muscle physiology

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muscle physiology
2013-10-29 00:37:44

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  1. the striated appearance of skeletal muscle is due
    orderly arrangement of the thick and thin filaments into A and I bands
  2. muscle fibers develop tension by
    contraction of scarcomeres and shortening
  3. myosin
    • is found in the A band
    • has ATPase activity
    • contains a globular head that forms the cross bridges between the thick and thin filaments
  4. actin
    • spherical and forms from a helical chain that forms the main structural component of the thin filaments
    • involed in preforming a power stroke during muscle contraction
    • found in the A band
    • form attachments with myosin cross bridges
  5. tropomyosin
    regulatory protein
  6. thick filaments in skeletal muscle are compesed of
  7. sarcomeres are arranage end to end as
  8. the I band of the sarcomere is characterized by
    the prescence of thin filaments and actin
  9. A band
    dark coloration
  10. Z lines
    extended down from the middle of the I band
  11. Cross-bridges
    • bind to actin during muscle contraction and are globular heads made of myosin
    • bend 45during muscle contraction
  12. order of muscle componenets from larger to smaller
    muscle fiber > myofibril > sarcomere > thin filament > troponin
  13. skeletal muscle fibers
    • have T tubles within their sarcomeres
    • Z lines extending down the middle of the bands
  14. the region between two Z lines is a
  15. skeletal muscle fibers
    • are some of the logest cells in the body
    • parallel to eachother and are not attached end-to-end within a muscle
    • do NOT contain Z lines within their A bands
    • are multinucleated
  16. characteristic that is shared by all types of the muscle tissues
    every type contains tropomyosin
  17. the functional unit of skeletal muscle is the
    sarcomere = the area btwn the Z lines
  18. troponin
    binds with calcium to allow sarcomere shortening
  19. the smallest unit of contraction with a skeletal muscle is a
  20. the function of tropomyosin
    prevent myosin cross bridges from attaching to the thin filaments
  21. troponin
    • 3 polypeptide sequence
    • inhibitory subunit that binds to actin
    • binds to tropomysosin and helps bing to actin
    • 3 binds to calcium
  22. sliding filament mechanism
    • this filaments slide inward toward the center of the A band 
    • during contraction thin filaments slide past the thick ones so that the actin and myosin overlap to a greater degree
    • 1. when the nervous system stimulates muscle fibers, the myosin heads on the thick filaments latch on to the myosin-binding sites on the actin thin filaments and the sliding begins
    • 2. the cross bridge attachments formnd break several times during contraction, acting like tiny ratchets to generate tension and propel the thin filaments toward the center of the sarcomere
    • 3. this event occurs simultaneously in sarcomeres through out the cell and the muscle cell shortens
    • 4. the Z discs (attached to thin filaments) pull toward the M line 
    • the muscle cell shortens: I bands shorten, the distance between sucessive Z discs shorten, the H zones disappear and A bands move closer together but their length does not change
  23. during contraction of the skeletal muscle fibers...
