Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-1106
    Keywords: Event-related potentials ; Readiness potential ; Movement preparation ; Supplementary motor area ; Motor cortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In two experiments movement-related cortical potentials preceding voluntary movement were recorded. In experiment 1, subjects performed four motor tasks involving joystick movements. The four tasks differed in complexity (single vs sequential movements) and in the mode of movement selection, i.e., whether a movement or movement sequence was made in fixed or in self-determined directions. The choice of these tasks was based, firstly, on previous electrophysiological studies suggesting an effect of task-complexity on the amplitude of the readiness potential (RP) and, secondly, on previous positron emission tomography (PET) studies showing that activity of the supplementary motor area (SMA) is influenced by the mode of movement selection. The results show that, for single movements, RP amplitude is higher preceding freely selected movements than preceding movements in a fixed direction. In experiment 2 this effect was replicated using button presses instead of joystick movements. The results converge with PET evidence obtained in similar tasks and establish that the RP is modulated by the mode of movement selection. This modulation is probably related to differential involvement of the SMA.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1432-0533
    Keywords: Peripheral nerve ; Expansion ; Elongation ; Paranodal widening ; Remyelination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Peripheral nerve elongation by a tissue expander may offer an alternative to nerve grafting in the management of segmental nerve loss. We investigated the morphological changes in peripheral nerve following slow nerve elongation by laser Doppler flowmetry controlled expansion in a rabbit sciatic nerve model. The animals were randomly assigned to one of four groups, with an expander volume of 0, 5, 10 or 15 cm3, respectively. An elongation of up to 40% was possible with preservation of clinical function. Nerve conduction velocity decreased in relation to elongation. Paranodal widening, followed by remyelination of the node, were early and constant morphological features. Demyelination and remyelination of whole internodes, and axonal degeneration occurred sporadically and did not correlate with elongation, rate of elongation or neurophysiological parameters. The model of laser Doppler flowmetry controlled nerve expansion provides a method for remodelling of myelin sheaths and lengthening of nerve fibers without axonal damage.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1432-0533
    Keywords: Key words Peripheral nerve ; Expansion ; Elongation ; Paranodal widening ; Remyelination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Peripheral nerve elongation by a tissue expander may offer an alternative to nerve grafting in the management of segmental nerve loss. We investigated the morphological changes in peripheral nerve following slow nerve elongation by laser Doppler flowmetry controlled expansion in a rabbit sciatic nerve model. The animals were randomly assigned to one of four groups, with an expander volume of 0, 5, 10 or 15 cm3, respectively. An elongation of up to 40% was possible with preservation of clinical function. Nerve conduction velocity decreased in relation to elongation. Paranodal widening, followed by remyelination of the node, were early and constant morphological features. Demyelination and remyelination of whole internodes, and axonal degeneration occurred sporadically and did not correlate with elongation, rate of elongation or neurophysiological parameters. The model of laser Doppler flowmetry controlled nerve expansion provides a method for remodelling of myelin sheaths and lengthening of nerve fibers without axonal damage.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract In order to study the motor unit action potential a computer simulation model was developed. It is based on the superposition of single muscle fibre potentials of the fibres belonging to the motor unit. The parameters which characterize each fibre (spatial position, diameter, and a dispersion of arrival time of the potential at the electrode) are chosen from statistical distributions which can be derived from anatomical and physiological data. The electrode type, position and dimensions can be specified. Simulated motor unit action potentials are presented in the time and frequency domain. The simulation results refer to (1) the influence of the electrode position and dimensions with respect to the motor unit territory, (2) the meaning of this model for the study of pathological phenomena, (3) the variability of some parameters characterizing the motor unit, (4) the selectivity of uni- and bipolar electrodes and finally (5) the influence of the geometrical situation of the motor end-plates within the muscle, on the shape of motor unit action potentials.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A computer model for the simulation of compound nerve action potentials, based on superposition of volume conducted single nerve fibre potentials, is presented. The model assumes that the intracellular fibre potential, the fibre diameter distribution and the electrical conductivities of different tissues are known. Volume conductor fields are calculated in the spatial frequency domain. The influence of important parametrrs in the model is evaluated numerically. It is shown that it is necessary to give up the usual assumption of homogeneity and isotropy in the extracellular medium. In the present model parameters are introduced which allow an overall description of the complex morphological and physiological structure of the nerve trunk. Simulation results indicate that the model is a rather promising tool in studying the main properties of compound action potentials which up till now have not been sufficiently well understood.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1433-8491
