Session 8: Muscle Flashcards
(141 cards)
1
Q
What is the sarcolemma?
A
The outer membrane of a muscle cell
2
Q
What is the sarcoplasm?
A
The cytoplasm of a muscle cell
3
Q
Muscle tissue take on which two forms?
A
Striated muscle
Non-striated muscle
4
Q
What two types of muscle are striated?
A
Skeletal muscle
Heart muscle
5
Q
What muscle type is non-striated?
A
Smooth muscle
6
Q
What are the three fibre types present in skeletal muscle?
A
Red
Intermediate
White
7
Q
Skeletal muscle forms what connections?
A
Fascicle bundles
Tendons
8
Q
Cardiac muscle forms what connections between cells?
A
Junctions join cells end to end
9
Q
Smooth muscle forms what connections?
A
Connective tissue
Gap Junctions
Desmosome-type Junctions
10
Q
Skeletal muscle is under what nervous control?
A
Somatic motor neurons
Voluntary control
11
Q
Cardiac muscle is under what nervous control?
A
Intrinsic rhythm
Involuntary autonomic modulation
12
Q
Smooth muscle is under what kind of control?
A
Involuntary
Autonomic
Intrinsic activity
Local stimuli
13
Q
What kind of power is achieved through skeletal muscle contraction?
A
Rapid, forceful
14
Q
What kind of power is achieved through cardiac muscle contraction?
A
Lifelong, variable rhythm
15
Q
What kind of power is achieved through smooth muscle contraction?
A
Slow, sustained (rhythmic)
16
Q
How do red filaments compare to white filaments in skeletal muscle in relation to their diameter, vascularisation and innervation?
A
Red filaments are smaller in diameter
Red filaments have a rich blood compared to white filaments
Red filaments have fewer neuromuscular junctions than white filaments
17
Q
Red filaments have how many mitochondria relative to white filaments?
A
Red filaments have numerous mitochondria compared to white filaments
18
Q
Red filaments have how much myoglobin compared to white filaments?
A
Red filaments have a rich supply of myoglobin compared to the white filament’s poor supply
19
Q
What kind of contraction is achieved through contraction of red filaments relative to white filaments (Speed, strength)?
A
Red: Slow, repetitive, weaker
White: Faster, stronger
20
Q
What enzymes are red skeletal fibres rich in?
A
Oxidative enzymes
21
Q
What enzyme (s) are white skeletal fibres rich in?
A
ATPase
22
Q
Myoglobin is present in which of the three muscle types?
A
Skeletal and cardiac, not smooth
23
Q
What is myoglobin?
A
A red protein containing haem, which functions as an oxygen storing molecule, providing oxygen to working muscles
24
Q
Under what conditions does haemoglobin especially give oxygen up to myoglobin?
A
Lowered pH (acidic conditions)
25
The individual muscle fascicles are wrapped in what?
Perimysium
26
The individual muscle fibres are wrapped in what?
Endomysium
27
What is the name of the layer of connective tissue that covers the entire muscle?
Epimysium
28
What are the 7 ways in which skeletal muscle can be arranged?
```
Circular
Convergent
Parallel
Unipennate
Multipennate
Fusiform
Bipennate
```
29
Extrinsic muscles of the tongue are responsible for what?
Protruding, retracting and moving the tongue from side to side
30
Intrinsic muscles of the tongue are responsible for what?
Allowing the tongue to change shape
31
Do extrinsic muscles of the tongue attach to bone?
Yes
32
Do intrinsic muscles of the tongue attach to bone?
No
33
What accounts for the mobility of the tongue?
Plasticity and strength of the connective tissue
| Multidirectional orientation of the muscle fibres
34
Skeletal muscles of the tongue often terminate by what?
Interdigitation with collagen and ECM of surrounding connective tissues
35
What is a muscle fibre?
A striated muscle cell
36
What is the sarcomere?
| What does it consist of?
The structural unit of a myofibril in striated muscle
Segment from Z line to Z line
Made up of actin and myosin filaments
37
What are the A bands of the sarcomere?
| How do they appear histologically?
