Chapter 9: Skeletal Muscle Flashcards
(241 cards)
1
Q
a single muscle cell is a
A
muscle fiber
2
Q
the muscle itself is ____ made up of___
A
an organ made of skeletal muscle tissue, connective tissue, nerves, and BV
3
Q
in what two ways can muscles be attached to bone?
A
- directly
2. indirectly
4
Q
how are muscles directly attached to bones?
A
by tendons
5
Q
how are muscles indirectly attached to bones?
A
by sheets of connective tissue
6
Q
what are the six main functions of skeletal muscle tissue?
A
- produce body movement
- maintain posture and body position
- support soft tissues
- guard body entrances and exits
- maintain body temperature
- store nutrients
7
Q
skeletal muscle produces movement by
A
pulling on bones
8
Q
Epimysium
A
dense sheath of collagen fibers around muscle
9
Q
the epimysium separates
A
muscles from other tissues and organs
10
Q
the epimysium is connected to
A
the deep fascia (dense connective tissue layer)
11
Q
muscle fascicle
A
bundle of muscle cells
12
Q
perimysium structure
A
fibrous layer containing collagen and elastic fibers dividing muscle into compartments
13
Q
function of the perimysium?
A
separates muscle fascicles and provides them with BV and nerves
14
Q
what type of connective tissue is the endomysium made of?
A
areolar
15
Q
myofibrils structure:
A
bundles of protein filaments
16
Q
myosatellite cells
A
stem cells that help repair damaged muscle tissue
17
Q
endomysium structure
A
thin layer of areolar CT, collagen, and elastic fibers around muscle fibres
18
Q
endomysium function:
A
supply muscle fibres with BV and nerves
19
Q
at the ends of skeletal muscles ____ merge to form ____
A
connective tissue layers; tendon or aponeurosis
20
Q
function of tendon
A
attaches muscle to specific point on a bone
21
Q
what makes an aponeurosis different from a tendon?
A
broad sheet with broad attachment to bone
22
Q
how do contracting muscles move bones?
A
pull on tendon/aponeurosis, which pulls on and moves bone
23
Q
what are myoblasts?
A
embryonic cells that fuse to form multinucleate cells that differentiate into skeletal muscle cells
24
Q
some myoblasts remain free in endomysium as ___ that__
A
myosatellite cells that help repair damaged muscle tissue
25
what happens to the myoblasts once they have differentiated into skeletal muscle fibers?
start making proteins for contraction
26
what is a benefit of skeletal muscle cells being multinucleated?
more copies of genes for protein/enzyme production
27
sarcolemma
plasmalemma
28
sarcoplasm
cytoplasm
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structure os myofibrils
small cylindrical structures arranged parallel inside muscle fiber and run the length
30
what gives skeletal muscles their striations?
arrangement of myofibrils
31
there are many ___ along myofibrils
mitochondria
32
what are myofilaments?
bundles of protein filaments inside myofibrils
33
what are thin myofilaments?
mostly actin
34
what are thick myofilaments?
mostly myosin
35
what are sarcomeres?
repeating functional units of skeletal muscle fiber
36
what are the 5 muscle striations?
1. z lines
2. i band
3. a band
4. M line
5. H band
37
what are z lines?
junction of adjacent sarcomeres by proteins at their thin filaments
38
what proteins join the sarcomeres at the z lines?
actinins
39
what is the i band?
lighter band with only thin filaments
40
what is the a band?
dark/dense region with thick filaments
41
what is the zone of overlap?
within A band; overlapping thick and thin filaments
42
what is the M line?
center of A band where adjacent thick filaments connect
43
what is the H band?
lighter region on each side of the M line with only thick filaments
44
the H band is only visible when?
