Muscle Flashcards
(106 cards)
1
Q
What is the method of excitation for skeletal muscle?
A
alpha motor-neurons
2
Q
What is the method of excitation for cardiac muscle?
A
self-depolarization
3
Q
The regular arrangement of ____ within the myofibrils gives them a striated appearance.
A
Proteins
4
Q
Invaginations of the sarcolemma, called the____, extend into the cell itself.
A
Transverse-tubules (t-tubules)
5
Q
The tunnels of the t-tubules provide a quick delivery system for the spread of ____ to the skeletal muscle cell.
A
Action potentials
6
Q
Excitation of skeletal muscle requires the release of _____ from the sarcoplasmic reticulum.
A
intracellular calcium
7
Q
The triad allows for a close coupling of what?
A
action potentials with intracellular calcium release
8
Q
What is the contractile unit of a skeletal muscle cell?
A
sarcomere
9
Q
Actin, thin filament, is composed of a globular protein called G-actin arranged into a double stranded helical structure called…
A
F-actin
10
Q
What myosin light chain serves as a structural role?
A
alkali light chain
11
Q
What myosin light chain is involved in regulating the ATPase capability of the myosin head?
A
regulatory myosin light chain
12
Q
Filamentous protein that lies in the groove of the double-stranded actin.
A
Tropomyosin
13
Q
What has a binding site for the myosin head, which is covered up by tropomyosin?
A
Each G-actin
14
Q
Each tropomyosin extends over …
A
7 G-actin molecules
15
Q
When calcium binds to the TnC subunit, this leads to …
A
a conformational change in troponin
16
Q
The conformational change in troponin from calcium binding to TnC, allows ….
A
tropomyosin to move out of the actin groove
17
Q
When tropomyosin moves out of the actin groove it …
A
exposes the actin active sites for myosin to bind to
18
Q
What binds tropomyosin?
A
TnT
19
Q
What is the function of TnI?
A
binds to actin, and inhibits actin and myosin from interacting
20
Q
The central point of the sarcomere to which the thick filaments are anchored by associated proteins
A
M line
21
Q
The anchor points for the thin filaments and the boundaries for the sarcomeres
A
Z-discs
22
Q
A region that contains the entire length of the thick filaments
A
A band
23
Q
A region that contains the portion of the thick filaments that does not overlap with the thin filaments
A
H zone
24
Q
A region that contains the portion of the thin filaments that does not overlap with the thick filaments
A
I band
25
Structural proteins maintain a _____ of fibers within a sarcomere, with the thin filaments arranged around the thick filaments.
hexagonal cross-section
26
During a muscle contraction in which the sarcomere shortens, what will happen to the length from Z-disc to Z-disc?
decrease
27
During a muscle contraction in which the sarcomere shortens, what will happen to the length of the H zone?
decrease
28
During a muscle contraction in which the sarcomere shortens, what will happen to the length of the A band?
stays the same
29
During a muscle contraction in which the sarcomere shortens, what will happen to the length of the I band?
decrease
30
Converts the electrical signal of an action potential into the chemical signal of neurotransmitter.
Alpha motor neuron
31
The steps of excitation-contraction coupling occur where?
at the neuromuscular junction
32
In the first step of the ECC, the action potential spreads down the axon of the alpha motor neuron, leading to a ...
depolarization of the end-bulb (fast-gated sodium channels)
33
In the ECC, the depolarization of the end-bulb leads to the opening of ...
voltage-gated calcium channels, and calcium flows down its electrochemical gradient into the cell
34
In the ECC, the influx of calcium into the cell leads to the fusion of membrane-bound vesicles, which contain ...
the neurotransmitter acetylcholine
35
The membrane bound vesicles containing acetylcholine, fuses with what?
The active zone of the plasma membrane
36
In ECC when the vesicles fuse with the plasma membrane, acetylcholine undergoes ...
exocytosis and diffuses through the synaptic cleft
37
In the ECC, the neurotransmitter is released at an area of the muscle fiber called the ...
motor end-plate
38
The binding of acetylcholine to its receptors on the motor end-plate leads to the opening of ...
ligand-gated cation channels
39
What type of receptors does the acetylcholine bind to?
ligand-gated cation channels; nicotine cholinergic receptors
40
Acetylcholine is enzymatically digested in the ...
synaptic cleft
41
The enzyme that digests acetylcholine is called
acetylcholinesterase
42
What portion of the digested ACh is typically taken up by the alpha motor neuron and can then be recycled to create new molecules of acetylcholine?
