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Flashcards in Muscle physiology Deck (31)
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1

What are the subdivisions of a muscle

Muscle - fascicles (bundles of muscle fibres) - fibres/cell - Myofibril (cylindrical element) - sarcomere - (end to end chain of repeating units) - Myofilaments - both thin and thick filaments

2

What is the Z-band

The length of one sarcomere

3

What happens to the Z band during contraction

Decreases in length

4

What is anchored to the Z line

Actin

5

What is the I band

Region of non overlapped actin - distance decreases during contraction

6

What is the A band

Length of the myosin filaments - remains the same during contraction - appears as a dark band

7

What is the H zone

Region of non overlapped myosin filaments
Distance decreases during muscle contraction

8

What is the M line

Bare zone

9

What is the role of titin

Anchored to the Z line and attached to myosin
Positions the myosin halfway between the z discs
Acts like a spring and prevents over contraction

10

What is the role of nebulin

Dictates the length of the actin filament
+ end of actin capped to prevent depolymerisation

11

What is the role of CapZ and alpha actinin

Make up the Z disc that actin is anchored to

12

What is the role of Tropomodulin

Caps the actin filament -end

13

What is a motor unit

The motor neuron and the muscle fibres it innervates - one neuron will innervate several fibres

14

How is fine control of contraction achieved

Comes from motor units that only innervate a small number of muscle fibres

15

What is the benefit of having more motor units

More of a graded contraction - known as spatial summation

16

What type of receptor is found at the neuromuscular junction

nAchRs - ligand gated ion channels

17

What is the skeletal muscle action potential similar to

Same as neuronal action potential
Short duration
Very negative resting potential

18

What channels lead to fast activation of the AP

Sodium channels

19

What can be said about the K channels that are open at rest and the ones that open to mediate repolarisation

They are different channels - slow activation of the K channels open at rest

20

What is the structure of the nAchR

Pentameric structure
2 alpha subunits
1 beta
1 gamma
1 delta

21

How many transmembrane domains does it have

4

22

How many Ach molecules need to bind before the receptor opens

2 - binding sites lie between the alpha and gamma subunits

23

What is Myasthenia Gravis

Most common neuromuscular junction disorder
Inappropriate antibodies to AchRs on the postsynaptic membrane
Igs bind to channel proteins and stop Ach binding
Weakness, tiredness, fatal if respiratory failure occurs

24

What is the effect of acetylcholinesterase inhibitors for MG treatment

Enhances Ach levels in the synaptic cleft
Prolongs Ach availability - allows more time for binding to receptors that are still functioning

25

What is the effect of corticosteroids for MG

Immunosuppressant - reduction of antibody levels - cyclosporin - reduce number for Ach

26

What is the effect of Immunoglobulins for MG

Antibody binds to injected Igs rather than AchR

27

What is the effect of plasmapheresis on MG

Filtration of the plasma - quick removal of antibodies

28

What is the effect of thymectomy on MG

Removal of thymus gland - removes ability of patients to secrete antibodies

29

What is a triad used in postsynaptic calcium handling

Consists of sarcoplasmic reticulum cisternae on either side of a t-tubule

30

What is the importance of T-tubules in muscle fibres

Create invaginations in the membrane so the action potentials run deeper within the membrane
Calcium influx is therefore close to the myosin and actin