    thin filaments slide inward to the A band center and as a result of cycles of cross-bridges binding and bending
  24. molecules involved in regulation of the cross bridge attachment
    • calsium ions
    • troponin 
    • myosin
  25. the H zone
    • the area within the middle of the A band  where the thin filaments do not reach
    • shortens or disappears during contraction
    • contains only thick filaments
  26. during muscle contraction
  27. changes in band pattern that occur during muscle relaxation
    • I bands get wider
    • H zones become wider
    • thick filaments remain the same length
  28. during contraction, asynchronous cycling of crossbridges
    prevents thin filaments from slipping backwards
  29. during exciation - contraction coupling
    • the AP travels down the T tubules
    • Ca2+ is released form the sarcoplasmic reticulum
  30. the T tubules
    • provide a mean of rapidly tansmitting the AP from the surfaces into the central portions of the muscle fiber
    • runs perpendicularly betwen the myofibrils
  31. sarcomere
    stores Ca2+
  32. sequences of events that are involved in muscle contraction
    • impulse reaches the axon's synaptic knob
    • synaptic vesicles fuse with neurons membrane and release ACh via exocytosis 
    • ACh bings to receptors on the muscle cell membrane
    • sodium channels open and soidum flows in
    • if enough sodium moves into the muscle cell, an impulse (AP) develops
  33. motor end plate
    provide attachment sites for ACh
  34. An action potential rapidly spreads to the central portions of a muscle cell by the means of
    T tubules
  35. binding of _____ to myosin permits the cross-bridge to _____
    • bindig of ATP
    • detach from actin
  36. the sarcoplasmic reticulum stores ______ when a muslce is relaxed and releases it for binding to ______ during contraction
    • SR stores Ca2+ 
    • binds with troponin
  37. one of the steps excitation-contraction occurs in the begining
    sodium channels open in the fiber's membranes
  38. characteristic of cross-bridges
    • they are comprised of myosin
    • they have an actin binding site
    • they have an ATPase binding site
    • they provide power stroking
    • globular myosin heads that protrude from the thick filaments 
    • they bend during muscle contraction
    • they detach from actin during muscle contraction
    • they are not found in the I band
  39. foot proteins
    • span the gap between a lateral sac of the SR and the adjacent T tubule
    • are are believed to serve as Ca2+ channels
  40. during a cross-bridge cycle in skeletal muscle
    cross bridge is energized when it hydrolyzes ATP
  41. cross-bridge interaction btwn actin and myosin in skeletal muscle is directly blocked by
  42. the energy for cross bridge cycling during muscle contraction is provided by
  43. relaxation of muscle
    • initaited by re-entry Ca2+ into the SR 
    • contraction force is declining
    • muscle tension decrease
    • muscle returns to its initial length 
    • detachment of actin from tropomyosin
    • troponin-tropomyosin complex is slipping back into its blocking position
    • Acetylcholinesterase destroys ACh to allow muscle membrane to return to resting potential 
    • Ca2+ is actively taken up by the lateral sacs of the SR when there is no longer a AP
  44. lack of ATP in skeletal muscle cell would most likely cause
    and increase in tension and inability to relax
  45. whole muscle tension depends on
    • number of muscle fibers contracting
    • tension produced by each cortracting fiber
    • extent of motor-unit recruitment
    • frequency of stimulation
  46. motor unit refer to
    a single motor neuron plus all of the muscle fibers it innervate
  47. twitch summation
    • the muscle fiber is stimulated again before the filaments have completely returned to their resting positions and strong muscle contractions occur but stronger AP do not occur
    • is means by which gradation of muscle contraction may be accomplished results from the additional release of Ca2+ within the cystol of muscle fibers
    • results from increasing the frequency at which motor units are firing with a muscle
  48. to pick up something heavier than your pencil, your nervous system could
    stimulate larger motor units
  49. based on the length-tension relationship
    a resting muscle that is shorter or longer than its 1o will generate less tesion at the onset of  contraction
  50. picking up a book at a constant speed requires that
    the muscle preform a concentric contraction
  51. muscle tension
    is created during muscle contraction as the tension generated by the contractile elements is transmitted via the connective tissue and tendons to the bones
  52. the origin of a muscle is its
