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X Physiology 1A > Muscle > Flashcards

Muscle Flashcards

1
Q

What are the 3 ways animal movements are generated?

A

ameboid movements, cilliary and flagella bending, muscle contraction

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2
Q

What does mucsocillary clearance maintain in the lungs

A

maintains the sterility of the lungs

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3
Q

Where is skeletal muscle located?

A

the skeleton

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4
Q

What is the anatomy of skeletal muscle?

A

striated

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5
Q

what sort of nervous control is skeletal muscle under?

A

voluntary

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6
Q

What is the function of skeletal muscle?

A

movement and heat production

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7
Q

where is cardiac muscle located?

A

the heart

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8
Q

What is the anatomy of cardiac muscle

A

striated

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9
Q

what sort of nervous control is cardiac muscle under?

A

involuntary (autonomic)

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10
Q

What is the function of cardiac muscle?

A

pump blood

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11
Q

where is smooth muscle located?

A

hollow organs

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12
Q

What is the anatomy of smooth muscle?

A

non-striated

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13
Q

what sort of nervous control is smooth muscle under?

A

involuntary

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14
Q

What is the function of smooth muscle?

A

movement and control of organ size

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15
Q

What is movement of the body the result of?

A

contraction of skeletal muscle across a joint

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16
Q

Do mechanical lever systems work at an advantage or disadvantage?

A

disadvantage

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17
Q

What does muscles working at a disadvantage mean?

A

must exert force even to hold something up

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18
Q

What is the force needed to counteract muscular disadvantage the sum of?

A

the weight held and the arm length

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19
Q

What is the velocity of a muscle amplified by?

A

lever system

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20
Q

What is maximized by the specific architecture of skeletal muscle?

A

force production and movement

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21
Q

What is the fasciculus?

A

collection of around 150 muscle cells bundled together

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22
Q

what is epimysium?

A

connective tissue that surrounds the entire muscle and eventually at the end of the muscle will form the tendon

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23
Q

what is perimysium?

A

connective tissue around the fasciculus

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24
Q

what is endomysium?

A

connective tissue which wraps around individual muscle cells

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25
Q

What is a myofibril?

A

cylinder of cells located within muscle fibres

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26
Q

What are myofibrils wrapped in?

A

sacroplasmic reticulum

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27
Q

What is a terminal cisternae of sarcoplasmic reticulum?

A

bulge at the end of the sarcoplasmic reticulum before the next myofibril and therefore next section of sarcoplasmic reticulum

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28
Q

What separates one piece of sarcoplasmic reticulum from the next?

A

transverse tubule

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29
Q

What is the sarcolemma?

A

cell membrane of muscle cell

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30
Q

What do the transverse tubules connect?

A

surface of muscle cell deep into muscle fibre

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31
Q

What is a triad formed of in muscle fibres?

A

a transverse tubule between 2 terminal cisternae

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32
Q

What is a single myofibril made up of?

A

repeating functional units

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33
Q

What is the functional unit of a myofibril?

A

sarcomere

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34
Q

What are the thicknesses of the 2 principal protein filaments of a sarcomere?

A

thick and thin

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35
Q

What is the name of the thick protein filament of a sarcomere?

A

myosin

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36
Q

what is the name of the thin protein filament of a sarcomere?

A

actin

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37
Q

What is myosin sandwiched between?

A

2 threads of actin

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38
Q

What is a myofibril built out of?

A

many sarcomeres

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39
Q

What produces the banding pattern seen in histological images of muscle cells?

A

filament organisation

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40
Q

What is a characteristic of skeletal muscle seen in histological images?

A

striations

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41
Q

How many nuclei are often present in a skeletal muscle fibre?

A

multiple

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42
Q

What does the Z line in a sarcomere show?

A

the edges of the sarcomere

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43
Q

What is the dark band of the sarcomere called?

A

A band

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44
Q

Where does the I band of a sarcomere sit?

A

straddles 2 sarcomeres

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45
Q

What is the line down the middle of the A band called?

