Muscle Structure and Function Flashcards
1
Q
Composition of a Muscle Fiber
A
-Sarcolemma
-Myofibril
-Myofilaments
2
Q
Sarcolemma
A
Cell membrane enclosing muscle fibers
3
Q
Myofibril
A
-composed of numerous stacked myofilaments
4
Q
Myofilaments
A
Myosin and actin
5
Q
Which are the thick myofilaments?
A
Myosin
6
Q
Which are the thin myofilaments?
A
Actin
7
Q
What forms actin myofilaments?
A
-Two chainlike strings of actin molecules
-Troponin
-Tropomyosin molecules
8
Q
What controls the binding of actin and myosin myofilaments?
A
-Troponin and tropomyosin molecules
9
Q
What forms myosin myofilaments?
A
-Head groups that attach to specific binding sites on actin molecule
10
Q
What is the critical role myosin head groups have?
A
-Muscle contraction and relaxation
11
Q
Contractile Unit
A
-Sarcomere, distinguished by bands and zones
12
Q
What portion of the myofibril is the sarcomere?
A
-Located between any two Z discs
13
Q
What does the Z discs link together?
A
-The thin filaments
14
Q
What is the A band?
A
-Portion of the sarcomere that extends over length of thick filaments and small portion of thin filaments
15
Q
What is the I band?
A
-Areas that only include actin filaments
16
Q
What is the H zone?
A
-A band area where there is no overlap with thin filaments
17
Q
What is the M line?
A
-The center of the H zone; wide middle portion of thick filament
18
Q
How is a muscle contraction initiated?
A
-By the interaction between thick and thin filaments within the sarcomere
19
Q
Cross-Bridge Interaction
A
- Coupling
- Contraction
- Uncoupling
- Recharging
20
Q
Coupling phase
A
-Calcium released makes troponin move to expose active sites of actin
-Myosin head will reach out + attach to actin forming the x-bridge
21
Q
Contraction phase
A
-Cross-bridge will generate force (power stroke) to pull thin filament one notch to the Mline
22
Q
Uncoupling phase
A
-Power stroke complete, myosin head will detach from actin and repeat cycle
23
Q
Recharging phase
A
-ATP hydrolysis occurs, releasing ADP and Pi, bounding to myosin head, reattaching to actin binding site
24
Q
Concentric (shortening) Contraction
A
-Sarcomere length is shorter (distance btw Z discs) than when fiber is at rest
-Closer to M line
25
Eccentric (lengthening) Contraction
-Sarcomere length is greater than a resting fiber
26
Isometric Contraction
-No change in length
27
What is happening in a Concentric contraction?
-Thin filaments overlap thick filaments
-Cross-bridge formed, broken, and re-formed
28
What happens in an Eccentric contraction?
-thin pulled away from thick filaments by an external force on muscle
-Cross-bridge broken, re-formed, and broken again
29
What happens to the Cros-bridge cycle when an eccentric contraction occurs?
-It is broken and re-formed as the muscle lengthens
30
What happens as the cross-bridge is re-formed?
-Tension is generated
31
What happens in an Isometric contraction?
-Active muscle fiber will not change length if the force created by the x-bridge cycling matches the external force
32
What initiates the muscle contraction?
Calcium influx
33
What fuels the cross-bridge cycle?
ATP hydrolysis
34
How is a Motor Unit organized?
-Cell body in Ventral Horn
-Motor axon extends to muscle
-Axon divides into a few or thousands of branches
-Each branch terminates in a motor endplate
35
Excitability
-Capacity of muscle fiber to react to stimulus
36
Contractibility
-Ability to create tension when stimulated from a motor neuron
37
Extensibility
-Capacity of a muscle tissue to stretch without damage
38
Elasticity
-Muscles tendency to return to original after being stretched
39
What affects the strength of the contraction?
-the changing # of motor units that are activated
-frequency at which they are activated
40
What affects the size of the motor unit?
-Depends of the function
-Controls fine movements
-Make small adjustments
41
How are motor neurons recruited?
-All or None Law
-Size Principle
42
All or None Law
-All muscle fiber will contract on the same stimulus
43
The Size Principle
-Small motor unit generate less tension than larger motor unit
-Will be stimulated first to save energy
44
When is the Size Principle in place?
