Session 7: Muscle Flashcards
1
Q
Myalgia
A
muscle pain
2
Q
Myasthenia
A
Muscle weakness
3
Q
Myocardium
A
Muscular middle layer of the heart
4
Q
Myopathy
A
Disease of the muscle
5
Q
Myoclonus
A
the sudden, involuntary jerking of a muscle or group of muscles
6
Q
Sarcolemma
A
The outer membrane of a muscle cell
7
Q
Sarcoplasm
A
Cytoplasm of a muscle cell
8
Q
Sarcoplasmic reticulum
A
Smooth endoplasmic reticulum of a muscle cell
9
Q
Muscle tissue constitutes ___% of body mass
A
40-50%
10
Q
Muscle generates ___ force through contraction to allow movement AND to support bodily functions e.g., digestion, blood flow
A
motile
11
Q
___ and myosin filaments interact to facilitate contraction of whole muscle cells in each case (i.e., in cardiac, skeletal, smooth)
A
Actin
12
Q
Three muscle tissue types
A
skeletal, smooth, cardiac
13
Q
Skeletal muscle
A
- Striated
- Multinucleated, peripheral nuclei
- Large cylindrical fibres arranged into fasicles
- Voluntary control
14
Q
Smooth muscle
A
- Non-striated
- Single central cigar-shaped nucleus
- Spindle-shaped fusiform cells
- Involuntary control
15
Q
Cardiac muscle
A
- Striated
- **1-2 centrally-located nuclei per cell **
- Branched cylindrical cells joining at intercalated discs
- Involuntary control
16
Q
Which muscle tissue types are striated
A
skeletal and cardiac
17
Q
Which muscle tissue types are non-striated
A
smooth muscle
18
Q
Compare/contrast the three types of muscle tissue types
A
Intercalated discs anchor adjacent cells on only cardiac muscle
19
Q
Function of skeletal muscle?
A
1) Movement
2) Posture
3) Stability of joints
4) Thermoregulation
20
Q
Skeletal muscle accounts for ___% of body mass and generates considerable heat in ___
A
Skeletal muscle accounts for 40% of body mass and generates considerable heat in thermoregulation
21
Q
The three layers of connective tissue in skeletal muscle
A
1) Epimysium = outer layer
2) Perimysium = surrounding each fascicle
3) Endomysium = surrounding each individual muscle fibre
22
Q
Myotendinous junction
A
- Specialised anatomical region that connects skeletal muscle to the tendon
- Primary point of force transmission from the myofilament to the tendon
23
Q
Aetiology of Skeletal Muscles
A
1) Mesenchymal stem cells differentiate into myoblasts which line up to form myotubes
2) These myotubes then elongate to form myofilaments
3) Actin and Myosin myofilaments start to form and nuclei move to periphery of the cell.
- Myoblasts that do not fuse, form satellite cells which sit on the outside of the muscle fibril.
- (Mesenchymal stem cells - Myoblasts - Myotubes - Myofilaments)
24
Q
How does skeletal muscle develop? (histology)
A
Myoblasts producing cardiac and smooth muscle cells do not fuse, but develop gap junctions at a very early stage
25
What is the name of the stem cell population in skeletal muscle that allow for hypertrophy and repair?
Satellite cells
26
Does cardiac muscle repair in adults?
No
27
Does cardiac muscle undergo hypertrophy? If so, via what process?
Cardiac muscle undergoes hypertrophy via sarcomerogenesis
28
Can smooth muscle undergo mitosis?
retain their **mitotic activity** and can form new smooth muscle cell
Yes e.g., the myometrium in pregnancy
Cardiac muscles - Incapable of regenerating
Skeletal muscle cells - by the help of satellite cells
29
Give an example of when smooth muscle undergoes mitosis?
The myometrium in pregnancy
30
Label the three layers in the following histological slide of skeletal muscle?
