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1、骨骼肌骨骼肌Skeletal Muscle n nA single skeletal-muscle cell is known as a muscle fiber (肌纤维）肌纤维）.n nThe nerve cells whose axons（轴轴突）突） innervate（支配）支配） skeletal muscle fibers are known as motor neurons（运动神经元）运动神经元）n n运动单位运动单位Motor Unit = a motor neuron + muscle fibers神经肌接头的传递神经肌接头的传递Nuromuscular transmis
2、sionn nThe alpha motoneuron branches, as it approches the muscle, sending axon terminals（轴突末梢）轴突末梢） to several skeletal muscle fibers.n nSynaptic transmission（突触传递）突触传递） occurs at the end-plate region （终板区）终板区）(i.e., the postsynaptic membranes 突触突触后膜后膜) of the skeletal muscle fiber.Ca 2+ 通道的开放和通道的开放
3、和Ach 的释放的释放n nThe axon terminal is enlarged into The axon terminal is enlarged into the terminal the terminal button.button. （末梢钮扣）末梢钮扣）末梢钮扣）末梢钮扣）Each terminal button Each terminal button contains thousands of vesicles that store Ach.contains thousands of vesicles that store Ach.n nPropagation of Pr
4、opagation of action potentialaction potential the terminal the terminal triggers the triggers the opening of Ca opening of Ca 2+2+ channels channels in the in the terminal button.terminal button.n nIt permits It permits Ca Ca 2+2+ to diffuse into the terminal to diffuse into the terminal buttonbutto
5、n from from extracellularextracellular fluid, which in turn fluid, which in turn causes the causes the release of Achrelease of Ach by by exocytosisexocytosis （出（出（出（出胞）胞）胞）胞）from the vesicles. from the vesicles. 终板电位终板电位 End plate potential n nBinding of Ach with the receptor site in the Binding of
6、 Ach with the receptor site in the motor end-plate induces the opening of motor end-plate induces the opening of channels ( both Nachannels ( both Na+ + and K and K+ +，为化学门控通道为化学门控通道为化学门控通道为化学门控通道). ).n nMore NaMore Na+ + moves inward than K moves inward than K+ + outward, outward, bringing about a
7、depolarization of the motor bringing about a depolarization of the motor end plate -This potential is known as end-end plate -This potential is known as end-plate potential (EPP). plate potential (EPP). （终板膜本身无电压门终板膜本身无电压门终板膜本身无电压门终板膜本身无电压门控钠通道，故不会产生动作电位，但可形成局控钠通道，故不会产生动作电位，但可形成局控钠通道，故不会产生动作电位，但可形成局
8、控钠通道，故不会产生动作电位，但可形成局部电流）部电流）部电流）部电流）n nLocal current can reach the threshold of Local current can reach the threshold of adjacent muscle fiber membraneadjacent muscle fiber membrane（邻近肌膜）邻近肌膜）邻近肌膜）邻近肌膜） and bring about an action potential.and bring about an action potential.乙酰胆碱酯酶乙酰胆碱酯酶Acetylcholine
9、sterasen nThe surface of the motor end plate contains the The surface of the motor end plate contains the enzymes enzymes acetylcholinesteraseacetylcholinesterase, which can break , which can break downdown（分解）分解）分解）分解） free Ach in the cleft. free Ach in the cleft. n nAs the concentration of free As
