Lecture 04 Skeletal Muscle Flashcards
0
Q
what sarcomeric band does not undergo a change in length during the contraction of a skeletal muscle?
A
A Band
1
Q
What refers to a chain of sarcomeres?
A
Myofibril
2
Q
Dihydropyridine (DHP) channels are part of what structure?
A
T tubules
3
Q
Ryanodine-sensitive calcium ion release channels are part of what structure?
A
Sarcoplasmic reticulum
4
Q
Which of the following events occurs first during the transmission of a signal from an alpha motor neuron to a skeletal muscle fiber? End-plate Depolarization Calcium Ion Influx into Axon Terminal Exocytosis of synaptic vesicles Sarcolemma action potential
A
Calcium Ion Influx into Axon Terminal
5
Q
Which of the following represents the factor by which the concentration of calcium ion increases in the cytosol after release from the sarcoplasmic reticulum 10 50 100 1000
A
100
6
Q
Which of the following maintains an optimum calcium concentration gradient to facilitate return of calcium to SR Calsequestrin SERCA DHP Ryanodine
A
Calsequestrin
7
Q
Fast twitch fibers have what characteristics?
A
More fatigable than slow twitch fibers
8
Q
Which of the following represents an example of an eccentric contraction?
- The triceps muscle during the throwing of a ball
- The triceps muscle while raising the body from the floor during a push-up
- The triceps muscle while lowering the body to the floor during a push-up
- The biceps muscle while raising the body during a pull up
A
3
9
Q
What is epimysium
A
Connective tissue surrounding entire muscle
10
Q
What is a muscle?
A
Made up of multiple fascicles
11
Q
What is perimysium?
A
Connective tissue surrounding individual fascicle
12
Q
What is a fascicle
A
A bundle of myofibers
13
Q
What is endomysium
A
Delicate connective tissue around each myofiber
14
Q
What is sarcolemma
A
The plasmalemma or cell membrane of a muscle fiber
15
Q
What is myofiber
A
Individual multinucleated muscle cell
16
Q
What is myofibril
A
A chain of sarcomeres within a myfiber
17
Q
What is myofilament
A
Actin and myosin filaments that make up a sarcomere
18
Q
What creates a triad?
A
Two cisternae with t tubule in between
19
Q
What is a T-tubule?
A
Invaginations of sarcolemma
20
Q
What are the four sections of sarcomeres?
A
Z lines, I bands, A bands, and H bands
21
Q
What is a Z disc?
A
Anchor actin filaments and are loacted at each end of a sarcomere
22
Q
What are I bands?
A
Composed entirely of actin and the width changes during contraction
23
Q
What are A bands?
A
Composed of actin and myosin and width does not change during contraction
24
What are H bands?
Composed of entirely myosin and width changes during contractions
25
When sarcomeres are aligned what pattern is produced?
Banding pattern characteristic of striated muscle. Bands are lined up
26
Where is the nucleus in a muscle fiber?
Nucleus pushed to the outside of the of the sarcomeres
27
What steps happen in the synaptic cleft and terminal end of nerve fiber?
1. Arrival of action potential at terminal end of nerve fiber
2. Opening of voltage-gated calcium channels on nerve fiber ending. Ca diffuse into the terminal
3. Neurotransmitter (Ach) are released from synaptic vesicles into synaptic cleft (exocytosis) and diffuses
4. 2 Ach attach to ligand-gated sodium channels of the sarcolemma
28
What happens once the ligand-gated sodium channels of the sarcolemma open?
1. There is a sodium ion influx that causes End - plate Depolarization and thus opens voltage-gated sodium channels (Sarcolemma action potential)
2. Voltage-gated channels on T tubules (DHP) interact with ryanodine receptors on the SR membrane
3. Opeing of ryanodine - releases calcium
4. Increase Calcium ion in cytosol activates the sliding filament mechanism
29
What is DHP?
Dihydropyridine receptors that are voltage sensitive. L - type calcium channels arranged in quadruplets. Causes conformation change in the ryanodine receptors
30
What happens once calcium is released into the cytosol?
Calcium binds to troponin C on the actin filament.
Troponin then conforms and cause tropomyosin to expose active sites on actin
Myosin heads bind to actin active sites
31
What activates the myosin head?
ATP bound to the myosin hydrolyzed to ADP and inorganic phosphate. Energy liberated from the hydrolysis of ATP activates the myosin forcing it to the cock position.
32
What are the cross bridge steps?
1. Activated myosin head binds to actin forming a cross bridge
2. Inorganic phosphate is released and the bond between actin and myosin becomes stronger
3. ADP is released and the activated myosin head power strokes.
4. When another ATP binds to myosin head, the link between myosin and actin weakens and the myosin detaches
33
When will the myosin sliding stop?
As long as the active sites are exposed the process will repeat. When Calcium ions are actively transported back into the Sarcoplasmic reticulum causing the troponin to return to original shape allowing tropomyosin to glide over and cover myosin binding sites on actin
34
Between what bands are the T tubules located?
Between the A-I interface. Because of that they can have cisterni on each side of the t tubules and become triads.
35
Once ryanodine channels open where does the Ca ions flow out of?
Out of the sarcoplamic reticulum
36
When does the ryanodine channels close?
