Muscle Flashcards
(166 cards)
1
Q
What are the 3 ways animal movements are generated?
A
ameboid movements, cilliary and flagella bending, muscle contraction
2
Q
What does mucsocillary clearance maintain in the lungs
A
maintains the sterility of the lungs
3
Q
Where is skeletal muscle located?
A
the skeleton
4
Q
What is the anatomy of skeletal muscle?
A
striated
5
Q
what sort of nervous control is skeletal muscle under?
A
voluntary
6
Q
What is the function of skeletal muscle?
A
movement and heat production
7
Q
where is cardiac muscle located?
A
the heart
8
Q
What is the anatomy of cardiac muscle
A
striated
9
Q
what sort of nervous control is cardiac muscle under?
A
involuntary (autonomic)
10
Q
What is the function of cardiac muscle?
A
pump blood
11
Q
where is smooth muscle located?
A
hollow organs
12
Q
What is the anatomy of smooth muscle?
A
non-striated
13
Q
what sort of nervous control is smooth muscle under?
A
involuntary
14
Q
What is the function of smooth muscle?
A
movement and control of organ size
15
Q
What is movement of the body the result of?
A
contraction of skeletal muscle across a joint
16
Q
Do mechanical lever systems work at an advantage or disadvantage?
A
disadvantage
17
Q
What does muscles working at a disadvantage mean?
A
must exert force even to hold something up
18
Q
What is the force needed to counteract muscular disadvantage the sum of?
A
the weight held and the arm length
19
Q
What is the velocity of a muscle amplified by?
A
lever system
20
Q
What is maximized by the specific architecture of skeletal muscle?
A
force production and movement
21
Q
What is the fasciculus?
A
collection of around 150 muscle cells bundled together
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
23
Q
what is perimysium?
A
connective tissue around the fasciculus
24
Q
what is endomysium?
A
connective tissue which wraps around individual muscle cells
25
What is a myofibril?
cylinder of cells located within muscle fibres
26
What are myofibrils wrapped in?
sacroplasmic reticulum
27
What is a terminal cisternae of sarcoplasmic reticulum?
bulge at the end of the sarcoplasmic reticulum before the next myofibril and therefore next section of sarcoplasmic reticulum
28
What separates one piece of sarcoplasmic reticulum from the next?
transverse tubule
29
What is the sarcolemma?
cell membrane of muscle cell
30
What do the transverse tubules connect?
surface of muscle cell deep into muscle fibre
31
What is a triad formed of in muscle fibres?
a transverse tubule between 2 terminal cisternae
32
What is a single myofibril made up of?
repeating functional units
33
What is the functional unit of a myofibril?
sarcomere
34
What are the thicknesses of the 2 principal protein filaments of a sarcomere?
thick and thin
35
What is the name of the thick protein filament of a sarcomere?
myosin
36
what is the name of the thin protein filament of a sarcomere?
actin
37
What is myosin sandwiched between?
2 threads of actin
38
What is a myofibril built out of?
many sarcomeres
39
What produces the banding pattern seen in histological images of muscle cells?
filament organisation
40
What is a characteristic of skeletal muscle seen in histological images?
striations
41
How many nuclei are often present in a skeletal muscle fibre?
multiple
42
What does the Z line in a sarcomere show?
the edges of the sarcomere
43
What is the dark band of the sarcomere called?
A band
44
Where does the I band of a sarcomere sit?
straddles 2 sarcomeres
45
What is the line down the middle of the A band called?
M line
46
What zone surrounds the M line?
H zone
47
How does the H zone appear under an electron microscope?
lighter than the A band
48
what are thick filaments made of?
myosin
49
Where do cross bridges originate from on myosin?
the myosin head
50
How do myosin filaments join together?
tail to tail
51
What are myosin cross bridges essential for?
muscle contraction
52
What is the role of the essential light protein chain around the neck of the myosin filament?
structural
53
What is the role of the regulatory light protein chain around the neck of the myosin filament?
modulates the activity of the myosin head
54
Where is the actin binding site located on a myosin filament?
myosin head
55
What are the thin muscle filaments composed of?
actin
56
How many chains of globular actin are there in an actin filament?
2
57
Where are the myosin binding sites found on actin?
within the globular actin chains
58
What is the contractile element of actin?
globular actin chains
59
what is tropomyosin?
rope like structure between 2 actin chains
60
What is the tropomyosin complex?
a regulatory protein made up of 3 subunits
61
What do cross bridges of myosin join?
myosin (thick) filaments to actin (thin) filaments at the actin binding sites
62
Which scientists provided experimental evidence for the molecular basis of skeletal muscle contraction?
