Muscle Contraction Flashcards
Slow twitch fibres
- contract slower
- less powerful contractions
- contract over longer periods of time
Eg: long distance running
Adaptations of slow twitch fibres
- large store of myoglobin ( stores oxygen)
- good blood supply
- lots of mitochondria
Fast twitch fibres
- contract faster
- more powerful contraction
- only work for short period of time
Eg: weightlifting
Adaptations of fast twitch fibres
- thicker = more powerful contractions
- more myosin filaments
- high conc of glycogen
- high conc of enzymes involved in anaerobic respiration
- contains phoshphocreatine = generates ATP from ADPin anaerobic conditions
How many proteins make up muscle myofibrils + muscle Fibre
2
Actin + myosin
Actin
- thin filament
- light coloured
- 2 strands twisted together
Myosin
- thicker filament
- dark coloured
- rod shaped fibres with bulbous heads on side
What are myofibrils
- cylindrical organelles that run along length of muscle fibres
- site of muscle contraction
( make up muscle fibres)
What are muscle fibres
- long specialised cells
- made of myofibrils
- share nucleus + sarcoplasm (cytoplasm)
What is a sarcolemma
- the shared membrane of muscle fibres
What is the sarcoplasmic reticulum
- organelle In shared cytoplasm (sarcoplasm)
- store of Ca2+ ions
What is the sarcoplasm
- shared cytoplasm around circumference of muscle fibres
- share nuclei + mitochondrial
What are sarcomeres
- units that make up myofibrils
- made up of myofilaments (actin)
What is a H band
- only thick myosin
- dark
What is a I band
- only thin actin
- light
What is a A band
Contains areas of both:
1- only myosin
2- myosin + actin overlap
What is the M line
- middle of sacromere
- where Actin filaments overlap with myosin
What is muscle contraction
- Myofilaments sliding past one another
What is sliding filament theory
How muscle contraction is coordinated in myofibrils
What is the z line
- end of a sacromere
Sliding filament theory
- depolarisation of sarcolemma by arriving action potential
-depolarisation causes myosin + actin filaments to slide past each other= sarcomeres contract - as many sarcomeres contract simultaneously = muscle fibres contract = whole muscle contracts
-sarcomeres relax + filaments slide back as muscle relaxes
What does myosin and actin have that allows muscle contraction
Myosin= bulbous heads
Actin= binding site
Allows filaments to bind together + movement of head allows filaments to slide past each other
How many binding sites do myosin heads have and what do they bind to
2
- actin
- ATP
What is tropomyosin
- protein located on actin filaments
- blocks Actin-Myosin binding site when at rest
- when muscle stimulated = protein moves revealing binding site
3 ways to make ATP rapidly
1- oxidative phosphorylation in aerobic respiration
2- glycolysis in anaerobic respiration
3- phosphocreatine = store of phosphate
- donates phosphate to ADP to form ATP = anaerobic but no lactate
- during periods of low muscular activity ATP can give back phosphate = phosphocreatine
Steps of muscle contraction
1- depolarisation of sarcolemma from arriving action potential
2- Sarcoplasmic reticulum release Ca2+ ions into sarcoplasm = tropomyosin changes shape revealing actin B sites
3- myosin head binds to actin
4- ATP hydrolysed to ADP = energy released cause myosin head to bend
5- filament “slide” past
Forming a New Cross bridge
- Myosin head bends back to original position
- Myosin forms cross bridge with binding site further along actin filament
Steps in halting muscle contraction
- No action potentials = sarcoplasm reticulum stops Ca2+ release
- Tropomyosin changes shape blocking actin binding site = myosin heads can no longer bind
-filaments return to resting position
Comparison between neuromuscular junction + synapse
Similarities
- neurotransmitters
- sodium potassium pump to maintain resting potential
Differences:
Neuromuscular:
- only excitatory
- only motor neurones
- neurotransmitter binds to membrane of muscle fibre (sarcolemma)
Synapse:
- inhibitory or excitatory
- can be any neurones
- neurotransmitter binds to post-synaptic neurone
What molecule binds to myosin head causing it to detach from actin
ATP
Why do slow twitch fibres need good blood supply and fast twitch fibres a high glycogen conc
1- slow twitch respire aerobically = need good O2 supply
2- fast twitch respite anaerobically at high intensity= need immediate energy source
3- slow twitch are low intensity = they have time for glucose to be supplied via blood/ don’t need their own store
Role of ATP hydrolyse
- activated by Ca2+ ions
- ATP to ADP + P
- for energy for muscle contraction
