Thesis (Ph. D.)--University of California, San Diego and San Diego State University, 2003. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

The semicircular canals detect head rotations and trigger compensatory movements that stabilize gaze and help maintain visual fixation. Mammals with large eyes and high visual acuity presumably require more precise gaze stabilization mechanisms because they experience degradation of spatial resolution at a lower threshold of uncompensated motion. Because semicircular canal radius of curvature is a primary determinant of canal sensitivity, species with large canal radii are expected to be capable of more precise gaze stabilization than species with small canal radii. Here the relationship between semicircular canal radius of curvature, eye size, and visual acuity is examined in a large sample of therian mammals. These results demonstrate that eye size and visual acuity both explain a significant proportion of the variance in mean canal radius of curvature after statistically controlling for the effects of body mass and phylogeny. These findings suggest that interspecific variation in semicircular canal radius of curvature is partly the result of selection for improved gaze stabilization in species with large eyes and acute vision. / text

Impact hammer is the current modal testing way in Dynapac testing department. Due to highly damped characteristic of big construction machines, there are a few weaknesses for modal testing when using hammer, such as short response time, limited frequency resolution, poor quality of frequency response functions. Therefore, a more advanced excitation equipment is needed to improve the measurement quality. The object for this study is to compare two different measuring methods. The thesis will show a comparison between the hammer testing and the shaker MIMO testing compared with analytical model in a highly damped system. It will also give a reference for further highly damped modal analysis and budgetary assessment to decide the budget expenditure. Result from shaker testing shows a little better correlation than hammer testing compared with FEM model. While the correlation between FEM model and measurement is bad due to many reasons, such as many local modes that can not excited, lack of excitation points, unexpected noise and error from the measurement. While considering the compared results obtained from this machine for now, a simpler structure experiment is suggested to be carried on in the future. Shorter length of stinger can be used to enable higher amplitude of force to excite the property on this machine.

Objectives: Determine the effect of contraction type and intensity, inertial loading, and visual feedback on various measures of hand tremor in subjects with essential tremor. Methods: Study 1. Twenty-three ET subjects and 22 controls held their hand in an outstretched position while supporting various submaximal loads (no-load, 5%, 15% and 25% 1-repetition maximum). Hand postural tremor and wrist extensor neuromuscular activity (EMG) were recorded. Study 2. Twenty-one ET subjects and 22 controls applied isometric wrist extension contractions with and without visual feedback. Various submaximal contraction intensities were evaluated (5%, 10%, 20% and 30% MVC). Force production and EMG were recorded. Study 3. Twenty-one ET subjects and 22 healthy controls performed slow wrist extension-flexion movements while supporting various submaximal loads (no-load, 5%, 15% and 25% 1-repetition maximum). Angular displacement and EMG were recorded. Results: Study 1. Inertial loading resulted in a reduction in postural tremor in ET subjects. The largest reduction in tremor amplitude occurred at the 15% load, which was associated with spectral separation of the mechanical reflex and central tremor component. Despite an increase in overall neuromuscular activity with inertial loading, EMG tremor power did not increase with loading. Study 2. Higher contraction intensities were associated with larger amplitude force fluctuations and greater EMG amplitudes. Tremor spectral power of force and EMG remained constant at all target intensities, resulting in a reduction in relative tremor power at higher contraction intensities. Visual feedback affected subjects in the control and ET groups similarly. Study 3. Subjects with more pronounced tremor spectral peaks had larger amplitude kinetic tremor, which was reduced with inertial loading. Despite an increase in overall neuromuscular activity with inertial loading, EMG tremor spectral power was only slightly increased with loading, which resulted in a large reduction in relative EMG tremor power. Conclusions: The effect of inertial loading on postural and kinetic tremor amplitude appears to be mediated in large part by its effect on the interaction between the mechanical reflex and central tremor components. The level of motor unit entrainment remains relatively constant in subjects with ET despite increasing contraction intensities. / Thesis (Ph.D, Rehabilitation Science) -- Queen's University, 2008-10-24 11:18:57.537

No description available.

Studies suggest that deficits in central regulation of stretch reflex thresholds (SRT) underlie both spasticity and other disorders of motor control. We investigated intra- and inter-evaluator reliability to quantify spasticity based on tonic SRT (TSRT) and the relationship between TSRT and Modified Ashworth Scale (MAS, clinical assessment of resistance to stretch). Spasticity was evaluated in 20 subjects with chronic stroke-related spasticity in two different days, by three evaluators. Twenty different velocity-dependent dynamic SRT (angle where biceps brachii EMG signal increased for a given velocity of stretch) were recorded. TSRT (excitability of motoneurons at 0°/sec) was then computed. Spasticity was also estimated with MAS. Reliability was moderately good for subjects with moderately high spasticity (intra--evaluator: 0.46 to 0.68, inter--evaluator: 0.53 to 0.68). There was no correlation between TSRT and MAS since they measure different phenomena. TSRT is a promising new measure of spasticity. Further improvements for its quantification are suggested.

