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Physiology > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

Skeletal muscles are under _____ control

A

voluntary (CNS)

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2
Q

Skeletal muscles are the target tissue for…

A

CNS A alpha motor output

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3
Q

Skeletal muscle is also known as striated muscle b/c of…

A

actin and myosin

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4
Q

Functions of skeletal muscle:

A
  • locomotion
  • maintenance of posture
  • heat production
  • respiration
  • speech
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5
Q

Myocytes convert…

A

chem signal E to mech E, which leads to contractions

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6
Q

Skeletal muscles produce heat b/c…

A

70-80% of nutrient E s given off as heat

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7
Q

Muscle fibers are the ____ in body

A

largest cells

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8
Q

T/F: myocytes undergo mytosis

A

F, # of muscle fibers are determined by the 2nd trimester in utero

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9
Q

Hypertrophy of fibers leads to…

A

enlargement of muscles

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10
Q

Skeletal muscles are innervated by…

A

A alpha motor unit

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11
Q

Muscle fibers attach to bones via…

A

tendons (CT)

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12
Q

Muscle fibers are arranged in…

A

antagonistic pairs on opposite sides of joints

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13
Q

Smaller joint angle has a muscle called ____ and the action is called ____

A

flexor, flexion

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14
Q

Increasing joint angle has a muscle called ____ and the action is called _____

A

extensor, extension

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15
Q

Myocytes:

A
  • cells that make up skeletal muscles (myofibers)

- multinucleate

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16
Q

Endomysium is also known as…

A

loose CT

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17
Q

Myocytes have…

A
  • cell membrane
  • cytoplasm
  • organelles
  • mitochondria
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18
Q

Fascicles:

A
  • bundles of muscle cells
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19
Q

Myocytes are surrounded by…

A

endomysium

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20
Q

Fascicles are surrounded by…

A

perimysium, which has blood vessels and nerves

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21
Q

Skeletal muscle:

A

groups of fascicles

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22
Q

Skeletal muscles are surrounded by…

A

epimysium (tough CT)

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23
Q

Tendons are formed from…

A

fused epimysium, perimysium, and endomysium

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24
Q

Sarcolemma:

A
  • muscle cell membrane
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25
Q

Sarcolemma is made of…

A
  • Na+/K+ ATPase
  • K+ leak channels
  • NMJ w/ somatic A alpha motor neuron
  • nicotinic receptors for Ach
  • T tubules
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26
Q

Nicotinic receptors in the sarcolemma:

A
  • ionotropic

- opens LG Na+ channels

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27
Q

Transverse (T) tubules are…

A

deep invaginations that dip into center of cell

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28
Q

T tubules carry…

A

membrane depolarization into the cell

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29
Q

T tubules have ______ receptors

A

dihydropyridine (DHP)

- voltage sensor

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30
Q

DHP receptors in the T tubules are linked to…

A

ryanodine (RYR) receptors on SR

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31
Q

Sarcoplasm:

A
  • cytoplasm of myofibers

- has glycogen and multiple organelles

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32
Q

Sarcoplasmic endoplasmic reticulum (SER) s the…

A

intracellular reservoir for Ca2+

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33
Q

SER is made of…

A
  • cysternae
  • calsequestrin
  • ryanodine receptors on membrane
  • SERCA
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34
Q

Cysternae:

A

enlarged terminal ends that contract the T-tubules

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35
Q

Triads:

A

cysternae of 2 areas of SER w/ T-tubules between them

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36
Q

Calsequestrin has a low affinity for…

A

Ca2+ binding protein

- this increases Ca2+ storage ability

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37
Q

RYR receptor on the membrane:

A
  • Ca2+ release channel

- activation through DHP coupling, which allows the release of Ca2+ into the cytoplasm

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38
Q

SERCA has…

A

Ca2+ ATPase, which pumps Ca2+ back into SER from cytoplasm

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39
Q

Myofibrils:

A

bundles of highly organized contractile proteins inside myofibers
- wrapped in SER

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40
Q

Sarcomeres:

A
  • repeating units of myofibrils

- contractile unit of cells

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41
Q

Sarcomeres has two contractile proteins (myofilaments):

A
  • regulatory proteins

- anchoring proteins

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42
Q

Sarcomeres are between…

A

2 z lines

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43
Q

Sarcomeres are made up of:

A
  • globular actin
  • tropomyosin
  • troponin
  • myosin
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44
Q

Actin:

A
  • thin filament

- polymer of 2 individual G-actin molecule, which forms double stranded F actin

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45
Q

Actin is perpendicular to and attach to…

A

z line

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46
Q

Actin has ________ sites

A

myosin binding

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47
Q

Types of regulatory proteins in sarcomeres:

A

part of inhibitory complex

  • tropomyosin
  • troponin
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48
Q

Tropomyosin:

A
  • long protein chain

- wraps around actin

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49
Q

Function of tropomyosin:

A

covers myosin binding sites when muscle isn’t activated

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50
Q

Troponin has:

A
  • Tnl: attaches to actin

- TnT: have affinity for tropomyosin

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51
Q

Function of troponin:

