Module 16 - Muscle I Flashcards
Types of muscle
- Skeletal
- Striated
- Smooth
The sarcomere: the 5 main parts of an overlap
Z(wischen) line: the gap between two Z lines is a sarcomere
M(ittele) line: contains myomesin and it marks the centre of the sarcomere
H(ell) zone: the (light) area between the M line and Z disc - contains only the myosin (no thick-thin overlap)
A band: length of an entire thick filament (includes some thick-thin overlap)
I band: where there is no thin-thick overlap (actin present only)
Myosins: what are they, what is their structure, what types of muscle myosins are there, and what is a key feature of myosin heads?
Highly diverse family of motor proteins powered by ATP hydrolysis
Hexamer with two essential chains, two regulatory chains, and two main chains which form an alpha-helical tail with two heads for actin binding
Muscle myosin is myosin class II - 9 different kinds in muscle types (8 skeletal/cardiac, 1 smooth)
Myosin head has ATPase activity
Actin: what does it do, what types are there, and how is either type formed?
Slide over myosin heads during muscle contraction, causing shortening of sarcomeres
G-actin: globular, assembles to form F-actin - this is the general actin form
F-actin: filamentous, linear polymer of G-actins - this is formed by AT/nucleotide hydrolysis
Troponin
Troponin C - interacts with calcium (allows for cross-bridge formation)
Troponin I - interacts with actin (inhibits cross-bridge formation)
Troponin T - interacts with tropomyosin
Tropomyosin
Controls muscle contraction and relaxation, interacts with troponin T
The role of Calcium in muscle contraction
When muscle contraction is signalled, Ca²⁺ concentration increases
Ca²⁺ bind to troponin C, triggering a conformational change of troponin and tropomyosin
The troponin complex shifts up, and the tropomyosin moves deeper into the actin groove revealing the myosin binding sites on the actin, allowing cross-bridge formation
Nerve cells to muscles
- Acetylcholine released by motor neurone
- Activates nACh receptors
- Sarcolemma depolarised, action potential triggered and spreads to T tubules
- DHP receptor activated. Triggers ryanodine receptor
- Calcium ions released from the sarcoplasmic reticulum
- Troponin C binds Ca²⁺ and is activated
- Muscle contraction initiated
- Calcium ions pumped back into SR
Parts of muscle fibres: F, E, P, E, T, T, T
Fascicle - A bundle of muscle fibres
Endomysium - the layer of connective tissue covering muscle fibres
Perimysium - cover fascicles
Epimysium - surround and cover the perimysium
T tubules - lead from sarcolemma into the interior of the muscle fibre (allows for greater signal transduction)
Triad - Regulates excitation-contraction coupling
Terminal cisterna - interact with T-tubules to form triads
Contraction limits
Too much or too little contraction is bad (force of contraction goes down) - ideal is around 1.1-1.2 micrometres
SERCA: what is it, what does it do?
Sarcoplasmic endoplasmic reticulum calcium ATPase
Transports calcium into the sarcoplasmic reticulum using ATP
Dihydropyridine receptor
Can be used to trigger muscle contraction as it is an L-type calcium channel (needs support, however) and simultaneously activates the ryanodine receptor
Ryanodine receptor
Allow for a larger, internal calcium supply to be accessed within the sarcoplasmic reticulum
As the DHP receptor is activated, it undergoes a conformational change which opens the Ryamodine receptor
DHP receptor tetrad
4 DHPr’s interact with one Ryanodine receptor
Titin
Largest protein in the human genome, the third most abundant
Keeps the shape and elasticity of muscle
