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Anatomy and Physiology > Chapter 9: Skeletal Muscle > Flashcards

Chapter 9: Skeletal Muscle Flashcards

1
Q

a single muscle cell is a

A

muscle fiber

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2
Q

the muscle itself is ____ made up of___

A

an organ made of skeletal muscle tissue, connective tissue, nerves, and BV

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3
Q

in what two ways can muscles be attached to bone?

A
  1. directly

2. indirectly

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4
Q

how are muscles directly attached to bones?

A

by tendons

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5
Q

how are muscles indirectly attached to bones?

A

by sheets of connective tissue

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6
Q

what are the six main functions of skeletal muscle tissue?

A
  1. produce body movement
  2. maintain posture and body position
  3. support soft tissues
  4. guard body entrances and exits
  5. maintain body temperature
  6. store nutrients
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7
Q

skeletal muscle produces movement by

A

pulling on bones

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8
Q

Epimysium

A

dense sheath of collagen fibers around muscle

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9
Q

the epimysium separates

A

muscles from other tissues and organs

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10
Q

the epimysium is connected to

A

the deep fascia (dense connective tissue layer)

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11
Q

muscle fascicle

A

bundle of muscle cells

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12
Q

perimysium structure

A

fibrous layer containing collagen and elastic fibers dividing muscle into compartments

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13
Q

function of the perimysium?

A

separates muscle fascicles and provides them with BV and nerves

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14
Q

what type of connective tissue is the endomysium made of?

A

areolar

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15
Q

myofibrils structure:

A

bundles of protein filaments

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16
Q

myosatellite cells

A

stem cells that help repair damaged muscle tissue

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17
Q

endomysium structure

A

thin layer of areolar CT, collagen, and elastic fibers around muscle fibres

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18
Q

endomysium function:

A

supply muscle fibres with BV and nerves

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19
Q

at the ends of skeletal muscles ____ merge to form ____

A

connective tissue layers; tendon or aponeurosis

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20
Q

function of tendon

A

attaches muscle to specific point on a bone

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21
Q

what makes an aponeurosis different from a tendon?

A

broad sheet with broad attachment to bone

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22
Q

how do contracting muscles move bones?

A

pull on tendon/aponeurosis, which pulls on and moves bone

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23
Q

what are myoblasts?

A

embryonic cells that fuse to form multinucleate cells that differentiate into skeletal muscle cells

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24
Q

some myoblasts remain free in endomysium as ___ that__

A

myosatellite cells that help repair damaged muscle tissue

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25
Q

what happens to the myoblasts once they have differentiated into skeletal muscle fibers?

A

start making proteins for contraction

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26
Q

what is a benefit of skeletal muscle cells being multinucleated?

A

more copies of genes for protein/enzyme production

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27
Q

sarcolemma

A

plasmalemma

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28
Q

sarcoplasm

A

cytoplasm

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29
Q

structure os myofibrils

A

small cylindrical structures arranged parallel inside muscle fiber and run the length

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30
Q

what gives skeletal muscles their striations?

A

arrangement of myofibrils

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31
Q

there are many ___ along myofibrils

A

mitochondria

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32
Q

what are myofilaments?

A

bundles of protein filaments inside myofibrils

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33
Q

what are thin myofilaments?

A

mostly actin

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34
Q

what are thick myofilaments?

A

mostly myosin

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35
Q

what are sarcomeres?

A

repeating functional units of skeletal muscle fiber

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36
Q

what are the 5 muscle striations?

A
  1. z lines
  2. i band
  3. a band
  4. M line
  5. H band
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37
Q

what are z lines?

A

junction of adjacent sarcomeres by proteins at their thin filaments

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38
Q

what proteins join the sarcomeres at the z lines?

A

actinins

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39
Q

what is the i band?

A

lighter band with only thin filaments

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40
Q

what is the a band?

A

dark/dense region with thick filaments

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41
Q

what is the zone of overlap?

A

within A band; overlapping thick and thin filaments

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42
Q

what is the M line?

A

center of A band where adjacent thick filaments connect

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43
Q

what is the H band?

