<p> Although most muscle spindle investigations have used the cat model and mvasiVe surgical measurement techniques, several investigators have used microneurography to record from the Ia and II fibres in humans during tendon vibration. In these studies the muscle spindle primary (Ia) endings are stimulated using transverse vibration of the tendon at reflex sub-threshold amplitudes. Others have used low amplitude vibration and the H-reflex (monosynaptic electrical response) to determine reflex properties during both agonist and antagonist voluntary contractions. Both of these methods explore only certain parts of the monosynaptic reflex arc; microneurography focus on the properties and firing characteristics of the muscle spindles themselves, whereas the H-reflex response to vibration is a representation of the response of the spinal cord as well as the muscle spindles. </p> <p> In the past we have developed a PC based instrument that uses Lab VIEW and a linear servomotor to study tendon reflex properties by recording H-reflexes (or stretch reflexes for mechanical stimuli) from single tendon taps or electrical stimuli to the afferent nerve. In this thesis we describe a further development of this system to provide precise vibrations of the tendon at up to 55 Hz with amplitudes up to 4 mm. The resultant vibration stretch reflex train is extracted from 2 major background noise sources, 60 Hz power line noise, and vibration artifact noise, of the EMG recording via phase coherent subtractive filtering. </p> <p> To demonstrate the versatility and efficacy of this system in studying the monosynaptic reflex arc, test results from several pilot studies are presented, using the system to vibrate the human distal flexor carpi radialis tendon: (i) whether stretch reflexes could be entrained with high frequency vibration, as contrary to H-reflexes, (ii) whether the responses were affected by low levels of agonist or antagonist contraction, in agreement with the existing pool of work on the subject using the H-reflex, (iii) whether a separation of the Ia (primary) and II (secondary) ending pathways is observable as individual but delayed responses at low vibration frequencies due to different activation characteristics, and axon diameters, of each ending. Possible physiological mechanisms that explain the resultant behaviour are also discussed. </p> / Thesis / Master of Applied Science (MASc)

The superior cervical ganglion (SCG) is the largest of the sympathetic chain ganglia which control a number of autonomic cardiovascular reflexes via neural activity in the postganglionic nerve trunk. In addition to the large principal neurons, these ganglia contain a minority population of smaller cells, the small intensely fluorescent or SIF cells, so named because of their intense fluorescence following treatments which reveal the presence of endogenous catecholamines (mainly dopamine in the rat). The physiological functions of the SIF cells are largely unknown and various roles have been proposed including (i) dopaminergic interneuron, which modulates ganglionic transmission, (ii) endocrine function, since many of them have a close association with the vasculature and (iii) chemosensory function, similar to that of the arterial chemoreceptors which sense blood gases and pH. Understanding the physiological role of SIF cells has been hampered by their small size, sparse distribution and relative inaccessibility, all of which render microelectrode electrophysiological studies difficult. In this thesis these limitations were overcome by use of (i) dissociated cell cultures of the rat SCG, in which growth conditions favoured SIF cell survival but not that of the principal neurons, and (ii) the novel high resolution patch clamp/whole cell recording technique which is ideal for the study of the electrophysiology of small cells. The ionic currents, which underlie many basic electrophysiological processes, were characterized in 5-16 day old cultures of SIF cells obtained from the SCG of neonatal rats. The main methodology consisted of whole cell recording under voltage clamp conditions, which permit the study of membrane ionic currents. Five main ionic currents were identified in all of the SIF cells ( > 100) studied: (i) a fast transient inward Na+ current, sensitive to the well-known blocker of voltage-gated Na+ channels i.e. tetrodotoxin or TTX; (ii) the delayed rectifier outward K+ current that is found in a variety of cell types; (iii) a Ca2+- activated outward K+ current, sensitive to Ca2+ channel blockers; (iv) a transient inward Ca2+ current which appears to be carried by N-type Ca2+ channels and (v) a slower, sustained inward Ca2+ current which appears to be carried by L-type Ca2+ channels. In addition a third type of outward K+ current, the fast transient K+ current or lA, was found in SIF cells obtained from 3-7 day old rats, but not from 1 day old rats. It therefore appears that this lA current, which is known to modulate firing frequency in neurons develops rapidly in vivo during the first postnatal week. This broad repertoire of ion channels in SIF cells suggests several possible sites for modulation by various agents including neurotransmitters, neuromodulators, or other chemosensitive agents. Since SIF cells were recently proposed to have arterial chemoreceptor function similar to glomus cells, the effect of one such stimulus, i.e. an acidic (intracellular) pH, was tested. It has recently been suggested that a decrease in intracellular pH is part of the pathway responding to extracellular stimuli in the glomus cell (Stea, Alexander and Nurse, in press). Acidification of the SIF cell's cytoplasm with the K+/H+ ionophore nigericin resulted in a suppression of both the fast inward Na+ current as well as the outward K+ current. However, these effects do not appear to beunique to SIF cells and therefore the possibility of a chemoreceptor role m the cardiovascular system requires further study. In summary, the characterization of the various ionic currents in SIF cells resulting from this thesis provides the necessary background which should eventually resolve not only the question of the physiological role of SIF cells in autonomic ganglia, but also help to understand the underlying mechanisms responsible for SIF cell function. / Thesis / Master of Science (MS)

