Comparison of electromyographic signals from monopolar current and potential amplifiers derived from a penniform muscle,the gastrocnemius medialis

Electromyograms (EMGs) are measured by bipolar surface electrodes that quantify potential differences. Bipolar potentials over penniform muscles may be associated with errors. Our assumption was that muscle activity can be quantified more reliably and with a higher spatial resolution using current measurements.The purpose of this work is: (a) to introduce the concept of current measurements to detect muscle activity, (b) to show the coherences observed over a segment of a typical penniform muscle, the gastrocnemius medialis where one would expect a synchronicity of the activation, and (c) to show the amount of mixing that is caused by the finite inter electrode resistance.A current amplifier was developed. EMGs were recorded at 40% of maximum voluntary contraction during isometric contractions of the gastrocnemius medialis. EMGs of twelve persons were recorded with an array of four peripheral and one central electrode. Monopolar EMGs were recorded for “all-potential”, “center at current” and “all-current” conditions. Coherence revealed the similarity of signals recorded from neighboring electrodes.Coherence was high for the “all-potential”, significant for the “current at center” condition and disappeared in the “all-current” condition.It was concluded that EMG array recordings strongly depends on the measurement configuration. The proposed current amplifier significantly improves spatial resolution of EMG array recordings because the inter-electrode cross talk is reduced.     

Electromechanical Models of the Outer Hair Cell Composite Membrane

The outer hair cell (OHC) is an extremely specialized cell and its proper functioning is essential for normal mammalian hearing. This article reviews recent developments in theoretical modeling that have increased our knowledge of the operation of this fascinating cell. The earliest models aimed at capturing experimental observations on voltage-induced cellular length changes and capacitance were based on isotropic elasticity and a two-state Boltzmann function. Recent advances in modeling based on the thermodynamics of orthotropic electroelastic materials better capture the cell’s voltage-dependent stiffness, capacitance, interaction with its environment and ability to generate force at high frequencies. While complete models are crucial, simpler continuum models can be derived that retain fidelity over small changes in transmembrane voltage and strains occurring in vivo. By its function in the cochlea, the OHC behaves like a piezoelectric-like actuator, and the main cellular features can be described by piezoelectric models. However, a finer characterization of the cell’s composite wall requires understanding the local mechanical and electrical fields. One of the key questions is the relative contribution of the in-plane and bending modes of electromechanical strains and forces (moments). The latter mode is associated with the flexoelectric effect in curved membranes. New data, including a novel experiment with tethers pulled from the cell membrane, can help in estimating the role of different modes of electromechanical coupling. Despite considerable progress, many problems still confound modelers. Thus, this article will conclude with a discussion of unanswered questions and highlight directions for future research.     

Neotropical bromeliads as food sources for birds: a systematic review and perspectives on the management of ecological interactions

The loss of interactions and ecosystem functions is a concerning by-product of pervasive Anthropocene species decline and extinction. Ecological interactions between species sustain the provision of ecosystem processes, especially those mediated by trophic relationships such as pollination and predation. At the local habitat scale, the diversity of natural food sources may increase the diversity of interactions, thus enhancing the stability of local communities and ecosystem functioning. Here I discuss the importance of bromeliads as a potential provider of additional trophic interactions with birds, a key animal group in the Neotropics. Based on 88 studies published between 1965 and 2020 across the Neotropical region, I observed that bromeliads act as ‘wildlife restaurants’ by providing an additional food source throughout the year in almost all Neotropical ecosystems for at least 162 bird species (mostly hummingbirds). These plants (both epiphytic and terrestrial forms) can provide nectar, flowers, water for drinking, invertebrates, small vertebrates, seeds, and fruits, as well as nest materials and substrates. Given these trophic relationships between bromeliads and birds, actions to restore the richness and abundance of these plants in changed habitats would potentially enhance the local diversity of birds. I discuss and recommend the use of bromeliad transplantations as a relevant conservation tool for birds and some implications for the maintenance of species and interaction diversity in natural and agricultural habitats.     