A

lighter region on each side of the M line with only thick filaments

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44
Q

the H band is only visible when?

A

when resting sarcomere

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45
Q

the sarcolemma is ___ and allows for ___ distribution of +/- charges

A

selectively permeable; uneven

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46
Q

change in charge in sarcolemma is initiated by ___ and Impulse spreads across__

A

neuron; entire sarcolemma

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47
Q

Tranverse (T) tubules are continuous with___ and extend into ___

A

sarcolemma; sarcoplasm

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48
Q

function of T tubules

A

form passageways through muscle fiber and encircle sarcomere

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49
Q

the sarcoplasmic reticulum is similar to

A

smooth er

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50
Q

enlarged sections of the sarcoplasmic reticulum are called ___ and are located __-

A

terminal cristernae, on either side of T tubule

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51
Q

triad is a pair of __ and one __

A

terminal cristernae and one T tubule

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52
Q

function of the SR (sarcoplasmic reticulum)

A

stores calcium that is actively pumped in from cytosol

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53
Q

muscle contraction starts when ___ are released form the SR into __, via __

A

Ca 2+ ions; cytosol; gated calcium channels

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54
Q

thin filaments are attached to __ with __

A

z lines; actin

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55
Q

thin filaments are made of 2 proteins

A
  1. tropomyosin

2. troponin

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56
Q

thin filaments have 2 actin types

A
  1. F-actin

2. G-actin

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57
Q

F-actin

A

filamentous: twisted, double strand of G-actin

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58
Q

G-actin

A

each have active site to bind to myosin

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59
Q

structure of tropomyosin

A

double-stranded protein wrapped around F-actin

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60
Q

function of tropomyosin

A

blocks myosin binding sites on G-actin, preventing actin/myosin interaction

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61
Q

troponin is made of __ subunits

A

3

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62
Q

troponin is attached to tropomyosin, making the __

A

troponin-tropomyosin complex

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63
Q

troponin is attached to____ and has binding sites for ___

A

g-actin; ca2+

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64
Q

the core of thick filaments is ___ which connects_

A

titin; thick filaments to Z lines; recoil after stretching

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65
Q

myosin is made of

A

2 twisted myosin subunits

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66
Q

myosin tails face the

A

M line

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67
Q

free myosin heads face __

A

out towards thin filaments

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68
Q

free myosin head is made of ___ and forms ___ with actin during ___

A

2 globular subunits; crossbridge; contraction

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69
Q

when muscles contract ___ slides over __

A

thin filaments; thick filaments

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70
Q

during contraction, H and I bands get ___, zones of overlap get __, Z lines move ___, and A band is __

A

smaller; larger; closer together, unchanged

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71
Q

sliding during muscle contraction occurs in ____ in ____

A

all sarcomeres; each myofibril

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72
Q

during contraction, all myofibrils ___ and so does the ___

A

shorten; muscle fiber

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73
Q

inside the cell is slightly ___ (+/-) than the outside

A

negative

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74
Q

a membrane potential is ___ distribution that represents a potential ___

A

an uneven; difference

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75
Q

membrane potentials are measured in

A

milivolts (mV)

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76
Q

neurons have a resting membrane potential of about

A

-70 mV

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77
Q

skeletal muscle fibers have a resting membrane potential of about

A

-85 mV

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78
Q

cytosol and extracellular fluid have ___ compositions

A

different

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79
Q

more K+ is located

A

inside cytosol

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80
Q

more Na + is located

A

outside in ECF

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81
Q

what accounts for the negative charge in cells?

A

proteins inside cant cross PM

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82
Q

what allows constant slow flow of Na+ and K+ down their [ ] gradient?

A

leak channels

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83
Q

Na+ __ the cell, K+ ___ the celll

A

enters; leaves

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84
Q

sodium potassium pumps export __ and import __

A

3Na+; 2K+ ( maintaining membrane potential)

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85
Q

what is the 1st step in an action potential?

A

small increase in membrane permeability to Na+, which rushes in and moves membrane potential in positive direction to threshold

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86
Q

what is the membrane potential threshold value?

