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Flashcards in 112 - Injury To Wrist Deck (69)
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1
Q

What are the 4 steps of muscle contraction?

A
  1. Attachment of myosin head to thin filament
  2. Movement of the cross-bridge producing tension
  3. Detachment of the myosin head and thin filament
  4. Energising of the head so it can repeat the cycle
1
Q

What type of collagen is predominant in tendons?

A

Type 1 collagen

2
Q

What are the 4 sources of ATP in skeletal muscle?

A
  1. Dephosphorylation of phosphocreatine
  2. Oxidation of free fatty acids from the blood
  3. Aerobic metabolism of carbohydrates (glucose)
  4. Anaerobic metabolism of carbohydrate (glycogen stores)
2
Q

Which muscle fibres are the most resistant to fatigue?

A

Type 1 and Type 2a

3
Q

What neurotransmitter is released at the neuromuscular junction?

A

Acetylcholine

3
Q

Where is the site of most muscle strains or “pulls”?

A

The myotendinous junction

3
Q

How many polypeptide chains make up a collagen fibre?

A

3 polypeptide chains woven into a triple helix.

3
Q

What is a consequence of an Achilles’ tendon rupture?

A

There is substantial weakness in plantarflexion of the foot.

4
Q

How can muscle contractions vary in strength?

A
  • Number of motor units recruited
  • Frequency of motor unit activation changes
4
Q

What collagen type is predominant in ligaments?

A
  • Type 1 collagen
  • Small amounts of type 3 .
6
Q

What proteins make up the thin filaments of a muscle?

A
  • Actin
  • Troponin
  • Tropomysin

6
Q

What is the main function of the fibrillar collagens?

A

To provide tensile/mechanical strength to a tissue.

7
Q

Describe oxidative muscle fibres.

A
  • Contain lots of mitochondria so have high capacity for oxidative phosphorylation
  • Rich blood supply of oxygen and fuel
  • Contain large amounts of myoglobin which allows greater rates of oxygen diffusion into the cell.
8
Q

What are the main fibril-associated collagens (FACIT)?

A
  • Type 9
  • Type 12
  • Type 14
  • Type 16
  • Type 19
9
Q

Define eccentric contraction.

A

A contraction where the muscle is lengthening despite the contraction mechanism being activated

10
Q

How many heads does each myosin molecule contain, and what is their function?

A

2 heads; extend from the molecule and form cross-bridges with actin

11
Q

How does central fatigue affect muscle activity?

A

The cerebral cortex fails to send excitatory signals to the muscle, therefore the muscle will not function

The “psychological” barrier to exercise.

13
Q

What is a motor unit?

A

A single motor neurone and the muscle fibres it innervates

14
Q

Which collagen connects the basal laminae of the skin to the connective tissue underneath?

A

Type 7

15
Q

What happens to pyruvate in the muscle under intense exercise? (anaerobic respiration)

A

It is converted to lactate

16
Q

What enzyme catalyses the dephosphorylation of phosphocreatine?

A

Phosphotransferase

16
Q

Define isotonic contraction.

A

Where the muscle shortens while the load on the muscle remains constant

18
Q

During muscle contraction which zones/bands of the sarcomere become shorter?

A
  • H zone
  • I band
19
Q

Why are type 1 fibres referred to as red muscle fibres?

A

They contain a large amount of myoglobin

19
Q

How are collagen molecules assembled into fibres?

A

In a quarter staggered arrangement

21
Q

What type of receptor does ACh bind to on the motor end plate?

A

Nicotinic receptor

22
Q

What ion initiates the binding of the cross-bridges between actin and myosin and where does it come from?

A

Ca2+; from the sacroplasmic reticulum when an action potential is conducted down the T-tubules from the motor end

plate

22
Q

Besides type 1 collagen, what other types of collagen are present in tendons?

A
  • Type 3
  • Type 5
24
Q

What is a motor neurone pool?

A

All the motor units that completely supply 1 muscle

25
Q

What are the main fibrillar collagens?

A
  • Type 1
  • Type 2
  • Type 3
  • Type 5
  • Type 11
26
Q

What is the function of elastin within the tendon?

A
  • Provides elastic properties to the tendon
  • Stores energy during movement
27
Q

What is the motor end plate?

A

The part of the muscle fibre that is directly under the terminal portion of its axon

28
Q

What physical sign develops when there is chronic partial denervation of a muscle?

A

Fasciculations in the affected muscle are seen

29
Q

The side chains of which amino acids covalently link to strengthen the collagen fibril?

A
  • Lysine
  • Hydroxylysine
30
Q

What can cause chronic partial denervation of a muscle?

A

Poliomyelitis - destroys motor neurones

Motor neurone disease

31
Q

What is the function of a retinaculum?

A

It is a band of fibrous tissue that holds tendons in place, usually near a joint to prevent bowstringing.

32
Q

What happens to the tendon in “wrap-around” regions?

A
  • The tendon develops fibrocartilage, with significantly higher proteoglycan content than the tendon
  • This develops to resist the compressive forces placed on the tendon by the bone.
32
Q

What happens to tendons due to exercise?