Epimysium = outer layer
Perimysium = middle layer (connective tissue surrounding each fascicle)
Endomysium = inner layer (surrounding every muscle fibre)
31
The weakest part of muscle/tendon complex which are susceptible to tears
The myotendinous junctions
32
Tendon fibrils ___ with folds in the sarcolemma, and are continuous with the connective tissue layers of muscle.
interdigitate
33
Give example of where skeletal muscle can be found in the human body
Intrinsic muscles of the tongue
## Footnote
- Originate in fibrous connective tissue
- Allow tongue to change shape, but not position
34
Histology of skeletal muscle fibres in ___ section
transverse
35
Histology of skeletal muscle fibres in ___ section
longitudinal
36
The ___ is the smallest functional unit of skeletal muscle
sarcomere
37
Abundant ___ lie between myofibrils in skeletal muscle. Nucleus pushed to the periphery
Mitochondria
38
The nucleus is pushed to the ___ in skeletal muscle cell
Periphery
39
A motor nerve impulse causes release of neurotransmitter ___ (ACh) at axon terminals supplying muscle fibres.
Acetylcholine
40
Acetylcholine activates the ___ receptors on muscle fibre membranes allowing any influx of sodium ions (Na+), depolarising the sarcolemma
Nicotinic
41
The activation of multiple motor neurons will activate more muscle fibres which ___ the force of contraction
Increases
42
Raised levels of what ion stimulates skeletal muscle contraction?
Ca2+
43
When action potentials (APs) arrive at the motor end plate - what neurotransmitter is released into the synaptic cleft?
Acetylcholine (ACh)
44
What does ACh release stimulate at the synaptic cleft?
ACh causes ligand-gated sodium channels on the sarcolemma to OPEN - this causes action potentials to be propagated deep into muscle fibres
45
Action potentials are propagated deep into muscle fibres through the invaginations in the sarcolemma - these invaginations are called...
T-tubules
46
How do calcium ions stimulate muscle contraction? What do they bind to?
Ca2+ stimulates muscle contraction by **binding to troponin subunit C** (TnC), this allows myosin binding sites to be revealed.
47
Calcium ions are returned to the ___ ___ via ATPase pumps after the muscle contraction has completed
Sarcoplasmic reticulum (SR)
48
The action potential triggers the release of calcium ions from what organelle in the skeletal muscle?
Sarcoplasmic reticulum (SR)
49
Sliding filament mechanism of contraction
Upon contraction
- Thin actin filaments pulled towards M-line (centre of sarcomere) - shortening sarcomere
Upon relaxation
- Titin spring allows sarcomeres to passively return to their original size
50
When impulse to contract stops, a ___ spring allows the sarcomere to passively return to their original size in skeletal muscle
Titin
51
What is the main component of thick filaments
Myosin
52
What is the main component of thin filaments
Actin
53
Describe structure of myosin
Each myosin is **shaped like two golf clubs twisted together**.
Myosin tails point toward M line in centre of sarcomere.
Myosin heads project outward from the shaft in spiralling fashion.
54
Contraction of skeletal muscle results from the interaction of ___ and ___ myofilaments
Thick, thin
55
Myosin hydrolyses ATP to provide energy to adopt a ___ position
Cocked
56
Globular actin (G-actin) polymerises to form ___ actin filaments
Helical
57
Each actin subunit has a binding site for myosin heads, but this is hidden by what protein?
Tropomyosin
58
Calcium ion binding to troponin C (TnC) in thin filaments in skeletal muscle causes a conformational shift in what protein? This conformational shift reveals a ___ binding site
Calcium ion binding to troponin C (TnC) in thin filaments causes a conformational shift in tropomyosin protein
## Footnote
This conformational shift reveals a myosin binding site
59
Briefly describe skeletal muscle contraction
1) Motor nerve impulse (AP) arrives at motor end plate - release of ACh into synaptic cleft
2) ACh binds nicotinic receptors at MTJ - cause influx of sodium (depolarisation) of muscle
3) AP propagated deep into muscle via T-tubules
4) T-tubule depolarisation activates ryanodine receptor on SR causing release of calcium ions
5) Calcium binds to troponin subunit C (TnC) causing troponin to change shape and remove blocking action of tropomyosin
6) Myosin cross-bridges alternately attach actin & detach - pulling actin filaments towards centre of sarcomere (M-line), shortening sarcomere. Release of ATP via hydrolysis.
60
The cardiac muscle (myocardium) is ___
Striated
61
Nuclei positioning in cardiac muscle cells
Nuclei **centrally**-positioned with **1-2 nuclei per cell**
62
Cardiac myocytes meet at ___ discs
Intercalated
63
What is the purpose of intercalated discs in cardiac tissue?
