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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 383 (1996), S. 71-72 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Tail shaking by the western diamondback rattlesnake (Crotalus atrox) produces a noise at frequencies audible to large mammals4'5. Rattling is accomplished by unfused, high-frequency muscular contractions, made possible by an extraordinarily high density of sarcoplasmic reticulum and T tubules (26% ...
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Key words MVC maximum voluntary contraction ; Myosin heavy chains ; Magnetic resonance imaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Humans produce less muscle force (F) as they age. However, the relationship between decreased force and muscle cross-sectional area (CSA) in older humans is not well documented. We examined changes in F and CSA to determine the relative contributions of muscle atrophy and specific force (F/CSA) to declining force production in aging humans. The proportions of myosin heavy chain (MHC) isoforms were characterized to assess whether this was related to changes in specific force with age. We measured the peak force of isokinetic knee extension in 57 males and females aged 23–80 years, and used magnetic resonance imaging to determine the contractile area of the quadriceps muscle. Analysis of MHC isoforms taken from biopsies of the vastus lateralis muscle showed no relation to specific force. F, CSA, and F/CSA decreased with age. Smaller CSA accounted for only about half of the 39% drop in force that occurred between ages 65–80 years. Specific force dropped about 1.5% per year in this age range, for a total decrease of 21%. Thus, quantitative changes in muscle (atrophy) are not sufficient to explain the strength loss associated with aging.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 155 (1985), S. 423-431 
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Thermal conductance was subdivided into the component conductances of the appendages and torso using a heat transfer analysis for the deer mouse,Peromyscus maniculatus, and the white rabbit,Oryctolagus cuniculus. Our analysis was based on laboratory measurements of skin temperature and respiratory gas exchange made between air temperatures of 8 and 34°C for the deer mouse, and from published data for the white rabbit. Two series conductances to heat transfer for each appendage and torso were evaluated: (1) internal (h in), for blood flow and tissue conduction to the skin surface, and (2) external (h ex), for heat loss from the skin surface to the environment. These two series conductances were represented in a single, total conductance (h tot). The limit toh tot was set byh ex and was reached by the torsoh tot of both animals. The increase in torsoh tot observed with air temperature for the mouse suggests that a pilomotor change in fur depth occurred. A control ofh tot below the limit set byh ex was achieved by theh in of each appendage. Elevation of mouse thermal conductance (C) resulted from increases in feet, tail, and torsoh tot. In contrast, the rabbit showed no change in torsoh tot between 5 and 30°C and earh tot exclusively increasedC over these air temperatures. We suggest that the hyperthermia reported for the rabbit at 35°C resulted fromC reaching the physical limit set by torso and nearh ex. Thus the ear alone adjusted rabbitC, whereas the feet, tail, and the torso contributed to the adjustment of mouseC.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 155 (1985), S. 433-436 
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Using a physical model of the capacity for non-evaporative heat loss and measurements of metabolic heat production, I evaluated the evaporative requirements for thermoregulation in the deer mouse,Peromyscus maniculatus, and the white rabbit,Oryctolagus cuniculus. The physical limit to non-evaporative heat loss was calculated from the heat transfer properties of the two animals and expressed as a maximum thermal conductance (C max). Two physiologically-based thermal conductances were derived from evaporative water loss, respiratory gas exchange and core temperature measurements made between 8 and 34°C on the deer mouse, and taken from published data for the white rabbit. The thermal conductance for non-evaporative heat loss (C) was calculated from net heat production, whereasC m represented the thermal conductance required to dissipate metabolic heat production. Evaporation is required when metabolic heat production exceeds the capacity for non-evaporative heat loss (as shown byC m〉C max). However, evaporation increased in both animals although additional capacity to lose heat remained (i.e.,C〈C max). Evaporation increased withC above 30°C for the mouse and at each 5°C measurement interval from 15 to 30°C for the rabbit. Thus, evaporation was greater than that required for thermoregulation for both animals as determined from a physical model of heat loss because both evaporation andC increased together to regulate heat loss.
    Type of Medium: Electronic Resource
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