1/8 Howard Muscle Contraction Flashcards
(81 cards)
1
Q
What are the 3 muscle cell types?
A
- Cardiac
- Skeletal
- Smooth
2
Q
What is the force of a muscle contraction generated by?
A
Interaction of actin and myosin
3
Q
Muscle contraction requires:
A
Transient elevation of intracellular Ca2+
4
Q
A muscle cell is also called:
A
Muscle fiber
5
Q
Muscle cell is living or dead?
A
It is alive
6
Q
Components of skeletal muscle fiber
A
- Sarcolemma (plasma membrane)
- Sarcoplasmic reticulum (SR)
- Mitochondria
- Myofibrils
7
Q
What is the intracellular organization of myofibrils?
A
- Many myofilaments form myofibril
- Many myofibrils within a skeletal muscle fiber
8
Q
Myofilaments in skeletal muscle
What are the thin strands?
What are the thick strands?
A
- actin (2 strands)
- myosin (1 thick strand)
9
Q
Components of troponin
A
TnT, TnC, TnI
10
Q
_____ binds tropomyosin
A
TnT
11
Q
_____ binds calcium ions
A
TnC
12
Q
_____ inhibits actin and myosin interaction
A
TnI
13
Q
3 components of muscle contraction
A
- excitation/contraction coupling
- unmasking myosin binding site
- sliding filament theory
14
Q
What are the two components of excitation-contraction coupling?
A
- Electromechanical coupling
- Electrochemical coupling
15
Q
Where is Ca2+ concentration the highest?
A
In the ER lumen
16
Q
What is the T-tubule?
A
Transverse tubule; invagination of the sarcolemma among the myofibrils
17
Q
what do T-Tubules facilitate?
A
Conduction of waves of depolarization (propagates action potential)
18
Q
Where do T-Tubules lie in skeletal muscle?
A
in the plane of the A-I junction in mammalian skeletal muscle
19
Q
Sarcoplasmic reticulum
A
Muscle SER
20
Q
Key role of SR
A
Regulation of [Ca2+] (stores)
21
Q
Explain the steps of excitation/contraction coupling
A
- AP reaches NMJ
- Vesicles containing Ach fuse with membrane
- Releases Ach into synaptic cleft
- Ach binds Ach receptor
- Opens ion channels (sodium in, K+ out)
- Triggers voltage-gated sodium channels
- Action potential propagates to T-tubules
- Reaches triad
- [Ca2+] increases
- contraction
22
Q
What is DHPR in a skeletal muscle cell?
A
dihydropyridine receptor - voltage sensor
23
Q
What is RyR in a skeletal muscle cell?
A
ryanodine receptor-calcium release channel
24
Q
A triad is found in _____ and is comprised of _____
A
Skeletal muscle; 2 adjacent terminal cisternae and one T-tubule
25
During electromechanical coupling, skeletal muscle contraction allows for direction interactions between _____ and _____. This induces a _____ which releases ______
DHPR in T-tubule and RYR in the SR; conformational change; Ca2+
26
Skeletal muscle contraction is an example of ______ coupling
Electromechanical coupling
27
To unmask the myosin binding site, Ca2+ binds to ____ and causes ____
Troponin; tropomyosin to move away from the myosin binding site
28
Low cytosolic Ca2+ means that the muscle is _____
Relaxed
29
Low cytosolic Ca2+ in a skeletal muscle cell causes:
- myosin binding sites are hidden
- Energized cross-bridge cannot form (cannot bind to actin)
30
What occurs when cystolic Ca2+ levels are high in a skeletal muscle cell?
1. Ca2+ binds to troponin causing tropomyosin to move AWAY from the myosin-binding sites
2. Myosin binding sites are exposed
3. Myosin binds to myosin binding sites on actin, forming a cross-bridge
31
What are the 3 components of sliding filament theory?
1. ATP hydrolysis
2. Cross bridge formation
3. Power stroke
32
Explain the steps of sliding filament theory (diagram shown)
33
What are the components of the sarcomere?
- Z lines
- A band
- H band
- I band
34
A sarcomere is defined as:
Z line to Z line
35
What is the A band?
Actin and myosin overlap
36
What is the I band?
Actin only
37
What is the H band?
Myosin only (middle)
38
During muscle contraction, what happens to the H band?
Disappears (he gone)
39
During muscle contraction, what happens to the I band?
Narrows (an I is skinny and narrow)
40
During muscle contraction, what happens to the Z lines?
Gets closer
41
During muscle contraction, what happens to the A band?
Nothing; remains unchanged
42
How does the sarcoplasmic reticulum of cardiac muscle compare to skeletal muscle?
- SR is less extensive
- Not enough stored Ca2+
43
In cardiac muscle, what kind of filaments and what bands are presents?