Allow for electrical and mechanical continuity
Act as substitutes for Z-discs where cells meet end-to-end
64
Action potentials in cardiac muscle are generated by ___ cells
Pacemaker
65
Where are pacemaker cells located in the heart?
Sinoatrial node (SA)
66
Heart rate and force of contraction can be modulated by which branch of the nervous system?
Autonomic nervous system (ANS)
67
What is the name of the junction type found in intercalated discs of cardiac muscle - that allows for electrical coupling?
**Gap junctions (G)**
These junctions **found in intercalated discs** allow for electrical coupling
68
Which junction type in cardiac muscle anchor cells and provides anchorage for actin filaments?
Adherens-type junctions (A)
69
Purkinje fibres
Specialised cardiac myocytes that lie adjacent to endocardium.
70
What is the function of Purkinje fibres
Rapid conduction of action potentials (more rapidly than cardiac muscle fibres) - allows ventricles to contract in a synchronous manner
71
Where cells meet end to end in cardiac muscle
Intercalated discs (act as substitutes for Z-discs) where cells meet end to end
72
Purkinje fibres conduct action potentials ___ rapidly than cardiac muscle fibres - allowing ventricles to contract in synchronous manner
More
73
Some adaptations of purkinje fibres that allow them to conduct action potentials rapidly?
- Abundant glycogen
- Sparse myofilaments
- Extensive gap junctions
74
What structures does smooth muscle support in the human body?
- Supports vascular structures
- Gut
- Respiratory tract
- Genitourinary system
75
Describe structure of smooth muscle cell
- Spindle-shaped (fusiform)
- Single, central nucleus
- Forms sheets, bundles or layers containing thousands of cells
76
Give examples of five disorders in which smooth muscle activity is clinically significant
1) High blood-pressure
2) Dysmenorrhea
3) Asthma
4) Atherosclerosis
5) Abnormal gut mobility
77
Is smooth muscle under voluntary control?
No - involuntary
78
Smooth muscle responds to stimuli in the form of...
1) Innervation
2) Hormones
3) Drugs
4) Local concentrations of blood gases (e.g., nitric oxide, NO)
79
Contraction of smooth muscle is ___ and more ___ than that of skeletal muscle
Slower, more sustained
80
Smooth muscle takes ___ times longer to contract than skeletal muscle
30 times longer
81
How are thick and thin filaments arranged in smooth muscle cells?
Thick (**myosin**) and thin (**actin**/tropomyosin) filaments **arranged diagonally within smooth muscle cells**
82
Actin and myosin are held in place by protein ___ bodies
Dense bodies
83
The arrangement of smooth muscle fibres causes the cell to become ___ when it contracts
Globular
84
Three examples of modified smooth muscle cells
1) Myoepithelial cells
2) Myofibroblasts
3) Myoid cells
85
Are T-tubules present in smooth muscle?
No, T-tubules are absent in smooth muscle
86
Myofibril
complex organelle composed of bundles of myofilaments
87
Modified epithelial cell
Myoepithelial cell
88
Myoepithelial cell
Stellate cells which form basketwork around secretory units of some exocrine glands (e.g., sweat, salivary and mammary glands).
Contract of these cells assist secretion into secretory ducts
89
___ cells in ocular iris contract to dilate the pupils
Myoepithelial
90
These modified smooth muscle cells produce a collagenous matrix, but also contract at sites of wound healing. They are also important in tooth healing.
Myofibroblasts
91
What structure is the arrow pointing to in this slide of a cardiac muscle? What is the function of this structure?
This is a intercalated disc
## Footnote
- It is the point at which cardiac myocytes meet and they allow for electrical and mechanical continuity
92
These modified smooth muscle cells surround seminiferous tubules. Their contraction helps sperm move towards efferent ducts.
Myoid cells
93
In which muscle is myosin activated by phosphorylation rather than by hydrolysing ATP directly?
Smooth muscle
94
Match the features listed to the labels in the following diagram showing the organisation of skeletal muscle
95
Match the features of a sarcomere to the labels shown in the figure below.
96
Identify muscle type in this photo
Smooth muscle
97
Identify muscle type in this photo
Cardiac muscle
98
Identify muscle type in this photo
Cardiac muscle
99
Identify muscle type from its ultrastructure
Skeletal muscle
100
Identify muscle type from its ultrastructure
Cardiac muscle
101
Identify the ultrastructural features characteristic of different types of muscle from the following diagrams...
