Hyperplastic esophagogastric polyps in two children with neurofibromatosis type 1.
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Child↗
Biomedical subjects
P Bawa
Publications and source records attributed to P Bawa.
Recruitment of motor units in human flexor carpi ulnaris.
In 1949, Denny-Brown reported that the motoneuron pool of the human flexor carpi ulnaris (FCU) muscle was fractionated into subpopulations, each subpopulation being activated during a different voluntary motor task. The following report presents data on motor unit recruitment in the human FCU muscle for the tasks of isometric flexion and ulnar deviation, cocontraction of the forearm muscles and non-isometric flexion of the wrist. These observations show that every FCU motor unit tested reliably, contributed to all four tasks, that is, no separate subpopulations were observed for any of the contractions tested. Furthermore, the order of recruitment was the same for all four tasks.
Action Potentials↗
Recruitment of motor units in response to transcranial magnetic stimulation in man.
1. Short-latency responses of single motor units (SMUs) and surface electromyographic activity (EMG) to transcranial magnetic stimulation (TMS) were examined in five different hand and forearm muscles of human subjects. 2. The response probability, P (number of extra spikes in the response peak above background per stimulus), was, in general, higher at the lower voluntary discharge rate of the motor unit than at the higher rate. 3. Increasing the strength of TMS increased the response probability of a tonically firing motor unit and at the same time recruited new units which discharged phasically during the response peak. This demonstrates rate coding and recruitment of motor units by excitatory inputs resulting from TMS when the motoneurone pool is tonically facilitated by a constant voluntary drive. 4. Next, TMS was delivered without any voluntary facilitation of motoneurones. The order of recruitment for up to four different motor units discharged by TMS was compared to that observed with voluntary input. The threshold of recruitment for each of the two inputs was estimated from the surface EMG value at which the unit was recruited. For these motoneurone pools (eleven sets of observations), the order of recruitment was the same with TMS and voluntary inputs. 5. From these data it is concluded that, despite the complex and phasic nature of the descending corticospinal volleys generated by TMS, it produces orderly recruitment and rate coding of motoneurones similar to that found for voluntary activation.
Action Potentials↗
Recruitment of motor units in human forearm extensors.
1. Experiments were conducted on single motor units of two forearm muscles, extensor carpi radialis (ECR) and extensor digitorum communis (EDC) of human subjects. Our interest was whether or not task groups could be identified in these forearm muscles, and, if so, was there orderly recruitment within each task group. 2. To test for the presence of separate task groups within ECR, motor-unit recruitment was examined for two isometric contractions:wrist extension and radial deviation. Each of the ECR motor units tested repeatedly discharged during contractions in both directions, indicating the absence of separate task groups in ECR for contractions in these two directions. 3. Recruitment order between pairs of ECR motor-unit action potentials was examined for wrist extension and radial deviation. For 58 paired comparisons, the order of recruitment was the same in both directions. In terms of force output, plots of twitch torque versus recruitment threshold of ECR motor units showed a positive correlation for both directions, wrist extension and radial deviation, demonstrating size-ordered recruitment of ECR motoneurons for both contractions. 4. The EDC motoneuron pool exhibited two partially overlapping subpopulations of motoneurons on the basis of task, one subpopulation recruited for middle finger extension and the second one for ring finger extension. Contractions involving the index and little fingers were not examined. It is concluded that motor-unit task groups do exist within EDC motoneuron pool. Plots of twitch torque versus recruitment threshold showed positive correlations for each of these two task groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Action Potentials↗
Effects of tetanic stimulation on monosynaptic and dorsal root reflexes in kittens.
The effects of tetanic stimulation of peripheral afferents were examined on monosynaptic reflexes and dorsal root reflexes in kittens of various ages. Concomitantly recorded monosynaptic and dorsal root reflexes resulting from the stimulation of muscle nerves showed similar post-tetanic changes, namely, predominantly post-tetanic depression in neonates and post-tetanic potentiation in older kittens or adults. However, the changes in post-tetanic responses expressed as a percentage of control in dorsal root reflexes were much smaller than those in monosynaptic reflexes. When dorsal root reflexes originating from muscle and cutaneous afferents were compared, dorsal root reflexes from the latter behaved quite differently. For all ages, post-tetanic effects on dorsal root reflexes arising from cutaneous afferents were either insignificant or very small. The possible mechanisms underlying differences in post-tetanic effects from muscle and cutaneous afferents in adults and neonates are discussed.
Aging↗
Comparison of stretch reflex activities and reaction times in two separate age groups of human subjects.
The effect of prior instruction on stretch reflex activity was compared in two separate age groups of healthy subjects. No clear differences were found for amplitude modulation and reaction items between the younger (25.6 +/- 3.2 years) and the older group (56.6 +/- 6.5 years) of subjects. A significant difference was observed in the absolute magnitudes of the background activity, short latency and long latency reflex activities which were higher in the older group of subjects than in the younger subjects.