Spinal stability describes the ability of the neuromuscular system to maintain equilibrium in the presence of kinematic and control variability, and may play an important role in the etiology of low-back disorders (LBDs). The primary mechanism for the neuromuscular control of spinal stability is the recruitment and control of active paraspinal muscle stiffness (i.e., trunk stiffness). The two major components of active muscle stiffness include the immediate stiffness contribution provided by the intrinsic stiffness of actively contracted muscles, and the delayed stiffness contribution provided by the reflex response. The combined behavior of these two components of active muscle stiffness is often referred to as "effective stiffness". In order to understand the neuromuscular control of spinal stability, stochastic system identification methods were utilized and nonparametric impulse response functions (IRFs) calculated in three separate studies in an effort to: 1) Quantify the effective dynamics (stiffness, damping, mass) of the trunk Nonparametric IRFs were implemented to estimate the dynamics of the trunk during active voluntary trunk extension exertions. IRFs were determined from the movement following pseudo-random stochastic force disturbances applied to the trunk. Results demonstrated a significant increase in effective stiffness and damping with voluntary exertion forces. 2) Quantify the reflex dynamics of the trunk Nonparametric IRFs were computed from the muscle electromyographic (EMG) reflex response following a similar pseudo-random force disturbance protocol. Reflexes were observed with a mean response delay of 67 msec. Reflex gain was estimated from the peak of the IRF and increased significantly with exertion effort. 3) Separate the intrinsic and reflexive components of the effective dynamics and determine the relative role of each in the control of spinal stability. Both intrinsic muscle and reflexive components of activation contribute to the effective trunk stiffness. To evaluate the relative role of these components, a nonlinear parallel-cascade system identification procedure was used to separate the intrinsic and reflexive dynamics. Results revealed that the intrinsic dynamics of the trunk alone can be insufficient to counteract the destabilizing effects of gravity. This illustrates the extreme importance of reflexive feedback in the maintenance of spinal stability and warrants the inclusion of reflexes in any comprehensive trunk model. / Ph. D.

