题干

如图一为人体手背皮肤(A)接受一定刺激后引起肱二头肌(E)发生收缩而产生屈肘动作的神经传导路径示意图.图二为从蛙体内剥离出某反射弧的一部分,甲为神经中枢,1、2、3、4为四个实验位点.请据图回答下列问题:

(1)在F处发生的信号变化是____ ,其兴奋的传递方向是单向的,原因是____ .

(2)受寒冷刺激上时,冷觉感受器对____ 离子的通透性增强,膜电位发生变化.动作电位沿神经纤维传导时,神经纤维细胞膜内侧局部电流的方向与动作电位传导方向____ (填相同或相反).

(3)欲探究图二中左侧神经为传入神经还是传出神经,方法步骤是:

①将微电流计的电极分别搭在实验位点2和3的神经纤维外(每个实验位点只能用一次);

②用电刺激实验位点4,若微电流计的指针偏转____ 次,则左侧神经元为传出神经.

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同类题1

根据短文理解,选择正确答案。

    Children in the United States eat too much pizza that some researchers now argue the food should join the ranks of sugary drinks and fast food for the harm they do to health.

    In a new study, the researchers found that pizza is a large source of calories, saturated fat(饱和脂肪)and salt in children's diets.Children should not eat more than two slices of pizza for a meal,and should pair that with salad, rather than with another high-calorie food,the researchers concluded.

    “Parents should aim to control pizza consumption(消费), particularly as a snack where it was shown to have a very adverse impact on children, and they should put their pizza dollars toward healthier brands.”Said Lisa Powel, director of the Illinois Prevention Research Center.

    Pizza has become a matter of focus in recent years for researchers who look at the meals children eat, rather than the nutrients within them.Studies have found pizza is among the greatest sources of calories for children.

    “Since pizza remains a common part of children's diet, we need to make 'healthy' pizza.”Powel said.To make pizza healthier, food producers should reduce its saturated fat and salt, and increase its whole grain content,” she said.

    Whether or not pizza is harmful enough to be picked out as an unhealthy food, the study attracts attention to a larger issue with the modern American lifestyle, said Alexis Tindall, who was not involved in the flow research. “Many foods are eaten too frequently and in large sizes,” said Tindall.To solve the problem, people don't have to give up eating pizza, but instead, they can eat smaller and healthier pizza,”she said.

    “Make it at home, instead of ordering it out where you don't have any control over how it's made.” Tindall said. “When we make it at home, we can choose healthier ingredients,increase the vegetables, reduce fat, and put in less cheese.Pizza doesn't have to be just pepperoni(意大利辣香肠)and cheese.”

同类题2

阅读下文,回答问题

父亲的斧头

    一把斧头完成的最后一道工序是淬火

    父亲的习惯是把一把刚刚淬过火的崭新斧头钳起来,将斧头对准砧子后的那尖角,在那上面用力啃一啃,看这把斧头的钢口如何,它能否吃得动这铁。

    正因为这样,那只砧子的尖角斧痕累累,刚刚削过的新痕泛着银白。而那把父亲才试过后用力抛在地上的斧头还很烫手,新斧头发着蓝光。

    这时候,父亲瞅一眼躺在前面的斧头,一只脚踩在砧墩上,端起那只水烟锅,咕嘟咕嘟抽起烟来。而此时,我就能歇歇手,赶快离开打铁铺,跑到大门外边去。我始终想远离这丁当作响的日子,跑到外面的世界闯荡。那时候我像一把刚刚打造好的斧头,准备磨快刃子,等待机会,狠狠砍生活两斧头。

    一次,放了暑假,父亲要我给他搭下手,打造一批镰刀。满山遍野的庄稼都黄了,都在等待镰刀来收割。人们需要镰刀,庄稼更需要镰刀,金黄的麦子都张了口,几乎要叫出声来。父亲心里很着急。我不在乎这些,我想我的事。

    我对父亲说,我不想打镰刀,我想去采药。我想像着采到了一大麻袋药。那时候我们那里的秦艽正在卖着好价线,我想自己挣回自己的学费。我觉着打镰刀挺费事的。

    父亲并没有反对我去采药。他说,去吧,去干你爱干的事。

    其实,我不知道什么是我爱干的事。比如说父亲,打一把斧头,打一张镰刀,然后抽一锅水烟,临睡时喝二两烧酒。这些他都肯定爱干,而且每样都干得从容不迫。找呢?截止那一个秋天,还没有干成一件事。我总是喜欢想入非非。

    我打定了主意去采药。我在离家二十里的山上转悠了三天就没有耐心了。别人总在低头工作,而我却怎么也找不到药,那些长在灌木中的药材总是与我擦身而过。

    二十里外我似乎听到父亲锻打镰刀的声音。我想,那些刚刚打好的镰刀正被它的主人磨得锋利无比,一张张镰刀正伸向成熟的麦子。

    父亲打完了镰刀,紧接着又开始打造斧头。父亲的斧头总是供不应求。

    我垂头丧气地站在父亲面前,父亲一声不吭,他钳起一把刚淬过火的斧头,在砧子上狠狠啃了两下。

    这时候,我确实该为我自己羞愧了。我不能眼看着自己把刚出炉的斧头就这样白白地锈掉,然后当废铁处理掉。我总得好好用上两下子,砍出两道新印子。父亲打造了大半辈子钢口很硬的斧头,不能败在我这把斧头上。

【注释】淬cuì火:把金属工件加热到一定温度,然后浸入冷却济(油、水等)急速冷却,以增加硬度。②秦艽jiāo:草本植物,可入药。