Microstructure And Contraction Flashcards
1
Q
What type of control is smooth muscle under?
A
Involuntary control
2
Q
What part of the nervous system does smooth muscle act under?
A
Autonomic nervous system
3
Q
What type of control is the skeletal muscle under?
A
Voluntary control
4
Q
What does skeletal muscle do?
A
Bring about movement
5
Q
What connects bone to muscle
A
A tendon
6
Q
What are skeletal muscles usually attached to?
A
Bones
7
Q
What is the microstructure of a muscle?
A
Myofilaments
Myofibril
Myofibre
Fascicles
Muscle
8
Q
What are muscle fasciculus surrounded by?
A
Perimysium
9
Q
What are myofibres surrounded by?
A
Endomysium
10
Q
What surrounded the bundles of muscles fascicles to hold them together?
A
Epimysium
11
Q
What is the nucleus state of muscle fibers?
A
Multinucleate
12
Q
What is the plasma membrane that covers the myofibres called?
A
Sarcolemma
13
Q
What is found in the sarcoplasm?
A
myoglobin and mitochondria
14
Q
What is the sarcoplasmic reticulum?
A
Network of fluid filled tubules
15
Q
What is one repeating unit of a myofibril called?
A
A sarcomere
16
Q
What two proteins do myofibril consist of?
A
Actin and myosin
17
Q
What is the thin filament called.
A
Actin
18
Q
Thick filaments are
A
Myosin
19
Q
What makes up the dark portion of the light and dark bands?
A
Myosin
20
Q
What separates sarcomeres?
A
Dense Z protein discs
21
Q
What is the I band?
A
The light bands with thin actin filaments
22
Q
Do myofilaments extend the length of the myofibres?
A
No
23
Q
What causes muscle contraction?
A
Movement of actin filaments over the myosin filaments, which shortens the length of the sarcomere
24
Q
How many heads does myosin have?
A
Two globular heads
25
What forms the single tail of myosin?
Two alpha helices
26
What forms a myosin filament?
The tails of several hundred molecules
27
What two other molecules do actin filaments contain?
Troponin and tropomyosin
28
What shape are actin molecules twisted into?
Helix
29
What happens to the I band when the muscle contracts?
Shortens
30
What happens to the A band during contraction?
Stays the same length
31
What is the A band?
The dark band
32
What happens to the distance between the Z discs during muscle contraction?
Shortens
33
Describe the initiation of muscle contraction?
1. Action potential arrives at end of motor neurone
2. Voltage gated Ca2+ channels open
3. Ca2+ enters pre-synaptic terminal
4. Triggers the exosytosis of vesicles
5. ACh released into the cleft
6. Binds to receptors
7. Generates action potential
34
How is ACh broken down?
Using acetylcholine esterase
35
Describe the activation of muscle contraction?
1. AP propagates along surface and into T tubules
2. dihydropyridine receptors in T tubule membranes sense change in voltage and changes shape of the protein linked to ryanoidine receptor
3. Ryanodine receptor then opens and releases Ca2+ out into space around filaments
4. Ca2+ binds to troponin
5. Causes tropomyosin to move, exposing the myosin head binding site
6. Ca2+ is then actively transported into the sarcoplasmic reticulum
7. Charged myosin head binds to exposed site on actin filament
8. This binding causes the myosin head to pívot pulling the actin filament towards center if sarcomere
9. ATP binds which causes the myosin head to be released
10. ATP hydrolysis provides energy to recharge the myosin head
36
What receptor detects the change in voltage when an action potential arrives at the T tubule
Dihydropyridine
37
What is the DHP receptor bound to?
Ryanodine receptor
38
What does Ca2+ bind to on the actin filament?
Troponin
39
What is covering the myosin binding site?
Tropomyosin
40
What is the power stroke?
The pivoting of the the myosin head to slide the actin chain over the myosin filament
41
What binds to the myosin head to charge the myosin head to move?
ATP
42
What is used to “recharge” the myosin head for more contraction?
ADP hydrolysis to make ATP
43
Describe the neural control of muscle contraction?
Upper motor neurone in the brain to lower motor neurones in the brainstem or spinal cord
44
What is a motor unit?
A single motor neurone together with all the fibers that it innervates
45
How many muscle fibers do each motor neurone supple on average?