    stationary end of attchment
  53. during an isotonic contraction
    the muscle's tension remains constant
  54. with eccentric muscle contractions
    muscle lengthens while contraction
  55. submaximal isometric contractions are important for
    maintaining postitions
  56. in a muscle fiber undergoing maximal tetanic stimulation the velocity of shortening ________ as the load ______
    decreases, increases
  57. if the load on a muscle is increased, eventually a load will be reached at which the veloity of shortening becomes zero. At this point, the muscle contraction is referred to as
  58. energy sources available to form ATP in muscle fibers in the absence of oxygen include
    creatine, phosphate and glycolysis
  59. the first means by which ATP is produced at the onset of contractile activity is
    transfer of energy and phosphate from creatine phosphate to ADP
  60. during aerobic exercise, the primary means for ATP production in muscle fibers involves
    oxidative phosphorylation
  61. myoglobin
    can store small amounts of Oand increases the rate of Otransfer from the blood into muscle fibers
  62. summation of simple twitches
    the twitches resulting from seperate AP added together
  63. different types of muscle fiber
    • the higher the ATPase activity, the faster the spped of contraction 
    • muscles with high ATP-synthesizing ability are more resistant to fatigue
    • oxidative types of muscle fibers contain myoglobin 
    • muscle fibers containing large amounts of myoglobin have a dark red color in comparison to the paler fibers, which have little myoglobin
  64. fast-glycolytic (type IIx) muscle fibers
    • have high myosin-ATPase activity
    • can carry out oxidative phosphorylation
    • fatigue rapidly
    • contain myoglobin
  65. fast-oxidative (type IIa) fibers
    can be converted into fast-glycolytic fibers by regular resistance activities and are most abundant in muscles specialized for maintaining low-intensity contractions for long periods of time without fatigue
  66. muscle cells of a marathon runner's lefs would exhibit
    • high resistance fatigue
    • low glycogen content
    • many mitochondria
    • slow speed of contraction
    • slow oxidative type I
  67. fatigue is the failure of a muscle fiber to maintain ______ as a result of previous contractile activity
  68. muscle fatigue can be caused by
    • lactiv acid accumulation 
    • depletion of ATP
  69. directly influences motor neurons
    • primary motor cortex
    • brain stem
    • afferent neurons (through intervening interneurons) 
    • NOT the cerebellum
  70. muscle atrophies
    • it decreases in mass
    • becomes weaker
  71. in the body's lever system, the fulcrums are represented by the
    • joints 
    • bones= levers
    • joints= fulcrums
    • muscle= applied force
  72. with the type of lever system exemplified by flexion of the elbow joint , whan an object is held in the hand
    • the power arm of the lever is the distance btwn the elbow joint and the insertion of the biceps muscle 
    • load arm of the lever is the distance btwn the elbow joint and the hand 
    • velocity and distance moved by the hand is amplified at the expense of the biceps muscle having to exert considerably greater force than the actual lad that is moved
  73. characteristic of most of the body's lever system
    • they work at a mechanical disadvantage '
    • muscles must exert greater forces than the load
  74. enlargement of muscle due to weight lifting is primarily a result of
    hypertropht and increased production of actin and myosin
  75. corticospinal system
    consists of fiber that originate within the primary motor cortex and terminate on motor neurons
  76. conscious initiation of muscle contraction is controlled by
    the cerebral cortex
  77. spastic paralysis occurs when
    excitatory inputs to motor neruons are unopposed bc of disruption of an inhibitory system in the brain stem
  78. during coactivation
    the gamma motor neuron and the alpha motor neuron systems to a skeletal muscle are activated simultaneously
  79. intrafusal muscle fibers
    are found within muscle spindles and contain sensory nerver endings that are activated by stretch
  80. extrafusal muscle fibers
    supplied by alpha motor neurons
  81. the stretch receptors in the central portion of the muscle spindle can be activated by
    • a passive strech of the whole muscle, including stretch of the  muscle spindles
    • contraction of the end proportions of the muscle spindle
    • gamma motor neuron stimulation of the muscle spindle
  82. stretch reflexes are important
    • for maintaining balance and posture
    • providing afferent inormation coordination complex muscle activity
