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A&P Lect.
Anatomy-Ch. 11
| what are the universal characteristics of muscle | responsiveness (excitability), conductivity, contractility, extensibility, eslasticity |
| what is excitation | the process in which action potentials in the nerve fiber lead to action potentials in the muscle fiber |
| steps of excitation 1: | nerve signal arrives at the synaptic knob and stimulates voltage-gated calcium channels to open. the calcium ions enter the synaptic knob |
| steps of excitation 2: | Calcium stimulates exocytosis of the synaptic vesicles, which release acetylcholine (ACh) into the synaptic cleft. One action potential causes exocytosis of about 60 synaptic vesicles, and each vesicle releases about 10,000 molecules of ACh. |
| steps of excitation 3: | ACh diffuses across the synaptic cleft and binds to receptor proteins on the sarcolemma. |
| steps of excitation 4: | 2 ACh molecules must bind to each receptor to open the channel. then Na+ diffuses into cell & K+ diffuses out and goes through end-plate potentials (EPP) |
| end plate potential (EPP) | the sarcolemma reverses polarity—its voltage quickly jumps from the RMP of −90 mV to a peak of +75 mV as Na+ enters, and then falls back to a level close to the RMP as K+ diffuses out |
| steps of excitation 5: | Areas of sarcolemma next 2 motor end plate have voltage-gated ion channels that open in response 2 EPP. Some r specific for Na+ & admit it 2 cell while others r specific for K+ & allow it to leave; thus create action potential; muscle fiber is now excited |
| exitation-contraction coupling | the events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract. |
| excitation steps continue 6: | A wave of action potentials spreads from the end plate in all directions, like ripples on a pond. When this wave of excitation reaches the T tubules, it continues down them into the sarcoplasm |
| excitation steps continue 7: | Action potentials open voltage-gated ion channels in T tubules; they r physically linked 2 calcium channels in terminal cisternae of sarcoplasmic reticulum;thus channels in SR open & calcium diffuses out of SR down its concentration gradient& into cytosol |
| excitation steps continue 8: | Calcium binds to the troponin of the thin filaments. |
| excitation steps continue 9: | The troponin–tropomyosin complex changes shape and sinks deeper into the groove of the thin filament. This exposes the active sites on the actin filaments and makes them available for binding to myosin heads. |
| contraction | the step in which the muscle fiber develops tension and may shorten |
| contraction step 10: | myosin head must have ATP molecule bound to initiate contraction process. Myosin ATPase hydrolyzes this ATP into ADP & phosphate (Pi). The energy released by this process activates the head, which “cocks” into an extended, high-energy position |
| contraction step 11: | The cocked myosin binds to an exposed active site on the thin filament, forming a cross-bridge between the myosin and actin. |
| contraction step 12: | Myosin releases the ADP and P i and flexes into a bent, low-energy position, tugging the thin filament along with it. This is called the power stroke. The head remains bound to actin until it binds a new ATP. |
| contraction step 13: | The binding of ATP to myosin destabilizes myosin–actin bond(breaking cross-bridge) myosin molecule is now prepared to repeat process;it will hydrolyze ATP, recock, attach to new active site farther down the thin filament, and produce another power stroke. |
| sliding filament theory | the myofilaments do not become any shorter during contraction; rather, the thin filaments slide over the thick ones and pull the Z discs behind them, causing each sarcomere as a whole to shorten |
| relaxation | When its work is done, a muscle fiber relaxes and returns to its resting length |
| relaxation step 14: | Nerve signals stop arriving at the neuromuscular junction, so the synaptic knob stops releasing ACh |
| relaxation step 15: | AChE breaks it down in2 frgmnts that cant stimulate muscle;synaptic knob reabsorbs frgmnts but when nerve signals stop no new ACh is released 2 replace that which is broken down;stimulation of muscle fiber stops |
| relaxation step 16: | Active transport pumps in the SR begin to pump Ca2+ from the cytosol back into the cisternae. Here, the calcium binds to a protein called calsequestrin (CAL-see-QUES-trin) and is stored until the fiber is stimulated again. |