10、 the concentration of free AChACh falls because falls because of its breakdown by of its breakdown by acetylcholinesteraseacetylcholinesterase, less , less AChACh is available to bind to the receptors. is available to bind to the receptors. n nWhen receptors no longer contain bound Ach, When recepto
11、rs no longer contain bound Ach, the ion channels in the end plate close. The the ion channels in the end plate close. The depolarized end plate returns to its resting depolarized end plate returns to its resting potential and can respond to the subsequent potential and can respond to the subsequent
12、arrival of arrival of AChACh. .神经神经-肌接头传递各环节肌接头传递各环节n nAction potential in presynaptic nerve terminal depolarization Ca2+ channels open intracellular Ca2+ acetylcholine vesicle release ACh synaptic cleft binds to postsynaptic ACh receptor postsynaptic membrane depolarization end-plate potential (EPP
13、) action potential in muscle cell occurs contraction of muscle cell.箭毒传说箭毒传说n n美洲的古印第安人在遇到敌人入侵时，女人和儿童在美洲的古印第安人在遇到敌人入侵时，女人和儿童在美洲的古印第安人在遇到敌人入侵时，女人和儿童在美洲的古印第安人在遇到敌人入侵时，女人和儿童在后方将箭毒木的汁液涂于箭头，供男人在战场上杀敌。后方将箭毒木的汁液涂于箭头，供男人在战场上杀敌。后方将箭毒木的汁液涂于箭头，供男人在战场上杀敌。后方将箭毒木的汁液涂于箭头，供男人在战场上杀敌。1859185918591859年土著民族在和英军交战时，这种毒箭
14、的杀伤力年土著民族在和英军交战时，这种毒箭的杀伤力年土著民族在和英军交战时，这种毒箭的杀伤力年土著民族在和英军交战时，这种毒箭的杀伤力使英军惊恐万分。使英军惊恐万分。使英军惊恐万分。使英军惊恐万分。n n传说西双版纳最早发现箭毒木汁液含有剧毒的是一位传说西双版纳最早发现箭毒木汁液含有剧毒的是一位传说西双版纳最早发现箭毒木汁液含有剧毒的是一位传说西双版纳最早发现箭毒木汁液含有剧毒的是一位傣族猎人。这位猎人被一只硕大的狗熊紧逼而被迫爬傣族猎人。这位猎人被一只硕大的狗熊紧逼而被迫爬傣族猎人。这位猎人被一只硕大的狗熊紧逼而被迫爬傣族猎人。这位猎人被一只硕大的狗熊紧逼而被迫爬上一棵大树，可狗熊仍不放过他
15、上一棵大树，可狗熊仍不放过他上一棵大树，可狗熊仍不放过他上一棵大树，可狗熊仍不放过他, , , ,生死存亡的紧要关头，生死存亡的紧要关头，生死存亡的紧要关头，生死存亡的紧要关头，猎人折断一根树枝刺向正往树上爬的狗熊，奇迹突然猎人折断一根树枝刺向正往树上爬的狗熊，奇迹突然猎人折断一根树枝刺向正往树上爬的狗熊，奇迹突然猎人折断一根树枝刺向正往树上爬的狗熊，奇迹突然发生了，狗熊立即落地而死。从那以后猎人就学会了发生了，狗熊立即落地而死。从那以后猎人就学会了发生了，狗熊立即落地而死。从那以后猎人就学会了发生了，狗熊立即落地而死。从那以后猎人就学会了把箭毒木的汁液涂于箭头用于狩猎。把箭毒木的汁液涂于箭头
16、用于狩猎。把箭毒木的汁液涂于箭头用于狩猎。把箭毒木的汁液涂于箭头用于狩猎。又称又称见血封喉血封喉树“七上八下九倒地七上八下九倒地”，意思就是说，意思就是说，如果谁中了箭毒木的毒，那么往高处如果谁中了箭毒木的毒，那么往高处只能走七步，往低处只能走八步，但只能走七步，往低处只能走八步，但无论如何，走到第九步，都会倒地毙无论如何，走到第九步，都会倒地毙命命箭毒木又名加独箭毒木又名加独树、剪刀、剪刀树等等高可达30米，多分布于赤道热带地区，国内则散见于广东、广西、海南、云南等省区。现为濒临灭绝的稀有树种，国家三级保护植物。南美箭毒南美箭毒 Curare n nThe deadly The deadly
17、 South American arrowhead poison South American arrowhead poison curarecurare binds strongly to the binds strongly to the AChACh receptors, but receptors, but it does not open their ion channels and is not it does not open their ion channels and is not destroyed by destroyed by acetylcholinesterasea
18、cetylcholinesterase. . n nWhen a receptor is occupied by curare, When a receptor is occupied by curare, AChACh cannot bind to the receptor. Hence, there is no cannot bind to the receptor. Hence, there is no EPP in the motor end plate and no contraction. EPP in the motor end plate and no contraction.
