Ch 9: Muscles and Muscle Tissues Flashcards
(148 cards)
1
Q
What are the 3 types of muscle tissue?
A
- Skeletal
- Cardiac
- Smooth
2
Q
Describe the basic characteristics of skeletal muscle?
A
- Striated
- Found in bones and skin
- Voluntary
- Require nervous system stimulation
3
Q
Describe the basic characteristics of cardiac muscle?
A
- Only in the heart
- Striated
- Involuntary
4
Q
Describe the basic characteristics of smooth muscle?
A
- Found in the walls of hollow organs
- Not striated
- Involuntary
5
Q
What are the prefixes associated with muscle?
A
Myo, mys, and sarco
6
Q
What are the special characteristics of muscle?
A
- Excitability
- Contractibility
- Extensibility
- Elasticity
7
Q
What is excitability?
A
Ability to receive and respond to stimuli
8
Q
What is contractibility?
A
Ability to shorten forcibly when stimulated
9
Q
What is extensibility?
A
Ability to be stretched
10
Q
What is elasticity?
A
Ability to recoil to resting length
11
Q
What are the 4 important muscle functions?
A
- Movement of bones or fluids
- Maintaining posture and body position
- Stabilizing joints
- Heat generation
12
Q
Identify the structural and organizational levels of the skeletal muscle
A
Muscle → Fascicle → Muscle fiber → Myofibril → Sarcomere → Myofilaments
13
Q
What is the purpose for nerves and blood vessels in the muscle?
A
Regulate contractions and deliver nutrients, oxygen, and remove waste
14
Q
What is the purpose for the connective sheaths?
A
Support cells and reinforce whole muscle
15
Q
What are the 3 muscle sheaths?
A
- Epimysium
- Perimysium
- Endomysium
16
Q
Describe the epimysium
A
Dense irregular connective tissue surrounding entire muscle
17
Q
Describe the perimysium
A
Fibrous connective tissue that surrounds fascicles
18
Q
Identify the terminology for a group of fibers?
A
Fascicles
19
Q
Describe the endomysium
A
Areolar connective tissue surrounding each muscle fiber
20
Q
Out of the 3 sheaths which is the outermost?
A
Epimysium
21
Q
Out of the 3 sheaths which is the innermost?
A
Endomycium
22
Q
What are the 2 places of skeletal muscle attachments?
A
Insertion and origin
23
Q
What is the difference between insertion and origin?
A
Insertion attaches to movable bone, origin is immovable
24
Q
Differentiate direct and indirect attachment
A
Direct is when epimysium is fused to periosteum of bone or perichondrium of cartilage
Indirect is when connective tissue wrappings extend beyond muscle as tendons or aponeurosis
25
Identify the components of a muscle fiber
1. Long, cylindrical cell with multiple nuclei
2. Sarcolemma: plasma membrane
3. Sarcoplasm: cytoplasm
4. Modified structures
26
What are glycosomes’ function?
Glycogen storage
27
What are myglobin’s function?
O2 storage
28
What are the identifiable structures of myofibrils?
1. actin
2. Myosin
3. Elastic filament
4. Dystrophin
5. Nebulin, Myomesin, C proteins
29
What is tropomyosin?
Prevents myosin from binding to actin active site
30
What is troponin?
Moves tropomyosin so actin active site is exposed
31
What is the importance of myosin?
Binds to actin during contraction
32
What is elastic filament of muscles?
1. Composed of protein titen
| 2. Holds thick filaments in places and assists with recoiling after stretch
33
What is dystrophin?
Links thin filaments to proteins of sarcolemma
34
What are the functions of Nebulin, myomesin, C proteins?
Binds filaments or sarcomeres together maintaining alignment
35
What contractile units that comprise myofibrils?
Sarcomeres
36
What are H zones?
lighter region in midsection of dark A band where filaments don't overlap
37
What are M lines?
Line of protein myomesin bisects H zone
38
What is a Z disc?
Coin-shaped sheet of proteins on midline of light I band that anchors thin filaments and connects myofibrils to one another
39
What are thick filaments?
