Flashcards in Skeletal Muscle 2 Deck (29)
How muscle of muscle is muscle fibres?
What are some features of skeletal muscle fibres?
long and cylindrical
10-100micro metres diameter
sacroplasm is 75% water
striated and multinucleated
fibres do not interconnect
What surrounds entire muscle
What surrounds fasicles
What surround muscle cell/fibre
What is beneath the endomysium?
sacrolemma, the cell membrane of the cell.
What does the sarcolemma have and what does this do?
Invaginations called t-tubules that allow for the rapid propagation of AP throughout the entire muscle cell. THis allows for 'localised contraction'
What is the function of the Sarcoplasmic reticulum?
Acts as an function reservoir of Calcium. Releases calcium which affects contractile proteins (sarcomere) and initiates contraction
Why is the location of the sarcoplasmic reticulum important?
It needs to be positioned atop of the muscle fibre in order for the released calcium to be quick and at an ample level for the contractile proteins
How does the SR control calcium re-uptake?
It has calcium ATPase pumps within its membrane that are constantly bringing calcium back into the SR
What are 'terminal cisternae'?
Terminal enlargements of the SR. Terminal cisternae interface with t-tubule, giving a 'triad'
What is the purpose of a triad?
Synchronised excitation-contraction coupling
What is the relationship between DHPRs and RyRs?
voltage sensor DHPR of the t-tubules are activated by the depolarisation of the AP. These communicate with the 'feet' of the RyRs channels (that extend from the membrane of the sarcoplasmic reticulum to the cytoplasm), initiating the release of Calcium
What structurally makes up a RyRs release channel
Four monomers of RyRs
What causes the delay between nerve AP and Muscle AP
Neuromuscular transmission. The neurotransmitter has to be released and diffuse across the synaptic cleft. This causes a delay, and therefore a slit offset between the two APs
refers to the time between a stimulus to the motor nerve and the subsequent contraction of the innervated muscle. This delay is caused by the time taken for nerve AP to propagate, time chemical transmission at the neuromuscular junction, then the subsequent steps in excitation-contraction coupling. This usually takes about 10ms
Role of Calcium
1) to bind to TnC causing a conformational change in the troponin complex, exposing the myosin binding site.
Role of ATP
1) ATP binds to the myosin head, breaking the link between myosin and actin
2) The ATPase activity of ATP provides the energy for the movement of the cycle.
protein of the troponin complex, binds actin and therefore INHIBITS the myosin head from binding to the myosin binding site on actin.
Protein of the troponin complex, co-operatively binds four calcium molecules. This must occur for contraction to be initiated.
Protein of the troponin complex that holds TnT TnC and TnI against the tropomyosin (Tm) molecule
Purpose of Nebulin
Holds the actin together so they dont fall apart during contraction.
Purpose of titin?
Adjustible molecular spring. Anchors the thick (myosin) filaments to the z-disk. Unlike the thin filaments, these are not already tethered.
What makes up a 'thin filament'?
Globular actin (G-actin ) are tethered together to form an alpha helix called F-actin. two F-actin molecules run together, and tropomyosin (Tm) runs with each F-actin.
What band does the thin filaments make up?
What makes up a 'thick filament'?
100's of myosin molecules, each with two paired myosin heads with ATPase activity. Heads are offset 1/3 of the way to ensure contact with actin right around the thick filaments. the heads are staggered.The tails of the thick filaments point towards and anchor onto the M-line
Bare zone of thick filaments is?
Zone in the middle of NO myosin heads, only tails
What aspect of the sarcomere changes with contraction
The I band as the thick and thin filaments overlaps more and more with contraction