19、 n nSince the skeletal muscles responsible for Since the skeletal muscles responsible for breathingbreathing（呼吸）呼吸）呼吸）呼吸）, curare poisoning can lead , curare poisoning can lead to death by asphyxiationto death by asphyxiation（窒息）窒息）窒息）窒息）. .肉毒杆菌毒素肉毒杆菌毒素 Botulin and AChn nBotulinBotulin is an enzyme
20、that is an enzyme that breaks down a breaks down a protein required for the binding and fusion of protein required for the binding and fusion of AChACh veseclesvesecles with the with the presynapticpresynaptic membrane. membrane. n nHence, Hence, it can block the release of acetylcholine it can bloc
21、k the release of acetylcholine from nerve terminalsfrom nerve terminals in neuromuscular in neuromuscular junctionjunction. .n n This poisoning is one of the most potent This poisoning is one of the most potent poisons, which can cause flaccid paralysis poisons, which can cause flaccid paralysis （肌肌
22、肌肌肉松驰性瘫痪）肉松驰性瘫痪）肉松驰性瘫痪）肉松驰性瘫痪）. .生物武器生物武器n n 它造价低，技术难度不大，隐秘性强，它造价低，技术难度不大，隐秘性强，可以在任何地方研制和生产。可以在任何地方研制和生产。n n有资料显示，以有资料显示，以1969年为例，当时每平年为例，当时每平方公里导致方公里导致50%死亡率的成本分别为：死亡率的成本分别为：传统武器传统武器2000美元；核武器，美元；核武器，800美元；美元；化学武器，化学武器，600美元；生物武器，美元；生物武器，1美元。美元。 肉毒杆菌毒素肉毒杆菌毒素-“穷人的原子穷人的原子弹弹”n n肉肉毒毒杆杆菌菌毒毒素素是是最最流流行行的的两
23、两大大生生物物武武器器之之一一, 是是一一种种廉廉价价和和高高效效的的杀杀人人武武器器，其其死死亡亡率率高高达达60%至至70%。受受害害者者症症状状是是头头痛痛、肢肢体体瘫瘫痪痪，如如不不及及时时治治疗疗将将在在2至至10天天内内死死去去。这这种种毒毒素素可可以以批批量量生生产产，并并可可通通过过皮皮肤肤吸吸收收、肺肺部部吸吸收收、眼眼睛睛接接触、等方式传染。触、等方式传染。肉毒杆菌毒素肉毒杆菌毒素-“富人的美容富人的美容剂剂”n n肉毒杆菌毒素除皱纹的原理很简单，肉毒杆菌毒素除皱纹的原理很简单，肉毒杆菌毒素除皱纹的原理很简单，肉毒杆菌毒素除皱纹的原理很简单，A A型肉毒型肉毒型肉毒型肉毒毒
24、素可以起到麻痹肌肉的作用，脸部注射后，毒素可以起到麻痹肌肉的作用，脸部注射后，毒素可以起到麻痹肌肉的作用，脸部注射后，毒素可以起到麻痹肌肉的作用，脸部注射后，阻断神经和肌肉之间的信息传导，可使局部肌阻断神经和肌肉之间的信息传导，可使局部肌阻断神经和肌肉之间的信息传导，可使局部肌阻断神经和肌肉之间的信息传导，可使局部肌肉瘫痪，肌肤因此舒展，皱纹便神奇般消失肉瘫痪，肌肤因此舒展，皱纹便神奇般消失肉瘫痪，肌肤因此舒展，皱纹便神奇般消失肉瘫痪，肌肤因此舒展，皱纹便神奇般消失n nA A型肉毒毒素注射过量可致人死命。但美容除型肉毒毒素注射过量可致人死命。但美容除型肉毒毒素注射过量可致人死命。但美容除型肉
25、毒毒素注射过量可致人死命。但美容除皱注射的皱注射的皱注射的皱注射的A A型肉毒毒素是人致死量的型肉毒毒素是人致死量的型肉毒毒素是人致死量的型肉毒毒素是人致死量的3%3%。注入。注入。注入。注入肌肉后它选择性使肌肉松弛，几乎无多余的肌肉后它选择性使肌肉松弛，几乎无多余的肌肉后它选择性使肌肉松弛，几乎无多余的肌肉后它选择性使肌肉松弛，几乎无多余的A A型肉毒毒素进入血液或进入人脑脊液。型肉毒毒素进入血液或进入人脑脊液。型肉毒毒素进入血液或进入人脑脊液。型肉毒毒素进入血液或进入人脑脊液。有机磷有机磷 Organophosphates and acetylcholinerasen nSome Some
26、 organophosphates,organophosphates, which are the main which are the main ingredients in certain pesticidesingredients in certain pesticides（农药）农药）农药）农药）and and “nerve gases”, “nerve gases”, inhibit inhibit acetylcholinesteraseacetylcholinesterase. . n nWhen When AChACh binds to the end plate recept
27、ors, binds to the end plate receptors, which is not destroyedwhich is not destroyed, producing a maintained , producing a maintained depolarization in the end plate and muscle depolarization in the end plate and muscle plasma membrane. plasma membrane. n nHence, Hence, sodium channels enter an inact
