问题 单项选择题

在有效不应期

A.无论多么强的刺激都不能引起反应
B.需要阈上刺激才能产生反应
C.不能产生动作电位
D.阈下刺激也可以诱发反应

答案

参考答案:C

解析:[考点] 兴奋性的变化
可兴奋细胞每产生一次兴奋,其膜电位将发生一次一系列周期性变化,膜的离子通道由备用状态经历激活、失活和复活等过程,兴奋性也随之发生相应的周期性变化,兴奋性的周期性变化,影响着可兴奋细胞对重复刺激的反应能力。心肌细胞的兴奋性周期变化有以下几个时期:(1) 绝对不应期,此期心肌对多么强的刺激都不能发生反应;(2) 有效不应期,此期包括绝对不应期和此期后到复极3期膜内电位达到约-60mV这一段时期内,此期内阈上刺激不能引起动作电位,但在膜电位从-55mV恢复达-60mV这一段时期内,阈上刺激可引起膜发生局部反应;(3) 相对不应期,从有效不应期完毕(膜电位约-60mV)到复极化基本上完成(约-80mV)这段时间里,阈上刺激可以引起心肌细胞发生动作电位;(4) 超常期,膜内电位由-80mV恢复到-90mV这一段时期内,阈下刺激即可引起动作电位。

单项选择题 A1/A2型题
阅读理解

阅读理解。

     Skiing only caught on for ordinary Chinese in the mid-1990s in the country's north and northeast, but has

since developed into a pastime that can be practiced nationwide. Here are four resorts (度假胜地) worthy of

consideration.

Yabuli Ski Resort

     The ski resort, built on Yabuli Sun Mountain, part of the Changbai Mountain Range, is located in China's

northernmost province, Heilongjiang.

     It has the best snow quality, skiing trails and impressive views. Wild animals are often spotted on the site.

     The resort serves as the primary training centre for China's national teams. It also has a trail vertical drop

from 200 meters to 1 200 meters with an average drop of 700 meters.

     What's cool: The largest ski resort in China.

Beijing Huaibei International Ski Resort

     This is a great destination for snowboarders and skiers to escape the rush life of the city and is a large

recreational spot that boasts excellent ski slopes, world-class facilities, beautiful natural scenery, as well as

convenient accommodation and dining services.

     Travelers are also able to take a bird's eye view of the Great Wall by catching a cable car along 1 200

meters.

     What's cool: Close to the Great Wall and Beijing's largest ski resort.

Shennongjia Ski Resort

     Opened in 2004, the ski resort is located in the inland of Shermongjia. It covers an area of 100 000 square

meters and is only 0.5 km from the Shennongjia National Nature Reserve.

     There are ski tracks for beginners and more than 20 coaches for tourists. While experiencing the excitement

of skiing, people can also admire Shennongiia's distinctive scenery of countless different odd mountain valleys,

unknown beautiful flowers and plants.

     What's cool: Largest winter sports complex for skiers from South and Central China.

Changbai Mountain Ski Resort

     The ski resort is an ideal place for skiing and ice-skating because of its well-constructed ski tracks,

comprehensive winter sports training facilities and breathtaking environment.

     Enthusiasts can also choose other activities including motor skiing, sleigh skiing, shooting and hunting. The

area's natural hot springs are another attraction of the resort.

     What's cool: The resort is located in the heart of Changbai Mountain Nature Reserve's thick forest and has

natural hot springs.

1. The passage is intended to _____.

A. encourage people to learn skiing during holidays

B. attract people to ski in these places

C. offer services of booking tickets for skiing

D. provide people with a better understanding of skiing

2. In what way is Changbai Mountain Ski Resort different from the other three resorts?

A. It has various training facilities.

B. It has coaches for tourists.

C. It has natural hot springs.

D. It has breathtaking natural scenery.

3. China's national teams are usually trained at _____.

A. Yabuli Ski Resort

B. Shermongjia Ski Resort

C. Changbai Mountain Ski Resort

D. Beijing Huaibei International Ski Resort