Myosin that run the entire length of an A band
40
What are thin filaments?
Actin that run length of I band and partway into A band
41
What is the difference between actin and myosin in regards to binding patterns?
1. Myosin contains binding sites for actin and ATP
| 2. Actin bears active sites for myosin head attachments and binding of tropomyosin and troponin
42
What is the function of the sarcoplasmic reticulum?
Stores and releases Ca2+ surrounding the myofibril
43
What are the components of a triad?
2 terminal cisterns and 1 T tubule
44
What is the purpose of T tubules?
Increases muscle fiber’s surface area by penetrating A band-I band junction
45
Do the lengths of think and thin filaments change?
No
46
Describe the relaxed state of the sliding filament model
Thin and thick filaments overlap only at ends of A band
47
What happens when the muscle contracts?
Thin filaments slide past thick filaments by myosin binding to actin forming a cross bridge
48
What occurs when there is a high intracellular calcium concentration?
1. Tropomyosin blocks active sites on actin
2. Myosin heads cannot attach to actin
3. Muscle fiber relaxed
49
What occurs when there is a low intracellular calcium concentration?
1. Ca2+ binds to troponin
2. Troponin changes shape and moves tropomyosin away from myosin-binding sites
3. Myosin heads bind to actin causing sarcomere shortening and muscle contraction
50
Discuss the cross bridge cycle?
1. Cross bridge forms when high-energy myosin attaches to thin filament
2. Myosin head pivots and pulls actin towards M line using power strokes
3. ATP attaches to myosin head and cross bridge detaches
4. Energy from hydrolysis of ATP cocks myosin head into high energy state
51
How does rigor mortis affect the cross bridge cycle?
No ATP generated to break cross bridges
52
What is required for the skeletal muscle to retract?
1. Activation
| 2. Exicitation-contraction coupling
53
What are the 2 layers of smooth muscles?
1. Longitudinal
| 2. Circular
54
Describe longitudinal smooth muscles
Fibers parallel to long axis of organ, when contraction occurs it dilates and shortens
55
Describe circular smooth muscles
Fibers in circumference of organs. When contracted lumen constricts and elongates organ
56
Describe peristalsis
Alternating contractions and relaxations of smooth muscle layer that mix and squeeze substances through lumen of hollow organs
57
Why would the SR be less developed than skeletal muscle?
Lacks connective tissue sheath and only consists of endomysium
58
Instead of troponin, how does the smooth muscle bind to calcium?
Caveolae pouches of sarcolemma sequester Ca2+, and calmodulin protein binds to Ca2+
59
What does smooth muscles lack when compared to skeletal?
1. Sacromeres, myofibrils, T tubules
2. Lower ratio of thick and thin filaments
3. Troponin complex
60
What are dense bodies?
Proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals
61
What does contraction of smooth muscles look like?
1. Actin and myosin interact by sliding filament mechanism
2. The trigger is caused by an increase in intracellular Ca2+
3. ATP energizes sliding process
62
What is the role of Ca2+ in smooth muscles?
1. Ca2+ binds to and activates calmodulin.
2. Activated calmodulin activates myosin (light chain) kinase
3. Phosphorylates and activates myosin
4. Cross bridges interact with actin
5. When intracellular Ca2+ levels drop → relaxation.
63
Why do smooth muscles have slower contractions and relaxation periods?
1. Slow ATPases
| 2. Myofilaments may latch together to save energy
64
What are the requirements of relaxing a smooth muscle?
1. Ca2+ detachment from calmodulin
2. Active transport of Ca2+ into SR and ECF
3. Dephosphorylation of myosin to reduce myosin ATPase activity
65
Describe the contraction of smooth muscles
1. Slow, synchronized
2. Cells electrically coupled by gap junctions
3. Some cells are self-excitatory and act as pacemakers for sheets of muscles
66
What is the stress-relaxation response?
1. Responds to stretch only briefly, then adapts to new length.
2. Retains ability to contract on demand.
3. Enables organs such as stomach and bladder to temporarily store contents.
67
What occurs during length and tension changes?
The muscle can contract when between half and twice its resting length
68
What is hyperplasia?