600
46
What happens when a single motor neurone is stimulated?
All the muscle fibers in that motor unit will contract
47
What is the best innervation ratio for high levels of fine control?
Neurones which innervate fewer muscle fibers
48
What is a type one motor unit?
Slow
49
What are type IIa muscle fibers?
Fast, fatigue resistant
50
What are type IIB motor units?
Fast and fatiguable
51
Which motor units have small cell body diameter?
Slow, type I
52
Which motor unit type have thicker axons?
Type IIA and IIB
53
What is the size difference in dendritic trees of the different motor units ?
Larger dendritic trees in Type IIA and Type IIB, smaller in type I
54
How are muscle fibers distributed throughout the muscle?
Randomly
55
Which muscle fiber type are rich in myoglobin?
Slow type I and type IIA (fast, fatigue resistant)
56
Which type of muscle fibers are used for aerobic activity?
Slow twitch fibres
57
Which muscle fibre type are used for anaerobic functions?
Fast and fatiguable muscle fibers
58
Which muscles have a high proportion of slow twitch fibers?
Muscles involved in postural control
59
What three factors are motor units classified by?
Amount of tension, speed of contraction and fatiguability
60
What are the two mechanisms by which the brain regulates the forces that a single muscle produces?
Recruitment and rate coding
61
Describe the recruitment mechanism?
The more motor units that are recruited, the larger the size of the force
62
What is the size principle?
The smaller motor units are recruited first
63
What happens during recruitment when more forces is needed?
More muscle units are recruited
64
Describe the rate coding principle?
The firing rate down the motor neurones to the motor unit changes as more force is needed to be produced
65
What is ramp contraction (summation)?
When the force of contraction increases over time due to more recruitment
66
How does recruitment regulate the stimulation of motor units?
By regulating the number of motor units that are recruited
67
Which motor unit is the first to be derecruited?
The motor unit which was recruited last - therefore this motor unit will be the one largest in size
68
What are neurotrophic factors?
Type of growth factor which prevent neuronal death and promote growth of neurones after injury
69
What does the motor unit and fibre characteristics depend on?
The nerve which innervates them
70
What happens to fast and slow twitch muscle fibers is they are cross innervated?
The fast becomes slow and slow becomes fast
71
What are the three main types of muscle contraction?
Isometric
Concentric
Eccentric
72
What is isometric contraction?
When the muscle unit produces forces but doesn’t change length
73
What is a concentric muscle contraction?
When the muscle shortened in order to produce movement
74
What is eccentric contraction?
When force is produced but the muscle fibers is getting longer
75
What is an example of eccentric muscle contraction?
When a person is lifting up a dumbbell which is too heavy for them
76
Which type of muscle contraction produces the most force?
Eccentric
77
Which type of muscle contraction can damage and tear muscle fibers?
Eccentric
78
Following training, what is the most common type of muscle fiber change?
Type IIB to IIA (FAST FATIGUABLE TO FATIGUE RESISTANT)
79
What can cause a change from type 1 to type 2 muscle fibers?
Severe deconditioning or spinal cord injury
80
What type of fibers are found in aged muscle?
Larger proportion of type 1 fibers
81
What provides evidence for the larger proportion of type 1 fibers in aged muscle?
Slower contraction time
82
What shift in muscle fibers type is associated with microgravity?
Slow to fast
83
Why is there a slow to fast shift in microgravity?
Less need for postural muscle innervation (slow)
84
Where is the sarcolemma in relation to the endomysium?
The sarcolemma lies under the endomysium which surrounds the muscle fibre
85
What is meant by a pennate arrangement of muscle fibres?
When muscle fibres are placed at angles to the tendon
86
What is a unipennate arrangement of muscle fibres?
When the muscle is going in the same direction as the tendon
87
What is a bipennate arrangement of muscle fibres?
When the muscle fibres are spread out in two direction from the tendon
88
What is a multipennate arrangement of muscle fibres?
When there are many tendons and many fibres
89
What is a parallel muscle fibre?
When the muscle fibre is straight across
90
What is meant by a fusiform muscle fibre?
When the middle of the fibre is thicker and larger in size than the two outer edges
91
What are the three shapes of muscle fibres?
parallel
fusiform
triangular
