Muscular System Flashcards
1
Q
What is myalgia?
A
Muscle pain
2
Q
What is myasthenia?
A
Weakness of the muscles
3
Q
What is the myocardium?
A
Muscular component of the heart
4
Q
What is myopathy?
A
Any disease of the muscles
5
Q
What is myoclonus?
A
A sudden spasm of the muscles
6
Q
What is the sarcolemma?
A
Outer membrane of a muscle cell
7
Q
What is the sarcoplasm?
A
Cytoplasm of a muscle cell
8
Q
What is the sarcoplasmic reticulum
A
The smooth ER of a muscle cell
9
Q
What are the three forms of muscle?
A
Cardiac, smooth and skeletal
10
Q
Which forms of muscle are striated?
A
Skeletal and cardiac
11
Q
Which forms of muscle are non-striated?
A
Smooth
12
Q
What is the cell length of skeletal muscle?
A
1mm-20cm
13
Q
What is the cell length of cardiac muscle?
A
50-100 micrometres
14
Q
What is the cell length of smooth muscle?
A
20-200 micrometres (but up to 0.5mm in uterus)
15
Q
What is the cell diameter of skeletal muscle?
A
10-100 micometres
16
Q
What is the cell diameter of cardiac muscle?
A
10-20 micrometres
17
Q
What is the cell diameter of smooth muscle?
A
5-10 micrometres
18
Q
What is the cell morphology of skeletal muscle?
A
Long parallel cylinders
Multiple peripheral nuclei
Striations
19
Q
What is the cell morphology of cardiac muscle?
A
Short branched cylinders
Single central nucleus
Striations
20
Q
What is the cell morphology of smooth muscle?
A
Spindle shaped
Tapering ends
Single central nucleus
No striations
21
Q
On the basis of certain stains, which three fibre types have been found in skeletal muscle?
A
Narrower red fibres
Intemediate pink fibres
Wider white fibres
22
Q
Which muscle fibre type has numerous mitochondria and rich vascularisation?
A
Red
23
Q
Which muscle fibre type is involved in faster, stronger contractions?
A
White
24
Q
Which enzymes are red fibres rich in?
A
Oxidative enzymes. Poor in ATPase
25
Which muscle fibre type has more neuromuscular junctions?
White
26
Where are the typical locations of red fibres?
Limb muscles, postural muscles of back
27
Where are the typical locations of white fibres?
Extraocular muscles, muscles controlling fingers
28
What is myoglobin?
A red protein containing haem, functioning as an oxygen-storing molecule providing oxygen to the working muscles
29
Where is myoglobin present?
In skeletal and cardiac muscle but not smooth
30
When does haemoglobin often give up oxygen to myoglobin?
When pH is lowered - active muscles produce CO2/lactic acid which results in more acidic conditions that promotes this transfer
31
If there are many nuclei and they are peripheral, which type of muscle is it?
Skeletal
32
What is the perimysium?
Connective tissue carrying nerves and blood vessels that surrounds a fascicle (bundle of muscle fibres)
33
What are the dark longitudinal streaks in a histological slide of skeletal muscle fibres?
Mitochondria
34
What is a striated muscle cell called?
Muscle fibre
35
What is a myofibril?
Any of the elongated contractile threads found in striated muscle cells.
36
Which are the thin filaments in muscle fibres?
Actin, tropomyosin, troponin
37
Which is the thick filament in muscle fibres?
Myosin
38
What is the A band?
The comparatively dark area entirely within a sarcomere. This area is composed of thick filaments and thin filaments.
39
What is the I band?
The lighter areas alternating with A-Bands; these areas straddle the Z-line and are composed of thin filaments
40
What is the H zone?
A subdivision of the A-Band in the center of the sarcomere where only thick filaments are present
41
Where do thin filaments attach?
Z line
42
Where do thick filaments attach?
Span the A band
43
What is the Z line?
The partitions within a muscle fibre that section it into sarcomeres.
44
What is the sarcomere?
The portion of a muscle fibre between two successive Z-lines.
45
What happens when destruction of muscles > replacement?
Atrophy
46
What happens when replacement of muscles > destruction?
Hypertrophy
47
What does disuse atrophy involve?
Loss of protein, reduced fibre diameter, loss of power
48
When do muscles start to atrophy with age?
+30 years old
49
How much loss of muscle is there by 80 years old?
50%
50
What does hypertrophy involve?
More contractile proteins, increase in fibre diameter, more power
51
What happens to the I band during contraction?
Shrinks
52
What happens to the A band during contraction?
Does not shrink
53
What happens to the H zone during contraction?
Shrinks
54
How is muscle length adjusted?
Increases by frequent stretching (addition of sarcomeres)
55
What is thought to often feature in some cardiac pathologies eg enlarged ventricles?
Overstretching, such that the A and I filaments can no longer re-engage
56
What is used as a marker for cardiac ischaemia?
Troponin assays
57
How soon is troponin released from ischaemic cardiac muscle?
Within an hour
58
How soon must you measure troponin levels after cardiac ischaemia?