A

M line

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46
Q

What zone surrounds the M line?

A

H zone

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47
Q

How does the H zone appear under an electron microscope?

A

lighter than the A band

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48
Q

what are thick filaments made of?

A

myosin

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49
Q

Where do cross bridges originate from on myosin?

A

the myosin head

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50
Q

How do myosin filaments join together?

A

tail to tail

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51
Q

What are myosin cross bridges essential for?

A

muscle contraction

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52
Q

What is the role of the essential light protein chain around the neck of the myosin filament?

A

structural

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53
Q

What is the role of the regulatory light protein chain around the neck of the myosin filament?

A

modulates the activity of the myosin head

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54
Q

Where is the actin binding site located on a myosin filament?

A

myosin head

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55
Q

What are the thin muscle filaments composed of?

A

actin

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56
Q

How many chains of globular actin are there in an actin filament?

A

2

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57
Q

Where are the myosin binding sites found on actin?

A

within the globular actin chains

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58
Q

What is the contractile element of actin?

A

globular actin chains

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59
Q

what is tropomyosin?

A

rope like structure between 2 actin chains

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60
Q

What is the tropomyosin complex?

A

a regulatory protein made up of 3 subunits

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61
Q

What do cross bridges of myosin join?

A

myosin (thick) filaments to actin (thin) filaments at the actin binding sites

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62
Q

Which scientists provided experimental evidence for the molecular basis of skeletal muscle contraction?

A

Andrew and Hugh Huxley

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63
Q

What did Andrew Huxley do in his experiment to look at muscle contraction?

A

used a light microscope to measure the lengths of A and I bands during contraction

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64
Q

What did Hugh Huxley do in his experiment to look at muscle contraction?

A

used an electron microscope to measure the length of the filaments during muscle contraction

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65
Q

What happens to sarcomere length during muscle contraction?

A

becomes shorter

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66
Q

Why do sarcomeres shorten during muscle contraction?

A

because actin filaments actively slide along between the myosin filaments

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67
Q

What structures mediate the shortening of a sarcomere?

A

cross bridges

68
Q

What parts of a sarcomere are pulled together during muscle contraction?

A

Z lines pulled towards M lines

69
Q

What is this sliding of actin filaments between myosin filaments known as?

A

the sliding filament mechanism

70
Q

What are cross bridges formed and dissociated between?

A

actin and myosin filaments

71
Q

Does each cross bridge generate a force independent of other cross bridges?

A

yes

72
Q

What is the total force produced by a contracting sarcomere determined by?

A

the number of cross bridges formed between myosin (thick) and actin (thin) filaments

73
Q

What does the the amount of overlap between myosin and actin filaments determine?

A

total force produced by the contracting sarcomere

74
Q

What is meant by the normal operating range of sarcomeres?

A

maximal force is produced (there is no one single value)

75
Q

What is the sarcomere length-tension relationship?

A

bell shaped relationship determined by cross-bridge formation between myosin and actin filaments

76
Q

What 3 factors generate tension in the muscle during the cross bridge cycle?

A

mechanical changes
chemical changes
ATP

77
Q

Describe the mechanical changes that take place during the cross bridge cycle?

A
  1. cross bridge binds to actin
  2. cross bridge moves the powerstroke
  3. ATP joins to myosin causing the cross bridge to detach from actin filament
  4. hydrolysis of ATP energises cross bridge
78
Q

At the end of stage 2 of the cross bridge cycle is the de-energised cross bridge still attached to actin?

A

yes

79
Q

Does each individual cross bridge go through the stages of the cross bridge cycle independantly?

A

yes

80
Q

Describe the chemical changes that take place during the cross bridge cycle

A
  1. cross bridge is energised with ATP and so binds to actin
  2. ATP is hydrolysed to ADP and Pi to release energy for power stroke. Actin and myosin remain bound
  3. ATP binds to myosin - causes cross bridge to detach from actin
  4. Hydrolysis of ATP energises cross bridge
81
Q

What are the 2 roles of ATP in the cross bridge cycle?

