Lecture 12 Flashcards
(66 cards)
1
Q
Three main types of muscle
A
Skeletal
Cardiac
Smooth
2
Q
Structure of skeletal muscle
A
Long, cylindrical, multinucleate cells with obvious striations
3
Q
Function of skeletal muscles
A
- voluntary movement
- locomotion
- manipulation of the environment
- facial expression
- voluntary control
4
Q
Image of skeltatal muscle
A
5
Q
Location of skeletal muscles
A
Attached to bones or occasionally skin
6
Q
Gross anatomy of skeletal muscle. In order - siums
A
- epimysium
- endomysium
- perimysium
- fascicles
7
Q
What is epimysium
A
Connective tissue sheathing the muscle
8
Q
What is endomysium
A
Protecting individual muscle fibres
9
Q
What is perimysium
A
Sheaths bundles of muscle fibres
10
Q
What are fascicles
A
Bundles of muscle fibres
11
Q
A
12
Q
How many motor neurons per muscle fiber?
A
1
13
Q
What is in between the motor neuron and the muscle fibre
A
Neuromuscular junction
14
Q
What is the sacrolemma?
A
Cell membrane of muscle fibre
15
Q
What a transverse T-tubule?
A
Invagination of sacrolemma into cell
16
Q
What is the sarcoplasmic reticulum
A
Store and release Ca2+
17
Q
A
18
Q
A
19
Q
A
20
Q
Myofibrils are made up of individual units called…
A
Sarcomeres
21
Q
Different lines of the sarcomere
A
22
Q
What causes muscle contraction
A
Thin and tick filaments attaching to eachother
23
Q
On the enedtron microphraph picture what do the different colours represent
A
Different degrees of overlapping in different areas
24
Q
Make sure you know:
A
- what the thick and thin filaments are made up from
- what the different striation colour signifies and how it will change during muscle contraction
25
Main components of the thin filament
Actin
- contains binding sites for thick filament
Tropomyosin
- protein strand that covers binding sites in relaxed state
Troponin
- sits on tropomyosin and responds to signals for contraction
26
Main components of the thick filament
Myosin
- main protein of thick filament, elongated with distinctive head
- head binds and “walks” along thin filament
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Sarcamere zones will be an essay question
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Different sacromere zones
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What is in the I band?
Just thin filament
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What is in the H-zone
Just thick filament
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What is the A-band
Anywhere where there is thick filament
32
What happens when an AP comes down the motor neuron
-Acetylcholine is released into the synaptic cleft
-Acetylcholine choline binds to ion channels in the post synaptic cleft which causes depolarisation of the muscle cell plasma membrane
- this sends an action potential along the sacrolemma
- T-tubes allow the AP to penetrate into the muscle
- it then causes calcium to be released by the sacroplasmic reticulum
- calcium can then interact with the sacromeres which make up the myofibrils
33
In the relaxed state what is the state of the actin binding sites
- binding sites of actin to myosin covered by tropomyosin
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State Actin binding site in the excited state and why
- binding of Ca2+ to troponin causes movement of tropomyosin exposing binding sites
- myosin (thick filament) binds to actin (thin filament)
35
Process of sarcomeere contraction - after head has bound
- myosin head changes shape and pulls thin filament to centre of sarcomere
- ATP binds to myosin and energy is utilized to detach myosin, reverting shape
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Use of ATP in contraction of the myofilaments
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Smaller
Same
Smaller
Smaller
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A I H zones during sarcomere contraction
- size of filaments dont change, just the degree of overlap
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Molecular basis of muscle contraction
- the ca2+ released from the sarcoplsmic reticulum when the muscle fibre is excised binds to the protein troponin
- the binding enables the troponin protein complex to “pull tropomyosin aside” so that it no longer covers the active sites on actin
- the heads of myosin molecules bind to the now exposed active sites on actin
- swing movement of myosin head pulls thin filament inwards
- head is detached andshape reverted if bound to ATP
40
Why do animals show rigour morris?
- Ca2+ leaks from sarcoplasmic reticulum into muscle fibres following death, exposing actin binding sites
- myosin automatically binds and pulls thin filament (no ATP required)
- new molecules of ATP needed for the unbinding of myosin and actin are not produced
- thus myosin remains attached to actin and the contracted muscles do not relax
41
What are the sytmptoms of nemaline myopathy?
- muscle weakness, swelling dysfunction, impaired speech
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What causes nemaline myopathy?
Mutations in at least 10 different genes
- NED (~50% of cases) - nebulin - governs length of thin filament
- ACTA1 (15-25% of cases) - actin isoform making up thin filament
43
Cardiac muscle features
- continuous rhythmic activity
- inherent mechanisms of activation that can be modulated by external autonomic and hormonal stimuli
- structurally intermediate to skeltetal and smooth muscle
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Structure of cardiac muscle
Branching, striated, generally uninuclueared cells that interdigitate at specailised junctions (intercalated discs)
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Function of cardiac muscle structure
- as it contracts, it propels blood into the circulation
- in voluntary control
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Location of cardiac muscle
Walls of the heart
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Image of cardiac muscle
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What joins the muscle cells together
Intecollated discs
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50
3 types of intercollated discs and what they do
Desmosomes: anchor cells to eachother via the cytoskeleton
Fascia adherens: anchor actin filaments and transmit contractile forces
Gap junctions: transmit contraction stimulus
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What do desmosomes do?
Anchor cells to eachother via cytoskeleton
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What do facia adherens do?
Anchor actin filaments and transmit contractile forces
- along the Z line
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What do gap junctions do
Tansmit contraction stimulus
54
Arrhythmogenic right ventricular cardiomyopathy is a disease of…
Desmosomes
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Arrhythmogenic right ventricular cardiomyopathy features
- cardiac muscles die and are replaced by fatty infiltration
- irregular heart beat - arrhythmia
- leads to heart attacks in otherwise healthy individuals
- genes for desmosomes proteins explains the prevelance (1:5000)
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Desmosomes of someone with arrhythmogenic right ventricular cardiomyopathy
- fewer desmosomes, those that are present, fragmented, different lengths of
- intracellular gap widening and distruption
- cell death
- widening of gap junction may contribute to arrythmogenicity
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Features of smooth muscle
- muscular component of visceral tissue e.g blood vessels, GI
- under inherent automatic and hormonal control - involuntary
- continuous contractions of slow force
- often whole muscle contracting in a wave like fashion
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Structure of smooth muscle
- spindle-shaped cells with central nuclei
- no striations
- Cells arranged closely to form sheets
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Function of smooth muscle
- propels substances or objects along internal passages
- involuntary control
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Location of smooth muscle
- mostly in the walls of hallow organs
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Image of smooth muscle
- collagen in between to allow for contraction and expansion
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Smooth muscle contraction - contractile filaments - where are the anchored
- contractile filaments cross-cross the cell
- anchored to cell at focal densities (D) in cytoplasm and focal adhesion densities (J) on cell membrane
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How smooth muscle contraction occurs
Ran out of time to make proper cue card
50 minutes in lecture 11
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Contractile filaments in their contracted and unconrtacted states
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