Skeletal Muscle Flashcards
1
Q
Skeletal muscles are under _____ control
A
voluntary (CNS)
2
Q
Skeletal muscles are the target tissue for…
A
CNS A alpha motor output
3
Q
Skeletal muscle is also known as striated muscle b/c of…
A
actin and myosin
4
Q
Functions of skeletal muscle:
A
- locomotion
- maintenance of posture
- heat production
- respiration
- speech
5
Q
Myocytes convert…
A
chem signal E to mech E, which leads to contractions
6
Q
Skeletal muscles produce heat b/c…
A
70-80% of nutrient E s given off as heat
7
Q
Muscle fibers are the ____ in body
A
largest cells
8
Q
T/F: myocytes undergo mytosis
A
F, # of muscle fibers are determined by the 2nd trimester in utero
9
Q
Hypertrophy of fibers leads to…
A
enlargement of muscles
10
Q
Skeletal muscles are innervated by…
A
A alpha motor unit
11
Q
Muscle fibers attach to bones via…
A
tendons (CT)
12
Q
Muscle fibers are arranged in…
A
antagonistic pairs on opposite sides of joints
13
Q
Smaller joint angle has a muscle called ____ and the action is called ____
A
flexor, flexion
14
Q
Increasing joint angle has a muscle called ____ and the action is called _____
A
extensor, extension
15
Q
Myocytes:
A
- cells that make up skeletal muscles (myofibers)
- multinucleate
16
Q
Endomysium is also known as…
A
loose CT
17
Q
Myocytes have…
A
- cell membrane
- cytoplasm
- organelles
- mitochondria
18
Q
Fascicles:
A
- bundles of muscle cells
19
Q
Myocytes are surrounded by…
A
endomysium
20
Q
Fascicles are surrounded by…
A
perimysium, which has blood vessels and nerves
21
Q
Skeletal muscle:
A
groups of fascicles
22
Q
Skeletal muscles are surrounded by…
A
epimysium (tough CT)
23
Q
Tendons are formed from…
A
fused epimysium, perimysium, and endomysium
24
Q
Sarcolemma:
A
- muscle cell membrane
25
Sarcolemma is made of...
- Na+/K+ ATPase
- K+ leak channels
- NMJ w/ somatic A alpha motor neuron
- nicotinic receptors for Ach
- T tubules
26
Nicotinic receptors in the sarcolemma:
- ionotropic
| - opens LG Na+ channels
27
Transverse (T) tubules are...
deep invaginations that dip into center of cell
28
T tubules carry...
membrane depolarization into the cell
29
T tubules have ______ receptors
dihydropyridine (DHP)
| - voltage sensor
30
DHP receptors in the T tubules are linked to...
ryanodine (RYR) receptors on SR
31
Sarcoplasm:
- cytoplasm of myofibers
| - has glycogen and multiple organelles
32
Sarcoplasmic endoplasmic reticulum (SER) s the...
intracellular reservoir for Ca2+
33
SER is made of...
- cysternae
- calsequestrin
- ryanodine receptors on membrane
- SERCA
34
Cysternae:
enlarged terminal ends that contract the T-tubules
35
Triads:
cysternae of 2 areas of SER w/ T-tubules between them
36
Calsequestrin has a low affinity for...
Ca2+ binding protein
| - this increases Ca2+ storage ability
37
RYR receptor on the membrane:
- Ca2+ release channel
| - activation through DHP coupling, which allows the release of Ca2+ into the cytoplasm
38
SERCA has...
Ca2+ ATPase, which pumps Ca2+ back into SER from cytoplasm
39
Myofibrils:
bundles of highly organized contractile proteins inside myofibers
- wrapped in SER
40
Sarcomeres:
- repeating units of myofibrils
| - contractile unit of cells
41
Sarcomeres has two contractile proteins (myofilaments):
- regulatory proteins
| - anchoring proteins
42
Sarcomeres are between...
2 z lines
43
Sarcomeres are made up of:
- globular actin
- tropomyosin
- troponin
- myosin
44
Actin:
- thin filament
| - polymer of 2 individual G-actin molecule, which forms double stranded F actin
45
Actin is perpendicular to and attach to...
z line
46
Actin has ________ sites
myosin binding
47
Types of regulatory proteins in sarcomeres:
part of inhibitory complex
- tropomyosin
- troponin
48
Tropomyosin:
- long protein chain
| - wraps around actin
49
Function of tropomyosin:
covers myosin binding sites when muscle isn't activated
50
Troponin has:
- Tnl: attaches to actin
| - TnT: have affinity for tropomyosin
51
Function of troponin:
anchors tropomyosin on actin
52
At rest, the attachment site for Ca2+ on troponin is...
empty
53
Myosin:
- thick filament
- polymer of ~250 myosin molecules
- between actin filaments
54
Myosin anchors to...
z line by titin
55
Titin:
- protein that spans z line to z line
| - stabilizes contractile filaments
56
Myosin is made of:
- tail: majority of fiber
| - heads: jut out from tail
57
Myosin heads contain...
