Muscle Flashcards
1
Q
What is myalgia?
A
Muscle pain
2
Q
What is myasthenia?
A
Muscle weakness
3
Q
What is myopathy?
A
Any disease of the muscle
4
Q
What is the sarcolemma?
A
The outer membrane of muscle cells
5
Q
What is the sarcoplasm?
A
The cytoplasm of a muscle cell
6
Q
What are the 3 major muscle types?
A
NAME?
7
Q
Is skeletal muscle striated?
A
Yes
8
Q
How big are skeletal muscle fibres?
A
- 1mm-20cm long
- 10-100µm in diameter
9
Q
What shape are skeletal muscle fibres?
A
Long parallel cylinders
10
Q
Describe the nuclei of skeletal muscle cells
A
Multiple peripheral nuclei
11
Q
How are skeletal muscles connected?
A
Fascicle bundles and tendons
12
Q
What controls skeletal muscle?
A
Motor neurones
13
Q
Are skeletal muscles under voluntary or involuntary control?
A
Voluntary
14
Q
Describe the action of skeletal muscles?
A
Rapid and forceful
15
Q
Is cardiac muscle striated?
A
Yes
16
Q
How big are cardiac muscle fibres?
A
- 50-100µm long
- 10-20µm in diameter
17
Q
Describe the shape of cardiac muscle?
A
Short, branched cylinders
18
Q
Describe the nuclei of cardiac muscle fibres?
A
Single, central nucleus
19
Q
How is cardiac muscle contraction controlled?
A
Intrinsic rhythm, under autonomic modulation
20
Q
Is cardiac muscle contraction voluntary or involuntary?
A
Involuntary
21
Q
Describe the nature of cardiac muscle rhythm?
A
Lifelong, variable
22
Q
Is smooth muscle striated?
A
No
23
Q
How big are smooth muscle fibres?
A
- 20-200µm long
- 5-10µm in diameter
24
Q
What shape are smooth muscle fibres?
A
Spindle shaped, tapering ends
25
Describe the nuclei of smooth muscle cells?
Single central nucleus
26
How is smooth muscle joined?
By connective tissue, gap and desmosome-type junctions
27
How is smooth muscle controlled?
Autonomic, intrinsic activity, caused by local stimuli
28
Is smooth muscle contraction voluntary or involuntary?
Involuntary
29
Describe the nature of smooth muscle contraction
Slow, sustained or rhythmic
30
How is skeletal muscle developed?
#NAME?
31
What does the myotube have?
A chain of multiple central nuclei
32
What happens to the chain of nuclei in myotubes?
They are gradually displaced to the cell periphery by newly synthesised actin and myosin filaments
33
What happens to myoblasts producing cardiac and smooth muscle?
They do not fuse, but develop gap junctions at a very early stage
34
How do skeletal muscle fibres differ from each other?
In their diameter and their natural colour in vivo
35
What stains corroborate the natural colour of skeletal muscle fibres?
Strain showing reaction to NADH in mitochondria
36
What are the 3 types of skeletal muscle fibre?
#NAME?
37
Which muscles are red, white and intermediate skeletal fibres present in?
All
38
What does the red:white:intermediate proportion depend on?
The functional role of the muscle
39
Comparatively, what is the diameter of red skeletal muscle fibres?
Smaller
40
What are red skeletal muscle fibres rich in?
- Myoglobin
- Vascularisation
- Mitochondria
- Oxidative enzymes
41
Of what do red skeletal muscle fibres have few?
#NAME?
42
What kind of contraction does red skeletal muscle fibres induce?
Slow, repetitive, weaker
43
How quickly does red skeletal muscle fatigue?
Slowly
44
Where are red skeletal muscle fibres found?
- Limb muscles of animals
- Postural muscles of back
- Breast muscle of migrating birds
45
Comparatively, how big are white skeletal muscle fibres?
Larger
46
What do white skeletal muscle fibres have lots of?
#NAME?
47
Of what do white skeletal muscle fibres have few?
- Myoglobin
- Vascularisation
- Oxidative enzymes
48
What kind of contraction do white skeletal muscle fibres induce?
Faster, stronger
49
Where are white skeletal muscle fibres typically found?
- Extra-ocular muscles
| - Muscles controlling fingers
50
What links muscle to bone?
Tendons
51
What is the epimysium?
Protective sheath over muscle
52
Where does the perimysium exist?
Between bundles of muscle fibres
53
Where are the blood vessels found with respect to the perimysium?
Outside of it
54
What are fasicles?
Bundles of muscle fibres wrapped by perimysium
55
Where is endomysium found?
Between muscle fibres
56
What are possible arrangements for muscle fibres?
- Convergent
- Circular
- Parallel
- Fusiform
- Unipennate
- Bipennate
- Multipennate
57
Where do skeletal muscle fibres interdigitate?
At myotendinous junctions
58
How do skeletal muscle fibres interdigitate?
With tendon collagen bundles
59
Where does the sarcolemma lie?
Between the collagen bundles and muscle fibres myofilaments
60
What do the extrinsic muscles of the tongue do?
Protrude to tongue, retract it and move it from side to side
61
Where does the extrinsic muscles of the tongue have insertions?
