Static and dynamic responses of slowly adapting joint receptors

1. (1) A systems analysis approach was used to study slowly adapting knee joint receptors. Transfer functions were obtained from the receptor response to sinusoidal inputs of knee joint angle over a range of frequencies from 0.01 to 7 Hz.2. (2) The Bode plots obtained in the dynamic studies revealed a high pass filter characteristic with a magnitude slope on the order of 5 dB/decade and a phase lead on the order of 22.5[deg]. The gain of the transfer function was found to be influenced by both the input angle excursion and the static bias angle.3. (3) The static angle sensitivity curves of the receptors were found to be `bell shaped' in some cases and to increase or decrease monotonically with joint angle in other cases.4. (4) The static sensitivity curve produced by a series of positive increments of joint angle was not the same as the static sensitivity curve produced by a series of negative increments of joint angle. Tentatively this finding is attributed to a non-Newtonian viscoelastic effect and is felt to limit the information available from a single, peripheral receptor.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22368/1/0000815.pd

The use of fuzzy control system methods for characterizing expert judgment uncertainty distributions

Fuzzy logic methods permit experts to assess parameters affecting performance of components/systems in natural language terms more familiar to them (e.g., high, good, etc.). Recognizing that there is a cost associated with obtaining more precise information, the authors particular interest is in cases where the relationship between the condition of the system and its performance is not well understood, especially for some sets of possible operating conditions, and where developing a better understanding is very difficult and/or expensive. The methods allow the experts to make use of the level of precision with which they understand the underlying process. The authors consider and compare various methods of formulating the process just described, with an application in reliability analysis where expert information forms a significant (if not sole) source of data for reliability analysis. The flow of information through the fuzzy-control-systems based analysis is studied using a simple, hypothetical problem which mimics the structure used to elicit expert information in Parse. They also characterize the effect of using progressively more refined information and examine the use of fuzzy-based methods as data pooling/fusion mechanisms

Electrocorticogram as the Basis for a Direct Brain Interface: Opportunities for Improved Detection Accuracy

A direct brain interface (DBI) based on the detection of event-related potentials (ERPs) in human electrocorticogram (ECoG) is under development. Accurate detection has been demonstrated with this approach (near 100% on a few channels) using a single-channel cross-correlation template matching (CCTM) method. Several opportunities for improved detection accuracy have been identified. Detection using a multiple-channel CCTM method and a variety of detection methods that take advantage of the simultaneous occurrence of ERPs and event-related desynchronization/synchronization (ERD/ERS) have been demonstrated to offer potential for improved detection accuracy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85993/1/Fessler183.pd

Direct observation of microtubule-f-actin interaction in cell free lysates

Coordinated interplay of the microtubule and actin cytoskeletons has long been known to be crucial for many cellular processes including cell migration and cytokinesis. However, interactions between these two systems have been difficult to document by conventional approaches, for a variety of technical reasons. Here the distribution of f-actin and microtubules were analyzed in the absence of fixation using Xenopus egg extracts as an in vitro source of microtubules and f-actin, demembranated Xenopus sperm to nucleate microtubule asters, fluorescent phalloidin as a probe for f-actin, and fluorescent tubulin as a probe for microtubules. F-actin consistently colocalized in a lengthwise manner with microtubules of asters subjected to extensive washing in flow chambers. F-actin-microtubule association was heterogenous within a given aster, such that f-actin is most abundant toward the distal (plus) ends of microtubules, and microtubules heavily labeled with f-actin are found in close proximity to microtubules devoid of f-actin. However, this distribution changed over time, in that 5 minute asters had more f-actin in their interiors than did 15 minute asters. Microtubule association with f-actin was correlated with microtubule bending and kinking, while elimination of f-actin resulted in straighter microtubules, indicating that the in vitro interaction between f-actin and microtubules is functionally significant. F-actin was also found to associate in a lengthwise fashion with microtubules in asters centrifuged through 30% sucrose, and microtubules alone (i.e. microtubules not seeded from demembranated sperm) centrifuged through sucrose, indicating that the association cannot be explained by flow-induced trapping and alignment of f-actin by aster microtubules. Further, cosedimentation analysis revealed that microtubule-f-actin association could be reconstituted from microtubules assembled from purified brain tubulin and f-actin assembled from purified muscle actin in the presence, but not the absence, of Xenopus oocyte microtubule binding proteins. The results provide direct evidence for an association between microtubules and f-actin in vitro, indicate that this interaction is mediated by one or more microtubule binding proteins, and suggest that this interaction may be responsible for the mutual regulation of the microtubule and actomyosin cytoskeletons observed in vivo

Endothelial cells use dynamic actin to facilitate lymphocyte transendothelial migration and maintain the monolayer barrier

The vascular endothelium is a highly dynamic structure, and the integrity of its barrier function is tightly regulated. Normally impenetrable to cells, the endothelium actively assists lymphocytes to exit the bloodstream during inflammation. The actin cytoskeleton of the endothelial cell (EC) is known to facilitate transmigration, but the cellular and molecular mechanisms are not well understood. Here we report that actin assembly in the EC, induced by Arp2/3 complex under control of WAVE2, is important for several steps in the process of transmigration. To begin transmigration, ECs deploy actin-based membrane protrusions that create a cup-shaped docking structure for the lymphocyte. We found that docking structure formation involves the localization and activation of Arp2/3 complex by WAVE2. The next step in transmigration is creation of a migratory pore, and we found that endothelial WAVE2 is needed for lymphocytes to follow a transcellular route through an EC. Later, ECs use actin-based protrusions to close the gap behind the lymphocyte, which we discovered is also driven by WAVE2. Finally, we found that ECs in resting endothelial monolayers use lamellipodial protrusions dependent on WAVE2 to form and maintain contacts and junctions between cells