A

-55mV

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87
Q

what is the 2nd step in an action potential?

A

voltage gated Na+ channels open, huge rush into cell resulting in depolarization

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88
Q

what is depolarization?

A

change of membrane potential to positive

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89
Q

what is the 3rd step in an action potential?

A

membrane potential recahes +30mV, Na+ gates close and voltage gated K+ channels open and K+leaves cell, resulting in repolarization

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90
Q

what is repolarization?

A

membrane potential returns to polarized state

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91
Q

what is the 4th step in an action potential?

A

voltage gated K+ channels close at resting potential

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92
Q

what is the 5th step in an action potential?

A

Na+/K+ pump restores original distribution

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93
Q

refractory period

A

time needed to get to original distribution, membrane cannot respond during this time

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94
Q

neurons and muscle fibers have ____ membranes

A

eletrically excitable

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95
Q

depolarization and repolarization create a___ wich spreads across __ in ___

A

electrical impulse; PM, less than 2msec

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96
Q

electrial impulses travel only ___ due to __

A

in one direction; refractory period

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97
Q

electrical impulses allow for

A

rapid communication

98
Q

neuromuscular junction (NMJ)

A

location where motor neuron controls a skeletal muscle fiber

99
Q

there are __NMJ per muscle fiber, but each motor neuron may ___

A

1; branch and control multiple muscle fibers

100
Q

what are the 3 components of the NMJ?

A
  1. axon terminal
  2. motor end plate
  3. synaptic cleft
101
Q

the axon terminal is located __ and has vessicles with ___

A

at the end of a motor neuron; acetylcholine

102
Q

the motor end plate of a muscle fiber has ___ that increase __, and contain ___ to break down ACh

A

junctional folds; # of ACh receptors; acteylcholinesterase (AChe)

103
Q

synaptic cleft

A

space between axon terminal and motor end plate

104
Q

when an action potential arrives at the NMJ, the change in membrane permeability causes the ___ to fuse with the ___ and ACh is ___ by ___

A

ACh vessicles; neuron PM; released by exocytosis

105
Q

ACh diffuses across the cleft and binds to ___ at __, which changes sarcolemma ___ permeabiliy, so it comes into the sarcoplasm

A

ACh-receptor membrane channels; motor end plate; Na+

106
Q

Na+ influx generates ___ in sarcolemma, ACh ___ and ACh-receptors__

A

action potential; breaks down (AChe); close

107
Q

action potential generated at motor plate immediately __

A

spreads across entire sarcolemma

108
Q

action potential moves down ___ between ___ of SR, which changes the ___ of SR

A

T-tubules, terminal cristernae; permeability

109
Q

SR releases stored ___ into ___ which begins ___

A

Ca2+; sarcomeres; contraction

110
Q

explain excitation-contracting coupling?

A

excitation (action potential) is coupled with contraction (sliding filaments shorten sarcomeres)

111
Q

what are the 7 steps of muscle fiber contraction cycle?

A
  1. resting sarcomere
  2. contraction cycle begins
  3. active sites exposed
  4. cross-bridges form
  5. myosin heads pivot
  6. cross-bridges detach
  7. myosin reactivates
112
Q

myosin heads in the resting sarcomere are ____ or ___

A

energized, or cocked

113
Q

cocking myosin heads requires ___

A

breakdown of ATP

114
Q

myosin head acts as __. __ and __ stay attached to head

A

ATPase, ADP and P

115
Q

what happens in the “contraction cycle begins” step of muscle contraction?

A

Ca2+ arrive from SR

116
Q

Ca2+ binds to ___ to change position and move ___, which ____ active sites on ___

A

troponin; tropomyosin; exposes; actin

117
Q

what happens in the “cross bridge formation” step of muscle contraction?

A

myosin binds to active sites on actin

118
Q

cross bridge formation causes myosin heads to ___ towards ___, this is called the ___

A

pivet; M line; power stroke

119
Q

the power stroke results in release of ___ and __

A

ADP and P

120
Q

how do the cross bridges detach?