Coordinated movements are regulated by the brain, spinal cord and sensory feedback. The interaction between the spinal cord and sensory feedback also play a significant role in facilitating plasticity and functional recovery after neural trauma. Cross-education describes training one side of the limb to enhance the strength of the homologous muscle on the contralateral side. Previous study with chronic stroke participants found significant strength gains in the more affected leg following unilateral dorsiflexion training on the less affected side, which suggested cross-education can be used to boost strength gain when training the more affected side is hard to initiate. However, there is lack of evidence showing cross-education in the arm muscles after stroke and the neural pathways mediating strength cross-education in stroke participants require further study. The modulatory role of sensory feedback in movement control has been studied by using cutaneous stimulation as a proxy of the sensory input from skin. Mechanistic studies on neurological intact participants show that cutaneous reflex pathways are widespread in the cervical and lumbar spinal cord and have a global effect on the muscles in the non-stimulated limbs. In rehabilitation training, sensory enhancement from prolonged electrical stimulation has been used to facilitate training outcomes for those had stroke and other neurological disorders. Therefore, cutaneous pathways may be important in regulating cross-education training-induced strength gain. The purpose of this dissertation was to explore the effects of upper limb cross-education strength training in chronic stroke participants and the role of sensory inputs in regulating intra- and interlimb neural excitability in neurologically intact participants. In the first project (Chapter 2), we explored the efficacy of cross-education strength training in wrist extensor muscles of chronic stroke participants. Strength improvements were found bilaterally with altered excitabilities in the cutaneous pathways on the untrained side. These results show the potential role of cutaneous pathways in mediating strength transfer after unilateral strength training which led us to further explore the factors may affect the cutaneous modulation. In neurologically intact participants, we investigated the effects forearm position (Chapter 4), stimulation trigger mode and parameters (Chapter 5) on the cutaneous reflexes in the stimulated limb. Following the findings from Chapter 3, 4, and 5, the interlimb effects of self-induced sensory enhancement on the cutaneous reflexes were examined in Chapter 6. Taken together, data from this thesis confirms the clinical application of cross-education in strength training after stroke. It addresses that exaggerated bilateral strength gains and neural plasticity can be induced following unilateral strength training on the less affected side. In addition, sensory enhancement may be applied to amplify cross-education effects in strength training. / Graduate / 2020-09-12

Abstract not available

Bibliographical note: p. 88. References: p. 89-93. / Contract DA36-039-AMC-03200(E). Grant DA-SIG-36-039-61-G14. Grant G-16526. Grant MH-04737-03.

In individuals with spinal cord injury (SCI) who have disrupted communication between the brain and spinal cord, vibration may mimic functions formerly served by the lost or impaired supraspinal inputs resulting in more normal reflex modulation and improved walking function. Three experiments assessed the effects of vibration on spinal locomotor-generating circuitry, spinal reflex activity, and walking function. In Experiment 1, localized leg vibration was used to elicit air-stepping responses in the lower extremities. We compared responses of individuals with SCI to those of non-disabled (ND) individuals and assessed the influence of severity injury and locomotor training on the air-stepping response in individuals with SCI. Our results indicate that vibration of the tensor fascia latae elicited more consistent and robust responses than vibration of the quadriceps or hamstrings muscles. Individuals with SCI had less consistent and robust responses than ND individuals. In those with SCI, neither severity of injury nor locomotor training influenced the robustness or consistency of the response. In Experiment 2, we investigated the effect of whole-body vibration (WBV) on spasticity, as measured by spinal stretch reflex (SSR) excitability, in individuals with SCI. We also assessed differences in the influence of WBV among individuals who used antispastic medications and those who did not. Subjects were tested before and after participation in a 3 day/week, 12-session WBV intervention. There was a significant reduction in spasticity that persisted for several days following the WBV intervention. The amount by which spasticity was reduced was not different in those who used antispastic agents compared to those who did not use these agents. In Experiment 3, we assessed the effects of the 12-session WBV intervention on walking function. WBV was associated with significant increases in walking speed, cadence, step length of the stronger leg, and consistency of hip-knee intralimb coordination. Increases in cadence and stronger-leg step length correlated with improvements in walking speed. These results suggest that WBV may represent an approach to decreasing spasticity, and may be useful for individuals in whom spasticity interferes with function. Furthermore, vibration appears to have a beneficial effect on walking function, perhaps by influencing spinal locomotor-generating circuitry.