A
  • Increase in collagen fibril size
  • Increased strength
  • Increased stiffness
33
Q

What are the 3 types of muscle fibre?

A
  1. Type 1
  2. Type 2a
  3. Type 2b
34
Q

What are the functions of a ligament?

A
  • Provide muscle attachment
  • Proprioception
  • Hold down soft tissue
  • Prevent over-stretching due to rich nerve supply
  • Hold bones together and limit movements between bones.
35
Q

Which collagen is the found in the majority of basement membranes?

A

Type 4 collagen

36
Q

What stabilises the structure of the collagen triple helix?

A

H-bonds between each molecule

37
Q

Define isometric contraction.

A

When a muscle develops tension but does not shorten or lengthen

38
Q

Where are the cell bodies found for lower and upper motor neurones?

A
  • Lower motor neurones = spinal cord
  • Upper motor neurones = cerebral cortex (motor area)
39
Q

What are the functions of proteoglycans in tendons?

A

They regulate the size of the collagen fibrils

They bind water to resist compression

40
Q

What is the enthesis?

A

It is a specialised area of fibrocartilage where the tendon inserts into the bone.

41
Q

How is the myotendinous junction adapted for the transfer of power from the muscle to the tendon?

A

The tendon digitates into the muscle, which provides a greater surface area for force transfer

43
Q

Where does Ca2+ bind in order to move tropomyosin from the myosin binding site on actin

A

It binds to troponin

45
Q

Where is ATP utilised in the cross-bridge cycle of muscle contraction?

A

It is used to energise the myosin head after it has dissociated from the thin filament

47
Q

How is Ca2+ removed from the sarcoplasm after a muscle contraction?

A

It is actively pumped back into the sacroplasmic reticulum

48
Q

What is a muscle cramp?

A
  • A painful, strong contraction caused by ischaemia or metabolic disturbances
  • Abnormally high numbers of AP are fired from the motor nerve during a cramp.
50
Q

Define recruitment.

A

The process of increasing the number of motor units that are active in a muscle at any given time.

51
Q

What happens to muscle during low intensity, long duration training?

A
  • Increase in mitochondria
  • Increased number of capillaries surrounding muscle fibres.
52
Q

What are the 4 main macromolecules found in the ECM

A
  1. Collagen
  2. Proteoglycan
  3. Glycoproteins
  4. Elastin
54
Q

Which muscle fibres type is referred to as slow twitch, and what is the cause for the “slowness”?

A

Type 1; it contains myosin that has a slower maximal rate at which it can hydrolyse ATP, therefore limiting the rate of cross-bridge formation.

55
Q

Which muscle protein is present in the thick filaments under microscopy?

A

Myosin

56
Q

What makes up 55% of the wet tendon weight?

A

Water

57
Q

Name an inhibitor of the nicotinic receptor on the motor end plate.

A

Curare; used for poison arrowheads

58
Q

What is the function of the enthesis?

A

It dissipates the compressive forces of the tendon reducing the risk of wear and tear injuries.

59
Q

What process is caused by the fall in ATP concentration in cells following death leading to stiff muscles.

A

Rigor mortis

60
Q

How does tropomyosin regulate muscle contraction?

A

When there is no need to contract there is very little Ca2+ present in the sarcoplasm.

In this situation, tropomyosin occludes the myosin-binding site on the actin molecule.

When Ca is present, the tropomyosin changes shape and this site becomes free

61
Q

What factors can cause peripheral fatigue of a muscle?

A
  • Contraction failure; APs not propagated along fibre
  • Lactic acid build up; H interferes with muscle proteins
  • ATP hydrolysis producing more H
  • Build up of ADP & Pi inhibiting cross-bridge formation
62
Q

How are the collagen fibres arranged within a ligament, and how does arranged assist in the ligament’s function?

A

The collagen is wound in a spiral which prevents rotation of the ligament in either direction.

64
Q

What happens to muscle in short duration, high intensity training?

A
  • There is hypertrophy of fast-glycolytic fibres
  • Increased synthesis of glycolytic enzymes
65
Q

What are the functions of tendons?

A
  • Allows muscle belly to be far from site of action
  • Eliminates the need for long muscle bellies and provides focus
  • Can change direction of muscle pull
  • Acts as a spring
  • Holds other tendons in place
66
Q

What type of contraction is most associated with muscle strains?

A

Eccentric muscle contractions

67
Q

What is the order of recruitment of muscle fibres?

A
  • 1st; slow oxidative fibres (type 1)
  • 2nd; fast oxidative (Type 2a)
  • 3rd; fast glycolytic (Type 2b)
68
Q

Define glycolytic fibres.

A
  • Few mitochondria, but high levels of glycolytic enzymes and glycogen
  • Relatively poor blood supply
  • Contain little myoglobin so termed white fibres
  • Type 2b
69
Q

What protein is attached to the ends of the myosin molecule and provide elasticity to the muscle?

A

The elastic protein titin