A

Energy source

Allosteric regulator

82
Q

How is ATP used as an energy source in the cross bridge cycle?

A

ATP hydrolysis provides the energy for cross bridge movement

83
Q

How is ATP used as an allosteric regulator in the cross bridge cycle?

A

binding of ATP to myosin breaks the link between actin and myosin. This allows the cycle to be repeated

84
Q

What are the 2 binding sites found on myosin head (cross bridge)?

A

actin binding site and ATP binding site

85
Q

What does binding of ATP to mysoin head binding site cause?

A

a confirmational change in the myosin head

86
Q

What effect does an alteration in the confirmation of the myosin head, caused by binding of ATP, have?

A

weakens the interaction between actin and myosin and so disassociation takes place

87
Q

What is the sliding filament mechanism the molecular basis of?

A

skeletal muscle contraction

88
Q

What process drives sarcomere contraction?

A

cross bridge cycling

89
Q

How are skinned muscle fibres prepared?

A

plasma membrane is made permeable to ATP and Ca2+ so they can freely diffuse in ad out of the cell.

90
Q

Which ions regulate skeletal muscle contractions?

A

calcium

91
Q

What is tropomyosin?

A

protein complex which constantly inhibits muscle contraction at rest

92
Q

How does tropomyosin inhibit muscle contraction?

A

myosin binding sites are hidden by the tropomyosin

93
Q

What happens to tropomyosin when 2 calcium ions are added?

A

moves deeper into the actin groove and unmasks the myosin binding sites relieving constant inhibition

94
Q

What does TnC do?

A

binds calcium to tropomyosin

95
Q

What does Tnl do?

A

inhibits cross bridge binding

96
Q

What does TnT do?

A

binds tropomyosin

97
Q

What triggers the contraction of skeletal muscle?

A

action potential

98
Q

What does one action potential illicit?

A

one muscle contraction

99
Q

What is the latent period?

A

delay between the firing of AP and initiation of muscle contraction

100
Q

What happens to the action potential once it reaches the end plate after synapsing at the neuromuscular junction?

A

local current flow on cell surface

101
Q

Where are calcium ions stored within the cell?

A

sarcoplasmic reticulum

102
Q

Why do calcium ions need to be stored in the sarcoplasmic reticulum?

A

the latent period between AP and contraction is too short for Ca2+ ions to be able to diffuse into the cell

103
Q

What does calsequestrin do in the sarcoplasmic reticulum?

A

stores high concentration of calcium ions

104
Q

How is calcium rapidly released from sarcoplasmic reticulum into myoplasm?

A

voltage gated channel

105
Q

How is calcium removed from the myoplasm once it has been used in attachment to tropomyosin?

A

calcium ATPase brings Ca2+ back into the sarcoplasmic reticulum via active transport

106
Q

What are the functions of T tubules?

A

conduct the action potential from the sarcolemma deep into the muscle fibre
convey the action potential to the sarcoplasmic reticulum causing the release of calcium

107
Q

Where does an action potential run after local current flow across the surface of the cell?

A

into the T tubule and the muscle fibre, close to the sarcoplasmic reticulum

108
Q

What is the function of the DHP receptor?

A

a voltage sensor

109
Q

What is the function of the ryanodine receptor?

A

calcium release channel in sarcoplasmic reticulum

110
Q

Where is the DHP receptor located?

A

T tubule membrane

111
Q

How is the DHP receptor affected by the arrival of an action potential?

A

the shape of the receptor alters which in turn affects the connected ryanodine receptor

112
Q

What happens when DHP receptor is activated by an action potential?

A

it’s shape is changed by the action potential which causes the attached Ryanodine receptor to open it’s gate causing calcium ions to flood out of the sarcoplasmic reticulum into the myoplasm

113
Q

What is the experimental evidence for regulation of muscle contraction by calcium ions?

