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Flashcards in Skeletal Muscle 2 Deck (29):
1

How muscle of muscle is muscle fibres?

Around 75-90%

2

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

3

What surrounds entire muscle

Epimysium

4

What surrounds fasicles

perimysium

5

What surround muscle cell/fibre

endomysium

6

What is beneath the endomysium?

sacrolemma, the cell membrane of the cell.

7

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'

8

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

9

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

10

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

11

What are 'terminal cisternae'?

Terminal enlargements of the SR. Terminal cisternae interface with t-tubule, giving a 'triad'

12

What is the purpose of a triad?

Synchronised excitation-contraction coupling

13

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

14

What structurally makes up a RyRs release channel

Four monomers of RyRs

15

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

16

Latent Period

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

17

Role of Calcium

1) to bind to TnC causing a conformational change in the troponin complex, exposing the myosin binding site.

18

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.

19

TnI

protein of the troponin complex, binds actin and therefore INHIBITS the myosin head from binding to the myosin binding site on actin.

20

TnC

Protein of the troponin complex, co-operatively binds four calcium molecules. This must occur for contraction to be initiated.

21

TnT

Protein of the troponin complex that holds TnT TnC and TnI against the tropomyosin (Tm) molecule

22

Purpose of Nebulin

Holds the actin together so they dont fall apart during contraction.

23

Purpose of titin?

Adjustible molecular spring. Anchors the thick (myosin) filaments to the z-disk. Unlike the thin filaments, these are not already tethered.

24

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.

25

What band does the thin filaments make up?

I band

26

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

27

Bare zone of thick filaments is?

Zone in the middle of NO myosin heads, only tails

28

What aspect of the sarcomere changes with contraction

The I band as the thick and thin filaments overlaps more and more with contraction

29

What maintains calcium at a low level?

The Ca2+ pump in the longitudinal SR (SERCA), this pump has a high affinity for Calcium, and transport