What are the two types of muscle contraction and how do they differ?
Isotonic – tension stays the same and length changes
Isometric – tension changes and length remains the same
What are the two subtypes of one of the types of muscle contraction?
Isotonic =
Concentric - shortening
Eccentric - lengthening
What is the Z-line made up of?
Alpha-actinin
CapZ
What are the two types of receptors involved in excitation-contraction coupling of skeletal muscle?
Dihydropyridine receptor
Ryanodine receptor
Describe the process of excitation-contraction coupling of skeletal muscle.
- An action potential propagates along a T tubule and reaches the Dihydropyridine receptor
- Depolarisation causes a conformational change in the DHPR allowing it to make contact with the Ryanodine Receptor on the sarcoplasmic reticulum
- RyR opens causing Ca2+ release from the SR
- This triggers the muscle contraction
What are the different components of a sarcomere?
Z-line Actin filaments CapZ and Tropomodulin Nebulin Titin Myosin Tropomyosin
What is the structure of actin?
Two twisted alpha helices
What does Titin do?
It holds the myosin in place
It is very large
Where are CapZ and Tropomodulin found?
At the ends of the actin filaments
What is the relationship between tension and load in isotonic and isometric contraction?
Isotonic – Tension > load
Isometric – Tension = load
What specialised structure links adjacent cardiomyocytes?
Intercalated Discs
What junctions are present in these structures?
- Desmosomes (holds membrane structures together)
- Gap Junctions (allows electrical communication between cells)
Which receptors are involved in excitation-contraction coupling of cardiac muscle?
Voltage Gated Calcium Channels
Ryanodine Receptors
Describe the process of excitation-contraction coupling of cardiac muscle.
- Action Potential propagates down T-tubules and leads to the opening of VGCCs
- This leads to influx of Ca2+
- Ca2+ then binds to the RyR making them open leading to Ca2+ release from the SR and a further increase in intracellular Ca2+
(Calcium Induced Calcium Release)
Describe the process of excitation-contraction coupling of smooth muscle
- Action potential reaches the VGCC and makes it open leading to Ca2+ influx
- Ca2+ binds to Calmodulin forming a Ca2+-CaM complex
- This complex activates myosin light chain kinase
- MLCK phosphorylates myosin light chains and leads to smooth muscle contraction
how do myofibrils and myofibrils relate?
myofibres are bundles of myofibril cells
describe myofibres?
myofibres are large, cylindrical, multinucleate and packed with myofibrils
what does the sarcoplasmic reticulum contain?
- cellular store of Ca2+ that will be released in order to cause contraction
what is the sliding filament theory ?
- presence of Ca2+ causes movement of troponin from tropomyosin which reveals the myosin binding site on the surface of the actin chains
- the charged myosin heads bind to the exposed binding sites on the actin, (ADP molecules released)
- The ADP discharge causes the myosin head to pivot in a Powerstroke pulling the actin filament towards the center of the sarcomere
- Then ATP binds to the myosin head and is hydrolyzed meaning the myosin head is released and recharged
what are features of cardiomyocytes?
- striated muscle cells
- linked by intercalated discs
- contains numerous gap junctions
- the gap junctions allow the action potentials to spread rapidly between cells