A

anchors tropomyosin on actin

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52
Q

At rest, the attachment site for Ca2+ on troponin is…

A

empty

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53
Q

Myosin:

A
  • thick filament
  • polymer of ~250 myosin molecules
  • between actin filaments
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54
Q

Myosin anchors to…

A

z line by titin

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55
Q

Titin:

A
  • protein that spans z line to z line

- stabilizes contractile filaments

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56
Q

Myosin is made of:

A
  • tail: majority of fiber

- heads: jut out from tail

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57
Q

Myosin heads contain…

A
  • actin binding site

- ATP catalytic site: forms cross-bridge w/ actin when actin’s myosin binding site is available

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58
Q

Actin and myosin form…

A

a lattice of parallel overlapping filaments

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59
Q

Z disc:

A

separates sarcomeres

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60
Q

M line:

A

center of A band aka myosin

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61
Q

A band:

A

entire length of myosin

- dark portion

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62
Q

I band:

A

only has actin

- lighter portion

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63
Q

H zone:

A

only has myosin

64
Q

Muscle contraction load:

A

force opposing contraction

65
Q

Muscle relaxation:

A

release of tension

66
Q

Muscle contraction results in…

A

force (muscle tension)

67
Q

Steps of muscle contraction:

A
  1. initiation of contraction by nerve signal @ NMJ
  2. excitation-contraction coupling
  3. contraction-relaxation cycling
68
Q

Excitation-contraction coupling depends on…

A

elevation of intracellular Ca2+ levels

69
Q

Contraction-relaxation cycling is the process of…

A

sliding filament

70
Q

One complete cycle of contraction-relaxation cycling results in a…

A

twitch

71
Q

Steps during the resting state of myofilament:

A
  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
Q

When myosin heads are cocked, they become…

A

“energized myosin” in ready state

73
Q

Tropomyosin is held in place by _____ on actin

A

troponin

74
Q

Tropomyosin prevents myosin from…

A

completing power stroke

75
Q

Myofiber has RMP of…

A

-90 mV

76
Q

T/F: at resting state, myosin is strongly bound to actin

A

F, it’s weakly bound

77
Q

Initiation of contraction at NMJ is regulated by…

A

SNS

- each myofiber gets direct neural innervation

78
Q

NMJ:

A

specialized synapse junction between axon terminal of alpha motor neuron and motor end plate

79
Q

NMJ is folded to…

A

increase SA for interaction w/ Ach

80
Q

Steps of initiation of contraction at NMJ:

A
  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
Q

What happens when AP in alpha motor neuron causes release of Ach at NMJ?

A
  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
Q

Agonists of Ach receptor:

A
  • metacholine
  • carbachol
  • nicotine
83
Q

Antagonist of Ach receptor:

A

curare

84
Q

Antibodies to Ach receptor are responsible for…

A

muscle paralysis of myasthenia gravis

85
Q

When channels open during the initiation contraction at NMJ, there is an influx of _____, and an efflux of _____

A
  • Na+ and Ca2+ influx

- K+ efflux

86
Q

Inhibitors of AchE:

A
  • neostigme

- physostigmine

87
Q

Duration of AP is…

A

1-5 ms

88
Q

When AP travels along membrane and down T-tubule…

A
  1. T-tubules open to ECF
  2. at triads, VG DHP receptors are activated
  3. RYR receptors (CA2+) of SER are activated
89
Q

When Ca2+ diffuses from SR into cytosol…

A
  1. Ca2+ binds to troponin C
  2. conformational change pulls tropomyosin off of actin’s myosin-binding site
  3. binding site exposed
90
Q

When actin binding site on myosin heads links w/ myosin binding site on actin…

A
  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
Q

What is tilting?

A

conformational change caused by cross-bridge of myosin heads binding w/ actin

92
Q

What is a power stroke?

A

myosin heads pull actin toward center of sarcomere

93
Q

muscle shortening:

A

development of muscle tension through cross-bridge cycling

94
Q

When muscles shorten…

A
  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
Q

When cross-bridges reform due to Ca2+ in cytoplasm…

A

they prevent muscle from stretching out between cycles

96
Q

Cycling of cross-bridges:

A
  • repeated formation and release of cross-bridges

- aka actin sliding model: myosin walks along actin to shorten muscles

97
Q

Cycling of cross-bridges will continue to…

A

pull actin toward center

98
Q

Cycling of cross-bridges allows for…

A

sarcomere shortening (force development)

99
Q

Sarcomere shortening will continue as long as…

A
  • cytosolic Ca2+ levels are high

- ATP is available

100
Q

Greater myosin overlaps results in…

A

shorter muscle and greater tension developed

101
Q

Normal muscle tone results in…

A

greatest muscle tension achieved during contraction

102
Q

Relaxation is the…

A

cessation of contraction

103
Q

During relaxation, there is an active pumping of…

A

Ca2+ back into SR via SERCA

104
Q

Active pumping of Ca2+ back into SR via SERCA leads to…

A
  • 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
Q

No new ATP results in…

A
  • the inability of cross-bridges to release from actin
  • prevents further shortening
  • muscles become locked / rigor
106
Q

Source of E for contraction:

