Lecture 5 - Skeletal Muscle Flashcards
1
Q
What kind of muscle is the most abundant in the body?
A
skeletal muscle
2
Q
How many muscle pairs are there?
A
<80
3
Q
What are the 3 kinds of muscle?
A
cardiac, smooth and skeletal
4
Q
Why striations in muscle happen?
A
due to repeating sequences of sarcomeres
5
Q
What are the 3 primary functions of skeletal muscle?
A
- Provide strength & protection to the skeleton by distributing
loads & absorbing shock - Enable bones to move at the joints
- Maintain body posture against force
6
Q
What are the 3 basic performance parameters that describe skeletal
muscle function?
A
- Movement production
- Force production
- Endurance
7
Q
What kind of work does skeletal muscle do?
A
dynamic and static
8
Q
What are the 2 functional units responsible for producing motion at a joint?
A
tendon and muscle belly
9
Q
What comprises the muscle belly (2)?
A
muscle fibers and connective tissue
10
Q
What are the levels of a whole muscle?
A
- muscle fascicle
- muscle fiber
- Myofibril
- Sarcomere
11
Q
What is the basic function unit of muscle?
A
the sarcomere
12
Q
What is related to a muscle’s contractile force?
A
the amount of actin and myosin
13
Q
How does contraction occur?
A
from the formation of cross-bridges between the myosin and actin myofilaments
14
Q
What are the 3 non-contractile elements?
A
- Intracellular protein
- Extracellular matrix (ECM)
- Tendons
15
Q
What is titin?
A
giant protein found in sarcomeres
16
Q
What is the function of titin?
A
maintains architectural integrity
17
Q
What is desmin?
A
protein that contributes to stability of myofilaments
18
Q
What is costamere?
A
protein complexes found in the cytoplasm
19
Q
What is the function of costameres?
A
link superficial sarcomeres to the cell wall and ECM and allow the force of contraction of one myofibril to be distributed laterally to adjacent myofibrils, the cell wall, and to the ECM
20
Q
What are the 3 components of intracellular protein?
A
titin, desmin and costameres
21
Q
What are the 3 systems of ECM?
A
endomysium, perimysium, epimysium
22
Q
What does the endomysium surround?
A
each cell
23
Q
What does the perimysium surround?
A
groups of cells (fascicles)
24
Q
What does the epimysium surround?
A
the whole muscle
25
When does the ECM proliferate and accumulate?
in diseased, injured and spastic muscle
26
What is adipose tissue in the ECM associated with?
worse functional performance
27
How is the ECM compared to individual muscle fibers?
stiffer
28
What do tendons bind to?
muscle belly to bone
29
How does size of tendons vary? (3)
* Muscle architecture
* Size of the muscle
* Size of the individual
30
What are the 2 factors that influence a muscle's ability to produce motion?
1. The length and orientation (architecture) of the fibers composing the muscle
2. The length of the muscle’s moment arm
31
How is passive ROM achieved?
when an outside force causes joint movement
32
What does passive ROM depend on?
shape of articular surfaces and surrounding soft tissues
33
How is active ROM achieved?
when muscles contract resulting in joint movement
34
What does active ROM depend on?
a muscle’s ability to pull the limb through a joints available ROM
35
How much can each sarcomere shorten?
approximately the length of its myosin
molecules
36
How much can muscle fibers shorten?
approximately 50-60% of their length
37
When is contraction velocity greater?
in longer muscle fibers
38
Which kind of myofibrils can shorten more?
the ones with more sarcomeres
39
Fibre arrangement can effect a muscle's ability to:(2)
* produce movement
* generate force
40
What are the 2 kinds of muscle architecture?
parallel and pennate
41
What are the 2 kinds of parallel muscles?
fusiform and strap
42
What are the 3 kinds of pennate muscles?
unipennate, bipennate and multipennate
43
What are parallel fiber muscle parallel to?
the length of the whole muscle
44
Fusiform muscles have ___ at both ends, so the muscle fibers taper to insert into the ___.
tendons
45
Strap muscles have less prominent ___, and there, their fibers taper less.
tendons
46
What are parallel fiber muscles composed of?
relatively long fibers, although these fibers still are shorter than the whole muscle
47
Which muscle only contains fibers that are about 90% of its length?
the sartorius
48
Where do the tendons extend in pennate fiber types?
most of the length of the whole muscle
49
How do fibers run in pinnate fiber types?
obliquely
50
What do the subcategories of pennate muscles depend on?
the number of tendons penetrating the muscle
51
What does the muscle moment arm depend on (2)?
