托福听力考试经常出现加试题，通常这样的情况下考试时间会延长。虽然说加试成绩不计入总分，但是大家还是会很紧张，因为毕竟我们不知道哪些是加试题。如果可以事前知道哪些是加试题，我们就不用那么紧张了。
神经元细胞
lecture神经胶质细胞研究。教授说早期对人类大脑的研究集中在神经细胞neuron，让一男生起来回答上节课的主要内容，男生说生物电生物电 bioelectricity 通过神经细胞传导，通过两个神经细胞的接触点传到下一个细胞，有趣的是。。说到这里被教授打断，说他答得已经很完整了(有题，问教授打断他的用意)。神经胶质细胞glial cells的作用在早期被忽视了，人们认为胶质细胞只有支持神经细胞的作用。后来人们发现胶质细胞也有传导信息的作用，不是通过生物电，而是化学物质传导。于是总共有三种传导方式，神经细胞间，胶质细胞间，神经和胶质细胞互相传导。而且发现胶质细胞的数量及其巨大，远多于神经细胞。同时还可能有修复神经细胞，决定哪些神经长的大[记得可能不准]。教授又说，胶质细胞可能与智力有关，越多智商越高，但这不确定。教授说对胶质细胞的研究是一个很open up的领域，建议学生们可以考虑毕业后作深入研究(有题)。
重要：biology 讲glial cell。以往人们对神经传导的研究仅限于neuron(神经元)，也叫nervecell。神经传导通过electrical communication从一个结点传到另一个结点，神经元被认为起主要作用，glial cell研究的很少，一直被忽略，被看作help the growth of neurons
(出题)，起辅助作用。后来偶然发现大脑中glial cell比neuron的数目多很多，glial cell引起了科学家的重视，开始研究它究竟起什么作用(此处出题，问glialcell怎么引起科学家注意的)。后来有一重大突破，
发现glial cell传导信号不是用的electricalsignal，而是用chemical conductor(一说chemical communication)(此处出题)。传统观点一直误以为glial cell也像nervecell一样用电信号。后来谈到glial cell可能的作用：使人更intelligent。对glial cell的认识目前十分有限，但相关研究已经开始流行，是大家毕业之后可选的研究课题(此处出题)
Glial cell isthought to help the growth of neurons. However, scientists accidentallydiscover that glial’s amount is much more than the neuron. So glial attractpeople’s attention. They use chemical conductor to communicate with others. Soglial to neuron, g to n, g to g, n to n are all available. In the past glialwas thought to support nerve cell.
Glial cells (神经胶质细胞)and Neurons (神经细胞)
Glial cells,commonly called neuroglia or simply glia, are non-neuronal cellsthat provide support and nutrition, maintainhomeostasis,form myelin,and participate in signal transmission in the nervoussystem. In the human brain, glia are estimated to outnumberneurons by about 10 to 1.[1]
Glial cellsprovide support and protection for neurons, the other main type of cell in the central nervoussystem. They are thus known as the "glue"胶水 of the nervous system. The four main functions ofglial cells are to surround neurons and hold them in place固定, to supply nutrientsand oxygento neurons供养, to insulate one neuron from another隔开, and to destroypathogensand remove dead neurons破坏病菌，转移死N.
Glia wasdiscovered in 1856by the pathologist Rudolf Virchow in his search for a 'connectivetissue' in the brain大脑的连接组织.The human brain contains about ten timesmore glial cells than neurons. [1]Following its discovery in the late 19th century, this fact underwentsignificant media distortion, emerging as the famous myth claiming that"we are using only 10% of our brain". The role of glial cells asmanagers of communications in the synapse突触 gap,thus modifying learning pace, has been discovered only very recently
In addition toneurons, the nervous system is populated with another category of cells, glialcells. Glial cells are approximately 10 times more plentiful than neurons, butsince they are approximately one-tenth the size, they take up equal size, gliais a Greek term meaning glue, researches originally believed that glial cellsserved as the putty that held the neurons together, recent research indicatesthat these cells provide very important contributions.
a neuron is thefunctioning unit of the nervous system, specialized to receive, integrate, andtransmit information, the flow of information moves in the following direction.
托福听力加试题的位置不固定，考生很难分辨哪一道是加试题，只能通过日常积累来判断。大家尽量不要凭空揣测，以免影响自己的托福成绩。