28、ive statesodium channels enter an inactive state. . Muscle does not contract in response to Muscle does not contract in response to subsequent nerve stimulation,subsequent nerve stimulation, and result is and result is death from asphyxiationdeath from asphyxiation（窒息）窒息）窒息）窒息）. .Organization of ske
29、letal musclen nSkeletal muscle is made of individual muscle fibers（肌纤维肌纤维肌纤维肌纤维）. .n nThe muscle fibers are made of fibrils（肌肌肌肌原纤维）原纤维）原纤维）原纤维）. .n nThe fibrils are divided into individual filaments（肌丝）肌丝）肌丝）肌丝）. .n nThe filaments are made up of the contractile proteins（收缩蛋白）收缩蛋白）收缩蛋白）收缩蛋白）. .肌丝肌丝
30、Filamentsn nThe myofibrils （肌原纤维）肌原纤维） contain thick （粗肌丝）粗肌丝）and thin filaments（细细肌丝）肌丝） composed of contractile proteins.n n粗肌丝粗肌丝Thick filaments contain the protein myosin （肌球蛋白，含有横桥）（肌球蛋白，含有横桥）.n nThin filaments contain proteins actin（肌动蛋白）（肌动蛋白）, tropomyosin（原肌球蛋原肌球蛋白）白）, and troponin（肌钙蛋白）肌钙蛋白
31、）.横管横管 T Tubule 与肌浆网与肌浆网 SR之间的关系之间的关系n nTransverse Tubule （T tubule 横管）横管）横管）横管）is formed as an invagination （凹入）凹入）凹入）凹入）of the surface of the muscle membrane. The action potential spreading over the surface of the muscle membrane is propagated into the network of T tubules, which forms contacts wi
32、th sarcoplasmic reticulum (SR肌浆网肌浆网肌浆网肌浆网) )n nSR contains a high concentration of Ca 2+, 肌质网肌质网 SR and Ca2+ releasen nThe T tubule membrane contains The T tubule membrane contains dihydropyridinedihydropyridine receptor receptor ( (二二二二氢吡啶受体氢吡啶受体氢吡啶受体氢吡啶受体, a , a voltage-sensitive receptor voltage-
33、sensitive receptor 电压敏感受体，电压敏感受体，电压敏感受体，电压敏感受体，L-L-型型型型CaCa2+2+ 通道通道通道通道) )n nWhen When an action potentialan action potential is propagated down is propagated down the T tubule, the local depolarization activates the T tubule, the local depolarization activates dihydrpopyridinedihydrpopyridine rece
34、potorrecepotor that in turn opens that in turn opens the the CaCa2+2+ release channel release channel （终池上的钙离子释终池上的钙离子释终池上的钙离子释终池上的钙离子释放通道放通道放通道放通道, also known as , also known as ryanodineryanodine receptor receptor ) on ) on SR.SR.肌钙肌钙蛋白及其作用蛋白及其作用n n由三个亚由三个亚由三个亚由三个亚单位组成：肌钙蛋白单位组成：肌钙蛋白单位组成：肌钙蛋白单位组成：肌
35、钙蛋白T T（TnT)TnT)、肌钙、肌钙、肌钙、肌钙蛋白蛋白蛋白蛋白I(TnI)I(TnI)和肌钙蛋白和肌钙蛋白和肌钙蛋白和肌钙蛋白C(TnC)C(TnC)n nTnTTnT与原肌球蛋白结合，将整个肌钙蛋白固定与原肌球蛋白结合，将整个肌钙蛋白固定与原肌球蛋白结合，将整个肌钙蛋白固定与原肌球蛋白结合，将整个肌钙蛋白固定在原肌球蛋白上。在原肌球蛋白上。在原肌球蛋白上。在原肌球蛋白上。n nTnCTnC可与可与可与可与Ca+Ca+结合。结合。结合。结合。n nTnITnI的作用是的作用是的作用是的作用是TnCTnC可与可与可与可与Ca+Ca+结合时，将信息传结合时，将信息传结合时，将信息传结合时，