When the sarcolemma repolarizes
37
What does calsequestrin do?
Binds the Ca within the sarcoplasmic reticulum so that when the ATP calcium pumps are uptaking Ca they are not working so hard. Controls the concentration of free calcium with in the SR.
38
The calcium pump on in the SR is what type of transport?
Active transport
39
What are ryanodine receptors?
(RyRs) calcium release channels that are located on the cisternae. Open in response to conformational change in DHP receptors
40
What is SERCA?
Sarcoplasmic reticulum calcium ATPase - Uses ATP to pump calcium back into the SR
41
Why is there no tension when the sarcomere is fully stretched out?
Because there is no interaction between the myosin and actin when fully stretched out
42
When is tension maximum in a sarcomere?
When there is interaction between actin and myosin. And actin filament has overlapped all the cross bridges.
43
At what point is no more tension possible?
Max point occurs when acting filaments touch
44
What happens when actin filaments overlap?
Tension drops toward 0 because no more sliding can occur
45
True or False
| When our bodies are at rest on a couch our muscles are 100% relaxed
No. There is some tension in all of our muscle. Keeps us sitting.
46
What is muscle tone?
Keep muscles in a slightly contracted state. Allows us to be ready to have a muscle contraction when needed
47
Where is ATP required for muscle contraction?
Sliding filament mechanism, pumping Ca ions from sarcoplasm into SR, pumping Na and K ions through the sarcolemma to reestablish resting potential
48
What is the concentration of ATP in muscle fiber?
4mmol which is enough to maintain contraction for 1-2 seconds
49
How does phosphocreatine restore ATP?
Phosphocreatine can release energy rapidly to ATP. Add phosphates back to ATP. Provides enough energy for 5-8 seconds of contraction when phosphocreatine is used with ATP
50
What are three methods of rephosphorylation of ATP?
Phosphocreatine, Glycolysis, oxidative metabolism
51
How does Glycolysis rephosphorylize ATP?
Can produce ATP and sustain contraction for 1 minute but there is a build up of pyruvic acid and which is converted to lactic acid.
52
What rephosphorylizes ATP the best for long-term contractions?
Oxidative metabolism: provides more than 95% of all energy needed for long-term contraction
Electron transport chain and kreb's cycle in the mitochondrion provides a lot of ATP
53
What are two main types of muscle contractions?
Isometric and isotonic
54
What is isometric muscle contraction?
Occurs when there is an increase in tension but not in length. Achieved by pushing on wall and muscle length remains the same but tension builds up
55
What is isotonic muscle contraction?
When muscle length changes
56
What are the two types of isotonic contractions?
Eccentric: Muscle gets longer : Force is greater than tension
Concentric: muscle gets shorter : Force is less than the tension
57
What are the two types of myofibers?
Dark, slow fibers (red)
| Light, Fast fibers (white)
58
What are fast muscle fibers?
They are fibers that contract rapidly but have less endurance. Fewer mitochondria, little myoglobin, use anaerobic respiration primarily. Larger concentration of ATPase
59
What are slow fibers?
Red fibers that contract more slowly but have more endurance. They have more mitochondria, use aerobic respiration, have more myoglobin, and have smaller concentration of ATPase
60
True or False
| In adulthood, one cane increase the number of myofibers?
False. Mass of myofiber can increase by increasing myoFRIBRILS
61
What happens if there is a lost of muscle tissue?
It will be replaced by scar tissue. Fibrous connective tissue
62
What muscle is predominantly composed of dark fibers in mammals?
Soleus
63
What muscle is predominantly composed of light fibers?
Gastrocnemius
64
What is a motor unit?
Neuron and the myofibers it innervates
65
What does the all - or - none really refer to?
A motor unit
66
What is summation?
Electrical events occur faster than mechanical events
67
How does summation work in skeletal muscle fibers?
Before the Ca returns to the SR the remaining Ca causes another action potential. Continued cycling between myosin and actin which increases the muscle tension. Each additional spike adds to the effects of the previous spikes
68
What is tetany?
If the frequency of spikes is fast enough, there is no time for relaxation between spikes and the muscle remains at maximal contraction.
69
How does the bone-muscle system often transmit forces?
Levers
| Bone is the lever. The joint is the pivot/fulcrum
70
What is an example of a First - class lever system? Explain the first - class lever system
Fulcrum is in the middle and raising chin using the sternocleidomastoids or similar muscles. In-force and out-force move in opposite directions
71
What is a second-class lever system? Give an example
Resistance (out-force) is in the middle. Example is raising the body on the ball of the foot. Fulcrum= ball of foot. Both in and out forces are on the same side of the fulcrum
72
What is a third - class lever system? Give an example
Effort (in-force) is in the middle. Lifting a weight in the palm of your hand. Both in and out forces are on the same side of the fulcrum. And both forces move in same direction
73
Where do machines transmit forces?
From one place to another
74
What two forces involve machines?
Force applied to the machine (in-force (Fi) or effort)
| Force derived from the machine (out-force (Fo) or resistance)
75
The force times it lever arm is a moment. Functional lever must have at least two moments. What are the two equations?
Mi=FiLi
Mo=FoLo
Equilibrium = FiLi = FoLo
76
Is our bicep elbow lever system designed for weight or speed?
Speed.