The thick myosin filaments
| They form the dark bands
38
What are the I bands of the sarcomere?
| How do they appear histologically?
The thin actin filaments with no overlap
They form the light bands
I for "Isotropic''
39
What is the M line of the sarcomere?
| How do they appear histologically?
The middle of the sarcomere
40
What is the H zone ad how does this appear histologically?
The H band or zone are the non-overlapping myosin filaments
41
What are the Z lines?
| How do they appear histologically?
The end of each sarcomere, attaching one sarcomere to the next
They appear as dark bands on histology
42
Which molecules come together to form the thin filaments of skeletal and cardiac muscle?
Actin
Tropomyosin
Troponin complex
43
Troponin assays are a useful tool for diagnosing what?
Cardiac Ischemia
44
The troponin complex is made up of what?
Troponin I
Troponin C
Troponin T
45
Troponin is released from ischaemic cardiac muscle within what time frame? And it must be measured within what time frame?
Released within: An hour
| Measured within: 20 hours
46
True of false: Quantity of troponin is proportional to the degree of damage
False, not necessarily
47
Which enzyme did troponin supersede as a marker for myocardial infarction?
Creatine Kinase (CK)
48
True or false: The amount of CK is proportional to the infarct size
True
49
What is a major disadvantage of using CK as a marker for ischaemic cardiac muscle?
The enzyme is also released into the blood by damaged skeletal muscle and brain, not necessarily specialised to damage to cardiac muscle
50
Name three things that can result in a rise in plasma CK
```
Intramuscular injection
Vigorous physical exercise
A fall (especially in the elderly)
Muscular dystrophy
Acute kidney injury
Rhabdomyolysis (severe muscle breakdown)
```
51
Describe the structure of an individual myosin molecule
Rod-like structure with two heads that protrude
52
Describe the structure of a myosin filament
Many individual myosin molecules whose heads protrude at opposite ends of the filament
53
Describe the structure of the actin filament
The actin filament forms a helix around which tropomyosin coils around. The troponin complex is attached to the tropomyosin molecule
54
In the centre of the sarcomere, the thick myosin filaments are lacking what?
Myosin heads
55
When in its high energy configuration, what is the myosin head doing?
Attaching to the actin myofilament forming a cross bridge
56
What is the importance of ionic calcium in muscle contraction?
Increased ionic calcium binds to troponin C of troponin which leads to a conformational change and moves tropomyosin away from myosin binding sites on actin, which means myosin can then bind
57
What occurs during the "working stroke" of muscle contraction?
The myosin head pivots and bends as it pulls on the actin filament, sliding towards the M line
58
What happens when the myosin head is in "low-energy" configuration?
The new ATP attaches to the myosin head and the cross bridge detaches
59
When ATP is hydrolysed into ADP and P what happens during contraction?
The myosin head detaches from actin and cocks back to starting position
60
What is essential for the releasing of tropomyosin's blockage of actin's active sites?
Ionic calcium
61
What is the neuromuscular junction?
Small terminal swellings of the axon that contain vesicles of acetylcholine (Ach)
62
What happens during initiation of contraction of skeletal muscle?
The nerve impulse travels along the motor neuron axon and arrives at the neuromuscular junction
63
What happens at the NMJ when a nerve impulse reaches it?
It releases acetylcholine (Ach) into the synaptic cleft causing local depolarisation of the sarcolemma
64
During skeletal muscle contraction, what happens once the sarcolemma is depolarised by Ach release?
Voltage-gated Sodium channels open and sodium ions enters the cell
65
General depolarisation of the sarcolemma and into T tubules causes what?
The voltage sensor proteins of the T tubule membrane to change their conformation and activates Ca2+ release from terminal cisternae into the sarcoplasm
66
Once Ca2+ is released into the sarcoplasm, what happens?
Ca2+ binds to troponin C (TnC) and the contraction cycle is initiated
67
Where is ionic calcium then return to following the initiation of the contraction cycle during muscle contraction?
The terminal cisternae of sarcoplasmic reticulum
68
What is muscle fibrillation?
The contraction of individual muscle fibres (muscle cells)
69
What is muscle fasciculation?
