问题 问答题 简答题

什么是阈值?什么是阈电位?

答案

参考答案:

固定刺激的持续时间和强度一时间变化率后,刚刚引起组织兴奋产生动作电位所需要的最小刺激强度称为阈强度,又称阈值。或者说刚刚能使细胞膜的静息电位除极到阈电位而引发动作电位时的外加刺激强度称为阈强度,或称阈值。细胞膜由静息电位减少(除极)到刚能引发动作电位时的临界膜电位称为阈电位。通常认为,阈电位的数值比静息电位小10~20mV,例如骨骼肌和心室肌细胞的静息电位为-90mV,其阈电位为-70mV。一般来说,细胞兴奋性的高低与阈值互呈反变关系,与静息电位至阈电位的差值也呈反变关系

单项选择题 B型题
单项选择题

Now which are the animals really to be pitied in captivity First, those clever beings whose lively urge for activity can find no outlet behind the bars of the cage. This is most conspicuous, even for the uninitiated, in the case of animals which, when living in a free state, are accustomed to roaming about widely. Owing to this frustrated desire, foxes and wolves housed, in many old-fashioned zoos, in cages which are far too small, are among the most pitiable of all caged animals.
Though pinioned swans generally seem happy, under proper care, by hatching and rearing their young without any trouble, at migration time things become different: they repeatedly swim to the lee side of the pond, in order to have the whole extent of its surface at their disposal, trying to take off. Again and again the grand preparations end in a pathetic flutter of their half wings ; a truly sorry picture !
This, however, rarely awakens the pity of the zoo visitor, least of all when such an originally highly intelligent and mentally alert animal has deteriorated, in confinement, into a crazy idiot, a very caricature of its former self. Sentimental old ladies, the fanatical sponsors of the societies for Prevention of Cruelty to Animals, have no compunction in keeping a grey parrot in a relatively small cage or even chained to a perch. Together with the large corvines, the parrots are probably the only birds which suffer from that state of mind, common to prisoners, namely, boredom.

According to the author in Paragraph 1, what animals suffer most in captivity

A. Climbing animals.
B. Hunting animals.
C. Parroting animals.
D. Singing animals.