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BMS235 Physiology and pharmacology > Muscle physiology > Flashcards

Muscle physiology Flashcards

1
Q

What are the subdivisions of a muscle

A

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

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2
Q

What is the Z-band

A

The length of one sarcomere

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3
Q

What happens to the Z band during contraction

A

Decreases in length

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4
Q

What is anchored to the Z line

A

Actin

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5
Q

What is the I band

A

Region of non overlapped actin - distance decreases during contraction

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6
Q

What is the A band

A

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

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7
Q

What is the H zone

A

Region of non overlapped myosin filaments

Distance decreases during muscle contraction

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8
Q

What is the M line

A

Bare zone

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9
Q

What is the role of titin

A

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

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10
Q

What is the role of nebulin

A

Dictates the length of the actin filament

+ end of actin capped to prevent depolymerisation

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11
Q

What is the role of CapZ and alpha actinin

A

Make up the Z disc that actin is anchored to

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12
Q

What is the role of Tropomodulin

A

Caps the actin filament -end

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13
Q

What is a motor unit

A

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

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14
Q

How is fine control of contraction achieved

A

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

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15
Q

What is the benefit of having more motor units

A

More of a graded contraction - known as spatial summation

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16
Q

What type of receptor is found at the neuromuscular junction

A

nAchRs - ligand gated ion channels

17
Q

What is the skeletal muscle action potential similar to

A

Same as neuronal action potential
Short duration
Very negative resting potential

18
Q

What channels lead to fast activation of the AP

A

Sodium channels

19
Q

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

A

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

20
Q

What is the structure of the nAchR

A 
Pentameric structure 
2 alpha subunits
1 beta
1 gamma 
1 delta
21
Q

How many transmembrane domains does it have

A

4

22
Q

How many Ach molecules need to bind before the receptor opens

A

2 - binding sites lie between the alpha and gamma subunits

23
Q

What is Myasthenia Gravis

A

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
Q

What is the effect of acetylcholinesterase inhibitors for MG treatment

A

Enhances Ach levels in the synaptic cleft

Prolongs Ach availability - allows more time for binding to receptors that are still functioning

25
Q

What is the effect of corticosteroids for MG

A

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

26
Q

What is the effect of Immunoglobulins for MG

A

Antibody binds to injected Igs rather than AchR

27
Q

What is the effect of plasmapheresis on MG

A

Filtration of the plasma - quick removal of antibodies

28
Q

What is the effect of thymectomy on MG

A

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

29
Q

What is a triad used in postsynaptic calcium handling

A

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

30
Q

What is the importance of T-tubules in muscle fibres

A

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

31
Q

What is the role of v gated Ca channels

A

L type channels in clusters of 4 allow calcium influx from the extracellular fluid
Ltype are mechanically coupled to ryanodine receptors - opening causes opening of ryanodine which releases of calcium stores in the sarcoplasmic reticulum
Calcium coming in feeds back to open more ryanodine receptors - Ca induced Ca release

BMS235 Physiology and pharmacology (42 decks)

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