Muscle Contraction Flashcards
What causes Myasthenia gravis?
It is autoimmune and it is caused by defects in signalling from nerve to muscle at neuromuscular junctions
What is contraction ?
The ability of a muscle to actively shorten and develop tension
What is skeletal muscle attached to?
Bone via a tendon
What makes up muscle ?
Muscle Fasciculus Fibre/Cell Myofibril Sarcomere Filaments
What are the thick and thin filaments ?
Thick - myosin
Thin - actin
When are H bands and I bands at maximum width?
In a relaxed muscle
What disappears in a fully contracted muscle ?
The H zone
What remains unchanged during muscle contraction and relaxation ?
A band width
What are T tubules important for ?
Spread of the AP across the membrane
What is stored in the sarcoplasmic reticulum ?
Calcium ions
Where do ATP and actin bind to myosin ?
At the double head
How could you describe the actin filament ?
Double stranded F-actin molecules comprising polymerised G-actin molecules
What regulatory protein is on the actin filament ?
Tropomyosin
What regulatory proteins lies on the tropomyosin ?
Troponin
Why is troponin important ?
This is where calcium binds enabling the muscle to contract
What happens when there is low Ca++ in the cell?
Tropomyosin blocks access to the myosin binding site of actin
What happens when troponin binds to Ca++?
There is a structural change which allows myosin to access its binding site on actin
What does the hydrolysis of ATP produce ?
ADP and Pi
What is released and what forms when myosin head attaches to myosin-binding site on actin?
Phosphate is released
Cross-bridge forms and myosin head pivots from 90-45
In the sliding filament hypothesis what causes actin to slide past myosin?
After the release of ADP, the cross-bridge generates force which causes actin to slide past myosin
What causes the cross bridge to detach ?
When another ATP is bound
What is the optimal length of a sarcomere ?
2.1-2.2 microns
Why are sarcomere usually at optimal length in the body ?
Tendon attachment
What happens at the neuromuscular junction?
Nerve and muscle cells are meeting and that incites that excitation which generates the high calcium conditions
What does acetylene choline bind to and what does this cause?
Nicotinic receptor
Opens receptor-operated channels, inward current produces local depolarisation (a graded potential)
How does the local currents depolarise the muscle membrane ?
Influx of Na+ ions
Where does the AP flow?
Via the T-tubules
What senses the T tubules during muscle contraction ?
Dihydropyridine receptors (L-type channels)
What do L-type channels trigger?
Ca++ release channels on sarcoplasmic reticulum to open and realise Ca++ init sarcoplasm
The channels are called ryanodine receptors
What happens during Rigor Mortis?
Ca++ leak out after death of the SR into the cell enabling actin-myosin binding however no ATP is synthesise and therefore cross-bridges cannot detach
What does the total force produced by single muscle fibre depend on?
The rate of muscle fibre stimulation by motor nerve
What does 2 close APs cause ?
Wave summation
What do a number of APs that are relatively close together cause?
Unfused tetanus
What do a number of APs that are very very close together cause?
Fused tetanus
What is an isotonic contraction ?
Constant tension
Change in length
What are the two types of isotonic contractions ?
Concentric - muscle shortens
Eccentric - muscle lengthens
What is an isometric contraction ?
Constant length
Produces tension
What are the 3 types of skeletal muscle fibres ?
Type I - slow
Type IIA - fast
Type IIB - fast
Describe slow twitch type I muscle fibre.
- postural muscle of back
- slow, sustained contractions required
- oxidative metabolism
- many mitochondria
- red - myoglobin
- resist fatigue
Describe fast twitch type IIA muscle fibre.
- soleus in calf
- fast contraction
- oxidative metabolism
- many mitochondria
- red-pink myoglobin
- intermediate fatigue resistance
Describe fast twitch type IIB muscle fibre.
- extraocular muscle
- rapid contractions
- anaerobic glycolysis
- few mitochondria
- white - little myoglobin
- high glycogen content
What are the two types of smooth muscle ?
Single unit smooth muscle
Multi unit smooth muscle
What are T-tubules called in smooth muscle ?
Caveolae
What does Ca++ bind to in smooth muscle contraction ?
Calmodulin
What type of muscle doesn’t have spontaneous activity ?
Skeletal muscle
What muscle has MLCK?
Smooth muscle
List the types of muscles from fastest and slowest contraction speed.
Skeletal
Cardiac
Smooth
Where can CA++ be found in Cardiac and smooth muscle ?
SR and ECF