- actin binding site
| - ATP catalytic site: forms cross-bridge w/ actin when actin's myosin binding site is available
58
Actin and myosin form...
a lattice of parallel overlapping filaments
59
Z disc:
separates sarcomeres
60
M line:
center of A band aka myosin
61
A band:
entire length of myosin
| - dark portion
62
I band:
only has actin
| - lighter portion
63
H zone:
only has myosin
64
Muscle contraction load:
force opposing contraction
65
Muscle relaxation:
release of tension
66
Muscle contraction results in...
force (muscle tension)
67
Steps of muscle contraction:
1. initiation of contraction by nerve signal @ NMJ
2. excitation-contraction coupling
3. contraction-relaxation cycling
68
Excitation-contraction coupling depends on...
elevation of intracellular Ca2+ levels
69
Contraction-relaxation cycling is the process of...
sliding filament
70
One complete cycle of contraction-relaxation cycling results in a...
twitch
71
Steps during the resting state of myofilament:
1. myosin heads bind ATP
2. ATP is partially hydrolyzed by ATPase portion of myosin head (forms ADP and Pi)
3. ADP and Pi in ATP binding site of myosin head induces conformational change
4. myosin heads turn perpendicular to rest of myosin molecule (cocked)
5. tropomyosin blocks binding site on actin
72
When myosin heads are cocked, they become...
"energized myosin" in ready state
73
Tropomyosin is held in place by _____ on actin
troponin
74
Tropomyosin prevents myosin from...
completing power stroke
75
Myofiber has RMP of...
-90 mV
76
T/F: at resting state, myosin is strongly bound to actin
F, it's weakly bound
77
Initiation of contraction at NMJ is regulated by...
SNS
| - each myofiber gets direct neural innervation
78
NMJ:
specialized synapse junction between axon terminal of alpha motor neuron and motor end plate
79
NMJ is folded to...
increase SA for interaction w/ Ach
80
Steps of initiation of contraction at NMJ:
1. AP in alpha motor neuron causes release of Ach at NMJ
2. AP travels along membrane and down T-tubule
3. Ca2+ diffuses from SR into cytosol
4. actin binding site on myosin heads links w/ myosin binding site on actin
5. muscle shortening
81
What happens when AP in alpha motor neuron causes release of Ach at NMJ?
1. Ach binds to nicotinic LGC of motor end plate
2. channels open
3. depolarization membrane potential toward -15 mV
4. activates VGC Na+ (AP initiated)
5. AchE degrades used Ach
82
Agonists of Ach receptor:
- metacholine
- carbachol
- nicotine
83
Antagonist of Ach receptor:
curare
84
Antibodies to Ach receptor are responsible for...
muscle paralysis of myasthenia gravis
85
When channels open during the initiation contraction at NMJ, there is an influx of _____, and an efflux of _____
- Na+ and Ca2+ influx
| - K+ efflux
86
Inhibitors of AchE:
- neostigme
| - physostigmine
87
Duration of AP is...
1-5 ms
88
When AP travels along membrane and down T-tubule...
1. T-tubules open to ECF
2. at triads, VG DHP receptors are activated
3. RYR receptors (CA2+) of SER are activated
89
When Ca2+ diffuses from SR into cytosol...
1. Ca2+ binds to troponin C
2. conformational change pulls tropomyosin off of actin's myosin-binding site
3. binding site exposed
90
When actin binding site on myosin heads links w/ myosin binding site on actin...
1. tilting occurs
2. frees ADP from ATP binding site
3. E stored in myosin head is released
4. myosin heads swivel
5. power stroke initiated
91
What is tilting?
conformational change caused by cross-bridge of myosin heads binding w/ actin
92
What is a power stroke?
myosin heads pull actin toward center of sarcomere
93
muscle shortening:
development of muscle tension through cross-bridge cycling
94
When muscles shorten...
1. new ATP binds to myosin and releases myosin head from actin
2. new ATP is partially hydrolyzed to "re-cock" head
3. if Ca2+ is still present in cytoplasm, cross-bridges reform ASAP
4. cycling of cross-bridges
95
When cross-bridges reform due to Ca2+ in cytoplasm...
they prevent muscle from stretching out between cycles
96
Cycling of cross-bridges:
- repeated formation and release of cross-bridges
| - aka actin sliding model: myosin walks along actin to shorten muscles
97
Cycling of cross-bridges will continue to...
pull actin toward center
98
Cycling of cross-bridges allows for...
sarcomere shortening (force development)
99
Sarcomere shortening will continue as long as...
- cytosolic Ca2+ levels are high
| - ATP is available
100
Greater myosin overlaps results in...
shorter muscle and greater tension developed
101
Normal muscle tone results in...
greatest muscle tension achieved during contraction
102
Relaxation is the...
cessation of contraction
103
During relaxation, there is an active pumping of...
Ca2+ back into SR via SERCA
104
Active pumping of Ca2+ back into SR via SERCA leads to...