In bone/cartilage
62
Are the intrinsic muscles of the tongue attached to bone?
No
63
What is the result of the intrinsic muscles of the tongue not being attached to bone?
It allows the tongue to change shape, but not position
64
How to the skeletal muscles of the tongue often terminate?
With interdigitation with the collagen and extracellular matrix of surrounding connective tissues
65
What accounts for the mobility of the tongue?
The plascity and strength of connective tissues, and multidirectional orientation of the muscle fibres
66
What is a striated muscle cell called?
A muscle fibre
67
What is the plasmalemma of a muscle cell sometimes called?
It’s sarcolemma
68
What is the sarcomere?
The unit of striated muscle- the distance between two Z lines
69
Which band appears dark?
A
70
Which band appears light?
I
71
What happens to the sarcomeres in the sliding filament mechanism?
They get shorter-
- I band and H zone shorten
- A band remains the same
72
What are skeletal muscles composed of?
Fasicles
73
What are fasicles composed of?
Muscle fibres (cells)
74
What are muscle fibres composed of?
Myofibrils
75
What are the myofibrils?
#NAME?
76
What forms the thin filaments of skeletal and cardiac muscle?
A complex of actin, tropomyosin and troponin
77
How can troponin assays be used as a diagnostic tool?
Can be used as a marker for cardiac ischaemia
78
What types of troponin especially are used as a marker for cardiac ischaemia?
I and T forms
79
How can troponin assays be used a marker for cardiac ischaemia?
It’s released from ischaemic cardiac muscle within an hour, so the smallest changes in troponin levels are indicative or cardiac muscle damage
80
Is the quantity of troponin found proportional to degree of muscle damage?
Not necessarily
81
Describe the structure of an individual myosin molecule
Has a rod-like structure from which two ‘heads’ protrude
82
What does each thick filament consist of?
Many myosin molecules
83
How do the heads of the myosin in the thick filament protrude?
At opposite ends of the filament
84
What do actin filaments form?
A helix
85
What happens to the actin helix?
Tropomyosin molecules coil around it
86
What is the effect of the tropomyosin molecules coiling around the actin helix?
It reinforces it
87
What is attached to each tropomyosin molecule?
A troponin complex
88
What is true of the thick filaments in the centre of the sarcomere?
Thet are devoid of myosin heads
89
What happens to the myosin head in areas of potential overlap?
They extend towards the actin filaments
90
What is the role of ionic calcium in the contraction metabolism?
- When increased amount of ionic calcium bind to TnC of troponin, a conformational change moves tropomyosin way from actin’s binding sites
- This displacement allows myosin heads to bind to actin, and contraction begins
91
What conformational change is made on binding of calcium?
The troponin has moved down, taking tropomyosin with it
92
What is the result of the action of calcium in muscle contraction?
Muscle contraction only occurs in the presence of calcium ions
93
What is the sliding filament theory of muscle contraction?
- Myosin cross bridge attaches to the actin myofilament
- ADP+Pi released, producing the working stroke- the myosin head pivots and bends as it pulls on the actin filament, sliding towards the M line
- New ATP attaches to the myosin head, and the cross bridges detaches
- As ATP is hydrolysed into ADP+Pi, cocking of the myosin head occurs
94
What state is myosin in at the point of forming cross bridges?
High energy conformation
95
What is meant by the high energy conformation of myosin?
It has ADP+Pi attached
96
When is myosin in the low energy conformation?
When it has ATP attached to the head
97
What is the purpose of the cocking of the myosin head?
Means myosin is ready to bind to a new actin filament
98
What causes movement of skeletal muscle?
Individual myosin heads attaching and flexing at different times
99
What is the rigor configuration?
When the myosin head is bound tightly to actin molecule
100
What causes rigor mortis?
In death, lack of ATP perpetuates the rigor configuration
101
What is at the end of the axons?
Small terminal swellings
102
What do the small terminal swellings of the axon contain?
Acetylcholine
103
What causes the release of acetylcholine?
A nerve impulse
104
What happens to released acetylcholine?
It binds to receptors on the sarcolemma
105
What is the result of acetylcholine binding to receptors?
Initiates an action potential propagated along the muscle
106
Where do nerves come from?
The motor neurone cell body of the spinal cord
107
What is each nerve coming from the spinal cord known as?
A motor neurone
108
What happens to the motor neurone axon?
It branches, and joins to muscle fibres
109
What initiates the contraction of skeletal muscle?
A nerve impulse along the motor neurone arriving at the neuromuscular junction
110
What does the nerve impulse arriving at the neuromuscular junction prompt?
The release of acetylcholine (ACh) into the synaptic cleft
111
What does the release of ACh cause?
Local depolarisation of the sarcolemma
112
What happens as a result of the depolarisation of the sarcolemma?
Voltage-gated Na + channels open, and so it enters the cell
113
What does the influx of Na + to the sarcolemma cause?
General depolarisation, that spreads into the sarcolemma and into T tubules
114
What happens to T tubules once they’ve been depolarised?
Voltage sensor proteins of the T tubules change their confirmation
115
What is activated due to the change in T tubule conformation?