36、将信息传给原肌球蛋白，引起后者发生构象变化并向肌给原肌球蛋白，引起后者发生构象变化并向肌给原肌球蛋白，引起后者发生构象变化并向肌给原肌球蛋白，引起后者发生构象变化并向肌纤蛋白双螺旋沟深部滑行，从而暴露肌纤蛋白纤蛋白双螺旋沟深部滑行，从而暴露肌纤蛋白纤蛋白双螺旋沟深部滑行，从而暴露肌纤蛋白纤蛋白双螺旋沟深部滑行，从而暴露肌纤蛋白的结合位点，使横桥与之结合。的结合位点，使横桥与之结合。的结合位点，使横桥与之结合。的结合位点，使横桥与之结合。粗肌丝、横桥与细肌丝的关系粗肌丝、横桥与细肌丝的关系n nPulling thin filaments inward by the bend of cross
37、bridges is directed toward the center of the thick filament.n nEach thick filament is surrounded by six thin filaments, all the which are pulled inward simultaneously through cross-bridge cycling during muscle contraction. 从从神经元动作电位到肌纤维收缩神经元动作电位到肌纤维收缩-(1)n n1. Action potential is initiated and propa
38、gates in motor neuron axon.n n2. Action potential triggers release of Ach from axon terminals at neuromuscular junctions.n n3. Ach binds to receptor sites on motor end plate in muscle fiber, opening Na+,K+ ion channel.从神经元动作电位到肌纤维收缩从神经元动作电位到肌纤维收缩-(2)n n4. More Na+ moves into the fiber at the motor e
39、nd plate than K+ move out, depolarizing the membrane, producing the end-plate potential (EPP).n n5. Local currents depolarize the adjacent plasma membrane to its threshold potential, generating an action potential that propagates over the muscle fiber surface and in to the fiber along T tubles.从神经元动
40、作电位到肌纤维收缩从神经元动作电位到肌纤维收缩-(3)n n6. Action potential in T tubules triggers release of Ca2+ from lateral sacs of SR.n n7. Ca2+ binds to troponin（肌钙蛋白）肌钙蛋白）肌钙蛋白）肌钙蛋白） on thin filaments, causing tropomyosin（原原原原肌球蛋白）肌球蛋白）肌球蛋白）肌球蛋白） to move away from its blocking position and thus uncovering cross-bridges
41、binding sites on actin（肌纤肌纤肌纤肌纤蛋白）蛋白）蛋白）蛋白）. .从神经元动作电位到肌纤维收缩从神经元动作电位到肌纤维收缩-(4)n n8. Energized myosin cross-bridges （高高能肌能肌球球蛋白横桥）蛋白横桥） on the thick filaments bind to actin（肌纤蛋白）肌纤蛋白）.（横桥之所以（横桥之所以（横桥之所以（横桥之所以处于高势能状态处于高势能状态处于高势能状态处于高势能状态, , 是因其头部具有是因其头部具有是因其头部具有是因其头部具有ATPATP酶活酶活酶活酶活, , 并并并并可将与其结合可将与其结
42、合可将与其结合可将与其结合ATPATP分解成分解成分解成分解成ADPADP和无机磷酸而贮和无机磷酸而贮和无机磷酸而贮和无机磷酸而贮能能能能. .）n n9. Cross-bridge binding triggers release of energy stored in myosin（肌球蛋白）肌球蛋白）, producing a movement of each cross bridge. 此时此时ADP和和无机磷酸便与横桥分离无机磷酸便与横桥分离无机磷酸便与横桥分离无机磷酸便与横桥分离n n10. 10. 在在在在ADTADT分离点，分离点，分离点，分离点， ATP binds to m
43、yosinATP binds to myosin（肌肌肌肌凝蛋白）凝蛋白）凝蛋白）凝蛋白）, , breaking linkage between actinbreaking linkage between actin（肌肌肌肌纤蛋白）纤蛋白）纤蛋白）纤蛋白）and myosinand myosin and thereby allowing and thereby allowing cross bridges to dissociate from actin.cross bridges to dissociate from actin.( (横桥头部横桥头部横桥头部横桥头部与与与与ATPATP
44、结合后，其对肌纤蛋白的亲和力降低，结合后，其对肌纤蛋白的亲和力降低，结合后，其对肌纤蛋白的亲和力降低，结合后，其对肌纤蛋白的亲和力降低，使其与纤动蛋白解离）使其与纤动蛋白解离）使其与纤动蛋白解离）使其与纤动蛋白解离）。n n11. ATP bound to myosin is split by myosin 11. ATP bound to myosin is split by myosin ATPaseATPase, transferring energy to myosin cross , transferring energy to myosin cross bridge once ag
