Lecture 12 Flashcards
Three main types of muscle
Skeletal
Cardiac
Smooth
Structure of skeletal muscle
Long, cylindrical, multinucleate cells with obvious striations
Function of skeletal muscles
- voluntary movement
- locomotion
- manipulation of the environment
- facial expression
- voluntary control
Image of skeltatal muscle
Location of skeletal muscles
Attached to bones or occasionally skin
Gross anatomy of skeletal muscle. In order - siums
- epimysium
- endomysium
- perimysium
- fascicles
What is epimysium
Connective tissue sheathing the muscle
What is endomysium
Protecting individual muscle fibres
What is perimysium
Sheaths bundles of muscle fibres
What are fascicles
Bundles of muscle fibres
How many motor neurons per muscle fiber?
1
What is in between the motor neuron and the muscle fibre
Neuromuscular junction
What is the sacrolemma?
Cell membrane of muscle fibre
What a transverse T-tubule?
Invagination of sacrolemma into cell
What is the sarcoplasmic reticulum
Store and release Ca2+
Myofibrils are made up of individual units called…
Sarcomeres
Different lines of the sarcomere
What causes muscle contraction
Thin and tick filaments attaching to eachother
On the enedtron microphraph picture what do the different colours represent
Different degrees of overlapping in different areas
Make sure you know:
- what the thick and thin filaments are made up from
- what the different striation colour signifies and how it will change during muscle contraction
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
Main components of the thick filament
Myosin
- main protein of thick filament, elongated with distinctive head
- head binds and “walks” along thin filament
Sarcamere zones will be an essay question
Different sacromere zones
What is in the I band?
Just thin filament
What is in the H-zone
Just thick filament
What is the A-band
Anywhere where there is thick filament
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
In the relaxed state what is the state of the actin binding sites
- binding sites of actin to myosin covered by tropomyosin
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)
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
Use of ATP in contraction of the myofilaments
Smaller
Same
Smaller
Smaller
A I H zones during sarcomere contraction
- size of filaments dont change, just the degree of overlap
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
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
What are the sytmptoms of nemaline myopathy?
- muscle weakness, swelling dysfunction, impaired speech
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
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
Structure of cardiac muscle
Branching, striated, generally uninuclueared cells that interdigitate at specailised junctions (intercalated discs)
Function of cardiac muscle structure
- as it contracts, it propels blood into the circulation
- in voluntary control
Location of cardiac muscle
Walls of the heart
Image of cardiac muscle
What joins the muscle cells together
Intecollated discs
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
What do desmosomes do?
Anchor cells to eachother via cytoskeleton
What do facia adherens do?
Anchor actin filaments and transmit contractile forces
- along the Z line
What do gap junctions do
Tansmit contraction stimulus
Arrhythmogenic right ventricular cardiomyopathy is a disease of…
Desmosomes
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)
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
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
Structure of smooth muscle
- spindle-shaped cells with central nuclei
- no striations
- Cells arranged closely to form sheets
Function of smooth muscle
- propels substances or objects along internal passages
- involuntary control
Location of smooth muscle
- mostly in the walls of hallow organs
Image of smooth muscle
- collagen in between to allow for contraction and expansion
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
How smooth muscle contraction occurs
Ran out of time to make proper cue card
50 minutes in lecture 11
Contractile filaments in their contracted and unconrtacted states
