【正文】 etylcholinesterase activity is inhibited, the synaptic concentration of acetylcholine will remain higher than normal. If this inhibition is irreversible, as in the case of exposure to many nerve gases and some pesticides, sweating, bronchial constriction, convulsions, paralysis, and possibly death can occur. Although irreversible inhibition is dangerous, beneficial effects may be derived from transient (reversible) inhibition. Drugs that inhibit acetylcholinesterase in a reversible manner have been shown to improve memory in some people with Alzheimer39。 in response to activation of this nerve supply, smooth muscle contracts (notably in the gut), the frequency of heart beat is slowed, and glands secrete. Acetylcholine is also an important transmitter at many sites in the brain at nervetonerve synapses. To understand how acetylcholine brings about a variety of effects in different cells it is necessary to understand membrane receptors. In postsynaptic membranes (those of the cells on which the nerve fibres terminate) there are many different sorts of receptors and some are receptors for acetylcholine. These are protein molecules that react specifically with acetylcholine in a reversible fashion. It is the plex of receptor bined with acetylcholine which brings about a biophysical reaction, resulting in the response from the receptive cell. Two major types of acetylcholine receptors exist in the membranes of cells. The type in skeletal muscle is known as ‘nicotinic’。s very difficult for me to understand what the speakers say. Every day we plete our home work on the puter and send our homework to the tutor. He or she will solve the difficulties and puzzles in tutorial. I love my TV University life which make my life colorful and meaningful. 14 請您刪除一下內(nèi)容， O(∩ _∩ )O 謝謝?。?！ 2021 年中央電大期末復(fù)習(xí)考試小抄大全，電大期末考試必備小抄，電大考試必過小抄Acetylcholine is a neurotransmitter released from nerve endings (terminals) in both the peripheral and the central nervous systems. It is synthesized within the nerve terminal from choline, taken up from the tissue fluid into the nerve ending by a specialized transport mechanism. The enzyme necessary for this synthesis is formed in the nerve cell body and passes down the axon to its end, carried in the axoplasmic flow, the slow movement of intracellular substance (cytoplasm). Acetylcholine is stored in the nerve terminal, sequestered in small vesicles awaiting release. When a nerve action potential reaches and invades the nerve terminal, a shower of acetylcholine vesicles is released into the junction (synapse) between the nerve terminal and the ‘effector’ cell which the nerve activates. This may be another nerve cell or a muscle or gland cell. Thus electrical signals are converted to chemical signals, allowing messages to be passed between nerve cells or between nerve cells and nonnerve cells. This process is termed ‘chemical neurotransmission’ and was first demonstrated, for nerves to the heart, by the German pharmacologist Loewi in 1921. Chemical transmission involving acetylcholine is known as ‘cholinergic’. Acetylcholine acts as a transmitter between motor nerves and the fibres of skeletal muscle at all neuromuscular junctions. At this type of synapse, the nerve terminal is closely apposed to the cell membrane of a muscle fibre at the socalled motor end plate. On release, acetylcholine acts almost instantly, to cause a sequence of chemical and physical events (starting with depolarization of the motor endplate) which cause contraction of the muscle fibre. This is exactly what is required for voluntary muscles in which a rapid response to a mand is required. The action of acetylcholine is terminated rapidly, in around 10 milliseconds。另外一個(gè)是自己的工作忙，不能及時(shí)地完成老師 布置 的學(xué)習(xí)任務(wù)。 自己通過一段時(shí)間的遠(yuǎn)程網(wǎng)絡(luò)，掌握了一定的學(xué)習(xí)方法，但是也有一定 13 的困難。按照自己的學(xué)習(xí)計(jì)劃認(rèn)真實(shí)施，做到課前預(yù)習(xí)，課后認(rèn)真復(fù)習(xí)，完成輔導(dǎo)師布置的學(xué)習(xí)任務(wù)。 開放英語（ 3） 作業(yè) 2 （ 17 頁） (Units 712) 第一部分 ：交際英語 一、 15CADDD 第二部分 ： 英語知識運(yùn)用 二、選擇填空 610DBBCC 1115ABBADB 三：完型填空 1620CADDB 2125BACAC 第三部分 ：閱讀理解 2630BCDDC 3135ADCDB 3640F F T T NG 第 四 部分： 寫作 12 How to Keep Healthy Nowadays, more and more people begin to realize the importance of keeping healthy. Without a healthy body, we can do nothing. Good health enables you to enjoy your life. How can we keep healthy? For me, there are three main ways to keep healthy. First, it is necessary to keep a balanced diet, which is the basis of good health. It is better for us to have enough fruit and vegetables every day. Secondly, it is important to take regular exercises, such as swimming, jogging doing yoga and so on. Last but not least, it is essential to keep in a good mood. Relaxation and entertainment are ways to renew our spirits and release our stress. When we make healthy habits a part of our everyday life, we are bound to keep healthy. 學(xué)習(xí)記錄卡 3 ( 第 25 頁 ) （ Units13~18） 學(xué) 習(xí) 過 程 1. A√B√C√ 2. A√B√C√ 3. A√B√C√ 4. A√B√C√ 學(xué) 習(xí) 內(nèi) 容 Unit13~18 中主要學(xué)習(xí)的語法項(xiàng)目 : 情態(tài)動詞、動名詞和動詞不定 式 、非限定性定語從句 、將來完成時(shí)、 完成時(shí)的被動語態(tài)、反意疑問句 這六個(gè)單元還沒有掌握的語言點(diǎn) : 完成時(shí)的被動語態(tài)、反意疑問句 這六個(gè)單元最喜歡的話題 Education after school and university 印象最深的 Cultural Note 是 Sandwich Course 階 段 性 學(xué) 習(xí) 體 會 總結(jié) : 自己以前的英語基礎(chǔ)不好，通過這幾個(gè)月的英語課程學(xué)習(xí)，自己又一次鞏固和強(qiáng)化了英 語知識。這是因?yàn)樽约旱碾娔X知識不夠好，沒有真正地適應(yīng)開放教育的新模式。這使我在學(xué)習(xí)上有了很大的信心。還體會到了如何才能夠成為一個(gè)合格的開放教育的學(xué)員。 另外一個(gè)原因是工作較忙，有時(shí)顧不上英語學(xué)習(xí)。 目前的問題是：我還不能充分地網(wǎng)絡(luò)資源。自己感覺到 又 重新拾起了英語。 由于自己的英語底子薄，基礎(chǔ)差，所以還不能夠完全掌握老師講的內(nèi)容。特別是通過上英語課程，我們不僅僅學(xué)習(xí)了英語語法知識，也學(xué)習(xí)到了學(xué)習(xí)方法。s very difficult for me to understand what the speaker says. Every day we plete our homework on the puter and send our homework to the tutor, t