Mechanical properties vary for different regions of the finger extensor apparatus

The extensor apparatus, an aponeurosis that covers the dorsal side of each finger, transmits force from a number of musculotendons to the phalanges. Multiple tendons integrate directly into the structure at different sites and the extensor apparatus attaches to the phalanges at multiple points. Thus, prediction of the force distribution within the extensor apparatus, or hood, and the transmission to the phalanges is challenging, especially as knowledge of the underlying mechanical properties of the tissue is limited. We undertook quantification of some of these properties through material testing of cadaver specimens. We punched samples at specified locations from 19 extensor hood specimens. Material testing was performed to failure for each sample with a custom material testing device. Testing revealed significant differences in ultimate load, ultimate strain, thickness, and tangent modulus along the length of the extensor hood. Specifically, thickness, ultimate load, and ultimate strain were greater in the more proximal sections of the extensor hood, while the tangent modulus was greater in the more distal sections. The variations in mechanical properties within the hood may impact prediction of force transmission and, thus, should be considered when modeling the action of the extensor apparatus. Across the extensor hood, tangent modulus values were substantially smaller than values reported for other soft tissues, such as the Achilles tendon and knee ligaments, while ultimate strains were much greater. Thus, the tissue in the extensor apparatus seems to have greater elasticity, which should be modeled accordingly.     

Snapping shrimp have helmets that protect their brains by dampening shock waves

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A reappraisal of the strength-duration test to assess neuromuscular impairment of critically ill patients

IntroductionNeuromuscular impairment (NMI) affects almost half of critically ill patients. The purpose was to investigate the role of neuromuscular electrical stimulation (NMES) to gain more insight into the nature of the NMI associated with ICU admission. To this aim, we analyzed the strength-duration (S-D) curves of the rectus femoris muscles of ICU patients compared to healthy volunteers.MethodsS-D curves were recorded from 44 healthy volunteers and 29 ICU patients. Three electrophysiological parameters were used to classify the neuromuscular function, from grade 0 (normal function), to grade 3 (no evocable muscle contraction). ICU patients underwent electroneurographic peroneal nerve testing (PENT) to analyze NMI by electroneurography (ENG).ResultsThree patients were classified as Grade 0; nine as mild NMI (Grade 1), 13 as Grade 2, and four showed unexcitable muscles (Grade 3). Mean CMAP amplitudes were 6.1, 3.4, 2.9 and 0.81 mV from Grade 0 to Grade 3, respectively. CMAP was inversely correlated to NMI grade (−1.7 mV, R² = 0.946, p < 0.05).ConclusionsThe normative parameters of the S-D curves obtained by NMES in healthy volunteers allowed identification of NMI in ICU patients. NMES was an affordable tool to evaluate NMI in ICU patients, providing additional information to that obtained by ENG.     

Floral mimesis inThelymitra nuda (Orchidaceae)

Insect pollination occurred inThelymitra nuda R. Br. on sunny days when the ambient temperature exceeded 20 °C. The flower buds on a raceme opened subsynchronously displaying the brightly-colored, actinomorphic perianth and exposed the contrastingly-colored, scented and ornamented column. InT. nuda the staminodes and the filament of the fertile stamen are fused to one another producing an inflated hood over the anther. This staminodal hood is terminated in two non-ornamental, but brightly-colored, central lobes and two terete lateral lobes bearing approximately 400 white trichomes. Each trichome bears a double chain of 30–40 spherical, rugulose cells. Female bees, in the genusLasioglossum (Halictidae), were observed to land directly on the hood and curled their bodies around the four lobed tip of the staminodal complex. The bees attempted to forage on the lobes as if they were collecting pollen from fertile, poricidal stamens. These bees applied thoracic vibration to the yellowish central lobes and actively scraped the trichome clusters (Pseudopollen) with their forelegs. Bees carried the pollinaria ofT. nuda dorsally on their abdomens. Abdominal contact with the rostellum appeared to occur when the female bee disengaged herself from the staminodal hood. Observations made of bees on co-blooming flowers, and analyses of pollen loads collected by bees suggested that the orchid flower mimics the guild of blue-purple flowers that lack floral nectar but offer pollen in poricidal anthers. The models ofT. nuda are co-bloomingLiliaceae in the generaDichopogon andThysanotus. However, nectarless, buzz-pollinated flowers are also extensively distributed over the orchid’s range. More than 30% of the flowers in theT. nuda population had their pollinaria removed, suggesting a high capacity for cross-pollination in an orchid genus usually considered to be self-pollinated via mechanical autogamy. This study confirmed previous predictions that column modifications represented a trend towards pseudanthery.