Monopolar electromyographic signals recorded by a current amplifier in air and under water without insulation

It was recently proposed that one could use signal current instead of voltage to collect surface electromyography (EMG). With EMG-current, the electrodes remain at the ground potential, thereby eliminating lateral currents. The purpose of this study was to determine whether EMG-currents can be recorded in Tap and Salt water, as well as in air, without electrically shielding the electrodes. It was hypothesized that signals would display consistent information between experimental conditions regarding muscle responses to changes in contraction effort. EMG-currents were recorded from the flexor digitorum muscles as participant’s squeezed a pre-inflated blood pressure cuff bladder in each experimental condition at standardized efforts. EMG-current measurements performed underwater showed no loss of signal amplitude when compared to measurements made in air, although some differences in amplitude and spectral components were observed between conditions. However, signal amplitudes and frequencies displayed consistent behavior across contraction effort levels, irrespective of the experimental condition. This new method demonstrates that information regarding muscle activity is comparable between wet and dry conditions when using EMG-current. Considering the difficulties imposed by the need to waterproof traditional bipolar EMG electrodes when underwater, this new methodology is tremendously promising for assessments of muscular function in aquatic environments.     

电压钳控制电流钳的设计

研究证明,传统膜片钳放大器在电流钳模式下记录到的快速电压信号会存在失真,且造成失真的根本原因是由于膜片钳的探头电路设计.为了克服这些缺陷重新设计了一种探头,新探头电路不仅能像传统的电压跟随器一样测量瞬态电压,而且适用于传统的电压钳工作模式.此外,一种命名为电压钳控制的电流钳技术被应用来改进传统的膜片钳放大器.用可变的低通滤波器来调整电压钳模块的响应速度,从而在实现膜电位钳位的同时准确记录快速电压信号.桥平衡电路用来消除命令电流流过串联电阻时带来的电压误差.而传统膜片钳中的快电容补偿环节则被改进用来补偿电极分布电容和探头放大器输入电容并提高电流钳模式下系统的响应速度.细胞模型实验结果表明,改进后的膜片钳放大器能够满足电生理研究中快速电位变化测量的需要.     

Novel schemes for hearing and orientation in insects

Severe size constraints are imposed on the hearing organs of insects, yet they perform sophisticated tasks of auditory processing. Recent research has shown how flies acoustically locate targets in space, how mosquitoes afford highly sensitive ears, and how crickets avoid deafening themselves with their songs. These findings unveil the exquisite analytical capabilities of highly specialized microscale auditory systems.     

The generation of DPOAEs in the locust ear is contingent upon the sensory neurons

Tympanal organs of insects emit distortion-product otoacoustic emissions (DPOAEs) that are indicative of nonlinear ear mechanics. Our study sought (1) to define constraints of DPOAE generation in the ear of Locusta migratoria, and (2) to identify the sensory structures involved. We selectively destroyed the connection between the (peripheral) sensory ganglion and the tympanal attachment points of the “d-cell” dendrites; d-cells are most sensitive to sound frequencies above 12 kHz. This led to a decrease of DPOAEs that were evoked by f ₂ frequencies above 15 kHz (decrease of 15–40 dB; mean 28 dB; n = 12 organs). DPOAEs elicited by lower frequencies remained unchanged. Such frequency-specific changes following the exclusion of one scolopidial sub-population suggest that these auditory scolopidia are in fact the source of DPOAEs in insects. Electrical stimulation of the auditory nerve (with short current pulses of 4–10 μA or DC-currents of 0.5 μA) reversibly reduced DPOAEs by as much as 30 dB. We assume that retrograde electrical stimulation primarily affected the neuronal part of the scolopidia. Severing the auditory nerve from the central nervous system (CNS) did not alter the DPOAE amplitudes nor the effects of electrical stimulation.