Choline portion
43
The binding of acetylcholine to ligand-gated receptors at the motor end-plate opens what?
non-specific cation channels
44
Both sodium and potassium pass through the non-specific cation channels, but because sodium influx is much greater than potassium efflux, ...
the cell (motor end-plate) depolarizes
45
Why is it impossible to generate an action potential in the motor end-plate region?
There are no fast voltage-gated sodium channels
46
Instead of an action potential the motor end-plate generates an ...
end-plate potential (EPP)
47
What is an end-plate potential (EPP)?
A localized electrical signal; an example of the excitatory post-synaptic potentials (EPSPs)
48
What sends electrical signals bidirectionally away from the motor end-plate to adjacent regions of the sarcolemma?
EPP
49
The electrically stimulated adjacent regions of the sarcolemma do contain ... that can open once threshold is reached. This allows an action potential to spread through out the sarcolemma and t-tubules.
voltage-gated sodium channels
50
What occurs due to quantal release of ACh from the terminal button?
miniature end-plate potentials (MEPP)
51
The motor end-plate lacks ...
a stable RMP
52
It is hypothesized that quantal release of ACh causing MEPPs occurs to maintain ...
the integrity of the neuromuscular junction
53
How does the production of MEPPs maintain the integrity of the neuromuscular junction?
the quantal release of ACh may keep the ACh receptors localized to the motor end-plate
54
The depolarization from a MEPP is not of sufficient magnitude to ...
depolarize adjacent regions of the sarcolemma to threshold
55
What are the 3 "safety" factors to ensure neuromuscular transmission?
1. More ACh is released than needed to depolarize the motor end-plate.
2. The MEP contains 4-12 times more ACh receptors than needed to ensure neuromuscular transmission
3. The EPP magnitude is 3-4 times greater than required to initiate depolarization of the sarcolemma
56
Physostigmine is an anti-acetylcholinesterase, what is the direct effect on neuromuscular transmission?
Prolonged post-synaptic response to ACh
57
w-Conotoxin blocks voltage-gated calcium channels in nerves, what is the direct effect on neuromuscular transmission?
Prevents exocytosis of ACh
58
Dendrotoxin blocks voltage-gated K+ channels, what is the direct effect on neuromuscular transmission?
Prevents repolarization of presynaptic membrane and increases release of ACh
59
Tetrodotoxin blocks voltage-gated Na+ channels, what is the direct effect on neuromuscular transmission?
Prevents nerve and muscle action potentials
60
Tetanus blocks synaptic vesicle exocytosis in inhibitory interneurons, what is the direct effect on neuromuscular transmission?
Produces skeletal muscle spasms
61
Curare blocks the acetylcholine receptor, what is the direct effect on neuromuscular transmission?
Produces flaccid paralysis
62
In order for the action potential to initiate muscular contraction , ...levels must rise.
intracellular calcium
63
The main source for calcium influx is via an organelle called the ...
Sarcoplasmic Reticulum (SR)
64
The SR contains a calcium binding protein called ...
calsequestrin
65
Calsequestrin helps to maintain a ...
lower concentration gradient in the SR for free calcium
66
What serves as reservoirs of calcium within the cell?
Junctional SR regions/terminal cisterns
67
As the action potential spreads down the t-tubules, ... in the sarcolemma are activated.
"L-type" calcium channels - dihydropyridine receptors (DHPR)
68
DHPRs serve as both ... in skeletal muscle and voltage-gated calcium channels inn cardiac muscle.
voltage sensors
69
In skeletal muscle, each DHPR is linked to a calcium release channel in the membrane of the SR, called a ...
ryanodine receptor (RYR)
70
As the wave of depolarization spreads along the sarcolemma and down the T-tubules, ____ are stimulated.