45、ain.bridge once again.（结合到结合到结合到结合到横桥头部的横桥头部的横桥头部的横桥头部的ATPATP被被被被ATPATP酶分解，又把能量贮存在横桥）酶分解，又把能量贮存在横桥）酶分解，又把能量贮存在横桥）酶分解，又把能量贮存在横桥）从神经元动作电位到肌纤维收缩从神经元动作电位到肌纤维收缩-(5)从神经元动作电位到肌纤维收缩从神经元动作电位到肌纤维收缩-(6)n n12. Cross bridges repeat steps 8 to 11, producing movement of thin filaments past thick filaments. Cycles
46、of cross-bridge movement continue as long as Ca2+ remains bound to troponin（肌钙蛋白）肌钙蛋白）肌钙蛋白）肌钙蛋白）. . Relaxed state of the musclen nThe normal concentration of Ca2+ in the cytosol that bathes the myofibrils（肌原肌原纤维）纤维） is too little to elicit contraction. Therefore, in the resting state, the troponin -
47、tropomyosin complex keeps the actin filaments inhibited and maintains a relaxed state of the muscle.Function of ATPn n 1. Hydrolysis of ATP by myosin energizes the cross bridges, providing energy for force generation.n n 2. Dissociates cross bridges bound to actin.n n 3. Provides the energy for the
48、active transport of Ca 2+ into lateral sacs of reticulum, lowering cytosolic Ca 2+.肌肉收的形式和力学分析肌肉收的形式和力学分析n nIsometric contraction（等长收缩）等长收缩）: When a muscle develops tension but does not shorten. (长度不变长度不变, 张力增张力增加加)n nIsotonic contraction（等张收缩）等张收缩）: When a muscle is shortening but its tension remai
49、ns constant. (长度缩短长度缩短,张力不变张力不变)等张收缩举例等张收缩举例An example of isotonic contractionn n手臂可以提起一个物体时的状态手臂可以提起一个物体时的状态手臂可以提起一个物体时的状态手臂可以提起一个物体时的状态n nLiftingLifting an object: an object: When the tension developing When the tension developing in your biceps becomes great enough to in your biceps becomes great
50、 enough to overcome the weight of the object in your hand, overcome the weight of the object in your hand, you can lift the object,you can lift the object, with the whole muscle with the whole muscle shortening.shortening.n nBecause the weight of the object does not Because the weight of the object
51、does not change as it is lifted, change as it is lifted, the muscle tension the muscle tension remains constant throughout the period of remains constant throughout the period of shortening.shortening. This is isotonic contraction. This is isotonic contraction. 等长收缩举例等长收缩举例An example of isometric co
52、ntractionn n想提起一重物想提起一重物想提起一重物想提起一重物, , 但太重提不起时的状态但太重提不起时的状态但太重提不起时的状态但太重提不起时的状态n nTryTry to lift an object: to lift an object: What happens if What happens if you try to you try to lift an object too heavy for you ,lift an object too heavy for you , that is , if the that is , if the tension you are
53、 capable of developing in your tension you are capable of developing in your arm muscles is less than that required to lift the arm muscles is less than that required to lift the object ?object ?n nThe muscle cannot shorten and lift the objectThe muscle cannot shorten and lift the object but but rem