Thick and thin filaments; alternating A and I bands
44
Name some features of Skeletal Muscle T-tubules
- T-Tubules lie in plane of A-I junction
- Dilated terminal cisternae
- Triad=2 terminal cisternae + 1 T Tubule
45
Name some features of cardiac muscle T-tubules
- T-tubules 2.5x larger (compared to skeletal muscle)
- SR terminals approximate T-Tubules
- Diad instead of traid
- Diads at Z band
46
Explain the steps of calcium-triggered calcium release:
1. Current spreads through _____ to contractile cells
2. action potentials travel along ____ and _____
3. What channels open and where?
4. What induces Ca2+ release from the SR?
1. gap junctions
2. plasma membrane and T tubules
3. Ca2+ channels open in plasma membrane and SR
4. Ca2+ induces Ca2+ release from SR
47
What is unique about calcium release in cardiac muscle?
Calcium triggered calcium release
48
What kind of coupling is Ca2+ induced Ca2+ release?
Electrochemical coupling
49
What establishes coupling mode in cardiac muscle?
DHPR isoform
50
In cardiac muscle, DHPR functions as:
Voltage-gated Ca2+ channel
51
Schematic of Ca2+ induced release of Ca2+ (go through and describe what is happening)
(practice going through diagram)
52
Smooth muscle:
1. Are striations present?
2. are T-tubules present?
3. voluntary or involuntary contraction?
4. how many nuclei present and where are they located in the cell?
1. no (no paracrystalline structure)
2. no
3. involuntary
4. 1 nuclei in center
53
____ is used for involuntary contraction in the ANS, hormonal, and local control
Smooth muscle
54
Shape of smooth muscle cells
Fusiform
55
What filaments are present in smooth muscle?
Thick and thin filaments
56
Smooth muscle is arranged in?
- Sheets
- Various thicknesses
- Continuous network
- Usually 2 layers perpendicular for peristalsis
57
What are the thin filaments present in smooth muscle?
Actin and caldesmon
58
What is caldesmon?
Protein in smooth muscle that blocks the active site of F-actin
59
True or false: like skeletal and cardiac muscle, smooth muscle contains tropomyosin and troponin
False - neither
60
What is the difference between smooth muscle myofilaments and skeletal?
Structural differences
61
Smooth muscle myofilaments are arranged in:
Interwoven array; dense bodies act as Z disks
62
Smooth muscle - myosin
1. heavy ________ (S1) project from the thick filaments whole length
2. the two ends lack ____
3. the middle has ______
4. _____ surface area for the interaction of actin with myosin II and permitting contractions of ______
1. meromyosin heads
2. heads
3. heads
4. larger; long duration
63
Smooth muscle contraction
1. dependent on ____
2. control different than _______
3. What is absent?
4. ________ different conformation
5. actin-binding site is masked by ends of _________
1. Ca2+
2. striated muscles
3. no troponin
4. myosin II
5. meromyosin
64
Steps of smooth muscle contraction
1. Calcium ions from caveolae and SR bind to calmodulin
2. Binds caldesmon, unmasking active site on actin
3. Ca2+-calmodulin complex activates myosin light chain kinase
4. Myosin light chain kinase phosphorylates one of the myosin light chains
5. Unfolds light meromyosin moiety
6. Form the typical golf club-shaped myosin molecule
7. Unmasks actin binding site
8. Permits interaction between actin and myosin
9. Contraction
65
Where is smooth muscle found?
GI, vascular system
66
What 3 signals contribute to a smooth muscle contraction?
Mechanical, electrical, and chemical signals
67
Mechanical stretching in smooth muscle is _____
Myogenic
68
Smooth muscle has what type of calcium channels?
L-type calcium channels
69
What neurotransmitters are involved in smooth muscle contraction?
NE
Angiotensin
Vasopressin
Endothelin-1
thromboxane
70
MLCK
Myosin light chain kinase
71
MLCK is responsible for:
Phosphorylating myosin light chain
| control if contraction occur or no cross-bridge activity
72
Smooth muscle: relaxation
1. reduced ________ of MLC
2. reduced release of _____ by the SR or reduced ______ entry into the cell
3. inhibition of _______ by increased intracellular concentration of _______
4. increased ________ of activated myosin
1. phosphorylation
2. Ca2+, Ca2+
3. MLCK, cAMP
4. dephosphorylation (MLCP)
73
_____ is used for calcium control in skeletal muscle
Calsequestrin in terminal cisternae
74
_____ is used for calcium control in cardiac muscle
Calcium from extracellular sources
75
_____ is used for calcium control in smooth muscle
Caveolae
76
____ is used for calcium binding in skeletal muscle
TnC (troponin)
77
____ is used for calcium binding in cardiac muscle
TnC (troponin)
78
____ is used for calcium binding in smooth muscle
Calmodulin
79
Nerve fibers are _____ in skeletal muscle
Somatic motor
80
Nerve fibers are _____ in cardiac muscle
Autonomic
81
Nerve fibers are _____ in smooth muscle
Autonomic