The stopping of an earlier intended action is best explained in a race between a go process and a stop process (Logan & Cowan, 1984). The finish line, to which each process races, has been likened to a point of no return, specifically one that marks the onset of a final ballistic (unstoppable) process. Of note is the typical relation of reduced go probabilities and faster go latencies at shorter signal onset asynchronies (SOAs). (The SOA is the time interval between presentation of the go signal and presentation of the stop signal.) We report, in some cases, sub-maximal surface electromyograms (EMGs) at onset when trying to stop a maximal speeded action. These data indicate reduced synaptic drive to reach the motor pools as a result of earlier stopping effects and, as such, hold important implications for a theory of control. First, we interpret these data to suggest that the point of no return is phantom. Sub-maximal EMGs indicate a point in the control stream beyond which some EMG will be later observed but, importantly, they fail to mark the onset of a final ballistic process if, once breached, the same process remains subject to further effects of stopping. The alternative interpretation, however, that of a final ballistic process that receives sub-maximal input which results in sub-maximal output (i.e., EMG onset) cannot be ruled out from these data. We used the Hoffmann (H) reflex to probe further the mechanism of control for stopping a voluntary action. The H-reflex, an involuntary reflex that is taken as an index of spinal control, is relevant to the control of stopping because it is typically facilitated a short time before EMG onset. In other words, it provides a window of control within which a final ballistic process would otherwise be expected to locate. Thus, we interpret the effects of stopping on the H-reflex before EMG onset as strong evidence against a final ballistic process. Second, while the race model can explain the relation between the go probabilities, the go latencies and the SOAs, it fails to explain the sub-maximal EMG onsets that describe that same action in some cases. We submit a mechanism of excitatory-inhibitory interaction at all times up to the motor pool to explain both sets of empirical data. The viability of this theory is demonstrated using computer analyses.

Issued also as Thesis (Ph. D.)--University of Michigan. / Bibliography: p. 61-62.

The stopping of an earlier intended action is best explained in a race between a go process and a stop process (Logan & Cowan, 1984). The finish line, to which each process races, has been likened to a point of no return, specifically one that marks the onset of a final ballistic (unstoppable) process. Of note is the typical relation of reduced go probabilities and faster go latencies at shorter signal onset asynchronies (SOAs). (The SOA is the time interval between presentation of the go signal and presentation of the stop signal.) We report, in some cases, sub-maximal surface electromyograms (EMGs) at onset when trying to stop a maximal speeded action. These data indicate reduced synaptic drive to reach the motor pools as a result of earlier stopping effects and, as such, hold important implications for a theory of control. First, we interpret these data to suggest that the point of no return is phantom. Sub-maximal EMGs indicate a point in the control stream beyond which some EMG will be later observed but, importantly, they fail to mark the onset of a final ballistic process if, once breached, the same process remains subject to further effects of stopping. The alternative interpretation, however, that of a final ballistic process that receives sub-maximal input which results in sub-maximal output (i.e., EMG onset) cannot be ruled out from these data. We used the Hoffmann (H) reflex to probe further the mechanism of control for stopping a voluntary action. The H-reflex, an involuntary reflex that is taken as an index of spinal control, is relevant to the control of stopping because it is typically facilitated a short time before EMG onset. In other words, it provides a window of control within which a final ballistic process would otherwise be expected to locate. Thus, we interpret the effects of stopping on the H-reflex before EMG onset as strong evidence against a final ballistic process. Second, while the race model can explain the relation between the go probabilities, the go latencies and the SOAs, it fails to explain the sub-maximal EMG onsets that describe that same action in some cases. We submit a mechanism of excitatory-inhibitory interaction at all times up to the motor pool to explain both sets of empirical data. The viability of this theory is demonstrated using computer analyses. / Education, Faculty of / Kinesiology, School of / Graduate