Within 20 hours
59
True or False:
Quantity of troponin is proportional to degree of damage
False
60
What is creatine kinase?
An important enzyme in metabolically active tissues like muscle
61
What can creatine kinase be used to diagnose?
Heart attacks (MIs)
62
True or False:
Creatine kinase increase is largely proportional to infarct size
True
63
What can a rise in plasma creatine kinase also result from?
Intramuscular injection, vigorous exercise, a fall (especially in the elderly), rhabdomyolysis, muscula dystrophy and acute kidney injury
64
What does each thick filament consist of?
Many myosin molecules, whose heads protrude at opposite ends of the filament
65
What does the actin filament fom?
A helix with tropomyosin molecules coiled around it
66
What is attached to each tropomyosin molecule?
Troponin complex
67
What happens when increased amounts of ionic calcium bind to TnC of troponin?
A conformational change that moves tropomyosin away from actin's binding sites - allowing myosin heads to bind actin and contraction to begin
68
As the myosin head pivots and bends, pulling the actin filament, what is released?
ADP and Pi
69
When new ATP attaches to the myosin head, what happens?
The cross bridge detaches
70
As ATP is splt into ADP and Pi in the last step of muscle contraction, what happens?
Cocking of the myosin head occurs
71
What is the rigor configuration?
Myosin head tightly bound to actin molecule
72
What causes rigor mortis?
Lack of ATP that thus perpetuates the tight binding of the myosin head to actin
73
What are the stages of muscle contraction?
Myosin head attaches to actin;
ATP binds the myosin head causing it to uncouple from actin;
Hydrolysis of ATP causes the uncoupled myosin head to bend and advance a short distance (5nm);
The myosin heaed binds weakly to actin filament causing release of Pi which strengthens binding and causes the power stroke in which the myosin head returns to its former position
ATP binds to the myosin head causing detachment from actin, myosin head binds tightly again and cycle repeats
74
What is a t tubule?
A deep invagination of the sarcolemma
75
What are the events leading to contraction of skeletal muscle?
1) Nerve impulse along motor neuron axon arrives at neuromuscular junction
2) Prompts release of acetylcholine into synaptic cleft causing local depolarization of sarcolemma
3) Voltage-gated sodium channels open causing sodium ions to enter the cell
4) General depolarization spreads over sarcolemma and into T tubules
5) Voltage sensor poteins of T tubule membrane change their conformation
6) Gated calcium ion release channels are activated
7) Calcium ions are rapidly released into sarcoplasm
8) Calcium ions bind to the TnC subunit of troponin, thus initiating the contraction cycle
76
In cardiac muscle, distinct myofibrils are absent. What do the myofilaments form instead?
Actin and myosin form continuous masses in the cytoplasm
77
In contrast to skeletal musscle, where do the T tubules of cardiac muscle lie in register with?
The Z bands, not the A-I junction
78
What is hypertrophy of the cells?
Enlargement of individual cells
79
What is hyperplasia of the cells?
Multiplication of the cells
80
How do tissues increase in size?
Hypertrophy or hyperplasia
81
What is the release of natriuretic peptdes by the heart usually in response to?
Heart failure - stimulated by atrial and ventricular distension
82
What are the main physiological actions of natriuretic peptides?
Reduce arterial pressure by decreasing blood volume or vascular resistance
83
What is Atrial Natriuretic Peptide (ANP)?
28 amino acid peptide that is synthesized, stored and eleased by atrial myocytes in response to atrial distension.
84
In which states are elevated levels of ANP found in?
Hypervolemic states which occur in congestive heart failure
85
What is Brain-type Natriuretic Peptide (BNP)?
32 amino acid peptide that is synthesised by the ventricles and brain.
86
What does proteolysis of pro-BNP result in?
pro-BNP (108 amino acids) results in BNP (32 amino acids) and the N terminal piece of pro-BNP - NT-pro-BNP (76 amino acids)
87
What are both BNP and NT-pro-BNP diagnostic markers for?
Heart failure
88
What to natriuretic peptides serve as?
A counter-regulatory system for the renin-angiotensin-aldosterone system
89
What are Purkinje fibres?
Purkinje fibers are special fibers that are located in the atrioventricular, or AV, bundle of the heart. Their function is to send nerve impulses to the cells in the ventricles of the heart and cause them to contract and pump blood either to the lungs or the rest of the body.
90
What do Purkinje fibres consist of?
Large cells with abundant glycogen, sparse myofilaments and extensive gap junction sites
91
Does contraction still rely on actin-myosin interactions in smooth muscle?
Yes
92
What are myoepithelial cells?
Modified smooth muscle cells forming a basketwork around the secretory units of some exocrine glands
93
How does skeletal muscle tissue regenerate?
Mitotic activity of satellite cells so that hyperplasia follows muscle injury. Satellite cells can also fuse with existing muscle cells to increase mass
94
Is cardiac muscle capable of regeneration?
No, following damage, fibroblasts invade, divide and lay down scar tissue
95
Can smooth muscle cells divide?
Yes. Smooth muscle cells retain their mitotic activity and can form new smooth muscle cells
