Flashcards in muscle Deck (122)
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What is myalgia?
-Muscle pain
1
What is myasthenia?
-Weakness of the muscles
2
What is myocardium?
-The muscle component of the heart
3
What is myopathy?
-Any disease of the muscles
4
What is myoclonus?
-Any sudden spasm of the muscles
5
What is sarcolemma?
-The outer membrane of a muscle cell
6
What is sarcoplasm?
-Cytoplasm of muscle cells
7
What is sarcoplasmic reticulum?
-The smooth endoplasmic reticulum of muscle
8
What are two characteristics of all types of muscle?
-Contractility
-Conductivity
9
What are the three types of muscle?
-Skeletal muscle
-Smooth muscle
-Cardiac muscle
10
Which types of muscle are striated?
-Skeletal muscle
-Cardiac muscle
11
Which type of muscle is non-striated?
-Smooth muscle
12
Where are skeletal muscle cells derived from?
-Mesodermally-derived multipotent myogenic stem cells
13
How do multinucleated skeletal muscle cells develop?
-Myogenic stem cells-> myoblasts which fuse together to form primary myotube with a chain of multiple central nuclei
14
Why are skeletal muscle nuclei displaced to the periphery?
-The synthesis of actin and myosin filaments displace the nuclei
15
What are the three types of muscle fibre?
-Narrow red
-Intermediate
-Wide white
16
Which muscle fibre is small in diameter?
-Red
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Which muscle fibre has poor vasculature?
-White
18
Which muscle cell has a poor store of myoglobin?
-White
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Which muscle fibre has the most mitochondria?
-Red
20
What are the contractions like in red skeletal muscle fibres?
-Slow, repetitive, weak
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What are the contractions like in white skeletal muscle fibres?
-Fast and strong
22
How do the red and white skeletal muscle fibres fatigue?
-Red-> slowly
-White-> radiply
23
Which skeletal muscle fiber has the most neuromuscular junctions?
-White
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Give an example of where red and white skeletal muscle fibres are found
-Red-> postural muscles of the back
-White-> extraocular muscles and the fingers
25
Describe the structural organisation of muscle units from bone to myofilaments
-Bone
-Tendon
-Muscle
-Fasicle
-Muscle fibre
-Myofibrils
-Myofilaments (actin and myosin)
26
How can you tell a fascicle from a muscle fibre?
-The fibre will have multiple nuclei on its sarcolemma
27
What is epimysium?
-Connective tissue sheath which surrounds the entire muscle
28
What is perimysium?
-Connective tissue sheath which surrounds fascicles
29
What is endomysium?
-Connective tissue sheath which surrounds muscle fibres
30
What is another name for a muscle fibre?
-Muscle cell
31
What are the different anatomical arrangements of muscles?
-Circular
-Convergent
-Multipennate
-bipennate
-Unipennate
-Parallel
-Fusiform
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What is a myotendinous junction?
-Where the muscle and tendon meet
33
How is skeletal muscle arranged at a myotendinous junction?
-The fibres interdigitate with tendon collagen bundles
34
What two types of skeletal muscle are found in the tongue?
-Extrinsic and intrinsic muscles
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What are the extrinsic muscles of the tongue attached to?
-The have insertions into bone and cartilage
36
What are the functions of the extrinsic tongue muscles?
-To protrude, retract and move the tongue from side to side
37
What is the function of the intrinsic muscles of the tongue?
-Allow the tongue to change shape but not position
38
How are nuclei arranged in muscle fibres?
-In rows at the periphery of the cell
39
What structures does the perimysium contain?
-Nerves
-Blood vessels
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What structures do endomysium contain?
-Capillaries
-Nerves
41
What are myofibrils made up of?
-Myofilaments (thin actin and thick myosin)
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How are myofilaments arranged?
-In a strict banding pattern of A and I bands
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What shade is the A band of a myofibril?
-Dark
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What shade is an I band of a myofibril?
-Light
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Where is the Z line located?
-In the centre of an I band
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What is a sarcomere?
-A contractional unit from Z line to Z line
47
What myofilament(s) do the A binds contain?
-Both actin and myosin as they overlap
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What myofilament(s) do the I bands contain?
-Actin only
49
What is the H zone?
-The segment within an A band which only contains myosin
50
Where is the M line?
-In the centre of an H zone
51
What is a pneumonic for remembering these bands?
-MHAZI (M is in H in A, Z is in I)
52
Which bands decrease in size during contraction and which stay the same length?
-I and H zones get smaller
-A remains the same
53
What happens to the size of the sarcomere during contraction?
-It decreases
54
What is the structure of an actin myofilament?
-Contains actin, troponin and tropomyosin which form a helix by troponin attaching to tropomyosin which then wraps around actin
55
What can troponin be used as a marker for?
-Cardiac ischaemia
56
Describe the structure of myosin
-An individual myosin molecule has a rod-like structure from which two heads protrude
-Each thick filament is made up many myosin molecules in such a way that the 'heads' protrude in a multidirectional way
-The filaments are devoid of myosin heads in the centre of the filament (where there is no overlap)
-The heads extend towards the actin filaments
57
What is the role of calcium in muscle contraction?
