Muscle Structure & Physiology Flashcards
(87 cards)
1
Q
Mature muscle cells have multiple nuclei within a single cytoplasm with many mitochondria.
What are those muscle cells called?
A
Syncytia
2
Q
Is skeletal muscle smooth or striated?
A
Striated
3
Q
striated muscle
Which muscle filaments are aligned and connected to the Z line by nebulin?
A
Actin
thin filaments
4
Q
Which muscle filaments are connected to the Z line by titin?
A
Myosin
thick filaments
5
Q
Actin is the thin filament in striated muscle.
What aligns and connects actin to the Z line?
A
Nebulin
6
Q
Myosin is the thick filament in striated muscle.
What connects myosin to the Z line?
A
Titin
7
Q
Extrafusal fibers are responsible for ___, and have ___ neurons.
A
responsible for movement (contraction) and have motor neurons
8
Q
Intrafusal fibers are responsible for ___, and have ___ neurons.
A
responsible for sensing stretch/pull with stretch receptors (muscle spindle organs) and motor and sensory neurons
9
Q
Which muscle fibers are responsible for movement/contraction?
A
Extrafusal fibers
10
Q
Which muscle fibers are responsible for sensing stretch?
A
Intrafusal fibers
11
Q
What is the epimysium?
A
Fascia containing the whole muscle
12
Q
What is the perimysium?
A
Fascia containing a fascicle of muscle fibers
13
Q
What is endomysium?
A
Fascia containing myofiber/muscle cell
14
Q
Which muscle fascia is involved in compartment syndrome?
A
Epimysium
15
Q
The epimysium’s density needs to allow for swelling, otherwise there is risk of ___.
A
rhabdomyoma
16
Q
Myofilament (actin and myosin) is found within bundles called ___ which make up myofibers.
A
myofibrils
17
Q
Myofibers are comprised of ___ and ___ filaments.
A
thick (myosin) and thin (actin) filaments
18
Q
When at rest, the binding site on thin filaments is ___ by the troponin-tropomyosin complex.
A
blocked
19
Q
When at rest, the binding site on thin filaments is blocked by the ___.
A
troponin-tropomyosin complex
20
Q
How are binding sites on actin unblocked?
A
Calcium binds to troponin to unblock the site
21
Q
What is the function of titin in the myofiber?
A
Provides elasticity and stabilizes myosin
22
Q
What is the function of nebulin in the myofiber?
A
Helps align actin
23
Q
Troponin holds ___ in place.
A
tropomyosin
24
Q
How does the muscle fiber react when motor neurons fire and release Ach?
A
- Acetylcholine release opens Na+ channels
- Na+ travels through T tubules
25
What is a sarcomere?
Functional myofibril unit (z-band to z-band)
26
The T tubule of a muscle is a channel for ___.
Na+ (sodium)
27
What is the function of the terminal cisterna of sarcoplasmic reticulum in the muscle?
Ca+ (calcium) storage
28
When the muscle is not contracting, there is active pumping of ___ from the muscle to ___.
pumping of **Ca+** from muscle to **sarcoplasmic reticulum**
29
What is the Z-band?
Electron dense band that anchors thin actin filaments (end of sarcomere)
30
What is the I-band?
Zone where actin filaments extend from Z-band to A-band
31
What is the A-band?
Structure composed of myosin filaments.
Actin filaments overlap myosin filaments to a variable extent, depending on the degree of muscle contraction.
32
Within the A-band, thin filaments form a ___ around each thick filament.
hexagonal array
| each thin filament is equidistant from three thick filaments
33
What is the H zone?
Pale region in the midportion of the A band where actin filaments end (only myosin present)
34
What is the M line?
Zone of intermolecular bridging and thickening of myosin filaments at the midline of the A-band, which forms a thin, slightly darker electron-dense bank
35
What is the name of the electron dense band that anchors thin actin filaments?
Z-band
36
What is the name of the zone where there is no myosin overlap in the sarcomere?
I-band
37
What is the name of the structure within the sarcomere composed of myosin filaments with varying actin filament overlap?
A-band
38
What is the name of the pale region in the midportion of the A-band where actin filaments end and there is only myosin?
H zone
39
What is the name of the zone of intermolecular bridging and thickening of myosin filaments at the midline of the A-band, forming a thin, slightly darker electron-dense bank?
M line
40
Where in the structure of muscles is there only actin?
I-band
41
Where in the structure of muscle is there only myosin?
H zone
42
When a muscle contracts, is it the I-band or the A-band that shortens?
I-band shortens, A-band is the same
43
Sarcoplasmic reticulum and transverse tubular systems regulate ___.
calcium distribution and storage
44
Sarcoplasmic reticulum surrounds each ___.
myofibril
45
How does the sarcoplasmic reticulum immediately respond to depolarization during muscle contraction?
SR **passively releases** Ca2+ ions **into the cell**
| via DHP and RyR receptors
## Footnote
follows diffusion gradient from high to low concentration
46
How does the sarcoplasmic reticulum immediately respond to cessation of neural activity during muscle relaxation?
SR **actively transports** Ca2+ back **into the cisternae**
47
How many lower motor neurons innervate a muscle fiber?
A fiber is innervated by a single lower motor neuron ending
48
How many muscle fibers are innervated by a lower motor neuron?