-In an isometric contraction
45
Which affects the magnitude of the response to a stimulus?
-# of muscle fibers in a motor unit
46
Which determines the conduction velocity of the nerve impulse?
-The diameter of the axon innervating a motor unit
47
Which affects the total force response of the muscle?
-# of motor units that are firing at any one time
48
Which affects the total response of the muscle?
-The frequency of motor unit firing
49
Wave summation
-Pace at which nerve signals are fired through the motor unit
50
What does the wave summation say?
-In sighting a motor unit before fully relaxing, the second contraction won't reach a stronger force compared to the first one
51
What are the characteristics of muscle fibers?
-Diameter
-Muscle color
-Capillarity
-Myoglobin content
-Speed of contraction
-Rate of fatigue
52
Type I (slow) fiber
-Small
Slow contraction but greater efficiency
-Longer duration/ endurance
53
What activity will the Type I fiber be ideal for?
-Sustained activities
-Example: Marathon running
54
Type IIA (intermediate) Fiber
-Larger
-Faster contraction
-Recover slowly
-Fatigue rapidly
55
What activity will the Type IIA fiber be ideal for?
-High intensity workouts
56
Type IIX or Type IIB (Fast) Fibers
-Large and powerful
-Fatigues the quickest
-Longer periods of rest to recover and replenish energy
57
What activity will the Type IIX/B fiber be ideal for?
-Heavy lifting
58
Postural / Stability
-High proportion of Type I fibers in relationship to Type II fibers
-Sustained activity due to slow fatigue
-Ex: Soleus
59
Nonpostural / Mobility
-High proportion of Type II fibers
-Produce large ROM
-More force, able to contract faster, higher power output
-Ex: Hamstrings and Gastroc.
60
Muscle Architecture
-arrangement of the fibers in relation to the axis of force
-size, arrangement, and length
61
Muscle Fiber Length
-Determined by the # of sarcomeres along the fiber
62
The more __________, the more a fiber can shorten.
-Sarcomeres
63
Muscle Length
-The longer the muscle, the more sarcomeres, shortening more
64
What is the advantage of having a long muscle?
-Able to move bony lever to which it is attached through a greater distance
65
Physiological Cross-Sectional Area (PCSA)
-a measure of the cross-sectional area of the muscle perpendicular to the orientation of the muscle fibers
66
Fusiform (strap) Muscles
-Parallel fibers to the long axis of the muscle and to e/other
-Ex: sternocleidomastoid/sartorius
67
Pennate Muscles
-Fiber arrangement oblique to muscle's long axis
-shorter and numerous fascicles
68
Unipennate Muscles
-Oblique fascicles fan out on only one side of a central muscle tendon
-Ex: Flexor pollicis longus
69
Bipennate Muscle
-Fascicles are obliquely set on both sides of a central tendon
-Ex: Biceps femoris/tibialis anterior
70
Multipennate Muscle
-Oblique fascicles converge on several tendons
-Ex: Soleus/subscapularis
71
Building a Muscle
-Endomysium surrounds individual fibers and their sarcolemmas
-Perimysium surrounds groups of fibers (fascicles)
-Epimysium on the outer layer of connective tissue
72
Superficial Fasciae
-Loose tissue, located directly under dermis (skin)
73
What does the Superficial fascia zone help with?
-mobility of the skin, insulator
74
Deep Fascia
-Compacted and regularly arranged collagenous fibers
75
What do Deep fasciae form?
-Tracts, bands, or retinaculae
76
What does the Retinaculae help with?