A

a new ATP attaches to each myosin head, releasing it from the actin

121
Q

once the cross bridges detach, the active site is available for __

A

another cross bridge

122
Q

free myosin heads split ATP into

A

ADP and P

123
Q

the energy released by myosin reactivation is used to __

A

recock myosin head

124
Q

the contraction cycle will repeat while __ and __ are available

A

calcium ions and ATP

125
Q

calcium levels stay high only if __ continue

A

action potentials

126
Q

when stimulus ends: SR calcium channels__

A

close

127
Q

when stimulus ends: ___ return ca2+ to ___

A

Ca2+ ion pumps; terminal cristernae (SR)

128
Q

when stimulus ends: troponin-tropomyosin complex ___

A

resumes original position, covering active sites on actin

129
Q

what are the 6 steps of excitation-contraction cycle?

A
  1. neural control
  2. excitation
  3. ca2+ ion release
  4. contraction cycle begins
  5. sarcomeres shorten
  6. muscle tension produced
130
Q

what happens in the 1st (neural control) step of excitation-contraction cycle?

A

action potential in motor neuron starts process at neuromuscular juntion

131
Q

what happens in the 2nd (Excitation) step of excitation-contraction cycle?

A

AP causes ACh release from motor neuron, which leads to excitation (AP) in sarcolemma

132
Q

what happens in the 3rd (Ca2+ release) step of excitation-contraction cycle?

A

muscle fiber AP travels through T-tubules/triads, releasing stored Ca2+

133
Q

what happens in the 4th (contraction begins) step of excitation-contraction cycle?

A

Ca2+ binds to troponin, exposing active sites on actin, cross bridges form and continue

134
Q

what happens in the 5th (sarcomeres shorten) step of excitation-contraction cycle?

A

thick and thin filaments slide over each other, shortening sarcomere and pulling ends of muscle fiber closer

135
Q

what happens in the 6th (muscle tension produced) step of excitation-contraction cycle?

A

muscle fiber shortening causes entire muscle to shorten, contraction produces a pull/tension on tendons

136
Q

muscle fibers are all or none; they are either __ or __

A

producing tension; relaxed

137
Q

___ number of crossbridges can form at optimal resting length of sarcomere

A

maximum

138
Q

optimal resting legth of sarcomere produces __ tension

A

most

139
Q

normal range of sarcomere length is between

A

75 and 130% of optimal length

140
Q

___, ___, and ___ prevent too much stretching/compression of sarcomere

A

connective tissue; muscle arrangement; bones

141
Q

what is a muscle twitch?

A

single-stimulus contraction relaxation sequence in muscle fibre

142
Q

duration of muscle twitch depends on __, __, and __

A

muscle type, location, environmental factors

143
Q

what does a myogram show?

A

development of muscle tension

144
Q

what are the 3 stages of a muscle twitch?

A
  1. latent period
  2. contraction phase
  3. relaxation phase
145
Q

what 2 things happen in the latent period of a muscle twitch?

A
  1. AP stimulates sarcolemma

2. Ca2+ released from sarcoplasm reticulum

146
Q

what 3 things happen is the contraction phase of a muscle twitch?

A
  1. ca2+ binds to troponin
  2. cross bridge cycling
  3. start of tension development to peak tension
147
Q

what 2 things happen in the relaxation phase of a muscle twitch?

A
  1. Ca2+ drops; cross bridges detach; active sites covered

2. tension returns to normal

148
Q

how long is a muscle twitch from peak tension to end of twitch?

A

~25msec

149
Q

tension produced by a skeletal muscle is determined by what 2 things?

A
  1. amount of tension produced by each muscle fiber

2. number of muscle fibers stimulated

150
Q

what are the 4 levels of muscle tension?

A
  1. treppe
  2. wave summation
  3. incomplete tetanus
  4. complete tetanus
151
Q

what is treppe?

A

stimulation of muscle fiber immediately after relaxation

152
Q

what does treppe produce?

A

increasing maximum tension

153
Q

is treppe demonstrated by most skeletal muscles?

