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Flashcards in Skeletal muscle innervation Deck (31)
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1

What is the skeletal muscle fibre Em?

-90mV

2

Where are T tubule invaginations in skeletal muscle?

Boundary between A and I bands

3

What neurones innervate skeletal muscle?

Somatic motor neurones

4

What is the function/advantage of T-tubules?

Spread the impulse so it can interact with the cells more rapidly

5

What does the T-tubule membrane lie adjacent to?

Pair of terminal SR cisternae forming a triad

6

Describe ECC in skeletal muscle?

Depolarisation T tubule membrane opens L type channel

LTCC adjacent (mechanically coupled) to RyR in SR membrane

Conformational change in LTCC transmitted to RyR, opens and release Ca2+ from SR

7

Is influx of Ca2+ (CICR) required for opening of RyR channel ?

No, contributes but not essential

8

How are LTCC and RyR spatially related?

Mechanically coupled - contact between SR and T-tubule

9

What does Ca2+ do after release from SR?

Bind to troponin C, causing conformational change

(TnI moves away from actin and TnT displaces tropomyosin)

Reveals binding sites for myosin on actin - disinhibition by Ca2+

10

Are all Ca2+ binding sites on TpC saturated in skeletal muscle?

Yes

11

How do T tubules compare in cardiac muscle to skeletal muscle?

Bigger and wider

12

Describre the process of cross bridge cycling?

ATP binds myosin head -myosin disengages

ATP hydrolysed by myosin head which causes pivot

Head forms cross bridge with actin monomer further along sarcomere

Pi release from myosin changes conformation, head swivels - power stroke

ADP released and cycle complete.

13

What triggers relaxation?

Ca2+ detaches from TpnC and goes into SR via SERCA or out of cell (Ca2+ ATPase or NCX)

14

What happens in rigor mortis?

Muscles in attached state but no more ATP to trigger disengagement so skeletal muscle stiff

15

3 ways to regulate active tension?

Selective recruitment of greater/smaller number of motor units

Changes in frequency of stimulation

Starting length of relaxed muscle

16

What does Ca2+ bind to inside SR so more calcium can move in?

Calsequestrin and calreticulin

17

What is the relationship between active tension and length in skeletal muscle?

Biphasic

18

What effect does increasing/decreasing sarcomere length from normal have on tension, how come?

Fewer cross bridges formed, tension decreases, force generated decreases

19

What is isometric contraction?

Tension generated by fibre without changing length

20

What is isotonic contraction?

Muscle contracts against constant load and shortens

21

What produces more tension isometric or isotonic contraction?

Isometric

22

What is meant by graded muscle response?

Normal contraction modified by nervous input to produce varying amounts of force

23

What is meant by frequency summation?

Increasing stimulation frequency

Less time between APs for Ca2+ uptake by SERCA to initiate relaxation

2nd depol reaches muscle when muscle not relaxed

Tension generated is combination of tension present in muscle and second contraction so summation of force generated

24

What is meant by tetanus?

No relaxtion, not enough time to recapture Ca2+ so continuous contraction (but depol doesn't generate any more tension)

25

Describe why twitches are separate at low AP frequency?

2nd depol occurs when muscle has relaxed and recovered (i.e. first twitch has ended)

26

What is a motor unit?

Alpha nerve and all the muscle fibres that it innervates

27

What do smaller motor units allow?

Finer control

28

What is meant by larger motor unit?

Single motor neurone supplies large number of fibres in muscle

29

How can activation of different types of motor units cause differences in tension?

Smaller motor units activate to generate smaller degree of tension

When more strength needed, larger motor units enlisted to activate larger muscle fibres

30

What is meant by recruitment?

Increasing activation or motor units to increase contraction (i.e. activate larger motor units)