54、ains at constant length in spite of the remains at constant length in spite of the development of tension. This is an isometric development of tension. This is an isometric contractioncontraction前负荷前负荷 Preload and后负荷后负荷 Afterloadn n前负荷前负荷: 肌肉在收缩前就加上肌肉上的肌肉在收缩前就加上肌肉上的负荷负荷. The force required to stretc
55、h the muscle to lengths beyond 2.0 m).n n后负荷后负荷: 肌肉开始收缩后遇到的负荷肌肉开始收缩后遇到的负荷. The weight that a muscle lifts during an isotonic contraction).最适长度最适长度 Optimal lengthn n最适长度最适长度最适长度最适长度: : The length at which the muscle fiber develops the greatest tension.n nAt an initial sarcomere length（肌小节肌小节肌小节肌小节长度）
56、长度）长度）长度） of 2.2 um, each cross-bridge can bind to an actin molecule on thin filaments, and a maximum force is generated.长度与张力的关系长度与张力的关系Length-tension relationshipLength-tension relationshipn nMaximal tetanic contraction can be achieved when a muscle fiber is at its optimal length.n nWhen it is lon
57、ger, fewer thin-filament binding sites are accessible for binding with thick-filament cross bridges, because the thin filaments are pulled out.n nWhen the fiber is shorter, fewer thin-filament binding sites are exposed to thick-filament cross bridges because the thin filaments overlap.体内长度与张力的关系体内长度
58、与张力的关系Length-tension Length-tension relationshipinrelationshipin the body the body n nIn the body, In the body, the muscle relaxed length is the muscle relaxed length is approximately their optimal length,approximately their optimal length, thus, the thus, the muscle are capable of achieving near-ma
59、ximal muscle are capable of achieving near-maximal tetanictetanic contraction most of the time. contraction most of the time. n nBecause of limitations imposed by attachment Because of limitations imposed by attachment to the skeleton, a muscle cannot be stretched or to the skeleton, a muscle cannot
60、 be stretched or shortened more than 30% of its resting optimal shortened more than 30% of its resting optimal length, length, even at the outer limits (130% and 70% even at the outer limits (130% and 70% of optimal length), the muscle are still able to of optimal length), the muscle are still able
61、to generate half their maximal tension.generate half their maximal tension.负荷与速度的关系负荷与速度的关系Load-velocity relationshipLoad-velocity relationshipn nThe greater the load, the lower the velocity at which a single muscle fiber shortens during an isotonic contraction.n nThe velocity of shortening is maxim
62、al when there is no external load . n nThe velocity of shortening progressively decreases with an increasing load, and falls to zero when load cannot be overcome by maximal tension.频率与张力的关系频率与张力的关系Frequency and tension relationFrequency and tension relationn n潜伏期潜伏期潜伏期潜伏期 Latent period: : Following