- lowered cytosolic [Ca2+]
- actin regulatory proteins slide back into place and covers myosin binding site
- termination of contraction until next AP triggers new influx of Ca2+
105
No new ATP results in...
- the inability of cross-bridges to release from actin
- prevents further shortening
- muscles become locked / rigor
106
Source of E for contraction:
- muscles
- phosphocreatine
- glycolysis
- oxidative metabolism
107
Muscles store enough ATP for...
8 twitches or maintain full contraction for 1-2 seconds
108
More ATP is metabolized aerobically in muscles when...
blood glucose is available
109
T/F: Fatty acids are not an E source
F
110
Phosphocreatine stores...
backup E
111
Muscle stores phosphocreatine ______ than ATP
5x more
112
Creatine kinase (CK) enzymes:
1. transfers P to ADP to make ATP
| 2. Moves P from ATP onto creatine
113
T/F: muscle cells have a high amount of creatine kinase
T
114
If there are high levels of CK in the blood, then there is damage...
at muscle tissues
115
Glycolysis:
breakdown of stored glycogen
116
Glycolysis occurs during...
anaerobic respiration and forms ATP rapidly
117
Glycolysis can reconstitute ATP for...
itself and phosphocreatine
118
Oxidative metabolism:
aerobic breakdown of carbs, fats, or proteins
119
Oxidative metabolism is a good E source for...
prolonged muscle use (hours)
120
Order of E sources that muscles use first in oxidative metabolism:
1. carbs
2. fats
3. proteins
121
Fatigue:
reversible inability to generate E for contraction
122
Two types of fatigue:
- central fatigue
| - peripheral fatigue
123
Central fatigue can be caused by...
- psychological
- low pH
- NMJ/CNS issues such as failure of communication
124
Peripheral fatigue is...
within muscle
125
Peripheral fatigue is caused by...
- elevated Pi
- decrease of Ca2+
- K+ imbalance
126
Efficiency of muscle contraction is determined by...
% of E converted to work instead of heat
127
Usually about _____ % of E is converted to work
< 25
| - rest is heat
128
Duration and magnitude of contraction is classified by...
- contractile speed
| - fatigue resistance
129
Duration and magnitude of contraction is dependent on...
type of myosin isoforms in muscle
130
Myosin isoforms determine the rate at which...
tension develops
131
T/F: all skeletal muscles are made of mixed myosin isoforms
T
132
Myosin isoforms have different...
ATPase activities, which alters the threshold for activation
133
Types of skeletal muscle fibers:
- type 1
- type 2A
- type 2X
134
Type 1 muscle fibers:
- slow
- red muscles
- small diameter
- long contraction duration
- oxidative aerobic respiration
- numerous mitochondria
135
Type 1 muscle fibers are dark red b/c of...
myoglobulin
136
Type 2A muscle fibers:
- fast twitch oxidative-glycolytic
- white muscles
- medium diameter
- short contraction duration
- extensive SER for fast Ca2+ release
- glycolytic ox w/ endurance training
- moderate # of mitochondria
- low myoglobulin
137
Both type 1 and type 2A have...
fatigue resistance
138
Type 2X muscle fibers:
- fast twitch glycolytic
- fastest
- largest diameter
- short contraction duration
- few mitochondria
- pale color
- glycolytic: more anaerobic than others
- easily fatigued
139
What do type 2A and type 2X have in common?
both have short contraction duration
140
Somatic motor unit is a...
functional contractile unit made up of a single A alpha motor unit and all skeletal muscle fibers it innervates
141
More # of fibers in a motor unit =
less control, but more force
142
T/F: all fibers in a single motor unit are not of the same type
F, all the same type
143
Muscle twitch:
brief contraction and relaxation in response to one AP in all muscle fibers w/in given motor unit
144
Weak CNS signal can stimulate...
small motor units
145
The larger the unit...
the larger the signal needed
146
Summation of individual twitches produce...
useful muscle contraction
147
Examples of summation of individual twitches:
- motor unit summation
| - wave/frequency summation
148
Motor unit summation:
recruitment of more motor units
| - ex: spatial summation
149
Spatial summation occurs when..
more and more muscle fibers are contracting
150
Wave/frequency summation:
increased frequency of AP w/in a given motor unit
- force developed is proportionate to cytosolic [Ca2+]
- ex: temporal summation
151
Temporal summation overwhelms ability of SR...
to pump Ca2+ back into reservoir
| - increases cytosolic [Ca2+]
152
Tetanus has two types:
- complete
| - incomplete
153
Complete tetanus:
fused contraction
| - muscle fibers continue to contract w/out relaxation
154
Incomplete tetanus:
unfused contraction:
| - stimulus are far apart enough to allow for partial relaxation between stimuli
155
Types of muscle contraction:
- isotonic
| - isometric
156
Isotonic muscle contraction:
muscle shortens w/ constant tension
157
Isometric muscle contraction:
muscle tightens, but doesn't shorten
| - used to maintain posture