when resting sarcomere
45
the sarcolemma is ___ and allows for ___ distribution of +/- charges
selectively permeable; uneven
46
change in charge in sarcolemma is initiated by ___ and Impulse spreads across__
neuron; entire sarcolemma
47
Tranverse (T) tubules are continuous with___ and extend into ___
sarcolemma; sarcoplasm
48
function of T tubules
form passageways through muscle fiber and encircle sarcomere
49
the sarcoplasmic reticulum is similar to
smooth er
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enlarged sections of the sarcoplasmic reticulum are called ___ and are located __-
terminal cristernae, on either side of T tubule
51
triad is a pair of __ and one __
terminal cristernae and one T tubule
52
function of the SR (sarcoplasmic reticulum)
stores calcium that is actively pumped in from cytosol
53
muscle contraction starts when ___ are released form the SR into __, via __
Ca 2+ ions; cytosol; gated calcium channels
54
thin filaments are attached to __ with __
z lines; actin
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thin filaments are made of 2 proteins
1. tropomyosin
| 2. troponin
56
thin filaments have 2 actin types
1. F-actin
| 2. G-actin
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F-actin
filamentous: twisted, double strand of G-actin
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G-actin
each have active site to bind to myosin
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structure of tropomyosin
double-stranded protein wrapped around F-actin
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function of tropomyosin
blocks myosin binding sites on G-actin, preventing actin/myosin interaction
61
troponin is made of __ subunits
3
62
troponin is attached to tropomyosin, making the __
troponin-tropomyosin complex
63
troponin is attached to____ and has binding sites for ___
g-actin; ca2+
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the core of thick filaments is ___ which connects_
titin; thick filaments to Z lines; recoil after stretching
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myosin is made of
2 twisted myosin subunits
66
myosin tails face the
M line
67
free myosin heads face __
out towards thin filaments
68
free myosin head is made of ___ and forms ___ with actin during ___
2 globular subunits; crossbridge; contraction
69
when muscles contract ___ slides over __
thin filaments; thick filaments
70
during contraction, H and I bands get ___, zones of overlap get __, Z lines move ___, and A band is __
smaller; larger; closer together, unchanged
71
sliding during muscle contraction occurs in ____ in ____
all sarcomeres; each myofibril
72
during contraction, all myofibrils ___ and so does the ___
shorten; muscle fiber
73
inside the cell is slightly ___ (+/-) than the outside
negative
74
a membrane potential is ___ distribution that represents a potential ___
an uneven; difference
75
membrane potentials are measured in
milivolts (mV)
76
neurons have a resting membrane potential of about
-70 mV
77
skeletal muscle fibers have a resting membrane potential of about
-85 mV
78
cytosol and extracellular fluid have ___ compositions
different
79
more K+ is located
inside cytosol
80
more Na + is located
outside in ECF
81
what accounts for the negative charge in cells?
proteins inside cant cross PM
82
what allows constant slow flow of Na+ and K+ down their [ ] gradient?
leak channels
83
Na+ __ the cell, K+ ___ the celll
enters; leaves
84
sodium potassium pumps export __ and import __
3Na+; 2K+ ( maintaining membrane potential)
85
what is the 1st step in an action potential?
small increase in membrane permeability to Na+, which rushes in and moves membrane potential in positive direction to threshold
86
what is the membrane potential threshold value?
-55mV
87
what is the 2nd step in an action potential?
voltage gated Na+ channels open, huge rush into cell resulting in depolarization
88
what is depolarization?
change of membrane potential to positive
89
what is the 3rd step in an action potential?
membrane potential recahes +30mV, Na+ gates close and voltage gated K+ channels open and K+leaves cell, resulting in repolarization
90
what is repolarization?
membrane potential returns to polarized state
91
what is the 4th step in an action potential?
voltage gated K+ channels close at resting potential
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what is the 5th step in an action potential?
Na+/K+ pump restores original distribution
93
refractory period
time needed to get to original distribution, membrane cannot respond during this time
94
neurons and muscle fibers have ____ membranes
eletrically excitable
95
depolarization and repolarization create a___ wich spreads across __ in ___
electrical impulse; PM, less than 2msec
96
electrial impulses travel only ___ due to __
in one direction; refractory period
97
electrical impulses allow for
rapid communication
98
neuromuscular junction (NMJ)
location where motor neuron controls a skeletal muscle fiber
99
there are __NMJ per muscle fiber, but each motor neuron may ___
1; branch and control multiple muscle fibers
100
what are the 3 components of the NMJ?
