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ZA - Science for Medicine > Muscles > Flashcards

Muscles Flashcards

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1
Q

What are the two types of muscle?

A

Striated and smooth

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2
Q

What makes muscles and when?

A

By mononucleate myoblasts in utero

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3
Q

What are muscles made of?

A

Bundles of fibers wrapped in connective tissue sheathes

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4
Q

What causes striations in muscles?

A

Sacromeres

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5
Q

What repairs muscle cells after injury?

A

Satellite cells which differentiate to form new muscle fibres

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6
Q

What is hypertrophy?

A

Gain in muscle size/mass

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7
Q

What happens once an action potential is fired on a muscle?

A
  1. Ca ions released from sacroplasmic reticulum.
  2. Ca ions bind to blocking protein troponin, altering its shape
  3. Change of troponin’s shape causes removal of blcoking protein tropomyosin.
  4. This exposes actin binding sites, letting myosin filaments bind to actin and form cross bridges.
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8
Q

How does Ca ions return to the SR?

A

Using ATP

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9
Q

What is an isometric twitch?

A

Contraction with a constant length

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10
Q

What is an isotonic twitch?

A

Contraction with a shortening load

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11
Q

What does less overlap of filaments mean?

A

Less tension in muscle

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12
Q

What happens with too much overlap of filaments?

A

They start to interfere with each other

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13
Q

What happens when muscles are stretched?

A

They contract hard to compesate

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14
Q

What happens when muscles are stretched too much?

A

Contraction becomes less efficient

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15
Q

What is recruitment?

A

When load increases, more motor units are required to compensate, allowing more muscle fibres to be involved in a movement.

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16
Q

What is the order in which type of fibres are recruited/activated first?

A

Slow oxidative - Fast oxidative - Glycolytic

17
Q

What is a motor unit?

A

A motor neuron and a muscle fibre

18
Q

What is denervation atrophy?

A

Muscle wasting due to destruction of the NMJ/nerve

19
Q

What is disuse atrophy?

A

When muscle isn’t used, causing atrophy/wasting

20
Q

How does aerobic exercise cause hypertrophy?

A

Increases number of mitochondria which increases vascularisation and diameter in fibre

21
Q

How does anaerobic exercise cause hypertrophy?

A

Increase in glycolysis rate in fibre increases diameter

22
Q

What is tetanus and what causes it?

A

Extended twitches caused by summation of action potentials

23
Q

What is unfused tetanus?

A

When action potentials fire rapid enough to cause twitching, but also not fast enough to stop cell repolarising

24
Q

What is fused tetanus?

A

When cells fire action potentials so rapidly it never repolarises

25
Q

Why is tetanic tension/ tension caused by tetanus greater than normal twitch tension?

A

Because Ca ions never get a chance to be low enough to allow tropomyosin to return to a blocking stage

26
Q

What is fatigue?

A

A state caused by over muscle stimulation, stops large amounts of ATP breaking and reforming cross bridges to sustain contraction.

27
Q

How is ATP used in contractions?

A

Hydrolysis of ATP energises X bridges

ATP binds to myosin causing disassociation of bridge bound to actin, starting new cycle

ATP powers return of Ca ions to SR

28
Q

What are oxidative fibres?

A

Have more mitochondria for oxidative phosphorylation

More vascular for O2 and nutrient delivery

Fibres are red and have low diameter

29
Q

Difference between slow and fast oxidative fibres?

A

Slow - can resist fatigue

Fast - has a intermediate resistance to fatigue

30
Q

What are glycolytic fibres?

A

Few mitochindria

High supply of glycolytic enzymes and glycogen.

Lower blood supply, white and large diameter.

31
Q

Where is smooth muscle found and what is it supplied by?

A

Hollow organs

Autonomic Nervous System

32
Q

What is the action of Ca ions on smooth muscle?

A

Ca ions released from SR

Binds to calmodium which binds to myosin light chain kinase

The kinase phosphrylates myosin x bridges with ATP, allowing it to form cross bridges with actin filaments

33
Q

What causes relaxation of the smooth muscle?

A

Myosin light chain phosphotase dephosphoryates the cross bridges

34
Q

Why can contraction be held for longer in smooth muscle? Example of use?

A

Low ATP consumption rate

Useful in blood vessels which need to stay open for longer periods of time

35
Q

Sources of cytosolic Ca ions?

A

The SR which is less in smooth than skeletal muscles. SR has no tubules and is randomly arranged.

Extracellular Ca ions - through voltage gated Ca channels

ZA - Science for Medicine (19 decks)

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