【正文】 on of the neuron. Muscarinic receptors, located at the synapses of nerves with smooth or cardiac muscle, trigger a chain of chemical events referred to as signal transduction. For a cholinergic neuron to receive another impulse, acetylcholine must be released from the receptor to which it has bound. This will only happen if the concentration of acetylcholine in the synaptic cleft is very low. Low synaptic concentrations of acetylcholine can be maintained via a hydrolysis reaction catalyzed by the enzyme acetylcholinesterase. This enzyme hydrolyzes acetylcholine into acetic acid and choline. If acetylcholinesterase 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’。 請您刪除一下內(nèi)容， O(∩ _∩ )O 謝謝?。。?2022 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。三者是小說藝術(shù)不可或缺的要素?？坍嬋宋锞鸵獙懗鋈宋锏膫€性，而人物個性是通過故事情節(jié)表現(xiàn)出來的，沒有情節(jié)，人物的個性就沒有發(fā)展的歷史，情節(jié)是人物性格形成、發(fā)展、變化的具體過程表現(xiàn)，使人物思想、情感、意志的外化。 3. 怎樣理解小說的“三要素”？ 答： 人物、情節(jié)、環(huán)境是小說的三要素。四個片段時(shí)空跨度之大，看上去并不連貫，但卻以“星星”為線索，星星像母親，星星像朋友，星星像巨人，給作者以親切和溫馨。鑒賞抒情散文，要善于從似乎散亂的情景片段中，去捕捉輻射于整個散文的神韻凝聚點(diǎn)。 2. 運(yùn)用抒情散文的鑒賞方法，解讀巴金的散文《繁星》。 從藝術(shù)的角度看，本詩大膽想象，如將黃河之水想象成“天上來”等等。全詩主要用“ ui”韻，但又不是一韻到底。君不見高堂明鏡悲白發(fā)，朝如青絲暮成雪 ”等長句節(jié)奏舒緩，而“岑夫子，丹邱生，將進(jìn)酒，杯莫?！钡榷叹溆质构?jié)奏變得急促有力。李白的《將進(jìn)酒》充分體現(xiàn)了這些特點(diǎn)。） 1. 運(yùn)用詩歌的鑒賞方法，解讀李白的詩《將進(jìn)酒》。 通過情節(jié)細(xì)膩完整地刻畫人物性格。科學(xué)情散文的鑒賞要注重其如何運(yùn)用文學(xué)手法來闡釋科學(xué)內(nèi)涵。 3. 科學(xué)散文鑒賞 答：科學(xué)情散文是以科學(xué)內(nèi)容為題材的散文，它短小、活潑、銳利，情與理融為一體，具有較強(qiáng)的文學(xué)性、科學(xué)性、知識性。它大都通過片斷的人、事、景、物傳達(dá)出作者的心聲，反映他完整的精神風(fēng)貌，表現(xiàn)他的思想感情。詞鑒賞不能局限于創(chuàng)作的歷史環(huán)境，要根據(jù)詞的特點(diǎn)，在詞所表現(xiàn)的具體的藝術(shù)畫面中發(fā)現(xiàn)能引起當(dāng)代人思想和情感共鳴的東西，開掘具有永恒生命力 的文化精神。對話精練，富含潛臺詞，并帶有強(qiáng)烈動作性。結(jié)構(gòu)既高度集中又自由靈活。 5. 戲?。簯騽∥膶W(xué)是戲曲、話劇、歌劇、舞劇、廣播劇、電視劇等劇本的總稱，也常專指話劇劇本。廣義的散文包括敘事散文、議論散文和抒情散文等，狹義的散文只指抒情散文。 4. 散文：散文指與詩歌、小說、戲劇并列的文學(xué)性作品。絕句委婉曲折，語言簡潔，似絕而續(xù)，以第三句為主，詩句承接宛轉(zhuǎn)變化。押韻上偶句押韻、首句可押可不押；對仗上，頷聯(lián)、頸聯(lián)必須對仗。⑥由于時(shí)間概念抽象，常借空間詞語表達(dá)。如，精衛(wèi)填海，葉公好龍。如，指鹿為馬。如，一塵不染，大徹大悟等。如口血未千。⑥從親屬稱謂看婚姻制度．例如