Lecture 4( mucle contraction) Flashcards
1
Q
How much tension is in a muscle fiber when no actin is overlapping the myosin filaments
A
zero
2
Q
at what point is the tension in the muscle the greatest
A
when actin filaments completely overlap myosin (sarcomere about 2.2 mirometers) until acin filament tips touch (sarcomere about 2micrometers long)
3
Q
what is the length of the sarcomere at max tension
A
2.2-2 micrometers
4
Q
Epimysium
A
Connective tissue surrounding entire muscle
5
Q
muscle
A
made up of multiple fascicles
6
Q
perimysium
A
CT surrounding individual fascicle
7
Q
Fascicle
A
a bundle of myofibers
8
Q
Endomysium
A
Delicate connective tissue around each myofiber
9
Q
Sarcolema (plasmalemma)
A
Cell membrane of the muscle fiber
10
Q
Myofibril
A
A chain of sarcomeres within a myofiber
11
Q
Myofilament
A
Actin and myosin filaments that make up a sarcomere
12
Q
what are T-tubules
A
invaginations of the sarcolemma
lie close to cisternae of sarcoplasmic reticulum
form triads with cisternae
two per sarcomere
13
Q
what are z discs (z lines)
A
anchor actin filaments
located at each end of a sarcomere
14
Q
What are the I-bands
A
Composed entirely of actin
width changes during contraction
15
Q
Does the width of the I bands change with contraction
A
Yes
16
Q
What are the A-bands
A
Composed of actin and myosin
- Think all filaments
- width does not change during contraction
17
Q
Does the width of the A-bands change with contraction
A
No
18
Q
What are the H-bands
A
Composed entirely of myosin
width changes with contraction
19
Q
does the width of the H bands change with contraction
A
Yes
20
Q
What Is the length of the sarcomere when the H band disappears
A
about 2 micrometers long
21
Q
what is the length of the sarcomere when the I-bands are absent
A
about 1.65 micrometers, this is when the z lines are smashed up against the myosin filaments
22
Q
do filaments themselves change length
A
No
23
Q
where are nuclei and mitochondria located in skeletal muscle
A
On the periphery of the cell
24
Q
what signals the release of Ach into the synaptic cleft
A
opening of voltage-gated calcium channels and influx of calcium into the axon terminal
25
what is the function of Ach on the sarcolemma
They open ligand gated sodium channels (creation of a local potential)
26
what are the voltage-gated channels on T-tubules called
DHP (dihydropyridine-channels)
27
What is the function of Dihydropyridine channels?
They interact and open ryanodine receptors on the SR membrane
28
What does calcium bind to in muscle fibers
Troponin C
29
how much does calcium concentration in the cytosol increase by after calcium release by the SR
Calcium is increased from 0.1micromols per liter to about 10 micromoles per liter
30
a conformational change in troponin C moves what away from active sites on actin
Tropomyosin
31
what are DHP receptors
Dihydropyridine receptors
voltage-sensitive L-Type calcium channels
located on the T-tubules
32
How are DHP receptors arranged
in quadruplets
33
do Dihydropyridine (DHP) receptors contribute to cytosol calcium levels?
Yes. They do so both actively and passively
A minute amount of calcium flows into the cytosol via these channels
They also cause a conformational change in the ryanodine receptors which then release more Calcium from the SR
34
where are RyRs (Ryanodine receptors located)
on the cisternae of the SR
35
What is the function of ryanodine (RyRs) receptors
Allow calcium into the cytosol from the SR
36
What is the function of SERCA
Sarcoplasmic Reticulum Calcium ATPases
| uses ATP to pump calcium back into the SR
37
What is Calsequestrin
in the SR maintains an optimum calcium concentration gradient to facilitate return of calcium to SR
38
what is preload
load on a muscle in the relaxed state (before it contracts)
39
The greater the preload does what to the tension
increases the amount of passive tension in the muscle
40
Preload generates what kind of tension in the muscle
Passive tension
41
what is passive tension
The force of resistance a muscle has to an applied load
42
What is afterload
load the muscle works against
43
When does an isotonic contraction occur
When the muscle generates more force than the afterload
44
when does an isometric contraction occur
when a muscle generates less force than the afterload
45
What is an isotonic contraction
same tone
46
What is an isometric contraction
same length
47
What is passive tension
produced by the preload
48
what is active tension
produced by cross bridge cycling
49
what is total tension
sum of active and passive tension
50
when does cross-bridge cycling begin
when free calcium is available and attaches to troponin
51
is ATP required to form the cross-bridge linking to actin
No
52
is ATP required to break the cross-bridge link with actin
Yes
53
increased cross-bridges to actin filaments means what
greater force of contraction
54