1. axon terminal
2. motor end plate
3. synaptic cleft
101
the axon terminal is located __ and has vessicles with ___
at the end of a motor neuron; acetylcholine
102
the motor end plate of a muscle fiber has ___ that increase __, and contain ___ to break down ACh
junctional folds; # of ACh receptors; acteylcholinesterase (AChe)
103
synaptic cleft
space between axon terminal and motor end plate
104
when an action potential arrives at the NMJ, the change in membrane permeability causes the ___ to fuse with the ___ and ACh is ___ by ___
ACh vessicles; neuron PM; released by exocytosis
105
ACh diffuses across the cleft and binds to ___ at __, which changes sarcolemma ___ permeabiliy, so it comes into the sarcoplasm
ACh-receptor membrane channels; motor end plate; Na+
106
Na+ influx generates ___ in sarcolemma, ACh ___ and ACh-receptors__
action potential; breaks down (AChe); close
107
action potential generated at motor plate immediately __
spreads across entire sarcolemma
108
action potential moves down ___ between ___ of SR, which changes the ___ of SR
T-tubules, terminal cristernae; permeability
109
SR releases stored ___ into ___ which begins ___
Ca2+; sarcomeres; contraction
110
explain excitation-contracting coupling?
excitation (action potential) is coupled with contraction (sliding filaments shorten sarcomeres)
111
what are the 7 steps of muscle fiber contraction cycle?
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
myosin heads in the resting sarcomere are ____ or ___
energized, or cocked
113
cocking myosin heads requires ___
breakdown of ATP
114
myosin head acts as __. __ and __ stay attached to head
ATPase, ADP and P
115
what happens in the "contraction cycle begins" step of muscle contraction?
Ca2+ arrive from SR
116
Ca2+ binds to ___ to change position and move ___, which ____ active sites on ___
troponin; tropomyosin; exposes; actin
117
what happens in the "cross bridge formation" step of muscle contraction?
myosin binds to active sites on actin
118
cross bridge formation causes myosin heads to ___ towards ___, this is called the ___
pivet; M line; power stroke
119
the power stroke results in release of ___ and __
ADP and P
120
how do the cross bridges detach?
a new ATP attaches to each myosin head, releasing it from the actin
121
once the cross bridges detach, the active site is available for __
another cross bridge
122
free myosin heads split ATP into
ADP and P
123
the energy released by myosin reactivation is used to __
recock myosin head
124
the contraction cycle will repeat while __ and __ are available
calcium ions and ATP
125
calcium levels stay high only if __ continue
action potentials
126
when stimulus ends: SR calcium channels__
close
127
when stimulus ends: ___ return ca2+ to ___
Ca2+ ion pumps; terminal cristernae (SR)
128
when stimulus ends: troponin-tropomyosin complex ___
resumes original position, covering active sites on actin
129
what are the 6 steps of excitation-contraction cycle?
1. neural control
2. excitation
3. ca2+ ion release
4. contraction cycle begins
5. sarcomeres shorten
6. muscle tension produced
130
what happens in the 1st (neural control) step of excitation-contraction cycle?
action potential in motor neuron starts process at neuromuscular juntion
131
what happens in the 2nd (Excitation) step of excitation-contraction cycle?
AP causes ACh release from motor neuron, which leads to excitation (AP) in sarcolemma
132
what happens in the 3rd (Ca2+ release) step of excitation-contraction cycle?
muscle fiber AP travels through T-tubules/triads, releasing stored Ca2+
133
what happens in the 4th (contraction begins) step of excitation-contraction cycle?
Ca2+ binds to troponin, exposing active sites on actin, cross bridges form and continue
134
what happens in the 5th (sarcomeres shorten) step of excitation-contraction cycle?
thick and thin filaments slide over each other, shortening sarcomere and pulling ends of muscle fiber closer
135
what happens in the 6th (muscle tension produced) step of excitation-contraction cycle?
muscle fiber shortening causes entire muscle to shorten, contraction produces a pull/tension on tendons
136
muscle fibers are all or none; they are either __ or __
producing tension; relaxed
137
___ number of crossbridges can form at optimal resting length of sarcomere
maximum
138
optimal resting legth of sarcomere produces __ tension
most
139
normal range of sarcomere length is between
75 and 130% of optimal length
140
___, ___, and ___ prevent too much stretching/compression of sarcomere
connective tissue; muscle arrangement; bones
141
what is a muscle twitch?
single-stimulus contraction relaxation sequence in muscle fibre
142
duration of muscle twitch depends on __, __, and __
muscle type, location, environmental factors
143
what does a myogram show?
development of muscle tension
144
what are the 3 stages of a muscle twitch?