Adult↗
Modulation of stretch activity with instruction.
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Adult↗
Dorsal root reflexes in kittens.
Dorsal root reflexes, evoked by stimulating the peripheral nerves, were recorded from dorsal roots in kittens in the age range 1/2 day to 66 days and adult cats. No dorsal root reflex (DDR) activity was observed in the newborns. Once it appeared on 4th-5th day, the DRR magnitude (amplitude and duration) increased monotonically with age showing a peak at the end of the 4th week. During the 5th week, the activity declined towards adult values.
Action Potentials↗
Posttetanic changes in the afferent and efferent activity of monosynaptic reflex in kittens.
Both the afferent volleys from the dorsal root and the monosynaptic reflex discharges from the corresponding ventral root were recorded with hook electrodes during stimulation of the nerves innervating the triceps surae muscles. The effects of conditioning high frequency tetanus on the magnitudes of these afferents and reflex volleys were examined in kittens of postnatal age 1-90 days and in adult cats. In young kittens under barbiturate anaesthesia, large-amplitude monosynaptic reflex discharge can be evoked without prior conditioning. The amplitude of this reflex discharge decreased with increasing age of the animal. Application of conditioning tetanic stimuli to the muscle nerves resulted in posttetanic depression followed by posttetanic potentiation of the monosynaptic reflex. The magnitude of posttetanic depression was much higher than that of potentiation in the first postnatal week. As the age increased, the magnitude of depression decreased while the magnitude of potentiation increased. The afferent volley showed a considerable posttetanic potentiation in older kittens and cats. No significant potentiation or depression was observed in the younger animals. Possible mechanisms contributing to posttetanic depression and potentiation are discussed.
Afferent Pathways↗
Limitations of the spike-triggered averaging technique.
The spike-triggered averaging technique, when used to obtain the twitch profile of a single motor unit, requires the maintenance by the subject of that unit's minimal rhythmic firing rate, which is typically between 8 and 12 pulses/sec. Literature on the rate-tension relationship of cat motor units shows that some twitches may start to fuse at stimulus rates as low as 2 pulses/sec. This fusion changes the mechanical characteristics of the observed apparent twitch from those of the unfused twitch. The present work has assessed the changes in contraction time, half-relaxation time, and twitch amplitude of slow versus fast twitch cat single motor units, when these units are demonstrating varying degrees of fusion of tension. As the stimulus rate applied to cat single motor units increased to those typically used during spike-triggered averaging, the values of all three twitch parameters decreased, with this decrease being more prominent for slow-contracting versus fast-contracting units.
Animals↗
Gradual changes in the recovery curve of monosynaptic reflex during postnatal development in kittens.
Conditioning-testing stimulus pulses were applied to soleus-gastrocnemius muscle nerves while reflexes were recorded from L7 ventral root in kittens (1-100 days). The rate of recovery of the monosynaptic test reflex response was monitored at different ages. These observations show that the very slow recovery rate seen in the newborns becomes much faster in the first 10 postnatal days, and it attains adult-like values in ca. 4 weeks after birth.
Age Factors↗
Firing patterns of human flexor carpi radialis motor units during the stretch reflex.
Single motor unit and gross surface electromyographic responses to torque motor-produced wrist extensions were studied in human flexor carpi radialis muscle. Surface EMG typically showed two "periods" of reflex activity, at a short and long latency following stretch, but both periods occurring before a subject's voluntary reaction to the stretch. The amplitude of EMG activity in both reflex periods increased monotonically with an increase in the torque load. The amplitude of the short-latency reflex response was very dependent on the motoneuron pool excitability, or preload. The amplitude of the long-latency reflex response also varied with the preload, but could, in addition, be modulated by the subject's preparatory set for a voluntary response to the imposed displacement. When a single motor unit that was not tonically active began to fire during the stretch reflex, it did so primarily during the long-latency period. When caused to fire repetitively by voluntary facilitation of the motoneuron pool, that same unit now showed activity during both periods of the stretch reflex. Further increases in either motoneuron pool facilitation or in perturbation strength resulted in a monotonic increase in response probability of a single motor unit during the short-latency period. However, the response probability of a single unit during the long-latency reflex period did not always vary in a monotonic way with increases in either torque load or motoneuron pool facilitation. For an additional series of experiments, the subject was instructed on how to respond voluntarily to the upcoming wrist perturbation. The three instructions to the subject had no effect on the response probability of a single motor unit during either the background or short-latency periods of the stretch reflex. However, prior instruction clearly affected a unit's response probability during the long-latency reflex period. Changes in the firing rate of motor units, and in the recruitment or derecruitment of nontonic units, contributed to this modulation of reflex activity during the long-latency period.
Adult↗
Voluntary and reflexive recruitment of flexor carpi radialis motor units in humans.