Do cross-bridges act independently of all others
yes
55
what is located on the myosin heads
ATP-ase
56
what is a sarcomeres resting length
about 2 micrometers
57
Tension in a muscle decreases when it is stretched beyond what length
2.2 micrometers
58
where is ATP required for muscle contraction
most is used for sliding filament mechanism
pumping of calcium ions from sarcoplam back into SR
pumping of sodium and potassium ions through the sarcolemma to reestablish resting potential
59
what is the concentration of ATP in a muscle fiber
about 4mmol
| enough to maintain contraction for 1-2 seconds
60
how long can the concentration of ATP in a muscle fiber maintain contraction
about 1-2 seconds
61
what is the purpose of phosphocreatine in muscles
- Releases energy rapidly
- Reconstitues ATP
- ATP=Phophocreatine provides enough energy for 5-8 seconds of contraction
62
ATP + phosphocreatine provides enough energy for how many seconds of contraction
about 5-8 seconds
63
How long can glycolysis sustain contraction
about 1 minute
64
what is a product of glycolysis in muscle contraction
lactic acid
65
what provides more than 95% of all energy needed for long-term contraction
Oxidative metabolism
66
What is Isometric contraction
contraction that occurs when there is an increase in tension but not in length
67
what is isotonic contraction
Muscle length changes
| - two types Eccentric and concentric
68
what is eccentric contraction
type of isotonic contraction
| - occurs when the muscle lengthens
69
What is a concentric contraction
type of isotonic contraction
| - occurs when the muscle shortens
70
what determines the myofiber type
The innervating neuron
71
how are muscle fibers classified
resistance to fatigue and speed of contraction
72
Characteristics of Fast (white) muscle
```
contract rapidly, but less endurance
fewer mitochondria
primarily use anaerobic respiration resulting in buildup of pyruvic and lactic acid
little myoglobin
larger concentration of ATPase
```
73
Characteristics of Slow (Red) muscle fibers
```
contract slowly but have more endurance
more mitochondria
primarily use aerobic respiration
more myoglobin
smaller concentration of ATPase
```
74
Can number of myofibers be increased after birth
NO
75
Can the number of myofibrils be increased after birth
yes
76
What is lost muscle tissue replaced by
Scar tissue (fibrous connective tissue
77
The mass of a myofiber and muscle may increase by what mechanism
increase in the number of MYOFIBRILS
78
what type of muscle is the soleus mostly composed of
Dark (slow twitch)
79
What type of muscle is the gastrocnemius mostly composed of
Light (fast twitch)
80
what is a motor unit
a neuron ad the myofibers it innervates
81
When a neuron fires does all of the myofibers in the motor unit contract
Yes
82
what effect would increased number of motor units have
increased force of contraction
83
What is summation
electrical events occur faster than mechanical events
increased speed in cycling
increases muscle tension
each additional spike adds to the effects of the previous spikes
84
How does summation increase the rate of cycling
additional spike occurs before previous calcium ions have been returned to the SR. This increases the total amount of calcium ion in the cytosol and increases the rate of cycling between the myosin and actin cross-bridges
85
what is tetany
Frequency of spikes is fast enough, that there is no time for a relaxation between spikes
- the muscle remains at maximal contraction
86
what is the position of the fulcrum in a first-class lever system
in the middle
87
Which direction do the in and out forces move in a first-class lever system
Opposite directions
88
In what direction and position are the forces in a second-class lever system
In and out forces move in the same direction and on the same side of the fulcrum
example raisin the body onto the ball of the foot
89
define a third-class lever system
effort (in-force) is in the middle
both in and out forces move the he same direction and are on the same side of the fulcrum
ex. lifting a weight in the palm of your hand
90
what term refers to a chain of sarcomeres
Myofibril
91
what sarcomeric band does not undergo a change in length during the contraction of skeletal muscle
A-band
92
what sarcomeric band is composed entirely of actin filaments
I-band
93
Dihydropyridine (DHP) channels are part of what structure
T-Tubules
94
Ryanodine-sensitive calcium ion release channels are part of what structure
SR
95
by what factor does calcium concentration in the cytoplasm increase after calcium is released by the SR
100
96
What maintains an optimum calcium concentration gradient to facilitate return of calcium to SR
Calsequestrin
97
Are fast twitch muscle fibers more fatiguable than slow twitch
Yes
98
Give an example of eccentric contraction
The triceps muscle while lowering the body to the floor during a push-up
