77 research outputs found
Extracellular current flow and the site of transduction by vertebrate hair cells
No full textThe transduction process of a vertebrate hair cell commences with the application of mechanical stimuli to the hair bundle, a cluster microvillous stereocilia and single axonemal kinocilium. In an effort to determine where within the hair bundle transduction occurs, I have measured extracellular potentials around the hair bundles of mechanically stimulated hair cells from the bullfrog's sacculus. Stimulus-dependent signals up to 17 microV in peak-to-peak amplitude have been found. These appear to be due to the flow of transduction current on the basis of their amplitude, phase, dependence on stimulus size and orientation, proportionality to membrane potential, and sensitivity to an ototoxic antibiotic. The responses are consistently larger near the top of the hair bundle than at its base, suggesting that the transduction apparatus lies at or near the distal ends of the stereocilia.</jats:p
Analysis of the microphonic potential of the bullfrog's sacculus
No full textThe sensory epithelium from the bullfrog's sacculus was mounted between two chambers and stimulated by moving the otolithic membrane with a piezoelectric stimulator. The evoked response was measured as the transepithelial “microphonic” potential or, when the epithelium was voltage clamped, as the microphonic current. Microphonic responses were similar to those recorded in other preparations: the whole organ produced a “2f” response (i.e., a response of a frequency twice that of the stimulus) which could be changed to a single-polarity response by stimulating cells of a single polarity; the response saturated asymmetrically with displacement, producing a rectification; and the amplitude declined at high and low frequencies. To determine the cellular elements responsible for generation of the microphonic potential, the equivalent circuit of the epithelium was estimated from morphological and electrophysiological data, and responses to step displacement stimuli were recorded. Four elements in particular shape the microphonic potential: the complex impedance of the extracellular current path, the saturating displacement-conductance curve, an adaptation mechanism which shifts that curve, and a voltage-dependent K+ conductance in the basolateral hair cell membrane. A quantitative model incorporating these elements accurately reproduces the observed responses.</jats:p
Kinetics of the receptor current in bullfrog saccular hair cells
No full textThe receptor current of hair cells from the bullfrog's sacculus was measured by voltage clamp recording across the isolated sensory epithelium. Several hundred hair cells were stimulated en masse by moving the overlying otolithic membrane with a piezoelectrically activated probe. As measured by optical recording of otolithic membrane motion, the step displacement stimuli reached their final amplitudes of up to 1 micrometer within 100 microseconds. The relationship between displacement and steady-state receptor current is an asymmetric, sigmoidal curve about 0.5 micrometer in extent. The time constant of the approach to steady state depends upon the magnitude of the hair bundle displacement and ranges from 100 to 500 microseconds at 4 degrees C; the time course is faster with larger displacements or at higher temperatures. Both the displacement-response curve and the kinetics of the response are changed by alterations in the Ca2+ concentration at the apical surface of the cells. The characteristics of the response are not consistent with simple models for the transduction process that involve enzymatic regulation of channel proteins or diffusible second messengers. Mechanical stimulation is instead posited to act directly by altering the free energy difference between the open and closed forms of the transduction channel, thereby inducing a redistribution between these states. The dependences of the response kinetics on displacement and on temperature suggest that the thermal interconversion between open and closed transduction channels is limited by an enthalpy of activation of about 12 kcal/mol.</jats:p
Frequency decoding of periodically timed action potentials through distinct activity patterns in a random neural network
No full text21.08.14 KB. Ok to add published version to spiral , OA pape
Transforming Difficult Conversations into Learning Conversations
No full textIt’s an image that is by no means uncommon: “the social justice conversation gone wrong,” the sort of political and/or religious argument that escalates and ultimately fails to broaden either party’s perspective. In this presentation, the presenters will illustrate: 1) what causes these “difficult social justice conversations,” 2) why these conversations are ineffective, 3) recommended behaviors designed to change these difficult conversations into impactful and transformative social justice conversations, and 4) a scientific overview highlighting why the recommended techniques are effective for promoting belief change regarding social justice
Avaliação de três tipos de tratamento na peritonite experimental em ratos Wistar.
No full textTrabalho de Conclusão de Curso - Universidade Federal de Santa Catarina, Centro de Ciências da Saúde, Departamento de Clínica Cirúrgica, Curso de Medicina, Florianópolis, 200
- …