The contraction of whole muscle fascicles, often under the innervation of a single motor neurone (As in motor neurone disease)
70
What are absent from cardiac muscle that are distinctly present in skeletal muscle?
What are formed instead?
Myofibrils
| Myofilaments of actin and myosin form continuous masses in the cytoplasm
71
____________ and _____________ penetrate through the cytoplasm between myofilaments
Mitochondria
| Sarcoplasmic reticulum
72
Longitudinal sections of cardiac muscle fibres show what?
Striations
Centrally positioned nuclei (1 or 2 per cell, no more than 2)
Intercalated discs
Branching
73
Transverse sections of cardiac muscle fibres show what?
Centrally positioned nuclei
Endomysium
Lobular profiles of branching fibres
74
Cardiac muscle fibres have what instead of the Z lines that are seen in skeletal muscle?
Intercalated discs
75
Where are the intercalated discs of cardiac muscle?
| What two types of junctions do they have?
Where the cells meet, end to end
| Gap junctions and adherens- type junctions
76
What is the purpose of the gap junctions at the intercalated discs?
Electrical coupling between cells to ensure that the cells contract together
77
What is the purpose of the adherens- type junctions at the intercalated discs?
Provide anchorage for actin filaments
78
What is different with regard to the arrangement of T-tubules in cardiac muscle compared to skeletal muscle?
The T-tubules of cardiac muscle are in lie with the Z disc rather than the A-I band junction
79
What is a diad? Are these found in skeletal or cardiac muscle?
The point at which the t-tubule meets a single terminal cisterna of the sarcoplasmic reticulum. Cardiac muscle
80
Where is the diad located in the cardiac myocyte?
At the Z line
81
What is a t-tubule?
A "transverse" tubule that is a deep invaginated of the sarcolemma
82
What is a triad?
The point at which the t-tubule meets a terminal cisterna of the sarcoplasmic reticulum on either side of it. They are found in skeletal muscle
83
Where is the triad typically located in skeletal muscle?
Along the A-I junction
84
What is the purpose of triads and diads in skeletal and cardiac muscle fibres?
Allows close association of t-tubules and sarcoplasmic reticulum which permits the release of ionic calcium into the sarcoplasm and subsequent muscle contraction
85
What is cell hypertrophy?
Enlargement of individual cells without an increase in number of cells
86
What is cell hyperplasia?
An increase in the number of cells due to mitosis
87
What is heart atrophy?
When the heart is smaller than the normal heart due to smaller individual cells that make up the heart
88
What is heart hypertrophy?
When the heart is bigger than the normal heart due to the larger individual cells that make up the heart
89
What are natriuretic peptides?
Peptide hormones that are synthesised by the heart, brain and other organs in response to atrial and ventricular distension, usually in response to heart failure
90
What are the main physiological actions of natriuretic peptides?
To reduce arterial pressure by decreasing blood volume and systemic vascular resistance
91
What is ANP?
| When would it be released?
Atrial natriuretic peptide
| When the atria are distended
92
Do normal hearts secrete extremely small or large amounts of ANP?
Extremely small amounts
93
In what patients would you find elevated levels of ANP?
Patients with left ventricular (LV) hypertrophy and mitral valve disease
(During hypervolemic states which occur in congestive heart failure)
94
What is BNP?
| Where is it synthesised?
Brain-type natriuretic peptide
| In the ventricles and the brain
95
Both BNP and NT-pro-BNP are sensitive, diagnostic markers for what?
Heart failure in patients
96
In response to cardiac distension, ANP causes what?
The kidney to raise glomerular filtration rate therefore excreting more sodium and water to reduce blood volume. This leads to reduction in cardiac output and systemic blood pressure
97
In response to cardiac distension, BNP causes what?
Vasodilation which causes blood pressure to lower as well as increased natriuresis and diuresis (sodium and water excretion)
98
Natriuretic peptides serve as a counter-regulatory system for what?
The renin-angiotesin-aldosterone system
99
In the heart, action potentials are generated where?
In the sinoatrial node (SA node)
100
Action potentials pass from the SA node to where?
To the atrioventricular node (AV node)
101
The impulses pass from the AV node to where?