A

calcium buffers and skinned muscle fibres

114
Q

What is effect of calcium on

troponin and tropomyosin?

A

calcium ions remove constant inhibition of skeletal contraction

115
Q

What is the function of sarcoplasmic reticulum in muscle contraction?

A

stores high concentrations of calcium and rapidly releases it into myoplasm

116
Q

What are the functions of transverse tubules in skeletal muscle contraction?

A

conduct action potential into muscle cells

117
Q

Summarise exitation-contraction coupling in skeletal muscle.

A

Action potential arrives at T tubule via local current flow
Action potential detected by DHP receptor
DHP receptor changes shape and so causes ryanodine channel to open and allow calcium ions to flood into myoplasm
Calcium binds to the troponin complex which relieves constant inhibition of muscle contraction
cross bridge formed and sliding filament process of muscle contraction takes place
Calcium ions are pumped back into sarcoplasmic reticulum by active transport
reduction in Ca2+ ion concentration leads to Ca2+ dissociating from tropomyosin complex constant inhibition of actin filament is reinstated

118
Q

What happens to force of muscle contraction when action potentials are close together but Ca2+ conc can return to normal between each?

A

force increases but would appear jagged on a graph as it drops slightly between each AP (unfused tetanus)

119
Q

What is unfused tetanus?

A

jagged increase in muscle force

120
Q

What happens to the force of a muscle contraction when action potentials are so close together that Ca2+ conc does not return to normal between each?

A

calcium con remains steady, force of contraction increases until it reaches maximum force and will remain there until calcium conc begins to drop. (fused tetanus)

121
Q

What is fused tetanus?

A

force of muscle contraction rising until it reaches maximum and only falling when calcium concentration falls.

122
Q

What is excitation-contraction coupling?

A

how action potentials regulate skeletal muscle contraction by triggering calcium release from the sarcoplasmic reticulum

123
Q

What does the frequency of action potential firing determine?

A

strength of skeletal muscle contraction by sustaining the intracellular calcium concentration

124
Q

What do calcium ions remove from skeletal muscle contraction?

A

constant inhibition by troponin-tropomyosin

125
Q

What is tension?

A

force exerted on an object by a contracting muscle

126
Q

What is load?

A

force exerted on muscle by the weight of an object

127
Q

What is isometric contraction?

A

where the muscle develops tension without changing length

128
Q

What is isometric contraction measured by?

A

tension generated

129
Q

What is isotonic contraction measured by?

A

rate of shortening

130
Q

What happens during eccentric contraction?

A

load exceeds muscle tension

131
Q

What is active tension produced by in the muscle?

A

muscle contraction

132
Q

What is passive tension produced by in the muscle?

A

connective tissue (epimysium, perimysium, endomysium) which resist the stretching of muscle fibres and accessory proteins (titin and nebulin)

133
Q

Where is titin located?

A

within the sarcomere between Z line and M line. Travels through the centre of myosin

134
Q

What is titin responsible for?

A

holding myosin in optimum position to form cross bridges with actin

135
Q

What does nebilin do?

A

determines the length of the actin thin filament

136
Q

What is the difference between fast and slow twitch muscle fibres?

A

fast; create fast and precise movements due to rapid hydrolysis of ATP
slow: create a slow and sustained contraction with slower hydrolysis of ATP

137
Q

Which muscle fibre, fast or slow twitch, is easily fatigued?

A

fast

138
Q

Which muscle fibre, fast or slow twitch, is not easily fatigued?

A

slow

139
Q

Give an example of location of fast twitch muscle fibres

A

extra occular muscle of the eye

140
Q

Give an example of location of slow twitch muscle fibres

A

soleus muscle on back of leg

141
Q

What type of muscle fibre are fast and slow twitch fibres and example of?

A

specialised muscle fibres

142
Q

What originates from the sinoatrial node?

A

electrical activity in the heart from ANS

143
Q

What about the structure of heart muscle cells means that contractions can be well co-oridinated?