Andrew and Hugh Huxley
63
What did Andrew Huxley do in his experiment to look at muscle contraction?
used a light microscope to measure the lengths of A and I bands during contraction
64
What did Hugh Huxley do in his experiment to look at muscle contraction?
used an electron microscope to measure the length of the filaments during muscle contraction
65
What happens to sarcomere length during muscle contraction?
becomes shorter
66
Why do sarcomeres shorten during muscle contraction?
because actin filaments actively slide along between the myosin filaments
67
What structures mediate the shortening of a sarcomere?
cross bridges
68
What parts of a sarcomere are pulled together during muscle contraction?
Z lines pulled towards M lines
69
What is this sliding of actin filaments between myosin filaments known as?
the sliding filament mechanism
70
What are cross bridges formed and dissociated between?
actin and myosin filaments
71
Does each cross bridge generate a force independent of other cross bridges?
yes
72
What is the total force produced by a contracting sarcomere determined by?
the number of cross bridges formed between myosin (thick) and actin (thin) filaments
73
What does the the amount of overlap between myosin and actin filaments determine?
total force produced by the contracting sarcomere
74
What is meant by the normal operating range of sarcomeres?
maximal force is produced (there is no one single value)
75
What is the sarcomere length-tension relationship?
bell shaped relationship determined by cross-bridge formation between myosin and actin filaments
76
What 3 factors generate tension in the muscle during the cross bridge cycle?
mechanical changes
chemical changes
ATP
77
Describe the mechanical changes that take place during the cross bridge cycle?
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
At the end of stage 2 of the cross bridge cycle is the de-energised cross bridge still attached to actin?
yes
79
Does each individual cross bridge go through the stages of the cross bridge cycle independantly?
yes
80
Describe the chemical changes that take place during the cross bridge cycle
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
What are the 2 roles of ATP in the cross bridge cycle?
Energy source
| Allosteric regulator
82
How is ATP used as an energy source in the cross bridge cycle?
ATP hydrolysis provides the energy for cross bridge movement
83
How is ATP used as an allosteric regulator in the cross bridge cycle?
binding of ATP to myosin breaks the link between actin and myosin. This allows the cycle to be repeated
84
What are the 2 binding sites found on myosin head (cross bridge)?
actin binding site and ATP binding site
85
What does binding of ATP to mysoin head binding site cause?
a confirmational change in the myosin head
86
What effect does an alteration in the confirmation of the myosin head, caused by binding of ATP, have?
weakens the interaction between actin and myosin and so disassociation takes place
87
What is the sliding filament mechanism the molecular basis of?
skeletal muscle contraction
88
What process drives sarcomere contraction?
cross bridge cycling
89
How are skinned muscle fibres prepared?
plasma membrane is made permeable to ATP and Ca2+ so they can freely diffuse in ad out of the cell.
90
Which ions regulate skeletal muscle contractions?
calcium
91
What is tropomyosin?
protein complex which constantly inhibits muscle contraction at rest
92
How does tropomyosin inhibit muscle contraction?
myosin binding sites are hidden by the tropomyosin
93
What happens to tropomyosin when 2 calcium ions are added?
moves deeper into the actin groove and unmasks the myosin binding sites relieving constant inhibition
94
What does TnC do?
binds calcium to tropomyosin
95
What does Tnl do?
inhibits cross bridge binding
96
What does TnT do?
binds tropomyosin
97
What triggers the contraction of skeletal muscle?
action potential
98
What does one action potential illicit?
one muscle contraction
99
What is the latent period?
delay between the firing of AP and initiation of muscle contraction
100
What happens to the action potential once it reaches the end plate after synapsing at the neuromuscular junction?
local current flow on cell surface
101
Where are calcium ions stored within the cell?
sarcoplasmic reticulum
102
Why do calcium ions need to be stored in the sarcoplasmic reticulum?
the latent period between AP and contraction is too short for Ca2+ ions to be able to diffuse into the cell
103
What does calsequestrin do in the sarcoplasmic reticulum?
stores high concentration of calcium ions
104
How is calcium rapidly released from sarcoplasmic reticulum into myoplasm?
voltage gated channel
105
How is calcium removed from the myoplasm once it has been used in attachment to tropomyosin?
calcium ATPase brings Ca2+ back into the sarcoplasmic reticulum via active transport
106
What are the functions of T tubules?
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
Where does an action potential run after local current flow across the surface of the cell?
into the T tubule and the muscle fibre, close to the sarcoplasmic reticulum
108
What is the function of the DHP receptor?
a voltage sensor
109
What is the function of the ryanodine receptor?
calcium release channel in sarcoplasmic reticulum
110
Where is the DHP receptor located?
T tubule membrane
111
How is the DHP receptor affected by the arrival of an action potential?
the shape of the receptor alters which in turn affects the connected ryanodine receptor
112
What happens when DHP receptor is activated by an action potential?