* the location of the muscle attachment on
the bone
* angle of application
52
What is the angle of application?
the angle formed between the line of pull of the muscle and the bone to which it attaches
53
___ moment arm = movement through theta requires less shortening.
shorter
54
___ movement arm = movement through theta requires more shortening.
longer
55
What is the formula for strength?
M = r x F
56
What are the primary factors influencing the muscle’s strength or ability to produce a moment? (3)
* Muscle size
* Muscle moment arm
* Stretch of the muscle
57
What is the most important determinant of tensile force generated by a muscle contraction?
muscle size
58
What relationship does muscle architecture impact?
the relationship between muscle size and force of contraction
59
What is the anatomical cross-sectional area?
the cross-sectional area (CSA) at the muscle’s widest point and perpendicular to the length of the whole muscle
60
What is the physiological cross-sectional area?
the area of a slice or slices of muscle that pass through all the fibers of a muscle
61
What is the overall tensile force of a muscle equal to?
the vector sum of the force of contraction of all the fibers (Ff)
62
What is the angle of pennation?
the angle at which the fibers insert into the tendon
63
What happens to PCSA when angle of pennation increases?
it increases
64
Which kind of muscle have a larger PCSA?
pennate muscles
65
What does PCSA respond to?
changes in activity level over time
66
What is optimal length of a muscle?
when the full length of the actin strands at each end of the sarcomere is in contact with the myosin
67
What does the length-tension relationship demonstrate?
the passive components generate an elastic recoil that begins at the muscle’s optimal length and increases as the muscle is stretch beyond the optimal length
68
When are the length-tension effects amplified?
in a contracting muscle
69
When does active insufficiency occur?
when a muscle is so short that it cannot generate enough contractile force to pull the limb through its available ROM
70
The ___ the muscle's moment arm, the ___ the moment the muscle produces with its contraction.
longer, greater
71
When is the muscle's moment arm at maximum?
when the muscle’s angle ofapplicationis90° I=dxsin90=d
72
How is contractile velocity of a muscle determined?
by the
macroscopic changes in length per unit time
73
What kind of contraction velocity does isometric contraction have?
zero
74
What kind of contraction velocity does concentric contraction have?
positive
75
As velocity increases, muscle force ___
decreases
76
Velocity = 0 (isometric) = ___ force
maximum
77
Velocity = large (concentric) = ___ force
minimum
78
What do eccentric contractions produce?
more force than either isometric (FI) or concentric contractions
79
What is the max eccentric strength estimated as?
1.5-2.0x max concentric strength
80
Force of an ___ contraction > force of an ___ contraction > force of a ___ contraction regardless of joint position
eccentric, isometric, concentric
81
What is a motor unit?
the individual muscle fibers innervated by a single motor nerve cell
82
What does an electromyogram reflect?
the number of motor units active and the frequency of their activity
83
In an isometric contraction, as force of contraction increases, what happens to EMG?
it increases
84
What does EMG indicate in non isometric contraction?
the relative
activity of the muscle, not its force of contraction
85
As a muscle’s mechanical advantage ___ , the level of recruitment needed (and hence the EMG) ___
increases, decreases
86
When does activation failure happen?
on individuals who have pain or are chronically inactive
87
A muscle lengthened or positioned with a large moment arm is said to be at a...
mechanical advantage
88
What are slow motor units populated by?
slow-twitch fibers
89
What are fast fatigue resistance motor units populated by?
medium-twitch fibers (IIa)
90
What are fast fatiguable motor units populated by?
fast-twitch fibers
91
What does prolonged stretch induce?
hypertrophy
92
What does prolonged shortening induce?
possible atrophy, loss/gain of sarcomeres, and transition toward type II fibers
93
How is hypertrophy increased?
* Increase in cross-sectional area of both type I and type II fibers in animal studies
* Possible transition from type II toward type I fibers