L-type calcium channels (DHPR)
71
DHPR stimulates the ... in the SR to open.
ryanodine calcium release channels
72
Once _____ opens, calcium flows down its concentration gradient from the SR and into the cytosol (sarcoplasm)
Ryanodine Receptor (RYR)
73
Because there is no influx of calcium from the ECF, the form of calcium release is called...
Calcium channel induced calcium release (CCICR)
74
What form of calcium release is not essential in skeletal muscle, but used from cardiac muscle excitation?
Calcium induced calcium release (CICR)
75
What type of calcium release does require the influx of calcium rom the ECF?
CICR
76
In CICR, depolarization of the t-tubule stimulates the ____ to open, and calcium moves down its concentration gradient into the cell.
L-type voltage-gated calcium channels to open
77
The calcium in the cell directly stimulates the RYR to release calcium from the ...
SR stores
78
T-tubules are located at the junction of the ...
A and I bands
79
In ECC, calcium flows down its electrochemical gradient, from the SR into the sarcoplasm, where it binds to the regulatory protein _____.
troponin
80
The binding of calcium to TnC leads to a conformational change that moves _____ from the actin active sites.
tropomyosin
81
When calcium binds to TnC & tropomyosin is removed from the actin active sites, the myosin head is free to bind to the thin actin filaments to ...
initiate contraction
82
In what state of the cross-bridge cycle does the myosin head use its ATPase capability to hydrolyze a bound ATP into ADP and phosphate?
Cocked state
83
In the cross-bridge cycle the hydrolysis of ATP allows the myosin head to "cock" and move into an appropriate binding position ....
further away from the M-line
84
With the ADP bound, the myosin head has a high affinity for ____
the actin filament
85
Cross-bridge formation can only occur if there is a ...
high intracellular concentration of calcium
86
If there is a high intracellular concentration of calcium and tropomyosin has moved away from the actin groove, the myosin head ...
binds to the actin filament, forming a bridge between the two filaments (cross-bridge state)
87
In what state of the cross-bridge cycle does the myosin head release its bound ADP and inorganic phosphate?
Power-stroke state
88
What powers the movement of the myosin head from a 90 degree angle to a 45 degree angle?
Energy from the ATP hydrolysis
89
In what state of the cross-bridge cycle does the myosin head remain attached to the actin filament?
Attached state
90
The binding of an ATP molecule to the myosin head allows the myosin to ...
release its attachment to actin
91
With ATP bound, the myosin has a ____ for the actin filament.
low affinity
92
In what state of the cross-bridge cycle does the binding of ATP to the myosin head allow it to release from actin?
Released state
93
If ATP levels become severely depleted, cross-bridges will remain in the attached state leading to ...
sustained skeletal muscle contractions (rigor mortis)
94
As long as ___ is present in the sarcoplasm, and ___ are plentiful, the contraction process will continue.
Calcium; ATP stores
95
In order to terminate muscle contraction, the cell must resequester calcium into the SR, this occurs largely through use of a ...
Sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) pump
96
The SERCA pump moves calcium from the ____ into the ____
sarcoplasm into the SR
97
What form of transport does the SERCA pump use?
moves calcium against its concentration gradient using primary active transport
98
SERCA channels are also associated with a regulatory protein called ...
phospholamban
99
When ____, phospholamban produces an increase in the activity of the SERCA pump.
phosphorylated
100
In the relaxation of skeletal muscle the regulatory protein phospholamban produces an increase in the activity of the SERCA pump, thus increasing the ....
Resequestration of calcium in the SR
101
In the relaxation of skeletal muscle when calcium is pumped into the SR, it is subsequently bound to ...
Calsequestrin
102
Calsequestrin maintains a ____ concentration of calcium in the SR.
low free
103
When calsequestrin maintains a low free concentration of calcium in the SR it provides a ____ for the SERCA channel to operate against.
lower concentration gradient
104
Another function of calsequestrin, besides maintaining a low free concentration of calcium, is localizing calcium in the _____
Junctional SR
105
By calsequestrin localizing calcium in the junctional SR, it makes it available for easy release during ...
CICR or CCICR
106
As SR calcium levels drop, calcium ...., and tropomyosin ....; preventing further interaction between the myosin and actin filaments, until another excitation occurs.
calcium dissociates from TnC, & tropomyosin re-covers the actin active site