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
What is the experimental evidence for regulation of muscle contraction by calcium ions?
calcium buffers and skinned muscle fibres
114
What is effect of calcium on
| troponin and tropomyosin?
calcium ions remove constant inhibition of skeletal contraction
115
What is the function of sarcoplasmic reticulum in muscle contraction?
stores high concentrations of calcium and rapidly releases it into myoplasm
116
What are the functions of transverse tubules in skeletal muscle contraction?
conduct action potential into muscle cells
117
Summarise exitation-contraction coupling in skeletal muscle.
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
What happens to force of muscle contraction when action potentials are close together but Ca2+ conc can return to normal between each?
force increases but would appear jagged on a graph as it drops slightly between each AP (unfused tetanus)
119
What is unfused tetanus?
jagged increase in muscle force
120
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?
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
What is fused tetanus?
force of muscle contraction rising until it reaches maximum and only falling when calcium concentration falls.
122
What is excitation-contraction coupling?
how action potentials regulate skeletal muscle contraction by triggering calcium release from the sarcoplasmic reticulum
123
What does the frequency of action potential firing determine?
strength of skeletal muscle contraction by sustaining the intracellular calcium concentration
124
What do calcium ions remove from skeletal muscle contraction?
constant inhibition by troponin-tropomyosin
125
What is tension?
force exerted on an object by a contracting muscle
126
What is load?
force exerted on muscle by the weight of an object
127
What is isometric contraction?
where the muscle develops tension without changing length
128
What is isometric contraction measured by?
tension generated
129
What is isotonic contraction measured by?
rate of shortening
130
What happens during eccentric contraction?
load exceeds muscle tension
131
What is active tension produced by in the muscle?
muscle contraction
132
What is passive tension produced by in the muscle?
connective tissue (epimysium, perimysium, endomysium) which resist the stretching of muscle fibres and accessory proteins (titin and nebulin)
133
Where is titin located?
within the sarcomere between Z line and M line. Travels through the centre of myosin
134
What is titin responsible for?
holding myosin in optimum position to form cross bridges with actin
135
What does nebilin do?
determines the length of the actin thin filament
136
What is the difference between fast and slow twitch muscle fibres?
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
Which muscle fibre, fast or slow twitch, is easily fatigued?
fast
138
Which muscle fibre, fast or slow twitch, is not easily fatigued?
slow
139
Give an example of location of fast twitch muscle fibres
extra occular muscle of the eye
140
Give an example of location of slow twitch muscle fibres
soleus muscle on back of leg
141
What type of muscle fibre are fast and slow twitch fibres and example of?
specialised muscle fibres
142
What originates from the sinoatrial node?
electrical activity in the heart from ANS
143
What about the structure of heart muscle cells means that contractions can be well co-oridinated?
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
What is the name of cardiac muscle cells?
cardiac myocytes
145
What is the desmosome in cardiac muscle?
holds 2 cardiac myocytes together
146
What is the function of the gap junction in cardiac muscle?
pathway for communication between cardiac myocytes. Electrical signal is passed across these junctions
147
What is the name of the cell junction in cardiac muscle?
intercalated disk
148
how does excitation-contraction coupling work in cardiac muscle?
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
What do contractile fibres of smooth muscle cells contain?
actin and myosin
150
What do supporting fibres of smooth muscle cells contain?
intermediate filaments (supporting fibres)
151
What is the function of dense bodies in smooth muscle cells?
links contractile fibres to supporting fibres and to plasma membrane
152
How can the contraction of m=smooth muscle be described?
slow and strong, contraction can be maintained for long periods of time
153
Describe multiunit smooth muscle cells
muscle fibres act independently. individual smooth muscle fibre, each is innervated with several points of attachment
154
give 3 examples of multiunit smooth muscle cells in the body
iris and cilliary body of the eye
pilo erector muscles of skin
some blood vessels
155
describe unitary smooth muscle cells
muscle cells act together as a functional unit. cells are coordinated, not each individual cell is innervated
156
What are found in unitary innervated cells and multiunit cells?
variscocities
157
How are non-innervated cells linked in unitary smooth muscle cells?
gap junctions
158
give 3 examples of unitary smooth muscle cells in the body
airways
GI tract
bladder
159
what are varicosities?
synaptic contacts
160
how does excitation-contraction coupling work in smooth muscle cells?
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
describe the regulation of contraction in cardiac and skeletal muscle.
```
cytosolic Ca2+ increases
Ca2+ binds to troponin
tropomyosin moved out of blocking position
myosin cross bridges bind to actin
leads to contraction
```
162
describe the regulation of contraction in smooth muscle.
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
What is the calcium sensor in skeletal and cardiac muscle?
troponin
164
What is the calcium sensor in smooth muscle?
calmodulin
165
What is the name of excitation-contraction coupling in cardiac and smooth muscle?
calcium-induced calcium release
166
does tetanus occur in cardiac muscle?
no