When smooth muscle cells can divide and increase numbers
69
How are smooth muscle contractions regulated?
1. Nerves
2. Hormones
3. Local chemical changes
70
How does smooth muscles vary in different organs?
1. Fiber arrangement and organization
2. Innervation
3. Responsiveness to various stimuli
71
What are the steps of innervation of smooth muscle?
1. No NMJ as in skeletal muscle.
2. Autonomic nerve fibers innervate smooth muscle at diffuse junctions.
3. Varicosities (bulbous swellings) of nerve fibers store and release neurotransmitters into diffuse junctions.
72
What are the categories of smooth muscle?
1. Unitary (visceral) muscle
| 2. Multiunit smooth muscle
73
Describe the structure of unitary (visceral) muscle
1. In all hollow organs except heart.
2. Arranged in opposing sheets.
3. Innervated by varicosities.
4. Often exhibit spontaneous action potentials.
5. Electrically coupled by gap junctions.
6. Respond to various chemical stimuli.
74
Describe the structure of multiunit smooth muscle
1. Located in large airways, large arteries, arrector pili muscles, and iris of eye.
2. Gap junctions; spontaneous depolarization rare.
3. Independent muscle fibers; innervated by autonomic NS; graded contractions occur in response to neural stimuli.
4. Has motor units; responds to hormones.
75
What stimulates the skeletal muscles?
Somatic motor neurons
76
Where do axons of motor neurons travel from?
CNS vis nerves to skeletal muscles
77
Describe the nervous impulse that releases acetylcholine (ACh)?
1. Action potential arrives at axon terminal of motor neuron
2. Voltage-gated Ca2+ channels open. Ca2+ enters the axon terminal moving down its electrochemical gradient
3. Ca2+ entry causes ACh to be released by exocytosis
4. ACh diffuses across the synaptic cleft binds to its receptors on the sarcolemma
5. ACh binding opens ion channels in the receptors that allow simultaneous passage of Na+ into the muscle fiber and K+ out of the fiber. This produces a change in membrane potential
6. ACh effects are terminated by its breakdown in synaptic cleft by acetylcholinesterase
78
What are the components of neuromuscular junctions?
1. Axon terminals
2. Synaptic cleft
3. Junctional folds
79
How is ACh terminated?
Acetylcholinesterase preventing continued muscle fiber contraction in absence of stimulus
80
What are the steps of action potential?
1. End plate potential
2. Depolarization
3. Repolarization
81
Describe end plate potential
1. Local depolarization where ACh binding opens chemically gated ion channels
2. Simultaneous diffusion of Na+ and K+
3. More Na+ diffuses in so interior of sarcolemma becomes less negative
82
What occurs in depolarization?
1. End plate potential spreads to adjacent membrane areas
2. Voltage-gated Na+ channels open
3. Na+ influx decreases membrane voltage toward critical voltage called threshold
4. If threshold reached, action potential initiated
83
What occurs in repolarization?
1. Na+ channels close and voltage-gated K+ channels open.
2. K+ efflux rapidly restores resting polarity.
3. Fiber cannot be stimulated - in refractory period until repolarization complete.
4. Ionic conditions of resting state restored by Na+-K+ pump.
84
Describe the events of excitation-contraction coupling that lead to cross bridge activity.
1. The action potential propagates along the sarcolemma and down the T tubules
2. Calcium ions are released
3. Calcium binds to troponin and removes the blocking action of tropomyosin
4. Contraction begins with myosin binding to actin
85
What are the channels that contribute to muscle contraction?
1. Nerve impulse reaches axon terminal → voltage-gated calcium channels open → ACh released to synaptic cleft.
2. ACh binds to its receptors on sarcolemma → opens ligand-gated Na+ and K+ channels → end plate potential
3. Opens voltage-gated Na+ channels → AP propagation
4. Voltage-sensitive proteins in T tubules change shape → SR releases Ca2+ to cytosol.
86
Differentiate between isometric and isotonic contractions.
Isometric has no shortening when muscle tension increases but does not exceed load
Isotonic is when the muscle shortens because muscle tension exceeds load
87
What is the difference between concentric and eccentric contractions?