  83. calium turns on cross bridges by physically repositioning the troporin-tropomyosin complex to uncover the actin cross-bridge binding sites in
    skeletal and cardiac muscle
  84. characteristics of SM
    • its contractionis initiated neurogenically only
    • cells are spindle shaped
    • can develop less tension per unit cross-sectional area compared to skeletal muscle
    • can maintain tension with comparatively less ATP consumption than skeletal muscle
    • the range of lenths over which SM is able to develop near maximal tension is much greater than skeletal muscle
    • a hollow organ enclosed by SM accomodates variable volumes with little change in pressure exerted on the contents
  85. cardiac muscle tissue
    • has gap junctions
    • has a moderatley developed SR
    • has slow myosin ATPase activity
    • stors calcium in the SR
  86. the reglation of smooth muscle contraction is mediated by the phosphorylation of _______  and  response of calcium binding to ______
    • myosin is phosphorylated
    • calcium binds to calmodulin
  87. ______ is not required for contraction of SM
  88. calcium that enters the cell during SM excitation binds with
  89. types of muscles that are myogenic
    • cardiac muscle
    • single-unit SM
  90. multi-unit SM
    • neurogenically activated
    • under ANS control
    • found in the iris of the eye
  91. single-unit SM
    • contains an abundance of gap junctions and forms functional syncytia
    • self-excitable
    • found in the walls of the digestive, reproductive and urnary tracts and small blood  vessels
  92. a functional syncytium
    can be excited to contract as a unit bc AP can be conducted from one cell to adjacent cells through gap junctions
  93. what is responsible for initiating contraction of SM
    stimulation of the autonomic nervous system
  94. repaying the oxygen deficit after strenuous exercise involves
    • removes lactate in the muscle cells
    • replenishing stores of creatine phosphate
    • replenishing store of glycogen
  95. pacemaker activity
    refers to spontaneously depolarizations of the membrane resulting from shifts in passive ionic fluxes accompanying automatic changes in channel permeability
  96. a functional syncytium of cardiac muscle cells means that they
    work as a unit mechanically and electrically
  97. cardiac muscle
    • contains tropomyosin
    • contains gap junctions
    • found only in the heart
    • is self-excitable
    • straited with intercalted disks
  98. True or False : muscle cells are the only cell types that contain intracellular contractile proteins
  99. True or False: all skeletal muscles are attached to the skeleton
  100. True or False:skeletal fibers are formed during embryonic development by the fusion of many smaller cells
  101. True or False a single muscle cell is know as a myofibril
    FALSE :  muscle fiber
  102. True or False: The H zone of the sarcomere consists of myosin but does not contain actin
  103. True or False: The M line is formed by a flattened disc-like cytoskeletal protein that connects the thin filaments of two adjoining sarcomeres
    • FALSE
    • Z-line
  104. True or False: thin and thick filaments in a sarcomere contain cross bridges
  105. True or False: myosin is considered to be a regulatory protein because it plays an important role in regulation of muscle contraction
    • FALSE 
    • tropomyosin and troponin
  106. True or False: the thick filaments overlap in the A band
  107. True or False: tropomyosin covers the cross bridge binding  sites on the thick filaments when the a sacomere is not contracting
    • FALSE
    • thin
  108. True or False: the thick filaments in a sarcomere contains cross bridges
  109. True or False: all cross bridges within a sarcomere stroke in unison when pulling the actin filaments
  110. True or False the functional unit of skeletal muscle is the myofibril
  111. during isometric contraction
    the muscle maintains constant length
  112. True or False: Foot proteins link the actin molecules together within a thin filament
  113. True or False: according to the sliding filament mechanism of muscle contraction, the thick filaments slide in closer together to shorten the sarcomere
  114. True or False: the T tubule is line with muscle cell's membrane
  115. True or False : according to the sliding filament mechanism  of muscle contraction, the muscle fibers of one motor unit slide in closer together between the muscle fibers of adjacent motor units
  116. True or False: the thick filaments within a myofibril have ATPase activity
  117. True or False: cross-bridges have actin binding sites that are normally covered by troponin and tropomyosin except during the excitation-contraction coupling
  118. True or False during muscle contraction the A band becomes shorter