1. latent period
2. contraction phase
3. relaxation phase
145
what 2 things happen in the latent period of a muscle twitch?
1. AP stimulates sarcolemma
| 2. Ca2+ released from sarcoplasm reticulum
146
what 3 things happen is the contraction phase of a muscle twitch?
1. ca2+ binds to troponin
2. cross bridge cycling
3. start of tension development to peak tension
147
what 2 things happen in the relaxation phase of a muscle twitch?
1. Ca2+ drops; cross bridges detach; active sites covered
| 2. tension returns to normal
148
how long is a muscle twitch from peak tension to end of twitch?
~25msec
149
tension produced by a skeletal muscle is determined by what 2 things?
1. amount of tension produced by each muscle fiber
| 2. number of muscle fibers stimulated
150
what are the 4 levels of muscle tension?
1. treppe
2. wave summation
3. incomplete tetanus
4. complete tetanus
151
what is treppe?
stimulation of muscle fiber immediately after relaxation
152
what does treppe produce?
increasing maximum tension
153
is treppe demonstrated by most skeletal muscles?
no
154
what is wave summation?
addition of one twitch to another: stimulation of muscle fiber before relaxation
155
what does wave summation produce?
increasing maximum tension
156
____ determines maximum time available to produce wave summation
duration of twitch
157
what is incomplete tetanus?
rapid cycle of contraction/relaxation
158
what does incomplete tetanus produce?
near-peak tension (levels off before max tension)
159
what makes incomplete tetanus "incomplete"?
still some relaxation
160
what is complete tetanus?
higher stimulation eliminates relaxation
161
what causes complete tetanus?
no calcium ions return to SR, but remain on troponin, keeping actin and myosin locked together
162
how often does complete tetanus occur in normally functioning muscles?
seldom
163
number of stimulated muscle fibers affects ___
muscle tension
164
what is a motor unit?
single motor neuron and all muscle fibers it controls
165
fewer fibers in a motor neuron produces what type of control?
fine, precise
166
motor unit recruitment
activation of more motor units to produce more tension
167
what units are activated first in motor unit recruitment?
smaller motor units, then larger motor units
168
larger motor units have ____ more ___ fibers
faster; powerful
169
motor unit recruitment results in ____ increase in muscle tension
smooth, steady
170
what is muscle tone?
resting tension in a skeletal muscle
171
what causes muscle tone?
variable number of motor units always active to produce low-level tension
172
muscle tone is regulated ___
subconsciously
173
increased muscle tone results in ___ resting metabolism
higher
174
what is isotonic contraction?
tension rises and skeletal muscle length changes
175
what are the two types of isotonic contractions?
1. concentric contraction
| 2. eccentric contraction
176
what is concentric contraction?
muscle tension rises until it exceeds load; as muscle shortens, tension remains constant
177
what is an example of concentric contractions?
flexing elbow while holding weight
178
in concentric contraction, speed of contraction is ___ proportional to load
inversely
179
what is eccentric contraction?
peak tension produced is less than load, causing muscle to elongate
180
what is an example of eccentric contraction?
returning weight from flexed to extended position
181
rate of elogation of muscle depends on ___ and ___
tension and load
182
in eccentric contraction, when contraction ends, load stretches muscle until ___, ___ or ___
1. muscle tears
2. tendon breaks
3. elastic recoil opposes load
183
what is isometric contraction?
muscle length does not change, tension never exceeds load
184
what are the 2 sources of ATP in muscles?
1. glycolysis
| 2. aerobic metabolism
185
site of glycolysis
cytosol
186
what is glycolysis?
anearobic breakdown of glucose to pyruvate
187
what much ATP and pyruvate are produced by glycolysis?