The order of recruitment of flexor carpi radialis (FCR) motor units was studied during voluntary and reflexive activation of the motoneuron pool for two adult subjects. During slow "voluntary" activation, the recruitment threshold for tonic motoneuron firing was determined, and then the twitch profile of the motor unit was computed by the spike-triggered averaging technique. A positive correlation (r = 0.79 and 0.68 for the two subjects, respectively) between recruitment threshold and twitch amplitude implies that recruitment of FCR motoneurons during slow ramp isometric contractions proceeds in order of increasing size. The accompanying paper describes the behavior of single motor units during the short- and long-latency periods of the stretch reflex. When the effects of sufficient voluntary facilitation (preload) combined with a sufficiently large torque step were just adequate to cause a motor unit to fire during the stretch reflex, its response was virtually always confined to the long-latency period. In addition, the first unit to begin responding to muscle stretch always had the lowest voluntary recruitment threshold relative to other units "visible" at that recording site. By making this unit tonic, the reflex response to the same load increased substantially during the short-latency reflex period, while a second unit increased its reflex response probability during the long-latency period. Thus the voluntary recruitment order of two or more motor units is preserved during the stretch reflex, and is in fact maintained within first the long-latency and then short-latency components of this reflex.
Adult↗
Recruitment order of motor units during the stretch reflex in man.
The recruitment pattern of single motor units contributing to the short- and long-latency periods of the stretch reflex was investigated in human adults. When non-tonic, a given unit responded to stretch during the long-latency reflex period. When made tonic, the same unit showed a reflex response during the short-latency period, while a higher threshold, non-tonic unit would respond during the long-latency period. The data show an orderly recruitment of motor units during both phases of the stretch reflex in man.
Adult↗
Recruitment order of motoneurons in stretch reflexes is highly correlated with their axonal conduction velocity.
Motor units of soleus and medial gastrocnemius (MG) muscles were studied in pairs during stretch reflexes in the decerebrate cat to determine the relation between their recruitment orders and axonal conduction velocities. In 97% of soleus pairs, the motor unit with the lower axonal conduction velocity was recruited first. Since the soleus is a homogeneous muscle in the cat, differences in motor-unit type are, therefore, not a sine qua non for orderly recruitment nor is recruitment random within homogeneous populations of motor units, as recently proposed (28). In the medial gastrocnemius, a heterogeneous muscle, the same high correlation (97%) between recruitment sequence and conduction velocity was observed. Thus, the factors that determine recruitment order in heterogeneous muscles are as closely correlated with axonal diameter as they are in homogeneous muscles. Comparison of axonal conduction velocities in our sample of MG units with those in three samples of type-identified MG units studied by other investigators also suggests that motor-unit type is not the critical factor controlling the sequence of activation in heterogeneous muscles. It is concluded that the combined effects of all presynaptic and postsynaptic factors that determine susceptibility to discharge in motoneurons during stretch reflexes are strictly correlated with their axonal conduction velocities, as predicted by the size principle.
Animals↗
Properties of locomotor generators in man.
There is little behavioural information on either the functional capacities or the limitations of the coupling system between the locomotor generators of limbs. In this experiment, 10 subjects produced maximal stepping frequencies under eight randomly-assigned conditions consisting of all combinations of standing and sitting, one leg and two legs, and auditorily-cued or self-paced. There was a significant difference in the mean maximum frequency while sitting and standing with higher frequencies found under the seated condition. There were no significant differences between the one-leg and two-legs condition and no significant difference was found between cued- and self-paced stepping. In three subjects who underwent ten training sessions, under all conditions, no significant learning effect was found. Both swing and stance phases showed a decrease with increasing frequency during cued stepping. These results are discussed in terms of the functional properties of locomotor generators in man.
Adult↗
Effect of core cooling on short and long latency reflex responses.
Subjects were immersed in 10 degrees C water until the rectal temperature dropped to 35 degrees C. Reflexes of wrist flexors were tested before and after cooling with tendon taps and torque motor produced perturbations. Comparison of pre- and post-cooling reflex responses showed that the longer latency reflex (LLR) was delayed in onset more than the short latency monosynaptic reflex (SLR) response. This implies that a portion of the LLR pathway is separate and distinct from the SLR pathway.
Adult↗
Does orderly recruitment of motoneurons depend on the existence of different types of motor units?
It has recently been proposed that the recruitment of motoneurons is correlated with their type rather than their size. To test this hypothesis the axonal conduction velocities (CVs) of 92 pairs of soleus motoneurons (all of the same histochemical type) were compared with their recruitment order. By means of spike-triggered averaging it has been shown that in 89 out of 92 pairs of soleus units the motoneuron with the lower CV was recruited first. The results indicate that orderly recruitment occurs in the absence of different types of motoneurons and is correlated with cell size within a cell type.
Action Potentials↗