-Influx of calcium into the the muscle fibril
-Binds to troponin causing a conformational change leading to dissociation from the tropomyosin, and causing tropomyosin to change position, exposing the active site of actin
-This allows the myosin head to bind to actin and contraction to begin
58
Describe the sequence of events in the sliding filament model
-Myosin head attaches to actin filament as ATP is hydrolysed
-Working stroke-> myosin head pivots and bends as it pulls on the actin filment, sliding it towards the M line
-Release of ADP and Pi
-A new ATP molecule binds to myosin causing the myosin cross-bridge to detach
-ATP hydrolysis causes the cycle to repeat
59
What is the cause of rigor mortis?
-Lack of ATP results in myosin heads staying bound to actin
60
What is a neuromuscular junction?
-The point at which an axon meets muscle containinf a small terminal swelling of the axon and a synaptic cleft
61
Describe the mechanism of innervation of muscle and excitation contraction coupling
-Nerve impulse along motor neurone arrives at neuromuscular junction
-Influx of calcium at the synaptic bulb causes the release of acetylcholine
-Acetylcholine diffuses across the synaptic cleft and fuses with nicotinic receptors located on the sarcolemma of the muscle causing depolarisation
-This cause voltage-gated Na+ to open, causing the action potential to enter
-Action potential (depolarisation) spreads along sarcolemma down T tubules and to two sarcoplasmic reticulum
-This causes the opening of voltage gated calcium channels at the terminal cisternae of the two adjacent sarcolasmic reticulum; calcium is released into the sarcoplasm
-Resulting in the sliding filament model
62
What happens to the calcium after the action poteltial is complete?
-Returned to the sarcoplasmic reticulum by active transport
63
What is the triad in skeletal muscle contraction?
-One T tubule causes calcium release from two sarcoplasmic reticulum
64
Describe the histology of cardiac muscle in longitudial section
-Striations
-Centrally positioned nuclei(one or two per cell)
-Intercalated discs
-Branching
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Why does cardiac muscle contain intercalated discs?
-For electrical and mechanical coupling with adjacent cells
66
Describe cardiac muscle in transverse section
-Centrally positioned nuclei
-Endomysium bearing rich supply of capillaries
-Some lobular profiles which represent branching
67
Are myofibrils arranged in bands in cardiac muscle?
-Yes however myofilaments of actin and myosin form continuous masses in cytoplasm
68
What other structures are present in the cytoplasm of cardiac muscle?
-Mitochondria
-Sarcoplasmic reticulum
69
How are intercalated discs associated with Z lines?
-Intercalated discs lay over the Z lines (Z lines become obscured in LM)
70
Why does cardiac muscle contain many gap junctions?
-For electrical coupling
71
What is the function of adherens-type junctions in cardiac muscle?
-To anchor the cells and provide anchorage for actin filaments
72
Where in skeletal muscle are the T tubules located?
-At the A I band junction
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Where do T tubules lie within cardiac muscle?
-At the points of intercalated discs and Z lines
74
What is meant by cardiac muscle having a diad not a triad?
-One T tubule serves on sarcoplasmic reticulum
75
How does muscle contraction occur in cardiac muscle?
-Same as skeletal muscle except electrical impulse is generated from the heart itself
76
Where are purkinje fibre located?
-Ventricle walls
77
-What generates the action potential in the heart and how does this travel to the ventricles?
-SAN generates
-Passes to AVN into ventricles
78
What is the function of the purkinje fibres?
-Transmit the action potential from the AVN to the ventricles to allow rapid conduction enabling ventricles to contract in a synchronous manner
79
Describe the characteristics of the purkinje fibres
-Large cells
-Abundant glycogen
-Sparse myofilaments
-Extensive gap junctions
80
Describe the histology of smooth muscles
-Spindle-shaped (fusiform)
-Have a central nucleus
-Non striated, no sarcomeres, no T tubules
81
What is the mechanism of contraction of smooth muscle? (simply)
-Actin-myosin interactions
82
How do contractions of smooth muscle differ from cardiac and skeletal contractions?
-Slower
-More sustained
-Require less ATP
83
Which of the muscle types is capable of being stretched?
-Smooth
84
What generic stimuli cause smooth muscle to contract?
-Nerves (ach)
-Hormones
-Drugs
85
What conformation do lots of smooth muscle cells make?
-Sheets
-Bundles
-Layers
86
-Where is smooth muscle most frequently located?
-The contractile walls of passageways or cavities
eg vascular structures, the GI, respiratory and genitourinary tract
87
When can smooth muscle become clinically significant?
-High bp
-Dysmenorrhoea
-Asthma
-Atherosclerosis
-Abnormal gut mobility
88
What are myofibroblast cells?
-Specialised smooth muscle cells involved in wound healing which produce a collagenous matrix but also contract the wound
89
What are myoepithelia?
