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Exercise Physiology

Muscle Structure and Function

QuestionAnswer
anatomy of skeletal muscle: epi, peri, endo epi (muscle) bundles of fasiculi, peri (fascile) bundles of fibers, endo (fiber) sacromeres, sacromeres are units of myofibrils
plasmalemma/sacrolemma cell membrane, fuses with tendon, conducts AP (ACh sreceptors), maintains pH, transports nutrients
satellite cells aid in muscle growth and development, aid in response to injury, immobilization, training
sacroplasm cytoplasm of fiber, stores glycogen and myoglobin
transverse T Tubules extensions of plasmalemma and carry action of AP deep into muscle fiber
sacroplasmic reticular (SR) stores Ca2+
sacromere and length contraile unit. z to z line. A, I bands, H zone, M line
A band vs I band. H zone vs M line A: actin and myosin, dark. I: actin and titin only. H zone: middle of A band where myosin heads are not. M line: middle of H zone
Structure of myosin (thick filament). two intertwined filaments stabilized by titin. globular heads. Stabalized by titin
actin structure (3 proteins), anchored? contains myosin binding site covered by P tropomyosin at rest. troponin anchored to actin and moves tropomyosin w Ca2+. Titin equally spaces out actin, nebulin anchors actin to Z disk
Titin role acts like s pring extending from Z to M. Increases stiffness w muscle activation and force development. Ca2+ binds to titin to increase muscle force when stretched. Stalizes sacromeres and centers myosin. prevents overstretch
What is a motor unit. How does it contribute to contractile force? single a-motor neuron and all fibers it innervates. more operating motor units=more force in contraction
what is a neuromuscular junction. What is its role in contraction? consists of synapse bt a-mtor neuron and muscele fiber. site of communication bt neuron and muscle
6 steps of muscle fiber contraction AKA describe excitation-contraction coupling 1. AP in brain 2.AP arrives at axon terminal, releasing acetylcholine 3. ACh crosses synapse, binds to ACh recptors on plasmalemma 4. AP down plasmalemma and T tub. 5. trigger Ca2+ reease from SR 6. Ca2+ enabled actin-myosin contraction
role of Ca2+ in muscle fiber AP arrives at SR from T tube (SR sensitive to e- charge) causing mass release of Ca2+ into sacroplasm. Ca2+ binds to troponin. Ca-trop move tropomyosin, allowing myosin to bind to actin
according to the sliding ligament theory, a series of contractions will continue to occur until... until Z disk reaches myosin filaments (max contraction) or APs stop and Ca2+ gets pumped back into SR
describe the sliding ligament theory see slide
What is ATP used for in excitation/contraction coupling? in sliding ligament theorey (contraction), ATP is hydrolized for E for contraction and also provides energy to pump Ca2+ back into SR for rest
peak tension and composition in body of Type 1 and Type 2 fibers 1: 50% in average muscle. peak tension 110ms AKA slow twitch. 2: Type 2a and 2x make up 25% in average muscle while Type 2c make up 1-3%. Peak tension is 50ms AKA fast twitch
What contributes to the varying speed of contraction cycling in different types of fibers? carying speed of myosin ATPase. Fast myosin ATPase=fast cocntraction cycling and vice versa
Describe how muscle biopsy is performed to examine types of fibers 10-100g piece of mucle is removed and frozen, sliced, then examined with microscope
How is the SR different in type 2 fibers? Type 2 have more highly developed SR thus can release Ca2+ faster so that inital velocity is 3-5x faster
how does motor units of diff fibers differ. What is the result? low threshold motor units are made off a smaller neuron than innervates less than 300 fibers while high threshold motor units are made of large neruons that innvervate more than 300. The more fibers innervation, the greater the F of contraction
In one fiber each, compare peak power of type 1, type 2a, 2x. What causes these differences? 2x>2a>1 due to various factors (SR, motor units). However, all fibers reach peak power at 20% of peak force
What is a type 1 muscle that everyone has soleus
Compare contrast the types of fibers see slide.
What determines the fiber type composition in a person's body? Genetic Factors deter which a-motor neurons innervate which fiber, Training Factors can induce 10% change in fiber type (endurace:1, strength:2, detraining), Aging can result is lost of high threshold motor units
What regulates muscle force generation? motor unit recruitment and rate of modulation (regulation) of active motor units
What is the general recruitment order of muscle fibers? Type 1, 2a, 2x
What is the Henneman's Size principle? how does it relate to the orderly recruitment and size principle? order of recruitment relates directly to size of a-motor unit so that the smallest motor units are recruited first. then midsize, then largest as fatigue sets in. This recruitment occurs in the same order every time
What are two types of muscle contraction? Explain each. static AKA isometric and dynamic. S: muscle produces force but do not change length- myosin cross bridges form and recycle (dont slide). D: muscle productes force and changes length. Join movement is produced.
Describe the subtypes of dynamic contraction Concentric: muscle shortens while producing force. Eccentric: muscle lengthens by producing force- cross bridges form but sarcomere lengthens
Explain the length-tension relation of the generation of force optimal force sarcomere length=optimal overlap. If too short or too stretched, little or no force develops.
Explain the speed-force relation of the generation of force (note difference bt concentric and eccentric contraction) Concentric: maximal forces development decreases at higher speeds. Eccentric: maximal force development increases at higher speeds.
Created by: kellyyrosse
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