A
  • muscles
  • phosphocreatine
  • glycolysis
  • oxidative metabolism
107
Q

Muscles store enough ATP for…

A

8 twitches or maintain full contraction for 1-2 seconds

108
Q

More ATP is metabolized aerobically in muscles when…

A

blood glucose is available

109
Q

T/F: Fatty acids are not an E source

A

F

110
Q

Phosphocreatine stores…

A

backup E

111
Q

Muscle stores phosphocreatine ______ than ATP

A

5x more

112
Q

Creatine kinase (CK) enzymes:

A
  1. transfers P to ADP to make ATP

2. Moves P from ATP onto creatine

113
Q

T/F: muscle cells have a high amount of creatine kinase

A

T

114
Q

If there are high levels of CK in the blood, then there is damage…

A

at muscle tissues

115
Q

Glycolysis:

A

breakdown of stored glycogen

116
Q

Glycolysis occurs during…

A

anaerobic respiration and forms ATP rapidly

117
Q

Glycolysis can reconstitute ATP for…

A

itself and phosphocreatine

118
Q

Oxidative metabolism:

A

aerobic breakdown of carbs, fats, or proteins

119
Q

Oxidative metabolism is a good E source for…

A

prolonged muscle use (hours)

120
Q

Order of E sources that muscles use first in oxidative metabolism:

A
  1. carbs
  2. fats
  3. proteins
121
Q

Fatigue:

A

reversible inability to generate E for contraction

122
Q

Two types of fatigue:

A
  • central fatigue

- peripheral fatigue

123
Q

Central fatigue can be caused by…

A
  • psychological
  • low pH
  • NMJ/CNS issues such as failure of communication
124
Q

Peripheral fatigue is…

A

within muscle

125
Q

Peripheral fatigue is caused by…

A
  • elevated Pi
  • decrease of Ca2+
  • K+ imbalance
126
Q

Efficiency of muscle contraction is determined by…

A

% of E converted to work instead of heat

127
Q

Usually about _____ % of E is converted to work

A

< 25

- rest is heat

128
Q

Duration and magnitude of contraction is classified by…

A
  • contractile speed

- fatigue resistance

129
Q

Duration and magnitude of contraction is dependent on…

A

type of myosin isoforms in muscle

130
Q

Myosin isoforms determine the rate at which…

A

tension develops

131
Q

T/F: all skeletal muscles are made of mixed myosin isoforms

A

T

132
Q

Myosin isoforms have different…

A

ATPase activities, which alters the threshold for activation

133
Q

Types of skeletal muscle fibers:

A
  • type 1
  • type 2A
  • type 2X
134
Q

Type 1 muscle fibers:

A
  • slow
  • red muscles
  • small diameter
  • long contraction duration
  • oxidative aerobic respiration
  • numerous mitochondria
135
Q

Type 1 muscle fibers are dark red b/c of…

A

myoglobulin

136
Q

Type 2A muscle fibers:

A
  • 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
Q

Both type 1 and type 2A have…

A

fatigue resistance

138
Q

Type 2X muscle fibers:

A
  • fast twitch glycolytic
  • fastest
  • largest diameter
  • short contraction duration
  • few mitochondria
  • pale color
  • glycolytic: more anaerobic than others
  • easily fatigued
139
Q

What do type 2A and type 2X have in common?

A

both have short contraction duration

140
Q

Somatic motor unit is a…

A

functional contractile unit made up of a single A alpha motor unit and all skeletal muscle fibers it innervates

141
Q

More # of fibers in a motor unit =

A

less control, but more force

142
Q

T/F: all fibers in a single motor unit are not of the same type

A

F, all the same type

143
Q

Muscle twitch:

A

brief contraction and relaxation in response to one AP in all muscle fibers w/in given motor unit

144
Q

Weak CNS signal can stimulate…

A

small motor units

145
Q

The larger the unit…

A

the larger the signal needed

146
Q

Summation of individual twitches produce…

A

useful muscle contraction

147
Q

Examples of summation of individual twitches:

A
  • motor unit summation

- wave/frequency summation

148
Q

Motor unit summation:

A

recruitment of more motor units

- ex: spatial summation

149
Q

Spatial summation occurs when..

A

more and more muscle fibers are contracting

150
Q

Wave/frequency summation:

A

increased frequency of AP w/in a given motor unit

  • force developed is proportionate to cytosolic [Ca2+]
  • ex: temporal summation
151
Q

Temporal summation overwhelms ability of SR…

A

to pump Ca2+ back into reservoir

- increases cytosolic [Ca2+]

152
Q

Tetanus has two types:

A
  • complete

- incomplete

153
Q

Complete tetanus:

A

fused contraction

- muscle fibers continue to contract w/out relaxation

154
Q

Incomplete tetanus:

A

unfused contraction:

- stimulus are far apart enough to allow for partial relaxation between stimuli

155
Q

Types of muscle contraction:

A
  • isotonic

- isometric

156
Q

Isotonic muscle contraction:

A

muscle shortens w/ constant tension

157
Q

Isometric muscle contraction:

A

muscle tightens, but doesn’t shorten

- used to maintain posture

Physiology (33 decks)

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