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1、,1,MUSCLES AND HOW THEY MOVE,chapter,Learning Objectives,w Learn the basic components of skeletal muscle, the muscle fiber, and the myofibril.,w Note the cellular events leading to a basic muscle action.,w Discover how muscle functions during exercise.,w Consider the differences in fiber types and t
2、heir impact on physical performance.,w Learn how muscles generate force and movement by pulling on bones.,Skeletal w Voluntary muscle; controlled consciously Over 600 throughout the body,Cardiac w Controls itself with assistance from the nervous and endocrine systems w Only in the heart,Smooth w Inv
3、oluntary muscle; controlled unconsciously In the walls of blood vessels and internal organs,Types of Muscles,SKELETAL MUSCLE STRUCTURE,SINGLE MUSCLE FIBER,Key Points,w An individual muscle cell is called a muscle fiber.,w A muscle fiber is enclosed by a plasma membrane called the sarcolemma肌漿膜.,Musc
4、le Fiber,w The cytoplasm of a muscle fiber is called the sarcoplasm.,w Within the sarcoplasm, the T tubules allow transport of substances throughout the muscle fiber.,w The sarcoplasmic reticulum stores calcium.,MICROGRAPH OF MYOFIBRILS,ARRANGEMENT OF FILAMENTS,ARRANGEMENT OF FILAMENTS IN A SARCOMER
5、E,ACTIN FILAMENT,MOTOR UNIT,Key Points,w Myofibrils are the contractile elements of skeletal muscle, with several hundred to several thousand composing a single muscle.,w A sarcomere is composed of filaments of two proteins, myosin and actin, which are responsible for muscle contraction.,Myofibrils,
6、w Myosin is a thick filament with a globular head at one end.,w An actin filamentcomposed of actin, tropomyosin, and troponinis attached to a Z disk.,w Myofibrils are made up of sarcomeres, the smallest functional units of a muscle.,1. A motor neuron, with signals from the brain or spinal cord, rele
7、ases the neurotransmitter acetylcholine (Ach) at the neuromuscular junction.,2. ACh crosses the junction and binds to receptors on the sarcolemma.,3. This initiates an action potential, providing sufficient ACh.,Excitation/Contraction Coupling,4. The action potential travels along the sarcolemma and
8、 through the T tubules to the SR releasing Ca2+.,6. Once a strong binding state is extablished with actin, the myosin head tilts, pulling the actin filament (power stroke).,7. The myosin head binds to ATP, and ATPase found on the head splits ATP into ADP and Pi, releasing energy.,8. Muscle action en
9、ds when calcium is actively pumped out of the sarcoplasm back into the sarcoplasmic reticulum for storage.fig1.9,Excitation/Contraction Coupling,EVENTS LEADING TO MUSCLE ACTION,Fig 1.8 a sarcomere in its relaxed and contracted state(I,A band and H zone),Fig 1.9 change in the myosin head during vario
10、us phases of the power stroke(number 1 and 2),Excitation/Contraction Coupling,w When myosin cross-bridges are activated, they bind strongly with actin, resulting in a change in the cross-bridge.,w The change in the cross-bridge causes the myosin head to tilt toward the arm of the cross-bridge and dr
11、ag the actin and myosin filaments in opposite directions.,w The tilt of the myosin head is known as a power stroke.,Sliding Filament Theory,w The pulling of the actin filament past the myosin results in muscle shortening and generation of muscle force.,CONTRACTING MUSCLE FIBER,w Hollow needle is ins
12、erted into muscle to take a sample.,w Sample is mounted框好, frozen, thinly sliced, and examined under a microscope.,w Allows study of muscle fibers and the effects of acute exercise and exercise training on fiber composition.,Muscle Biopsy,w High aerobic (oxidative) capacity and fatigue resistance,w
13、Low anaerobic (glycolytic) capacity and motor unit strength,w Slow contractile speed (110 ms to reach peak tension) and myosin ATPase,Slow-Twitch (St,type) Muscle Fibers,w 10180 fibers per motor neuron,w Low sarcoplasmic reticulum development,w Moderate aerobic (oxidative) capacity and fatigue resis
14、tance,w High anaerobic (glycolytic) capacity and motor unit strength,w Fast contractile speed (50 ms to reach peak tension) and myosin ATPase,Fast-Twitch (Fta,typea) Muscle Fibers,w 300800 fibers per motor neuron,w High sarcoplasmic reticulum development,w Low aerobic (oxidative) capacity and fatigu
15、e resistance,w High anaerobic (glycolytic) capacity and motor unit strength,w Fast contractile speed (50 ms to reach peak tension) and myosin ATPase,Fast-Twitch (FTx,type x) Muscle Fibers,w 300800 fibers per motor neuron,w High sarcoplasmic reticulum development,SLOW- AND FAST-TWITCH FIBERS,GEL ELEC
16、TROPHORESIS,SINGLE MUSCLE FIBER PHYSIOLOGY,The difference in force development between FT and ST motor units is due to the number of muscle fibers per motor unit and the larger diameter of the FT fibers.,Did You Know?,Table 1.1 and table 1.2.,PEAK POWER GENERATED BY FIBERS,w Genetics determine which
17、 type of motor neurons innervate our individual muscle fibers.,w Muscle fibers become specialized according to the type of neuron that stimulates them.,w Endurance training, strength training, and muscular inactivity may result in small changes (less than 10%) in the percentage of FT and ST fibers.,
18、What Determines Fiber Type?,Aging may result in changes in the percentage of FT and ST fibers.,w Endurance training has been shown to reduce the percentage of FTx fibers, while increasing the fraction of FTa fibers.,Key Points,w Skeletal muscles contain both ST and FT fibers.,w ATPase in FT fibers a
19、cts faster providing energy for muscle action more quickly than ATPase in ST fibers.,Slow- and Fast-Twitch Muscle Fibers,Key Points,w Motor units supplying FT fibers are larger (e.g., more fibers per motor neuron) than those supplying ST fibers; thus, FT motor units can recruit more fibers.,w ST fib
20、ers have high aerobic endurance and are suited to low-intensity endurance activities.,Slow- and Fast-Twitch Muscle Fibers,w FT fibers are better for anaerobic or explosive activities.,w For a motor unit to be recruited into activity the motor nerve impulse must meet or exceed the threshold.,All-Or-N
21、one-Response,w More force is produced by activating more motor units.,w When this occurs, all muscle fibers in the motor unit act maximally.,w If the threshold is not met no fibers in that unit act.,Principle of orderly recruitment states that motor units are activated in a fixed order, based on the
22、ir ranking in the muscle.,Orderly Recruitment of Muscle Fibers,Slow-twitch fibers, which have smaller motor neurons, are recruited before fast-twitch fibers.,RAMPLIKE RECRUITMENT OF FIBERS,Table 1.3 percentage and cross-sectional areas of typeand type fiber.,w Number of motor units and muscle size(type2type1),w Frequency of stimulation of the motor units fig1.12,w Sarcomere length fig1.13(b and c peak tension),Factors Influencing Force Generation,w Speed of muscle action (shortening or lengthening) fig1.14,MUSCLE LENGTH vs FORCE PRODUCTION,