Concentric: muscle shortens and does work
Eccentric: muscle generates force as it lengthens
88
What causes the force and duration of contractions to vary?
Stimuli of different frequencies and intensities
89
What is a motor unit?
Motor neuron and all muscle fibers it supplies
90
Would you have small or larger number motor units for fine control movements?
Small
91
Why doe muscles contract asynchronously?
To prevent fatigue
92
What is a muscle twitch?
Motor unit’s response to single action potential of its motor neuron
93
Describe the 3 phases of a muscle twitch
1. Latent period: E-C coupling, no muscle tension
2. Period of contraction where cross bridges form and tension increases
3. Period of relaxation where Ca2+ re-eners into SR and tension declines to 0
94
Which is faster muscle contraction or relaxation?
Contraction
95
How do muscle twitches vary based on structural variation?
Variations in metabolic properties and enzymes between muscles causes differences in strengths
96
What is a graded muscle response?
Varying strength of contraction for different demands
97
How are responses graded?
1. Changing frequency of stimulation
| 2. Changing strength of stimulation
98
How does the muscle contracts more vigorously?
Stimulus strength increases above threshold
99
What are the different types of stimulus frequencies?
1. Muscle twitch
2. Waved summation
3. Unfused tetanus
4. Fused tetanus
100
What is the stimulus frequency of a muscle twitch?
Single stimulus results in a single contractile response
101
What is the stimulus frequency of a wave summation?
Increased stimulus frequency leading to a second contraction of greater force
102
What is the stimulus frequency of a unfused tetanus?
When stimuli are given quickly to where muscle contraction reaches maximal tension
103
What is the stimulus frequency of a fused tetanus?
Having no muscle relaxation that leads to muscle fatigue
104
What are the different types of stimulus strengths?
1. Recruitment
2. Subthreshold stimuli
3. Threshold stimulus
4. Maximal stimulus
105
What is the purpose for recruitment?
Controls force of contractions by activating more muscle fibers
106
What happens when muscle reaches maximal stimulus?
Force of contraction can no longer increase
107
Describe recruitment and its relationship with size
1. Motor units with smallest muscle fibers recruited first
2. Motor units with larger and larger fibers recruited as stimulus intensity increases
3. Largest motor units activated only for most powerful contractions
108
What is subthreshold stimuli?
When there is no observable contraction
109
What is threshold stimulus?
When stimulus strength causing first observable muscle contraction
110
What is maximal stimulus?
Strongest stimulus that increases contractile force
111
What is muscle tone?
Constant, slightly contracted state of all muscles
112
What causes muscle tone?
Spinal reflexes when groups of motor units alternately activated in response to input from stretch receptors in muscles
113
Describe the process of ATP regeneration
1. Direct phosphorylation of ADP by creatine phosphate
2. Anaerobic pathway
3. Aerobic respiration
114
What occurs during the anaerobic pathway?
1. Glucose is degrades to 2 pyruvic acid in glycolysis
2. Pyruvic acid converted to lactic acid
3. Lactic acid is diffused into the blood, used as fuel by liver, kidneys, and heart, then converted back to pyruvic acid or glucose
115
What occurs during the aerobic pathway?
Breaking down glucose to CO2, H2O, and large amounts of ATP
116
What fuels are produced by aerobic pathways?
1. Glycogen
2. Bloodborne glucose
3. Pyruvic acid from glycolysis
4. Free fatty acids
117
What is aerobic endurance?
Length of time muscle contracts using aerobic pathways
118
What is anaerobic threshold?
Point at which muscle metabolism converts to anaerobic
119
What is muscle fatigue?
The muscles inability to contract despite continued stimulation
120
When would muscle fatigue occur?
1. Ionic imbalance
| 2. Prolonged exercise that damages SR and interferes with Ca2+ regulation and release
121
What is a contracture?
Continuous contractions
122
What is EPOC?
1. Oxygen reserves replenished
2. Lactic acid converted to pyruvic acid
3. Glycogen stores replaced
4. ATP and creatine phosphate reserves replenished
123
How much of energy is given off as heat?