2 for each glucose
188
aerobic metabolism provides ___% of ATP needs of resting cell
95
189
site of aerobic metabolism
mitochondria
190
most ATP comes from what stage of aerobic metabolism?
ETC
191
how many ATP per pyruvate are made by aerobic metabolism?
15
192
most energy is stored as ___
glycogen
193
glycogen makes up ___% of muscle weight
1.5
194
free ATP supports only __ muscle twitch
-10
195
creatine phosphate supplies energy for about __sec
15
196
creatine is assembled from
amino acids
197
muscle metabolism at rest has a ___ ATP demand
low
198
when the muscle is as rest, the mitochondria produce ___ ATP
surplus of
199
during muscle metabolism at rest, __ and __ are absorbed from the bloodstream
fatty acids and glucose
200
during muscle metabolism at rest, fatty acids and glucose make __ to covert __ to __ and ___ to __
ATP; creatine; creatine phosphate; glucose; glycogen
201
muscle metabolism at moderate activity relies on __ metabolism of ___ to make __
anaerobic; pyruvate; ATP
202
what happens to O2 consumption during muscle metabolism at moderate activity?
increases
203
during muscle metabolism at moderate activity, there is no fatigue until __, __, and __ reserves are exhausted
glycogen, lipid, amino acid
204
muscle metabolism at peak activity requires ___ ATP demands
enormous
205
mitochondria at maximum production provides ~__ of ATP needs
1/3
206
the rest of ATP demands at peak activity are produced by
glycolysis
207
excess pyruvate converts to
lactate
208
increase in lactate and H+ results in ____ which is characterized by a ___ in pH
lactic acidosis, decrease
209
lactic acidosis causes muscle __
fatigue
210
muscle fatigue means
muscle can no longer perform at required level
211
what is the major factor in muscle fatigue?
decreased pH
212
why does decreased pH affect muscle fatigue?
decreases calcium/troponin binding
| alters enzyme activity
213
what is the recovery period?
time needed to return conditions in muscle fibers to preexertion levels
214
anaerobic metabolism is ___ than aerobic, but only goes until ___-
faster; glycogen reserves are depleted
215
anaerobic is ___ efficient than aerobic
less
216
anaerobic ___ pH
lowers (lactic acid)
217
anaerobic ___ body temperature
raises
218
during the recovery period, __ is available and lactate is converted to __
O2; pyruvate
219
during the recovery period, pyruvate makes __ or recycled to ___
ATP; glucose/glycogen
220
aerobic captures ___% of energy released
42
221
anaerobic captures __% of energy released
4-6
222
___% of body heat produced by resting skeletal muscle
70-80%
223
what is the cori cycle?
shuttling of lactate to liver and glucose back to muscles
224
most lactate produced during peak activity goes to
the liver
225
the liver converts lactate to ___ and releases it__
glucose; back to the blood
226
what are the 3 major types of skeletal muscle fibers?
1. fast
2. slow
3. intermediate
227
fast fibers reach peak tension in ___ sec
<0.01
228
structure of fast fibers
large in diameter, densely packed myofibrils, large glycogen reserves, few mitochondria
229
fast fibers produce __ contractions
powerful
230
fast fibers fatigue __
rapidly
231
why do fast fibers fatigue fast?
most ATP produced anaerobically
232
slow fibers take ___x longer to contract than fast
3
233
the contractions of slow fibers are __ and get energy __
long, sustained; aerobically
234
structure of slow fibers
extensive capillary network; myoglobin pigment binds O2 and makes muscle appear dark
235
intermediate fibers more closely resemble __-, but have more __ and __
fast fibers; capillaries; fatigue-resistant
236
hypertony
muscle enlargement form repeated exhaustive stimulation
237
muscles can increase in size due to (5)
1. more mitochondria
2. more glycogen
3. more/wider myofibrils
4. more myofilaments
5. steroid hormones
238
muscle atrophy
decreased muscle size, tone, and power
239
causes of muscle atrophy (from decreased stimulation) (3)
1. normal aging
2. paralysis/nervous sytem damage
3. reduced use
240
muscular dystrophy
inherited diseases that produce muscular weakness/deterioration
241
most common/understod forms of muscular dystrophy are (2)
Duchenne (DMD) and Becker (BMD)
