a part to play in the diagnosis of difficult paediatric problems.

Adolescent↗
PubMed1984

Immune-recognition of Schistosoma mansoni primary sporocysts may require specific receptors on Biomphalaria glabrata hemocytes.

Cellular interactions, leading to cell-mediated cytotoxicity when Biomphalaria glabrata hemocytes encapsulate Schistosoma mansoni sporocysts, have been investigated. Rabbit antibodies (IgG), when bound to antigens on sporocyst surfaces, prevent the normal cytoadherence (CA) of hemocytes from both susceptible and resistant host snails. Since interference with CA occurs with even fixed sporocysts, the effect is not due to IgG stimulated modulation of the parasite surface. Using two antisera with some overlapping specificities, and quantitative immunofluorescent antibody technique (QIFAT), we determined the concentrations of IgG needed to place equivalent amounts of IgG on the sporocysts. At these concentrations, CA was affected differentially, implying that interference was due to the specific antigens bound, and not due simply to the presence of IgG. Also with QIFAT we determined how much F(ab')2 and IgG from anti-sporocyst serum were needed to block an equivalent amount of antigenic determinants from access by whole FITC labelled IgG. Sporocysts whose surface antigens were equally blocked were equally unadherent for hemocytes, supporting the notion that the nature of obscured antigens, and neither the Fc portion nor the larger size of intact IgG protein, was responsible for the effect on CA. These surprising results imply a role for specific antigen binding sites on snail hemocytes.

Animals↗
PubMed1983

The maturation of cutaneous reflexes studied in the upper limb in man.

Cutaneous reflex responses have been recorded from forearm flexor and extensor muscles following electrical stimulation of the fingers. Recordings have been made from premature infants, term infants and children between the age of 6 weeks and 11 years. In the new-born, stimulation of the fingers elicits such a powerful reflex that, in general, individual stimuli will evoke a reflex synchronous action potential in both forearm flexor and extensor muscles. Individual stimuli delivered to the fingers also elicit reflex synchronous muscle action potentials in forearm flexor and extensor muscles in patients with clinical signs of upper motor neurone lesion affecting the upper limb; this has not been observed in normal adult subjects. The latency of the reflex response in the term infant is about 18 msec. Comparison of this value with the latency of the tendon jerk for these muscles would indicate a central delay for the cutaneous reflex of about 3 msec. The latencies of the cutaneous reflex and tendon jerk remain constant over the first 5 years of life. The size of the short-latency cutaneous reflex response decreases progressively over the first year of life. In the second year of life stimulation of the fingers produces long- as well as short-latency increases in recorded muscle electrical activity. The maturation of the cutaneous reflex response is discussed in terms of the maturation of function of the corticospinal tract.

Action Potentials↗
PubMed1982

Cutaneous reflex responses and their central nervous pathways studied in man.