63、the action potential , there is a interval of a few milliseconds before the tension in muscle fiber begins to increase ( the processes associated with excitation -contraction coupling )n n单收缩单收缩单收缩单收缩 Single twitch: : A mechanical response of a muscle fiber to a single action potential 频率与张力的关系频率与张力
64、的关系Frequency and tension relationFrequency and tension relationn n强直收缩强直收缩强直收缩强直收缩Tetanus : : A maintained contraction in A maintained contraction in response to repetitive stimulation. response to repetitive stimulation. n n不完全强直收缩不完全强直收缩不完全强直收缩不完全强直收缩Incomplete tetanus: : At low At low stimulation
65、 frequencies, the tension may stimulation frequencies, the tension may oscillate as the muscle fiber partially relaxes oscillate as the muscle fiber partially relaxes between stimuli. between stimuli. n n完全强直收缩完全强直收缩完全强直收缩完全强直收缩Complete tetanus: : Produced at Produced at high frequency, with no osci
66、llations.high frequency, with no oscillations.强直收缩与横桥结合位点强直收缩与横桥结合位点Tetanus and cross-bridge binding sitesn n随着动作电位产生的频率增加，钙持续升高，随着动作电位产生的频率增加，钙持续升高，随着动作电位产生的频率增加，钙持续升高，随着动作电位产生的频率增加，钙持续升高，最大数量的横桥结合位点都被打开，所以可达最大数量的横桥结合位点都被打开，所以可达最大数量的横桥结合位点都被打开，所以可达最大数量的横桥结合位点都被打开，所以可达到最大的强直收缩到最大的强直收缩到最大的强直收缩到最大的强直收
67、缩. .n nAs frequency of action potential increases, the duration of elevated Ca2+ concentration increases and maximal number of cross-bridge binding sites remain uncovered, so that maximal tetanic contraction is reached.生理条件下的骨骼肌收缩生理条件下的骨骼肌收缩n n在生理条件下在生理条件下, 支配骨骼肌的传出神经总支配骨骼肌的传出神经总是发出连续的神经冲动是发出连续的神经冲动
68、(动作电位动作电位), 所以所以骨骼肌的收缩几乎都是强直收缩骨骼肌的收缩几乎都是强直收缩.n n骨骼肌弱收缩通常是由较小的运动单位骨骼肌弱收缩通常是由较小的运动单位motor unit) 产生产生, 而骨骼肌的强收缩是而骨骼肌的强收缩是多由较大的运动单位产生多由较大的运动单位产生.n n骨骼肌强直收缩时骨骼肌强直收缩时,肌细胞连续兴奋肌细胞连续兴奋,使使胞浆内的胞浆内的Ca2+浓度持续上升浓度持续上升, 可利用的横可利用的横桥结合位点数目达到最大桥结合位点数目达到最大, 故收缩张力可故收缩张力可达到一个相对稳定的最大值达到一个相对稳定的最大值.Types of smooth musclen n
69、1. 1. Single-unit smooth muscle:Single-unit smooth muscle: The whole The whole muscle responds to stimulation as a single unit. muscle responds to stimulation as a single unit. This occurs because each muscle fiber is linked This occurs because each muscle fiber is linked to adjacent fibers by to ad
70、jacent fibers by gap junction.gap junction.n n2. 2. Multiunit smooth muscle:Multiunit smooth muscle: Because these Because these muscles have muscles have few gap junctionsfew gap junctions, each muscle , each muscle fiber responds independently of its neighbors, fiber responds independently of its neighbors, and the muscle behaves as multiple units.and the muscle behaves as multiple units.
