Structure of Muscle part 2 Flashcards
What is the sarcoplasm?
Muscle cell cytoplasm
What is the sarcolemma?
Muscle cell membrane
What are the characteristics of the sarcolemma?
- excitable
- motor end plate
- T-tubule (transverse tubules)
What are the motor end plates of the sarcolemma?
Contact surface with axon terminal
What are T-tubules?
Extension of sarcolemma into the sarcoplasm
- ‘holes’ into the cytoplasm
What does the structure of the T-tubules allow?
Allows the depolarising signal (for contraction) to conduct deep into the muscle fibre.
What is the sarcoplasmic reticulum?
Specialised form of the endoplasmic reticulum that surrounds the myofibrils
What are cisternae?
Areas of the endoplasmic reticulum dedicated to Ca2+ storage
What is a triad?
Structure within the skeletal muscle consisting of the T-tubule and cisternae
What is a myofibril?
Bundle of myofilaments surrounded by cisternae
(slide 4)
How far does a myofibril extend?
Same as mucle fibre, one end of muscle to the other
What is a sarcomere?
Repetitive, contractile units of the muscle fiber in the myofibril
What is a Z line in a sarcomere?
Zigzag line that marks end of each sarcomere
What is a M line in a sarcomere?
Middle of sarcomere
What surrounds both sides of the M line?
- thick and thin filaments
- thin filaments (and titin)
(slide 5)
What is the zone of overlap in a sarcomere?
Overlap of thick and thin filaments
What is the H band?
Has thick filaments either side of the M line, bisecting A band
What is the A band?
Area containing thick and thin filaments on both sides of the M line
What is the I band?
Area containing thin filaments (and titin) bisected by the Z line
What do thick filaments within the sarcomere consist of?
Many myosin molecules per filament
- golf club shape
- long tail topped by a head
- head forms cross-bridges with the thin filament
What are the 2 conformations of myosin?
- low energy conformation (flexed/bent)
- high energy conformation (entended)
How does the myosin go from low to high energy conformation?
ATP attaches to the head of myosin
What do thin filaments within the sarcomere consist of?
3 different proteins:
- actin - G actin ball containing myosin-binding site
- tropomyosin - string covering myosin-binding site
- troponin - complex attached to actin
What is the actin protein in a thin filament?
Binds to myosin heads
What is the tropomyosin protein in a thin filament?
Long, fibrous molecule (string)
- blocks interaction between actin and myosin when relaxed, by lying directly on the myosin-binding site
What is the troponin protein in a thin filament?
- binds reversibly to Ca
- moves tropomyosin away from the actin active site