60%
124
What is shivering?
Muscle contractions to generate heat when cold
125
The number of cross bridges that allow force of contraction depends on what factors?
1. As more muscle fibers are recruited → more force.
2. Relative size of fibers – bulkier muscles & hypertrophy of cells → more force.
3. Frequency of stimulation → increased frequency → time for transfer of tension to non-contractile components → more force.
4. Length-tension relationship – muscle fibers at 80–120% normal resting length → more force.
126
What is muscle velocity influenced by?
1. Muscle fiber type
2. Load
3. Recruitment
127
Describe three types of skeletal muscle fibers
1. Slow oxidative fibers
2. Fast oxidative fibers
3. Fast glycolytic fibers
128
Why do most muscles contain a mixture of fiber types?
To range contractile speed and have fatigue resistance
129
What are the 2 characteristics of muscle fiber types?
1. Speed of contraction: slow or fast fibers
| 2. Metabolic pathways for ATP synthesis
130
What determines speed of contraction?
1. Speed at which myosin ATPases split ATP
| 2. Pattern of electrical activity of motor neurons
131
What is the difference between oxidative and glycolytic fibers?
Oxidative uses aerobic pathways, glycolytic fuse anaerobic glycolysis
132
What happens when no load is added to muscles?
Muscles contract faster
133
What happens when recruitment is initiated?
Contractions are faster and duration of contraction increases
134
Aerobic exercise increases what components of the muscle?
1. Muscle capillaries
2. Number of mitochondria
3. Myoglobin synthesis
135
What is the result of resistance exercise?
1. Muscle hypertrophy
| 2. Increased mitochondria, glycogen stores, and connective tissue which increases muscle strength and size
136
What are the components of the overload principle?
1. Forcing muscle to work hard promotes increased muscle strength and endurance.
2. Muscles adapt to increased demands.
3. Muscles must be overloaded to produce further gains.
4. Overuse injuries may result from lack of rest.
5. Best programs alternate aerobic and anaerobic activities.
137
What causes disuse atrophy?
1. 5% of muscle strength declines per day when immobilized without neural stimulation
2. Fibrous connective tissue replaces lost muscle tissue and rehabilitation is impossible
138
What is muscular dystrophy?
1. Group of inherited muscle-destroying diseases; generally appear in childhood.
2. Muscles enlarge due to fat and connective tissue deposits.
3. Muscle fibers atrophy and degenerate.
139
Describe Duchenne muscular dystrophy
The most common and severe type that is inherited, sex-linked, carried by females and expressed in males (1/3500) as lack of dystrophin.
140
What is the purpose of dystrophin?
1. Cytoplasmic protein that stabilizes sarcolemma.
| 2. Fragile sarcolemma tears → Ca2+ entry → damaged contractile fibers → inflammatory cells →muscle mass drops.
141
What are some ways to help dystrophy?
1. Prednisone improves muscle strength and function
2. Myoblast transfer therapy that coaxes dystrophic muscles to produce more utrophin
3. Viral gene therapy and infusion of stem cells with correct dystrophin genes show promise.
142
What are the developmental aspects of muscles?
1. Cardiac and skeletal muscle become amitotic, but can lengthen and thicken in growing child.
2. Myoblast-like skeletal muscle satellite cells have limited regenerative ability.
3. Cardiomyocytes can divide at modest rate, but injured heart muscle mostly replaced by connective tissue.
4. Smooth muscle regenerates throughout life.
143
How does body strength per muscle mass differ in males and females?
They are the same
144
Compare the body mass percentages skeletal muscles take up in males and females
1. Males: 42%
| 2. Females: 36%
145
What kind of contractile activities does ATP source?
1. Move and detach cross bridges
2. Calcium pumps in SR
3. Return of Na+ and K+ after E-C coupling
146
How long does it take for ATP to deplete?
4-6 seconds
147
Which pathway produces the most ATP?
Aerobic pathway
148
How does neural regulation assist with smooth muscle contractions?
Neurotransmitters bind causing an increases Ca2+