    Keywords: Dermatome ; Somato sensory evoked potential (SEP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We describe a method for obtaining cortical evoked potentials after stimulation of the lumbosacral and cervical dermatomes in healthy volunteers. Such dermatomal evoked potentials are expected to contribute to the diagnosis of lumbar and cervical root entrapment. Normative data are presented for each dermatome including left-right differences. A significant correlation was found between absolute latencies and body length for the lumbosacral segments. This correlation was virtually absent in the cervical segments. The latency difference between the same cervical or lumbosacral dermatome left and right was also independent of body length for all segments.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    ISSN: 1573-9686
    Keywords: Muscle fiber action potentials ; Needle electrodes ; Volume conduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Needle recorded electromyographic signals can be expected to be influenced by the presence of the needle, the electrical double layer at the metal-electrolyte interface, and by an edematous layer around the needle electrode. The magnitude of each of these effects is derived from a cylinder symmetrical volume conductor model. Analytical solutions of Laplace's equation have been derived. These are used for simulating single muscle fiber action potentials (SFAPs) recorded by a typical single fiber electrode. The results indicate that there is no short-circuiting effect, in spite of the presence of a highly conducting needle shaft, which is due to the high impedance of the electrical double layer. The insulating properties of the double layer cause the SFAP amplitudes to increase, when the muscle fiber passes the electrode at the side of the leading-off point. The edematous layer counteracts this increase depending on the thickness and the conductivity of this layer. Only slight SFAP waveform changes are found.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 1573-9686
    Keywords: Parameter estimation ; Single muscle fiber action potentials ; Multielectrode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract From regular one-channel registrations of single muscle fiber action potential no measures on the recording configuration can be derived. When multichannel recordings are made, experimental parameters such as the distance between muscle fiber and needle electrode can be estimated. With the help of a volume conductor model, the single fiber activity at each of the electrodes can be predicted as a function of the recording conditions. Within known physical and physiological constraints such a model approach can be inverted (the inverse model) and used to estimate basic experimental conditions. From eight simultaneous single fiber action potential recordings we estimated (a) the distance between fiber and needle, (b) the axial position of the needle with respect to the muscle fiber, (c) a factor related to the muscle tissue anisotropy, and (d) a factor combining the muscle fiber diameter and the effective muscle tissue conductivity. With the help of a model describing the influence of the needle shaft it is made plausible that the needle inhomogeneity influences the results of the proposed procedure.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electromyography (EMG) system is presented that noninvasively records the electrical activity of a muscle with 126 densely spaced skin-surface electrodes. The electrodes are arranged in a two-dimensional array and integrated in a single container for ease of application. Signals are recorded "monopolarly", with a reference electrode placed at a distance from the array. With this recording configuration, the surface EMG (sEMG) potential distribution can be described not only as a function of time, but also topographically. The availability of topographical information opens up a range of applications. Some of these have been described previously. However, the system presented is unique in that it allows exploration of all clinical and scientific possibilities of topographical sEMG. In its design, special attention was paid to user-friendliness and flexibility. With high-density multichannel sEMG, both the properties of a whole muscle and those of single motor units, the functional units of a muscle, can be studied. The latter belong to a realm that was long considered accessible only with needle-EMG, a conventional, invasive diagnostic technique. It is demonstrated that the additional topographical information can be used to characterize motor units in a way that is partially superior to needle EMG. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2724-2731 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Potential distributions around a model nerve fiber are computed by using analytical methods. The fiber is situated either in a homogeneous isotropic unbounded conductor or in a homogeneous isotropic cylinder. In the latter case the source is placed either centrically or eccentrically. The potential distributions are used to derive the precise electric field distribution. The results are presented in equipotential and field line maps. It is described how the inherent numerical problems in the calculations can be avoided. It is demonstrated that the boundaries of the volume conductor and the nature of the source (potential source, current source) can significantly influence the field, even at large distances from this source.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...