| relaxation step 17: | As calcium ions dissociate from troponin, they are pumped into the SR and are not replaced. |
| relaxation step 18: | Tropomyosin moves back into the position where it blocks the active sites of the actin filament. Myosin can no longer bind to actin, and the muscle fiber ceases to produce or maintain tension |
| length tense relationship | The amount of tension generated by a muscle and, therefore, the force of its contraction depend on how stretched or contracted it was before it was stimulated, among other factors |
| threshold | minimum voltage necessary to generate an action potential in the muscle fiber and produce a contraction |
| latent period | delay |
| twitch | a quick cycle of contraction and relaxation |
| contraction phase | Once the elastic components are taut, the muscle begins to produce external tension and move a resisting object, or load. |
| relaxation phase | The contraction phase is short-lived, because the SR quickly reabsorbs Ca2+ before the muscle develops maximal force. As the Ca2+ level in the cytoplasm falls, myosin releases the thin filaments and muscle tension declines |
| recruitment/ (MMU) multiple motor unit | process of bring more motor units into play |
| temporal summation/ wave summation | At a still higher stimulus frequency (20–40 stimuli/s in fig. 11.15c), each new stimulus arrives before the previous twitch is over. Each new twitch “rides piggy-back” on the previous one and generates higher tension |
| treppe | pattern of increasing tension with repetitive stimulation |
| incomplete tetanus | Wave is added upon wave, so each twitch reaches a higher level of tension than the one before, and the muscle relaxes only partially between stimuli. This effect produces a state of sustained fluttering contraction called |
| complete (fused) tetanus | At a still higher frequency, such as 40 to 50 stimuli/s, the muscle has no time to relax at all between stimuli, and the twitches fuse into a smooth, prolonged contraction |
| isometric contraction | contraction without a change in length |
| Isotonic contraction | contraction with a change in length but no change in tension |
| 2 forms of isotonic contraction | concentric and eccentric |
| concentric contraction | a muscle shortens as it maintains tension—for example, when the biceps brachii contracts and flexes the elbow |
| eccentric contraction | a muscle lengthens as it maintains tension |
| myokinase | transfers P i from one ADP to another, converting the latter to ATP. |
| creatine kinase | obtains P i from a phosphate-storage molecule, creatine phosphate (CP), and donates it to ADP to make ATP. This is a fast-acting system that helps to maintain the ATP level while other ATP-generating mechanisms are being activated. |
| phosphagen system | ATP and CP that provide nearly all the energy used for short bursts of intense activity |
| glycogen–lactic acid system | The pathway from glycogen to lactic acid that produces enough ATP for 30 to 40 seconds of maximum activity |
| muscle fatigue | the progressive weakness and loss of contractility that results from prolonged use of the muscles. |
| oxygen debt | he difference between the resting rate of oxygen consumption and the elevated rate following an exercise; it is also known as excess postexercise oxygen consumption (EPOC) |
| muscle size | The strength of a muscle depends primarily on its size; this is why weight lifting increases the size and strength of a muscle simultaneously. A muscle can exert a tension of about 3 to 4 kg per sq cm of cross-sectional area. |
| fascicle arrangement | Pennate muscles such as the quadriceps femoris are stronger than parallel muscles such as the sartorius, which in turn are stronger than circular muscles such as the orbicularis oculi. |
| size of active motor units | Large motor units produce stronger contractions than small ones. |
| myocytes | Any of the three types of muscle cells |
| cardiocytes | aka Cardiac myocytes |
| cardiac and smooth muscle are | involuntary muscles |
| difference between cardica muscle, smooth muscle, and skeletal muscle | skeletal-associated with skeletal system; cardiac muscle- associated with the heart; smooth muscle-Walls of viscera and blood vessels, iris of eye, piloerector of hair follicles and has no striations |
Created by:
sg109