A

no

154
Q

what is wave summation?

A

addition of one twitch to another: stimulation of muscle fiber before relaxation

155
Q

what does wave summation produce?

A

increasing maximum tension

156
Q

____ determines maximum time available to produce wave summation

A

duration of twitch

157
Q

what is incomplete tetanus?

A

rapid cycle of contraction/relaxation

158
Q

what does incomplete tetanus produce?

A

near-peak tension (levels off before max tension)

159
Q

what makes incomplete tetanus “incomplete”?

A

still some relaxation

160
Q

what is complete tetanus?

A

higher stimulation eliminates relaxation

161
Q

what causes complete tetanus?

A

no calcium ions return to SR, but remain on troponin, keeping actin and myosin locked together

162
Q

how often does complete tetanus occur in normally functioning muscles?

A

seldom

163
Q

number of stimulated muscle fibers affects ___

A

muscle tension

164
Q

what is a motor unit?

A

single motor neuron and all muscle fibers it controls

165
Q

fewer fibers in a motor neuron produces what type of control?

A

fine, precise

166
Q

motor unit recruitment

A

activation of more motor units to produce more tension

167
Q

what units are activated first in motor unit recruitment?

A

smaller motor units, then larger motor units

168
Q

larger motor units have ____ more ___ fibers

A

faster; powerful

169
Q

motor unit recruitment results in ____ increase in muscle tension

A

smooth, steady

170
Q

what is muscle tone?

A

resting tension in a skeletal muscle

171
Q

what causes muscle tone?

A

variable number of motor units always active to produce low-level tension

172
Q

muscle tone is regulated ___

A

subconsciously

173
Q

increased muscle tone results in ___ resting metabolism

A

higher

174
Q

what is isotonic contraction?

A

tension rises and skeletal muscle length changes

175
Q

what are the two types of isotonic contractions?

A
  1. concentric contraction

2. eccentric contraction

176
Q

what is concentric contraction?

A

muscle tension rises until it exceeds load; as muscle shortens, tension remains constant

177
Q

what is an example of concentric contractions?

A

flexing elbow while holding weight

178
Q

in concentric contraction, speed of contraction is ___ proportional to load

A

inversely

179
Q

what is eccentric contraction?

A

peak tension produced is less than load, causing muscle to elongate

180
Q

what is an example of eccentric contraction?

A

returning weight from flexed to extended position

181
Q

rate of elogation of muscle depends on ___ and ___

A

tension and load

182
Q

in eccentric contraction, when contraction ends, load stretches muscle until ___, ___ or ___

A
  1. muscle tears
  2. tendon breaks
  3. elastic recoil opposes load
183
Q

what is isometric contraction?

A

muscle length does not change, tension never exceeds load

184
Q

what are the 2 sources of ATP in muscles?

A
  1. glycolysis

2. aerobic metabolism

185
Q

site of glycolysis

A

cytosol

186
Q

what is glycolysis?

A

anearobic breakdown of glucose to pyruvate

187
Q

what much ATP and pyruvate are produced by glycolysis?

A

2 for each glucose

188
Q

aerobic metabolism provides ___% of ATP needs of resting cell

A

95

189
Q

site of aerobic metabolism

A

mitochondria

190
Q

most ATP comes from what stage of aerobic metabolism?

A

ETC

191
Q

how many ATP per pyruvate are made by aerobic metabolism?

A

15

192
Q

most energy is stored as ___

A

glycogen

193
Q

glycogen makes up ___% of muscle weight

A

1.5

194
Q

free ATP supports only __ muscle twitch

A

-10

195
Q

creatine phosphate supplies energy for about __sec

A

15

196
Q

creatine is assembled from

A

amino acids

197
Q

muscle metabolism at rest has a ___ ATP demand

A

low

198
Q

when the muscle is as rest, the mitochondria produce ___ ATP

A

surplus of

199
Q

during muscle metabolism at rest, __ and __ are absorbed from the bloodstream

A

fatty acids and glucose

200
Q

during muscle metabolism at rest, fatty acids and glucose make __ to covert __ to __ and ___ to __

A

ATP; creatine; creatine phosphate; glucose; glycogen

201
Q

muscle metabolism at moderate activity relies on __ metabolism of ___ to make __

A

anaerobic; pyruvate; ATP

202
Q

what happens to O2 consumption during muscle metabolism at moderate activity?

