问题 问答题 简答题

何谓肌紧张?试述肌紧张的生理意义、产生机制和调节。

答案

参考答案:

肌紧张的概念:肌紧张是指缓慢、持续牵拉肌腱时所发生的牵张反射。其表现为骨骼肌经常处于一定程度的持续收缩状态,从而产生一定的张力,故又称为肌张力。

其生理意义是:维持身体的姿势,并作为一切躯体运动反射的基础。

肌紧张的产生机制:缓慢、持续牵拉肌腱,如股四头肌肌腱,使被牵拉肌肉(如股四头肌)内的感受器肌梭兴奋,冲动经Ⅰa类和Ⅱ类纤维传入脊髓,通过两个以上的中间神经元及突触接替,再兴奋脊髓前角的α运动神经元,使其所支配的受牵拉肌肉的梭外肌(慢肌)纤维收缩,肌紧张或肌张力产生。

肌紧张的调节:①脊髓,由脊髓前角发出的γ运动神经元支配梭内肌纤维,γ运动神经元兴奋→梭内肌纤维收缩→肌梭对牵拉刺激的敏感性提高→维持了传入纤维和传出纤维的放电频率,维持了肌紧张。

②脑干及其以上水平,脑干网状结构内存在调节肌紧张和肌运动的两个区域,分别称为易化区和抑制区。易化区范围较大,其作用是加强肌紧张和肌肉运动,同时它接受来自前庭核和小脑前叶两侧部的兴奋冲动;抑制区范围较小,其作用是抑制肌紧张和肌肉运动,同时它接受来自大脑皮质运动区、纹状体和小脑前叶蚓部的激动冲动,在正常机体内二者功能基本平衡,并通过下行纤维保持了脊髓(α和γ)运动神经元的传出活动,保持了肌紧张。易化区和抑制区任何一方的下行冲动发生改变时,肌紧张及肌肉运动也将发生相应的变化。

单项选择题

An Indian anthropologist, Chandra Thapar, made a study of foreign cultures, which had customs similar to (91) of his native land. One culture in (92) fascinated him because it reveres one animal (93) sacred, much as the people in India (94) the cow. The things he discovered might interest you (95) you will be studying India as part of this course.
The tribe Dr. Thapar (96) is called the Asu and is found on the American continent north of the Tamhumara of Mexico. Though it seems to be a (97) developed society of its type, it has an overwhelming (98) with the care and feeding of the rac—an animal much like a bull in size, strength and temperament. In the Asu tribe, it is almost a social (99) to own at least one (100) not more rats. People not possessing at least one are (101) in low esteem by the community because they are too poor to (102) one of these beasts properly. Some members of the tribe, to (103) their wealth and social prestige, even own (104) of racs.
(105) the rac breed is not very healthy and usually does not live more than five to seven years. Each family invests large (106) of money each year to keep its rac healthy and shod, for it has a tendency to throw its shoes often. There are rac (107) in each community, perhaps more than one if the community is particularly (108) . These specialists, however, due to the long period of ritual training they must undergo and (109) the difficulty of obtaining the right selection of charms to treat the rac, demand (110) offerings whenever a family must treat an ailing rac.

A.held

B.taken

C.viewed

D.looked upon

单项选择题