Sarcomere Structure Flashcards
What are the 3 layers that separate Muscles and what is contained in each of them?
Endomysium - separates muscle fibres
Perimysium - lies between fascicles/fasciculi
Epimysium - dense sheath on surface of bundles of fascicles
What are the 3 components of muscles?
Muscle fibre (cell) -> Fascicle -> muscle
Where is force from muscles transmitted to?
The force is transmitted from muscles through tendons to the bone
What are the 3 components of a muscle fibre cell and their function?
Sarcolemma - true cell membrane that encloses the muscle fibre
Sarcoplasm - intracellular fluid that fills spaces between myofibrils
Myofibril - mainly composed of acting and myosin filaments
Where does the nuclei of a muscle fibre cell sit?
On the outside on top of the sarcolemma
What is the sarcomere?
The portion of myofibril that lies between two Z-disks
Draw and label the structure of a sarcomere?
How do you recognise the A band under a microscope?
Its quite dark
What band is split half by the ends of 2 different sarcomeres? And what colour is this band?
I band
Light
What is in the H-zone?
The very middle of the Sacromere
What disks define the end of the sarcomere?
the 2 Z-disks
What is a myofibril?
The name for the individual rod like strand of muscle tissue/cell which all bundle together to form a fasicle
What is the M line?
The M line runs down the middle of the sarcromere and in the middle of the A band
What is the purple partin the sarcromere?
Thin actin filament
What is the dark proportion of the myofibril?
Thick myosin filament
How does Myosin attach to Actin?
Via its cross bridges which have actin binding sites
What does the myosin tails made from?
two intertwined heavy chains
What are the 2 binding sites found on Myosin fillaments?
Actin binding sites and ATP binding sites
What do cross bridges do?
Attach to Actin and move their chains
What filaments are thick and what ones are thin?
Myosin filaments are thick
Actin filaments are thin
Give 2 features of Actin?
Actin is a contractile protein
Each G actin has a binding site for myosin
What 2 other molecules are found in actin filaments?
Tropomyosin and Troponin
What is the function of Tropomyosin?
Tropomyosin is a regulatory protein which overlaps the binding sites on actin for myosin, so it inhibits interation with myosin when Tropomyosin is in its relaxed state
What is the function of Troponin?
Troponin is a regulatory calcium binding protein which forms a complex with the other proteins of the thin filament (Actin. and Tropomyosin)
Troponin binds to calcium and once its bound it changes conformation to pull tropomyosin away from the myosin interaction sites which regulates skeletal muscle contraction because it moves tropomysin away allowing the myosin to bind to actin.
What protein attaches to keep myosin and actin in place together?
Titin
Where does Titin attach to?
The Z-line
What is the function of Titin?
To provide elasticity and stabilise myosin
What is the role of Nebulin?
Nebulin helps align actin
What are the 4 stuctural proteins?
Titin
Z line protein (alpha-actinin)
M-line proteins (myomesin, M-protein)
Nebulin
What are the 4 contractile proteins, which are involved in contraction and movement of filaments?
Actin
Myosin
Tropomyosin
Troponin complex
What is responsible for giving skeletal and cardiac muscles their striated appearance?
The thick and thin arrangement in Myofibrils
Draw the what a Myofibril looks like and 3 different cross sections of where thick, thin and mixed filaments would occur
What would you expect to see in cross sections of the I band, H zone, M line and the outer edge of the A band?
What kind of structures would you expect to see in an A-band?
Primarily myosin filaments in the region of overlap
What kind of structures would you expect to see in an I-band?
Actin filaments bisected by Z-line
What kind of structures would you expect to see in the H-zone?
Region of A-band which contains only myosin filaments
What occurs when a muscle goes from being relaxed to contracted?
The myosin and actin filaments move closer together and overlap more
H zone and the I band both shorten
What are T-tubules and their function?
T-tubules are invagination of the sarcolemma of skeletal and cardiac muscle
- Action potential is propagated from the end plate along the surface of the muscle fibre (sarcolemma)
- Action potential is propagated into the fibre down the T-tubule membrane
- Depolarisation of the T-tubule membrane is ‘signalled’ to the membrane of the terminal cisternae
Draw how the T-tubules, Sarcoplamic reticulum and terminal cisternae interact with myofibrils?
What is the Sarcoplasmic reticulum and its function?
Its the same as the endoplasmic reticulum found in most cells (contains tubules for sorting and transporting things)
Calcium is stored and release from here following membrane excitation
How do T-tubules and Sarcoplasmic reticulum interact?
They are connection with junctions made from 2 intergral proteins, one in the T-tubules membrane and one in the Sarcoplasmic reticulum
The T-tubule protein is a modified voltage-sensitive calcium channel called dihydropyridine receptor (DHP) which acts as a voltage sensor
The Sarcoplasmic reticulumprotein is called ryanodien receptor (RYR) which forms a calcium channel
How does T-tubules transport the action potentials?
T-tubule brings action potentials into the interior of the muscle fibre
Where is calcium stored in the muscle?
In the Sacroplasmic reticulum