-Specialised smooth muscle cells known as satellite cells which form a basketwork around the secretory units of some exocrine glands to help secretion via contraction eg sweat, salivary, mammory and iris
90
Outline the contraction of smooth muscle
-Thick and thin myofilaments are arrananged diagonally within a cell, spiralling down the long axis
-Smooth muscle contracts in a twisting way
-Requires Ca2+ (binds to CaM, binds to MLCK, phosphorylates myosin-> sliding filament model)
-Intermediate filaments attach to dense bodies in the sarcoplasm
91
Describe the nature of repair of skeletal muscle
-Cannot divide
-Can regenerate-> mitotic activity of satellite cells result in hyperplasia after muscle injury
-Satellite cells fuse with existing muscle to increase muscle mass
92
Describe the nature of repair of cardiac muscle
-Not capable of regeneration
-Following damage fibroblasts invade, divide and lay down scar tissue
93
Describe the nature of smooth muscle repair
-Retain mitotic activity and form new smooth muscle cells
-Evident in pregnant uterus which undergoes hypertrophy and hyperplasia
94
Describe the process of skeletal muscle remodelling
-The contractile proteins actin and myosin can increase/decrease in number
-This is known as remodelling and is a continual process
-All the myofilaments can be replaced within two weeks
95
How does atrophy of skeletal muscle occur?
-Destruction of the myofilaments during remodelling is greater than replacement
96
How does hypertrophy of skeletal muscle occur?
-Replacement of the myofilaments during remodelling is greater than destruction
97
What is the cause of hypertrophy in skeletal muscle?
-Increased demand, ie exercise
98
What happens to skeletal muscle cells when they undergo hypertrophy?
-Increase metabolic demand
-Sarcoplasmic reticulum swelling
-Increased mitochondria
-Increased Z line width
-Increased ATPase
-Increased density of T tubules
-Increased contractile proteins
99
What are the main causes of atrophy?
-Immobility, age, denervation
100
How long after denervation does re-innervation need to occur for full use?
-3 months
101
What increases uptake of acetylcholine at the neuromuscular junction?
-Motor neurone is embedded into the muscle with the muscle having a highly-folded endplate to increase surface area
102
What terminates acetylcholine in the synaptic cleft?
-Acetylcholine esterase
103
What causes myasthenia gravis?
-Autoimmune destruction of the endplate ach receptors, specifically by IgG
104
What does autoimmune destruction of the achR in myasthenia gravis do to the endplate?
-Causes the loss of junctional fold resulting in widening of the synaptic cleft
105
What are the signs and symptoms of myasthenia gravis?
-Fatiguability and sudden falling
-Drooping upper eyelids (ptosis)
-Blurred vision
106
Why does sudden falling occur in myasthenia gravis?
-Muscles fail die to lack of excitation caused by the lack of AchR
107
Why are the eyes one of the first structures to be effected in myasthenia gravis?
-Have a low amount of muscle and therefore are effected easier
108
Why do the symptoms in myasthenia gravis fluctuate?
-Based on general state of health
109
What are the treatment options for myasthenia gravis?
-Acetylcholinesterase inhibitors (pyridostigmine)
-Immune suppressants
-Plasmapheresis
-Thymectomy
110
How can acetylcholinesterase inhibitors treat myasthenia gravis?
-Ach not as quickly broken down so it can stimulate muscles for longer
111
How can plasmapheresis treat myasthenia gravis?
-Removal of specific IgG from serum
112
How can a thymectomy treat myasthenia gravis?
-Thymus is producing abnormal lymphocytes, removal will stop production
113
How does botulism disrupt the neuromuscular junctions?
-Reduces acetylcholine release and thus decreases excitation of muscles
114
How does organophosphate poisoning disrupt neuromuscular junctions?
-Decreased production of acetylcholinesterases; ach stays active for longer; overexcitation of muscles
115
What type of disorder is muscular dystrophy?
-Genetic
116
How is muscular dystrophy characterised?
-By progressive muscle weakness and wasting
117
What is the cause of muscular dystrophy?
-Complete absence of the protein dystrophin (protein for stength) causing the muscles to tear apart upon contraction
118
What is the consequences of muscle fibres tearing?
-Muscle wastage
-The enzyme creatine phosphokinase is liberated into the serum causing calcium to enter the cell resulting in necrosis
-Pseudohypertrophy (swelling) occurs before fat and connective tissue replace muscle fibres
119
Outline the pathophysiology of malignant hyperthermia
-Large quantities of calcium released from sarcoplasmic reticulum of skeletal muscle due to altered calcium channel gated kinetics so ca2+ is not taken back up into SR
-Causes hypermetabolic state
-Sustained Ca2+ elevation allows excessive stimulation of glycolytic metabolism
-Causes respiratory and metabolic acidosis
-Causes rigidity due to all muscles contracting at once
-High heat generation due to hypermetabolic state
120
What type of disease and what are triggering agents of malignant hyperthermia?
-Inherited disease
-Anaesthetic gases
121