-Maintains relationship between tendon and their respective joints and joint axes
77
Passive Elastic Components
-Include the Parallel and Series Components
78
Parallel Elastic Components
-Function in parallel with the muscle contractile unit; when a muscle lengthens or shortens, the tissues do the same
79
Series Elastic Component
-Tendon functions in series with the contractile elements; when at rest, tendon relaxed and may be crimped (slack)
-tendon under tension when muscle actively produces tension
80
Total Tension
-includes both active or passive components
81
Passive tension
-tension created by lengthening the muscle beyond the slack length of the tissues (stretching muscle) at rest
82
Isometric Length-Tension Relationship
-direct relationship between isometric tension + length of the sarcomeres in muscle fibers
83
Optimal Sarcomere Length
Plateau of active tension curve
84
Decrease of active tension
-when muscle is lengthened because fewer x-bridges can be formed
85
Decrease of active tension
-when muscle is shortened; x-bridges already connected, losing capacity to shorten any further
86
Passive tension Increases
-with elongation of the muscles as it continues to be stretched
87
Active Insufficiency
-2 joint muscles have been maximally SHORTENED across 2 joints and can no longer generate additional or maximal torque
88
Passive Insufficiency
-2 joint muscles have been maximally LENGTHENED across 2 joints and can no longer generate maximal torque in that position
89
Force-Velocity Relationship
-the ability of a muscle to generate force is affected by the speed at which a concentric / eccentric contraction happens
90
Maximum velocity of muscle shortening (concentric contraction)
-No force is produced; only when there is no load on the muscle
91
Shortening velocity decreases
-force during concentric contraction increases
92
Zero velocity
-isometric contraction
93
Force increases dramatically and then plateaus
-Muscle is lengthened actively (eccentric contraction)
94
The greater the # of cross-bridges that are formed,
-the greater the tension
95
Are large or small cross-sections better in the capacity of producing more tension?
-Large cross sections
96
When does tension increase?
-When velocity of active shortening decreases and velocity of active lengthening increases
97
Recruitment order of the motor units
-Units with slow conduction velocities are generally recruited first
98
Type of muscle fibers in the motor units
-Type II muscle fibers develop maximum tension more rapidly than Type I; rate of cross-bridge formation, breaking, and re-formation may vary
99
Length of the muscle fibers
-Long fibers have a higher shortening velocity than shorter fibers
100
Magnitude of the resistance
-A given muscle force production, greater resistance to the muscle action will result in a slower contraction
101
Size of motor units
-Larger units produce greater tension
102
and Size of muscle fibers in cross section of muscle
-Larger cross section, greater amount of tension produced
103
Frequency of firing of motor units
-Higher the frequency of firing, greater tension
104
Fiber arrangement
-Pennate fiber = > # muscle fibers = large x-sectional area = > tension
105
Type of muscle contraction
Greater Tension:
Isometric > concentric
Eccentric > isometric
106
Velocity
-Speed of short increases < tension in concentric
-Speed of active length increases > tension in eccentric
107
Golgi Tendon Organ (GTO)
-sensitive to tension and may be activated either by an active muscle contraction or by an excessive passive stretch
108
Muscle Spindle
-sensitive to length and the velocity of lengthening of the muscle fibers
109
What does the GTO adjust?
-Muscle tension by sending message to the CNS via Ib afferent neurons when excited
110
What are muscle spindles concerned about?
-State of stretch of a muscle; message sent to spinal cord and CNS via the group Ia afferent neurons
-movement will be affected
111
Immobilization Effects
-Depend on immobilization position (short or lengthened), % of fiber types w/in muscle, length of immobilization period
112
Shortened Position Changes
-Decrease in # of sarcomeres, increase length
-increase in perimysium
-Thick endomysium
-Collagen fibril orientation more circumferential
-increase in ratio of connective tissue to muscle fiber tissue
-decreased muscle mass and muscle atrophy
113
Lengthened Position Changes
-Increase in # sarcomeres, decrease in length
-increased endomyseal + perimyseal connective tissue
-muscle hypertrophy, can be followed by atrophy
114
Overuse
-causes injury to tendons, ligaments, bursae, nerves, cartilage, and muscle
115
What causes overuse?
-repetitive trauma that does not allow time for complete repair of tissue
116
Muscle Strain
-Injuries from single high-force contraction of the muscle while the muscle is lengthened by external forces
117
What does the muscle fail at during Muscle Strain?
-The interface between muscle and tendon
118
Eccentric Exercise-Induced
-injuries may occur with a single bout of eccentric exercise
119
Sarcopenia
loss of muscle mass with age due to loss of fibers and decrease in size of existing fibers
120
Connective Tissue Changes with Age
-Increases within a muscle; causes decreased ROM and increased muscle stiffness