Can include hundreds of myofibers
| motor unit
49
What is a motor unit?
Multiple muscle fibers innervated by one motor neuron
50
What characteristic of a lower motor neuron influences muscle fiber type?
Conduction speed
51
All muscle fibers in a motor unit are the same fiber type.
What are the two fiber types?
* Type I (slow twitch, red, dark meat)
* Type II (fast twitch, white, white meat)
52
In humans, all muscles consist of which fiber type(s)?
All muscles consist of a mix of Type I (slow) and Type II (fast)
53
Type I/slow twitch muscle fibers function predominantly for ___ muscles.
Type II/fast twitch muscle fibers function predominantly for ___ muscles.
Type I: **postural**
Type II: **major movers**
54
Fill in the following for **type I** fiber:
Contraction speed:
Color:
Motor neuron:
Metabolism:
Endurance:
Contraction speed: **slow** (postural)
Color: **red**
Motor neuron: **alpha 2** (lower threshold, slower conduction velocity)
Metabolism: **aerobic** (higher myoglobin, mitochondria)
Endurance: **high**
55
Fill in the following for type II fiber:
Contraction speed:
Color:
Motor neuron:
Metabolism:
Endurance:
Contraction speed: **fast**
Color: **white**
Motor neuron: **alpha 1** (higher threshold, faster conduction velocity)
Metabolism: **anaerobic** (less myoglobin)
Endurance: **low**
56
Why could type I fibers transform into type II fibers and vice versa in the Buller et al. study?
Innervation determines fiber type
57
How do type I muscle fibers (slow twitch/postural) respond to endurance training?
They don't hypertrophy, number of mitochondria increases
58
How do type II muscle fibers (fast twitch) respond to strength training?
Hypertrophy
59
Which structure is responsible for calcium ion regulation in sarcomeres?
Sarcoplasmic reticulum
60
What is the most important factor in determining muscle fiber type?
Lower motor neuron conduction velocity
61
What is the sliding filament theory?
During muscle contraction, actin filaments slide past myosin filaments in a series of cross-bridge cycles
62
# sliding filament theory
Each cross-bridge cycle consists of what four steps?
1. Rest
2. Excitation
3. Contraction
4. Relaxation
63
Which phase of sliding filament theory involves Ca2+ binding to troponin, exposing binding sites for myosin?
Excitation
64
What occurs during the contraction phase of sliding filament theory?
Bound myosin rotates its head, producing a "power stroke"
65
# sliding filament theory
What is required for the myosin head to release actin?
ATP binds to myosin head
66
# sliding filament theory
What is the result of ATP binding to the myosin head?
* Ca2+ moves back into the sarcolemma
* Troponin-tropomyosin complex moves to block interaction between actin and myosin
67
In which phase of sliding filament theory does the myosin head bind to ATP and detach from actin?
Relaxation
68
# sliding filament theory
What occurs between the relaxation and rest phases?
* Actin binding sites physically blocked
* ATP is hydrolyzed, adding ADP to myosin head
69
# sliding filament theory
What is required for the myosin head to be ready to bind to actin (again)?
ADP must be bound to myosin head (rest phase)
70
# sliding filament theory
At which phase does myosin have the highest affinity for actin?
Rest phase
71
# sliding filament theory
What allows for calcium to be released before it binds to troponin-tropomyosin complex?
Action potential changes DHP and RyR receptors (allowing calcium release)
72
During which phase of sliding filament theory will myosin heads bind with actin?
Contraction
73
# sliding filament theory
How long can the contraction phase continue?
As long as action potential is sustained
## Footnote
ATP binds to myosin head, detaches, then starts again
74
# sliding filament theory
After the relaxation phase, and the action potential ending, where will calcium go?
Sequestered in sarcoplasmic reticulum
| by active transport
75
# recruitment
Graded contractions are built by ___.
repeated contraction
76
# length-tension curve
Tension produced during contraction is related to which feature of the muscle?
Sarcomere length
77
# length-tension curve
What is meant by "functional length" of a sarcomere?
Strength at mid range of motion
78
# length-tension curve
The greatest strength of a muscle occurs in the ___ of its arc of motion.
middle
79
# length-tension curve
The greatest strength of a muscle occurs in the middle of its arc of motion.
What would happen if you were to work only in this area?
Muscle contracture and decreased range of motion/function
80
# force velocity curve
Velocity depends on which features of the muscle?
Number of sarcomeres in a cell and force applied
81
# force velocity curve
There is an ___ relationship between force applied and muscle contraction velocity.
inverse
82
# force velocity curve
As load on a muscle increases, the contractile system ___, and ___ occurs.
contractile system **yields**, and **lengthening** occurs
83
# force velocity curve
As load on a muscle increases, shortening velocity ___.
slows
84
# force velocity curve
A muscle has developed maximum force and reached a velocity of 0.
What is the term for this point?
Isometric load/isometric contraction
## Footnote
point between safe exercise and overload
85
Where in the force velocity curve does most muscle failure happen?
After isometric load, during eccentric loading/overload
| muscle is now lengthening instead of shortening
86
What is tetanus?
The fusion of individual contractions or twitches to form a continuous contraction
87
What is the term for the fusion of individual contractions or twitches to form a continuous contraction?
Tetanus
