Muscles - Contraction Flashcards
Outline smooth muscle contraction
1- Ca2+ binds to calmodulin
2- Ca2+-calmodulin complex activates MLCK
3- MLCK phosphorylates myosin light chain
4- MLC interacts with actin
5- contraction occurs
6- Ca2+ levels drop
7- MLCP dephosphorylates MLC
8- contraction stops
What is a kranocyte?
Connective tissue cell that sits on top of synaptic cleft
What is myasthenia gravis?
Autoimmune condition
Autoantibodies block ACh receptor at neuromuscular junction
Reduced synaptic transmission
Muscle weakeness
What makes up the troponin complex and their function?
TnI - connects troponin complex to actin
TnC - calcium binding site
TnT - tropomyosin binding site
Outline the events before skeletal muscle contraction
1- AP arrives at neuromuscular function
2- ACh released
3- VGNC open + influx of Na+
4- depolarisation spread across sarcolemma + down T tubules
5- Ca2+ released into sacroplasm
6- Ca2+ binds to TnC subunit on troponin
7- conformational change exposes actin-myosin bindings sites to allow for contraction
Outline skeletal muscle contraction (sliding filament model)
1- myosin heads bind to actin molecules
2- ATP binds to myosin head
3- myosin head uncouples from actin
4- ATP hydrolysis»_space; myosin head bends
5- myosin head binds to actin
6- Pi released > power stroke
7- ATP binds to myosin head > detachment from actin
Compare and contrast the repair in different types of muscles
Skeletal muscle - cannot divide
- regenerate through satellite cells
Cardiac muscle - cannot regenerate
- scar tissue forms
Smooth muscle - retain their mitotic activity
- can form new muscle cells
Roles of muscles in movement
- agonists - prime movers
- antagonists - oppose prime movers
- synergists - assist prime movers
- neutralisers - prevent unwanted actions
- fixators - act to hold body part immobile whilst another body is moving
Describe first class levers
Example
‘See saw’
L F E
e.g. flexion/extension of head
Describe second class levers
Example
‘Wheelbarrow’
F L E
e.g. planar flexion of foot
Describe third class levers
Examples
‘Fishing rod’
L E F
e.g. bicep curls
What is muscle tone regulated by?
Motor neuron activity
Muscle elasticity
Use
Gravity
Outline the mechanism of muscle hypertrophy
Overstretching
A and I bands can no longer re-engage
New muscle fibrils are produced
New sacromeres added in middle of existing sarcomeres
What is the mechanism of muscle atrophy?
Disuse
Surgery
Disease
Loss of protein
Reduced fibre diameter
Loss of muscle power
Outline Duchene muscular dystrophy
What does it cause?
- X linked recessive
- mutation of dystrophin gene
- allows for excess Ca2+ to enter muscle > Ca2+ taken up by mitochondria > H2O follows > muscle cell bursts > release of creatine kinase + myoglobin > Rhabdomyolysis
Define muscle tone
Tension in a muscle at rest
Define muscle strength
The muscle’s ability to contract and create force in response to resistance
What is the difference in Ca2+ binding in cardiac vs smooth muscle contraction?
Cardiac: bind to troponin C
Smooth muscle: binds to calmodulin
What does a person with Duchene muscular dystrophy look like?
- sway back
- belly sticks out
- shoulders + arms held back awkwardly
- poor balance ‘clumsy’
- foot from
- thin weak thighs + butt muscles
What structure in defective in myasthenic syndrome
Synaptic boutons
Outline organophosphate poisoning
- inactivate Ach esterase at neuromuscular junction
- results in continuous stimulation of skeletal muscles, uncoordinated contraction > coma + death if not treated
What is malignant hypothermia caused by?
Mutation in RyR1 receptor
What are muscarinic symptoms of organophosphate poisoning?
SLUDGE
- Salivation
- Lacrimation
- Urination
- Defecation
- GI cramping
- Emesis - vomiting
What are nicotinic symptoms of organophosphate poisoning?
MTWTF
- Muscle cramps
- Tachycardia
- Weakness
- Twitching
- Fasciculations