Gated Ca 2+ -release channel of adjacent terminal cisternae
116
What happens once the Gated Ca 2+ -release channels are activated?
Ca 2+ is released rapidly from terminal cisternae into sarcoplasm
117
What happens when Ca 2+ is released into the sarcoplasm?
It binds to the TnC subunit of troponin, activating the contraction cycle
118
What happens to Ca 2+ in the sarcoplasm once it has performed it’s function?
It is returned to the terminal cisternae of the sarcoplasmic reticulum
119
What features do cardiac muscle fibres have?
- Striations
- Centrally positioned nuclei
- Intercalated disks
- Branching
120
How many nuclei do cardiac muscle fibres have per cell?
1 or 2
121
What is the purpose of intercalated discs?
For electrical and mechanical coupling with adjacent cells
122
How does cardiac muscle differ from skeletal muscle?
Distinct myofibrils are absent
123
What is present instead of distinct myofibrils in cardiac muscle?
Myofilaments of actin and myosin form continuous masses in the cytoplasm
124
What arrangement do intercalated disks have?
Step like
125
What do intercalated discs act as substitutes for?
Z bands where cells meet end to end
126
What junctions to intercalated discs have?
#NAME?
127
What is the purpose of gap junctions in intercalated disks?
Electric coupling
128
What is the purpose of adherens-type junctions?
To anchor cells and provide anchorage for actin filaments
129
How to the T tubules of cardiac muscle differ from those in skeletal muscle?
They lie in register with the Z bands, and not the A-I junction
130
What does the close association of the sarcoplasmic reticulum and T tubules at diads permit?
The release of ionic calcium into the sarcoplasm and subsequent muscle contraction
131
What do all cardiac muscle cells exhibit?
Spontaneous rhythmic contraction
132
Where is the spontaneous rhythmic contraction of cardiac muscle cells evident?
In embryonic cardiac muscle and in isolated mature muscle cells in tissue culture
133
How are action potentials generated in the heart?
In the sinoatrial node
134
What happens once an action potential has been generated in the sinoatrial node?
It passes to the atrioventricular node, and from there to the ventricles
135
How are nerve impulses carried in the heart?
By specialised myocardial cells called Purkinje fibres
136
What cells make up the Purkinje fibres?
Distal conducting cells
137
What do tracts of Purkinje fibres do?
Transmit action potentials from ventricles from the AV node
138
In what cells are Purkinje fibres large?
Those with;
- Abundant glycogen
- Spare myofilaments
- Extensive gap junction sites
139
Do Purkinje fibres conduct impulses faster or slower than cardiac muscle fibres?
Faster
140
What does the rapid conduction of Purkinje fibres enable?
Ventricles to contract in a synchronised manner
141
What shape are smooth muscle cells?
Fusiform
142
What features do smooth muscle cells not have?
- Striations
- Sarcomeres
- T tubules
143
What does contraction of smooth muscle rely on?
Actin-myosin interactions
144
Describe the contraction of smooth muscle compared to skeletal and cardiac?
Slower, more sustained, requires less ATP
145
What is the cause of the differences in contraction of smooth muscle?
Due to latch system
146
How long can smooth muscles remain contracted for?
Hours or days
147
Can smooth muscles be stretched?
Yes
148
What stimuli do smooth muscles respond to?
- Nerve signals
- Hormones
- Drugs
- Local concentration of blood gases
149
What structures do smooth muscles form?
#NAME?
150
What walls do smooth muscles often form?
Contractile walls of passageways or cavities
151
What do contractile walls have the ability to do?
Modify volume
152
Where are contractile walls found?
- Vascular systems
- Gut
- Respiratory tract
- Genitourinary system
153
Where can smooth muscle be of clinical significance?
- High blood pressure
- Dysmenorrhea
- Asthma
- Atherosclerosis
- Abnormal gut mobility
154
How can modified smooth muscle cells occur?
- Singly as myoepithelial cells
| - As myofibrast cells
155
What are myoepithelial cells?
Stellate cells forming a basketwork around the secretory units of some exocrine glands
156
Give 4 examples of where myoepithelial cells are found
- Sweat glands
- Salivary glands
- Mammary glands
- Ocular lens
157
What does contraction of myoepithelial cells around glands do?
Assists secretion of sweat, saliva or milk into secretory ducts
158
What is the purpose of myoepithelial cell contraction in the ocular lens?
Dilates the pupil
159
What do myofibroblasts do?
Produce collagenous matrix at sites of wound healing, and also contract
160
What are most smooth muscle cells innervated by?
Autonomic nervous system fibres
161
What do the autonomic nervous system fibres that innervate smooth muscle cells do?
Release their neurotransmitters from varicosities into a wide synaptic cleft
162
How are smooth muscles thick and thin filaments arranged?
Diagonally within cells, spiralling down the long axis
163
What is the result of the arrangement of the filaments in smooth muscle?
It contracts in a twisting way
164
What do intermediate filaments in smooth muscle attach to?
Dense bodies
165
Where are dense bodies found?
Scattered throughout the sarcoplasm, and occasionally anchor into the cytoplasm