  119. True or False: muscle relaxation does not take place until all of the ATP is used up
  120. True or False: in order for relaxation to occur, ACh must be removed from the muscle cell's receptors
  121. True or False: acetylcholinesterase removes ACh from receptors
  122. True or False: the contraction phase of a muscle cell lasts longer than the refractory period
  123. True or False: rigor mortis occurs when Ca2+links actin and the myosin globular head together in a rigor complex
  124. True or False: Muscle cells require ATP in order to relax, following a contraction
  125. True or False: more tension is developed during twitch summation than during a single twitch bc the duration of elevated cytosolic Ca2+ concentration increases during summation, thus increasing the availability of cross-bridge binding sites
  126. True or False: gradation of muscle contraction can be accomplished by stimulating variable portions of each muscle fiber
  127. True or False: Summation events result om increasing amounts of cytoplasmic calcium levels
  128. True or False: a motor unit is a single muscle plus all of the motor neurons that innervate it
  129. True or False: Muscles that have a fine degress of control have small motor units
  130. True or False: the larger motor units within a muscle, the more precisely controlled the gradations of contraction
  131. True or False: increasing the number of recruited motor units in a muscle increases its force or strength of contraction
  132. True or False: with twitch summation, the muscle fiber is stimulated so rapidly that it does not have an opportunity to returnto resting potential between stimuli
  133. True or False: tetnus occurs when a muscle fiber is stimulated so rapidly that it is not allowed to relax btwn stimulations, resulting in a smooth, sustained contraction
  134. True or False: the shorter a muscle fiber is before the onset of a contraction, the greater the force that can be developed upon the subsequent contraction bc the thin filaments are already partially slid inward
  135. True or False: the metabolic capability of a muscle fiber can affect the degree of tension it can develop
  136. True or False: denervated muscle fibers become progressively smaller and their content of actin and myosin decreases
  137. True or False: a skeletal muscle produces motion by pulling the origin toward its insertion
  138. True or False: bones serve as fulcrums for muscle action
    • FALSE
    • joints
  139. True or False: the muscle-lever systems work at a mechanical disadvantage
  140. True or False: muscle tension does not change in isometric contractions
  141. True or False: the skeletal muscle shortens during concentric, isotonic contraction
  142. True or False: in an isotonic contraction, about 50% of the energy is consumed is realized as external work and the remainig50% is converted to hear
  143. True or False:the work performed by a muscle is the force it develops divided by distance
  144. True or False: oxidative phosphorylation occurs within the mitochondria of the muscle cells
  145. True or False: repaying the oxygen deficit involves the formatino of lactate in fatigues muscle cells
  146. True or False: anaerobic exercise is endurance-type exercise
  147. True or False:central fatigue of a muscle directly results from the accumulation of lactic acid in the muscle
  148. True or False: slow-oxidative muscle fibers have a high resistance to fatigue
  149. True or False: fast-oxidative muscle fibers have a high concentration of mitochondria
  150. True or False: fast-glycolytic muscle fibers do not require as much oxygen use as slow-oxidative fibers
  151. True or False: slow-oxidative muscles fibers would be found in high density in the leg muscles of an olympic sprinter
  152. True or False: a skeletal muscle undergoes hypertrophy mainly by producing many more muscle fibers
  153. True or False: atrophy can develop in a muscle by either denervation or disuse
  154. True or False: skeletal muscles are capable of limited repair after injury
  155. True or False: single-unit SM has no innervation
  156. True or False: the corticospinal system controls fine, descrete, voluntary body movements
  157. True or False:  the 2 types of fast twitch fibers are interconvertible depending on the type of conditioning they recieve
  158. True or False: single unit SM and cardiac muscle are both self-excitable
  159. True or False: both multi-unit SM and single unit SM are under motor control from the autonomic nervous system
  160. True or False: all smooth muscle is myogenic
  161. True or False: the strengthe and the rate of contraction of the heart can be influenced by the ANS
  162. True or False: the heart initiates its own AP without any external stimulation