A

contractile mechanism of one cell lines up with that of the next cell/cells around it (e.g. Z lines are in line) all the way across the muscle

144
Q

What is the name of cardiac muscle cells?

A

cardiac myocytes

145
Q

What is the desmosome in cardiac muscle?

A

holds 2 cardiac myocytes together

146
Q

What is the function of the gap junction in cardiac muscle?

A

pathway for communication between cardiac myocytes. Electrical signal is passed across these junctions

147
Q

What is the name of the cell junction in cardiac muscle?

A

intercalated disk

148
Q

how does excitation-contraction coupling work in cardiac muscle?

A

Action potential is detected by voltage gated calcium channel which is separate from sarcoplasmic reticulum and Ryanodine receptor
channel opens and calcium ions flood from T tubule into cardiac myocyte
This triggers the opening of Ryanodine receptor which causes calcium to be released into myoplasm from SR
Calcium binds to the troponin complex which relieves constant inhibition of muscle contraction
cross bridge formed and sliding filament process of muscle contraction takes place
Calcium ions are pumped back into sarcoplasmic reticulum by active transport
Calcium ions are also removed from the myocyte through an antiporter. Na+ is brought into the cell to allow Ca2+ to be moved out by secondary active transport. This relies on primary active transport by Na+K+ ATPase

149
Q

What do contractile fibres of smooth muscle cells contain?

A

actin and myosin

150
Q

What do supporting fibres of smooth muscle cells contain?

A

intermediate filaments (supporting fibres)

151
Q

What is the function of dense bodies in smooth muscle cells?

A

links contractile fibres to supporting fibres and to plasma membrane

152
Q

How can the contraction of m=smooth muscle be described?

A

slow and strong, contraction can be maintained for long periods of time

153
Q

Describe multiunit smooth muscle cells

A

muscle fibres act independently. individual smooth muscle fibre, each is innervated with several points of attachment

154
Q

give 3 examples of multiunit smooth muscle cells in the body

A

iris and cilliary body of the eye
pilo erector muscles of skin
some blood vessels

155
Q

describe unitary smooth muscle cells

A

muscle cells act together as a functional unit. cells are coordinated, not each individual cell is innervated

156
Q

What are found in unitary innervated cells and multiunit cells?

A

variscocities

157
Q

How are non-innervated cells linked in unitary smooth muscle cells?

A

gap junctions

158
Q

give 3 examples of unitary smooth muscle cells in the body

A

airways
GI tract
bladder

159
Q

what are varicosities?

A

synaptic contacts

160
Q

how does excitation-contraction coupling work in smooth muscle cells?

A

arrival of action potential to plasma membrane opens voltage gated Ca2+ channels, other Ca2+ voltage independent channels open.
Ca2+ floods into cell and opens Ryanodine receptors which allow Ca2+ to move out of SR
Ca2+ also moved out of SR due to intracellular signal received from a cell surface receptor
Binds to calmodulin which then binds to myosin kinase, using ATP to phosphorylate cross bridge formation

161
Q

describe the regulation of contraction in cardiac and skeletal muscle.

A 
cytosolic Ca2+ increases
Ca2+ binds to troponin
tropomyosin moved out of blocking position
myosin cross bridges bind to actin
leads to contraction
162
Q

describe the regulation of contraction in smooth muscle.

A

cytosolic Ca2+ increases
Ca2+ binds to calmodulin
Ca2+-calmodulin complex binds to myosin light chain kinase
myosin light chain kinase uses ATP to phosphorylate myosin cross bridges
phosphorylated cross bridges bind to actin
leads to contraction

163
Q

What is the calcium sensor in skeletal and cardiac muscle?

A

troponin

164
Q

What is the calcium sensor in smooth muscle?

A

calmodulin

165
Q

What is the name of excitation-contraction coupling in cardiac and smooth muscle?

A

calcium-induced calcium release

166
Q

does tetanus occur in cardiac muscle?

A

no

X Physiology 1A (9 decks)

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