A

increases

203
Q

during muscle metabolism at moderate activity, there is no fatigue until __, __, and __ reserves are exhausted

A

glycogen, lipid, amino acid

204
Q

muscle metabolism at peak activity requires ___ ATP demands

A

enormous

205
Q

mitochondria at maximum production provides ~__ of ATP needs

A

1/3

206
Q

the rest of ATP demands at peak activity are produced by

A

glycolysis

207
Q

excess pyruvate converts to

A

lactate

208
Q

increase in lactate and H+ results in ____ which is characterized by a ___ in pH

A

lactic acidosis, decrease

209
Q

lactic acidosis causes muscle __

A

fatigue

210
Q

muscle fatigue means

A

muscle can no longer perform at required level

211
Q

what is the major factor in muscle fatigue?

A

decreased pH

212
Q

why does decreased pH affect muscle fatigue?

A

decreases calcium/troponin binding

alters enzyme activity

213
Q

what is the recovery period?

A

time needed to return conditions in muscle fibers to preexertion levels

214
Q

anaerobic metabolism is ___ than aerobic, but only goes until ___-

A

faster; glycogen reserves are depleted

215
Q

anaerobic is ___ efficient than aerobic

A

less

216
Q

anaerobic ___ pH

A

lowers (lactic acid)

217
Q

anaerobic ___ body temperature

A

raises

218
Q

during the recovery period, __ is available and lactate is converted to __

A

O2; pyruvate

219
Q

during the recovery period, pyruvate makes __ or recycled to ___

A

ATP; glucose/glycogen

220
Q

aerobic captures ___% of energy released

A

42

221
Q

anaerobic captures __% of energy released

A

4-6

222
Q

___% of body heat produced by resting skeletal muscle

A

70-80%

223
Q

what is the cori cycle?

A

shuttling of lactate to liver and glucose back to muscles

224
Q

most lactate produced during peak activity goes to

A

the liver

225
Q

the liver converts lactate to ___ and releases it__

A

glucose; back to the blood

226
Q

what are the 3 major types of skeletal muscle fibers?

A
  1. fast
  2. slow
  3. intermediate
227
Q

fast fibers reach peak tension in ___ sec

A

<0.01

228
Q

structure of fast fibers

A

large in diameter, densely packed myofibrils, large glycogen reserves, few mitochondria

229
Q

fast fibers produce __ contractions

A

powerful

230
Q

fast fibers fatigue __

A

rapidly

231
Q

why do fast fibers fatigue fast?

A

most ATP produced anaerobically

232
Q

slow fibers take ___x longer to contract than fast

A

3

233
Q

the contractions of slow fibers are __ and get energy __

A

long, sustained; aerobically

234
Q

structure of slow fibers

A

extensive capillary network; myoglobin pigment binds O2 and makes muscle appear dark

235
Q

intermediate fibers more closely resemble __-, but have more __ and __

A

fast fibers; capillaries; fatigue-resistant

236
Q

hypertony

A

muscle enlargement form repeated exhaustive stimulation

237
Q

muscles can increase in size due to (5)

A
  1. more mitochondria
  2. more glycogen
  3. more/wider myofibrils
  4. more myofilaments
  5. steroid hormones
238
Q

muscle atrophy

A

decreased muscle size, tone, and power

239
Q

causes of muscle atrophy (from decreased stimulation) (3)

A
  1. normal aging
  2. paralysis/nervous sytem damage
  3. reduced use
240
Q

muscular dystrophy

A

inherited diseases that produce muscular weakness/deterioration

241
Q

most common/understod forms of muscular dystrophy are (2)

A

Duchenne (DMD) and Becker (BMD)

Anatomy and Physiology (13 decks)

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