1. Cutaneous reflex responses have been recorded in human first dorsal interosseous and extensor digitorum brevis muscles following electrical stimulation of the digital nerves of the index finger and second toe respectively.2. Recordings have been made in normal subjects and in patients with central nervous lesions.3. Cutaneous reflex responses in first dorsal interosseous were triphasic, consisting of initial short latency excitation, followed by inhibition, followed by prominent long latency excitation. Cutaneous reflex responses in extensor digitorum brevis were biphasic, consisting of short and long latency periods of excitation.4. Estimated central delay for the initial excitatory components of the cutaneous reflex in first dorsal interosseous and extensor digitorum brevis muscles ranged from 2.4 to 6.2 ms (mean 4.6 ms) and 0.6 to 4.1 ms (mean 2.3 ms) respectively.5. Differences in latency between short and long latency excitatory components of the cutaneous reflexes recorded in first dorsal interosseous and extensor digitorum brevis muscles ranged from 16 to 18 ms (mean 17.3 ms) and 27 to 32 ms (mean 29.3 ms) respectively.6. Differences in time delay between short and long latency excitation in first dorsal interosseous and extensor digitorum brevis muscles when compared in individual subjects ranged from 9 to 14 ms (mean 12 ms). These values lay within 0-7 ms (mean 4 ms) of estimates in each subject of conduction time along central pathways between T12 and C7 spinal segments.7. Differences in latency between short and long latency excitatory components of the cutaneous reflex recorded in first dorsal interosseous were 3.5-8.5 ms longer than the estimated minimum time for impulse conduction along a pathway travelling through the dorsal columns to cerebral cortex and returning by way of the corticospinal tract.8. The long latency excitatory component of the cutaneous reflex in first dorsal interosseous muscle is reduced and often delayed in patients with dorsal column lesions.9. The long latency excitatory and short latency inhibitory components of the cutaneous reflex in first dorsal interosseous muscle are absent in patients with damage to motor cortex.10. The long latency excitatory component of the cutaneous reflex in first dorsal interosseous muscle is reduced in amplitude and often delayed in patients with motoneurone disease causing damage to the corticospinal tract. The timing of short latency excitatory and inhibitory components is unchanged.11. It is concluded that the short latency excitatory and inhibitory components of the cutaneous reflex response of first dorsal interosseous muscle have a spinal pathway and that the interneurones mediating the inhibitory component are under descending extrapyramidal control from systems whose inputs are deranged by damage to motor cortex.12. It is concluded that the long latency excitatory component of the cutaneous reflex response of first dorsal interosseous muscle is of supraspinal origin requiring transmission of afferent impulses through the dorsal columns, a relay in the sensori-motor cortex and then descending transmission to the lower motoneurone pool by way of the corticospinal tract.

Adolescent↗
PubMed1981

Changes in the recruitment threshold of motor units produced by cutaneous stimulation in man.

1. The effect of cutaneous stimulation on the recruitment of motor units has been studied during slowly increasing voluntary contractions of human first dorsal interosseous muscle. 2. Continuous electrical stimulation of the index finger at 4 x threshold for perception caused an increase in the recruitment threshold of units normally recruited at contraction strengths less than 1.5 N and a decrease in the recruitment threshold of units normally recruited at contraction strengths greater than 1.5 N. 3. It is concluded that the recruitment order of motor units during gradually increasing voluntary muscle contraction is not fixed but depends in part on cutaneous input.

Action Potentials↗
PubMed1981

The effects of digital nerve stimulation on the firing of motor units in human first dorsal interosseous muscle.

1. The effect of cutaneous stimulation on the firing of single motor units has been studied during voluntary contractions in human first dorsal interosseous muscle. 2. Electrical stimulation of the index finger at 3 x threshold for perception reduced the firing rate of most units recruited at voluntary contraction strengths less than 1.5 N and increased the firing rate of all units recruited at contraction strengths greater than 1.5 N. The firing rate of all slow twitch units (contraction time greater than 75 msec) was reduced. The behaviour of fast twitch units was mixed but at this stimulus strength all units recruited at contraction strengths greater than 1.5 N had their firing rate increased. 3. Tested at different stimulus strengths, the stronger the stimulus the more the firing rate of low threshold units was reduced. The firing rate of units recruited at high contraction strength was increased by weak stimuli but reduced by strong stimuli. 4. It is concluded that stimulation of the index finger shifts the weighting of synaptic input associated with a voluntary contraction to favour the activity of the more powerful fast twitch motor units in first dorsal interosseous muscle.

Action Potentials↗
PubMed1980

The reflex responses of single motor units in human hand muscles following muscle afferent stimulation.