Reflex effects evoked by graded electrical stimulation of the posterior articular nerves (PAN) of the ipsi- and contralateral knee joints were investigated using both micro-electrode recordings from 7 - motoneurones and recordings from single muscle muscle spindle afferents. Spindle afferent responses were also recorded using natural stimulation of different types of receptors, to elucidate if the articular reflexes onto the y -motoneurones were potent enough to significantly alter the muscle spindle afferent activity. Stretches of the ipsilateral posterior (PCL) and anterior (ACL) cruciate ligaments, pressure on the ipsi- and contralateral knee and ankle joint capsules, and passive flexion/extension movements of the joints in the contralateral hind limb were performed. The occurrance of different sensory endings in the ACL and PCL was examined using gold chloride staining for neuronal elements. All experiments were performed on chloralose anaesthetized cats. More than 90% of the static and dynamic y -motoneurones were responsive to electrical stimulation of the PAN. Most 7-cells responded to low intensity electrical stimulation. Excitatoiy reflex effects predominated on both static and dynamic posterior biceps-semitendinosus (PBSt) 7 -cells, while excitatory and inhibitory effects occurred with an about equal frequency on triceps-plantaris (GS) 7-cells. The fastest segmental route for excitatory PAN effects on hind limb 7-motoneurones seems to be di- or trisynaptic, while the path for inhibitory effects seems to be at least one synaps longer. Physiological stimulations of ipsi- and contralateral joint capsules and of ipsilateral cruciate ligaments were all found to evoke frequent and potent changes in spindle afferent responses from the GS and PBSt muscles. It was shown that these effects were due to reflexes onto dynamic and static fusimotor neurones caused by physiological activation of articular sensory endings. Both ipsi- and contralateral joint receptor stimulation evoked excitatory as well as inhibitory fusimotor effects. The highest responsiveness was found during stimula­tion of the cruciate ligaments, i.e. 58% for GS and 47% for PBSt primary spindle afferents to PCL stimula­tion, and 73% for GS and 55% for PBSt primary spindle afferents to ACL stimulation. Significant altera­tions in spindle afferent activity was encountered at very low traction forces applied to the cruciate ligaments (5-10 N). The low thresholds, the tonic character of the stimuli, and the fact that different types of sensory endings were demonstrated in the cruciate ligaments (i.e. Ruffini endings, Pacinian corpuscles, Golgi ten­don organ like endings and free nerve endings), indicate that the fusimotor effects observed were caused by activation of slowly adapting mechanoreceptors, most likely Ruffini endings and/or Golgi tendon organ like endings. The potent reflex effects on the muscle spindle afferents elicited by increased tension in the cruciate ligaments indicate that these ligaments may play a more important sensory role that hitherto believed, and it is suggested that they may be important in the regulation of the stiffness of muscles around the knee joint, and thereby for the joint stability. The possible clinical relevance and the mechanisms by which joint receptor afferents, via adjustment of the muscle stiffness, may control joint stability are discussed. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1989, härtill 7 uppsatser.</p> / digitalisering@umu

In this thesis sensorimotor integration in the human spinal cord was investigated in the intact (Chapters 2 and 3) and injured nervous systems (Chapter 4-stroke; Chapter 5-spinal cord injury (SCI)). In Chapter 2, I characterized a short-latency reflex pathway between sensory receptors of the lower leg and the erector spinae (ES) muscles of the lower back that may play a role in the maintenance of posture and balance. The ES reflexes were evoked bilaterally by taps applied to the Achilles tendon and were modulated by task. Furthermore, these reflexes involved a larger contribution from cutaneous receptors in the lower limb, rather than muscle spindles. In Chapter 3, I investigated changes in reflex transmission along the H-reflex pathway throughout 10 s trains of neuromuscular electrical stimulation (NMES) using physiologically relevant frequencies (5-20 Hz) and during functionally relevant tasks (sitting and standing) and background contraction amplitudes (up to 20% MVC). The results of this study revealed strong post-activation depression of reflex amplitudes, followed by significant recovery during the stimulation, both of which were influenced by stimulation frequency and background contraction amplitude, but not task. During 10 Hz stimulation, reflex amplitudes showed complete recovery (i.e. back to their initial values), and at times, complete recovery occurred by the third reflex in the train. These results demonstrate that transmission along the H-reflex pathway is modulated continuously during periods of repetitive input. In Chapters 4 and 5, I studied the extent to which a novel stimulation protocol that incorporated wide pulse widths (1 ms) and high frequencies (up to 100 Hz) (wide-pulse NMES; WP-NMES), could enhance electrically-evoked contractions through a central contribution in individuals with stroke or SCI. This central effect arises from the electrical activation of sensory axons, which in turn, reflexively recruit motoneurons in the spinal cord. After stroke, contractions evoked by WP-NMES were larger in the paretic arm than the non-paretic arm. After SCI, transmission along the H-reflex pathway was observed throughout trains of WP-NMES; direct evidence of a central contribution. These results suggest that maximizing the central contribution during WP-NMES may be useful for maintaining muscle quality after neurological injury.