A = T-tubule
B = Terminal cisterna of sarcoplasmic reticulum
C = Mitochondrion
D = Caveolus
E = Dense body
102
Caveolae
Calcium stores in place of the sarcoplasmic reticulum of cardiac and skeletal muscle
103
Varicosities
Swellings of autonomic fibres that modulate smooth muscle contraction and mirror the motor units of skeletal muscle
104
Dense bodies
Attachment points for thin filaments that facilitate a "cork-screw" pattern of contraction
105
Which muscle is being described?
Appear striated in longitudinal sections
## Footnote
Skeletal and cardiac
106
Which muscle is being described?
1-2 central nuclei
## Footnote
Cardiac
107
Which muscle is being described?
Fusiform structure
## Footnote
Smooth
108
Which muscle is being described?
Contract via sliding filaments
## Footnote
Skeletal, smooth and cardiac
109
Which muscle is being described?
Somatic innervation
## Footnote
Skeletal
110
Which muscle is being described?
Relatively rich in glycogen stores
## Footnote
Skeletal
111
Which muscle is being described?
Branching structure
## Footnote
Cardiac
112
Which muscle is being described?
Single central nuclei
## Footnote
Smooth
113
Which muscle is being described?
High capacity for regeneration
## Footnote
Smooth
114
Which muscle is being described?
Actin filaments attach to dense bodies
## Footnote
Smooth
115
Which muscle is being described?
Gap junctions provide electrical continuity
## Footnote
Cardiac and smooth
116
Which muscle is being described?
No capacity for regeneration (in adults)
## Footnote
Cardiac
117
Which muscle is being described?
Supported by connective tissue
## Footnote
Skeletal, smooth and cardiac
118
Which muscle is being described as relatively rich in glycogen stores?
Skeletal
119
Which muscle is being described by a branching structure?
Cardiac
120
Which muscle has single central nuclei?
Smooth
121
Which muscle has a high capacity for regeneration?
Smooth
122
Which muscle has actin filaments that attach to dense bodies?
Smooth
123
Which muscles have gap junctions that provide electrical continuity?
Cardiac and smooth
124
Which muscle has no capacity for regeneration (in adults)?
Cardiac
125
Which muscles are supported by connective tissue?
Skeletal, smooth and cardiac
126
Which muscle cells join at intercalated discs?
Cardiac
127
Which muscles have autonomic innervation?
Cardiac and smooth
128
Which muscle is commonly associated with internal tubes e.g., GI tract?
Smooth
129
Which muscle has fascicular organisation?
Skeletal
130
Which muscle has limited capacity for regeneration?
Skeletal
131
Which muscle has multiple, flattened, peripheral nuclei?
Skeletal
132
What is a feature of type IIa and type IIb muscle?
Fast contraction speed
133
What is a feature of type IIb muscle?
High glycogen content
134
What is a feature of type I muscle?
Slow rate of fatigue
135
What is a feature of type I and type IIa muscles?
Rich blood supply
136
What is a feature of type IIb muscle?
Common in extraocular muscles
137
What is a feature of type IIa muscle?
Common in major muscles of the leg
138
What is a feature of type I and type IIa muscles?
Oxidative phosphorylation is a major source of ATP
139
What is a feature of type I muscle?
Common in postural muscles e.g., of back
140
What is a feature of type I muscle?
Low glycolytic enzyme activity
141
What is the role of intermediate filament desmin in muscle?
It is found throughout the cytoplasm and gives stability to muscle cells
142
Agonism of which adrenergic receptor will stimulate smooth muscle relaxation?
beta-2
143
Agonism of which adrenergic receptor will stimulate smooth muscle contraction?
alpha-1
144
Agonism of which adrenergic receptor will stimulate lipolysis of fats?
beta-3
145
Agonism of which adrenergic receptor will stimulate increased heart rate & force of contraction?
beta-1
146
What feature allows cardiac muscle to sustain aerobic respiration for longer than skeletal muscle?
Large numbers of mitochondria
147
What is the major fuel source used by cardiac myocytes?
Triglyceride
148
Skeletal and cardiac muscle cells can use which important fuel source during vigorous activity?
Creatine phosphate