1. Changes in the probability of firing of motor units active during voluntary muscle contraction have been studied in human first and second dorsal interosseous muscles in response to muscle afferent stimulation. 2. Short latency, possibly monosynaptic, excitatory responses were found in both first and second dorsal interosseous muscles following brief mechanical pulses applied to the belly of first dorsal interosseous. A second longer latency excitatory response followed the first with a mean latency of 25 msec. 3. All units in both muscles showed qualitatively the same responses but units recruited at low levels of voluntary contraction strength were more responsive to muscle afferent input than units recruited at high contraction strengths. The excitatory effect of muscle afferent input within the two motoneurone pools appears to be weighted in the same way as the more complicated input associated with a gradually increasing voluntary contraction. 4. These findings are discussed in relation to the relative importance of short and long latency reflex effects of muscle afferent input in the control of hand movements.

Action Potentials↗
PubMed1980

The reflex responses of single motor units in human first dorsal interosseous muscle following cutaneous afferent stimulation.

1. Changes in the probability of firing of motor units active during voluntary muscle contraction have been studied in human first dorsal interosseous muscle in response to cutaneous afferent stimulation. 2. Electrical stimulation of the digital nerves of the index finger produces a reflex response consisting of three phases, early excitation followed by inhibition followed by late excitation. 3. Motor units recruited at low levels of voluntary contraction strength had larger early inhibitory and larger late excitatory responses than those recruited at higher levels of force. 4. Taking together the size of the short latency excitatory and inhibitory responses, units recruited at low levels of voluntary contraction strength and with slow twitch contraction times had predominantly inhibitory responses. In contrast, units in which the short latency excitatory responses predominated had fast twitch contraction times and were recruited at high levels of contraction strength. 5. It is concluded that for the cutaneous reflex pathway there are differences in the balance of excitatory and inhibitory sets of interneurones impinging on first dorsal interosseous motoneurones which are related to the kind of muscle unit innervated.

Action Potentials↗
PubMed1979

Augmentation of clinical services in rural areas by health sciences students.

Over a five-year period 230 senior-level students in medicine, nursing, and pharmacy served in clinics located throughout five rural communities. Students participated in the development of the clinics and in the organization of services that otherwise would not have been delivered. Community-based preceptors helped integrate the students' learning about community processes. The project provided experiential learning and interdisciplinary interactions that were enthusiastically received by the students. Follow-up surveys suggested that the experience reinforced interest in eventual practice in rural areas and in interdisciplinary settings. The project demonstrated that students were able to provide clinical services which were useful and acceptable to the communities and which were supported by local practitioners.

Ambulatory Care Facilities↗
PubMed1979

Motor unit organization of human medial gastrocnemius.

1. The properties of fifty-seven motor units in human medial gastrocnemius have been studied using controlled intramuscular microstimulation, glycogen depletion and muscle biopsy. 2. Motor units could be divided into three classes on the basis of their mechanical properties. Type S units were slow, small and fatigue resistant. Type FR units were fast, intermediate in size, and fatigue resistant. Type FF units were fast, large and fatigable. 3. Glycogen depletion of a number of type S and FF units revealed them to be composed of type 1 and type 2b muscle fibres respectively. 4. The results suggest that during slowly increasing voluntary contractions where units are recruited in order of size, type 1 and 2a muscle fibres would be employed at low force levels followed by type 2b muscle fibres in stronger contractions.

Action Potentials↗
PubMed1979

Muscle spindle discharge in normal and obstructed movements.

1. The discharge activity of muscle spindle endings located in tail and hind limb muscles was recorded during voluntary movements in the cat. 2. During active shortening of the receptor-bearing muscles, both primary and secondary endings tended to fall silent. This was more pronounced, the higher the rate of muscle shortening. We suggest that in unobstructed movements in which muscle velocities exceed 0.2 resting lengths per second (lr/sec), the firing patterns of spindle afferents are dominated by their responses to the length variations. At velocities lower than 0.2 lr/sec, fusimotor action may predominate. 3. When active muscle shortening was unexpectedly halted, both primary and secondary endings resumed firing, but the increases in discharge rate were not as abrupt as might have been expected had there been strong co-activation of fusimotor and skeletomotor neurones. Rather, for the types of movements studied, fusimotor action appears to have been quite modest.

Action Potentials↗