Ventricles
102
What are the specialised myocardial cells that carry impulses to the ventricular muscle called?
Purkinje fibres
103
Purkinje fibres relatively are small or large cells?
Large
104
Purkinje fibres are abundant in what?
Glycogen
105
Purkinje fibres have sparse what?
Myofilaments
106
Purkinje fibres have extensive what between cells?
Gap junctions
107
Do purkinje fibres conduct action potentials more or less rapidly than cardiac muscle fibres?
More rapidly (3-4m/s compared to 0.5m/s)
108
What does the rapid conduction of action potentials by purkinje fibres enable?
Contraction of ventricles in a synchronous manner
109
Smooth muscle cells are described as what shape? Where is the nucleus located?
Fusiform (Spindle-shaped)
| In the centre of the cell
110
Is smooth muscle striated?
No
111
Does smooth muscle contain sarcomeres?
No
112
Does smooth muscle contain T tubules?
No
113
Smooth muscle contraction relies on what?
Actin-myosin interactions
114
Why do we not see the regular banding of actin and myosin filaments in smooth muscle?
They are not lined up in a regular way
115
Compared to other muscle types, smooth muscle contraction is what?
(In relation to speed, duration and energy-requirement)
Slower
More sustained
Requires less ATP
116
Smooth muscle can remain contracted for _____ or ______
hours
| days
117
Is smooth muscle capable of being stretched?
Yes
118
Smooth muscle responds to stimuli in the form of what?
Nerve signals
Hormones
Drugs
Local concentrations of blood gases
119
Smooth muscle can form _____, bundles or ________ containing thousands of cells.
Sheets
| Layers
120
Smooth muscle often forms contractile walls of passageways or cavities in order to do what?
Modify the volume passing through them
121
Where might you find smooth muscle?
Vascular structures
The gut
The respiratory tract
The genitourinary system
122
Is smooth muscle voluntary or involuntary?
Involuntary
123
When smooth muscle contracts with pathological affect it can cause what conditions?
```
Asthma
High blood pressure
Atherosclerosis
IBS
Detrusor muscle instability
```
124
Modified smooth muscle can occur singly as which two cell types?
Myoepithelial cells
| Myofibroblast cells
125
What are myoepothelial cells?
Stellate (Star-shaped) cells that form a basketwork around secretory units of some exocrine glands (e.g.sweat,salivary,mammary)
126
Myoepithelial cells found in the ocular iris contract to do what?
Dilate the pupil
127
What are myofibroblasts?
Sites of wound healing that produce collagenous matrix but also contract (they contain actin and myosin)
128
In what processes are myofibroblasts prominent?
Wound contraction
| Tooth eruption
129
Most smooth muscles are innervated by what?
The autonomic nervous systeem
130
What are varicosities?
Enlarged regions of autonomic nerves that release neurotransmitters into a wide synaptic cleft
131
How are smooth muscle thick and thin filaments are arranged?
Diagonally within the cell spiralling down the long axis
132
How do smooth muscle cells contract?
In a twisting way
133
What do intermediate filaments of smooth muscle attach to?
Dense bodies
134
Where are dense bodies found in smooth muscle?
Throughout the sarcoplasm and occasionally anchor to the sarcolemma
135
Are calcium ions necessary for contraction of smooth muscle?
Yes
136
What is the nature of repair possible in a mature skeletal muscle?
Cells cannot divide but the tissue can regenerate by mitotic activity of satellite cells
Hyperplasia follows muscle injury
137
How does skeletal muscle undergo hypertrophy?
By satellite cells fusing with existing muscle cells to increase mass
138
What is the nature of repair possible in mature cardiac muscle?
Cardiac muscle is incapable of regeneration
139
What happens to cardiac muscle following damage?
Fibroblasts invade, divide and lay down scar tissue
140
What is the nature of repair possible in mature smooth muscle?
Smooth muscle cells retain their mitotic activity and can form new smooth muscle cells
141
Where is smooth muscles ability to form new smooth muscle cells particularly evident?
In the pregnant uterus where the muscle wall becomes thicker by hypertrophy and by hyperplasia
