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BRS Y1 > Week 6- Muscle Microstructure & Contraction > Flashcards

Week 6- Muscle Microstructure & Contraction Flashcards

1
Q

What are the 3 types of muscle?

A

Smooth muscle
Cardiac muscle
Skeletal muscle

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2
Q

What type of control is associated with smooth muscle?

A

Involuntary control

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3
Q

What branch of the nervous system controls smooth muscle?

A

Autonomic nervous system

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4
Q

What type of control is associated with cardiac muscle?

A

Contracts autonomously

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5
Q

What branch of the nervous system controls cardiac muscle?

A

Influenced by the autonomic nervous system and circulating chemicals

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6
Q

What type of control is associated with skeletal muscle?

A

Voluntary control

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7
Q

What is the purpose of skeletal muscles?

A

To cause movement by contracting (they are attached to bone)

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8
Q

Where is smooth muscle found?

A

In the walls of airways

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9
Q

What are some different arrangements of muscle fibers?

A 
Parallel- all fibers in same direction
Fusiform- large bulge of fibers in the middle
Triangular-fibers form a triangle
Multipennate
Bipennate
Unipennate
Pennate- offset at an angle
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10
Q

What is the significance of having different arrangements of muscle fibers?

A

Where the ligament is attached, the direction of the muscle fibers etc has an impact on the movement. The different orientations of fibers effects the tension in the muscle

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11
Q

Describe the structure of muscles from macroscopic to microscopic

A

Muscle, fascicles, myofibre, myofibril, myofilaments (actin and myosin)

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12
Q

What are fascicles?

A

Bundles of muscle fibers

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13
Q

What surrounds muscle fiber?

A

Endomysium

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14
Q

What is compartment syndrome? How is this significant in connective tissue?

A

When blood leaks into a compartment
Connective tissue is very rigid and doesnt allow expansion so if it happens in connective tissue can be very very painful and cause death of the tissue

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15
Q

What surrounds fascicles?

A

Perimysium

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16
Q

What cells give rise to myocytes?

A

Myoblasts

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17
Q

What is special about the nucleation of muscle?

A

It is multinucleated

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18
Q

What is the plasma membrane that covers myofibres called?

A

Sarcolemma

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19
Q

What is the network of fluid filled structures called in muscles?

A

Sarcoplasmic reticulum

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20
Q

What is the rough size of a myofibril?

A

1-2 micrometer

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21
Q

What are the 2 main proteins that make up a myofibril?

A

Actin and myosin

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22
Q

Out of actin and myosin which is the thin filament and which is the thick filament?

A

Actin-thin

Myosin- thick

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23
Q

What is the repeating unit of a muscle called?

A

Sarcomere

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24
Q

What muscle types are striated?

A

Cardiac and skeletal

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25
Q

What separates z discs?

A

Dense protein

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26
Q

What letter represents dark bands?

A

A band

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27
Q

What letter represents light bands?

A

I band (actin thin)

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28
Q

Where is the m line in a sarcomere found?

A

In the middle of 2 z discs

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29
Q

What structures mark the boundaries of a sarcomere?

A

2 adjacent z discs

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30
Q

What is actin attached to?

A

The z disc

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31
Q

Describe the structure of myosin

A

Has 2 globular heads
Single tail formed by 2 alpha helices
Tails of several hundred molecules form one filament

32
Q

Describe the structure of actin

A

Actin molecules are twisted into a helix
Each molecule has a myosin binding site
Contain troponin and tropomyosin

33
Q

On actin what molecule cover myosin binding sites

A

Troponin

34
Q

What happens to the H, A and I bands during contraction?

A 
H= narrowed or disappeared
A= stayed the same
I= becomes shorter
35
Q

What filament is pulled during contraction?

A

Actin is pulled by myosin, z plates move closer together

36
Q

How is muscle contraction initiated?

A

Lower motor neurone sends down a signal into the musculoskeletal synapse

Action potential opens voltage gated Ca2+ channels

Calcium enters presynaptic terminal

Vesicles fuse w membrane and Ach is released

Ach binds to postsynaptic receptors

Local currents are set up

Ach is brocken down and contraction stops

37
Q

What breaks down acetylcholine?

A

Acetylcholinesterase

38
Q

What happens in the muscle fiber once action potential is set up on the sarcolemma to cause release of calcium?

A

AP goes down t tubules

At edge of t tubules are receptors ( DHP receptor and ryanodine receptor which is connected to calcium)

Activation of receptors cause calcium to be released from the sarcoplasmic reticulum

39
Q

What are the names of the 2 receptors found at the end of t tubules? What do they do?

A

DHP receptor
Ryanodine receptor

They trigger the release of calcium from the sarcoplasmic reticulum

40
Q

How does calcium cause muscle contraction?

A

Calcium binds to troponin

Tropomyosin moves, exposing myosin binding site

Crossbridges on the actin filment form due to myosin binding to actin

The binding and discharge of ADP causes the myosin head to pivot (power stroke) pulling the actin fiber to the center of the sarcomere

ATP binding releases the myosin head from the actin chain

41
Q

What does calcium bind to on an actin fiber?

A

Troponin

42
Q

What causes the myosin head to pivot (ie cause a power stroke)

A

The binding and discharge of ADP

43
Q

What molecule is required to release the myosin head from actin after a power stroke?

A

ATP

44
Q

What recharges the myosin head after a power stroke?

A

ATP hydrolysis

45
Q

Which protein does the pulling in muscle contraction?

A

Myosin

46
Q

Where are upper motor neurones located?

A

In the primary motor cortex of the brain (sits in front of the central sulcus)

47
Q

Where are lower motor neurones located?

A

Brainstem or spinal chords

48
Q

Define a motor unit

A

A single motor neuron together with all the muscle fibers it innervates

49
Q

What does the stimulation of one motor unit cause?

A

The contraction of all muscle fibers in that unit

50
Q

How many neurons can innervate a muscle fiber?

A

Only one!!!

51
Q

On average, how many muscle fibers are innervated by one motor neuron?

A

600

52
Q

What causes us to have more dextrous control over a muscle?

A

Motor neurons innervating fewer muscle fibers

53
Q

What is an innervation ratio?

A

The number of muscle fibers controlled by a motor neurone

54
Q

What are the 3 types of motor units?

A

Slow (S- type I)
Fast, fatigue resistant (FR- type IIA)
Fast, fatiguable (FF-type IIB)

55
Q

Describe the cell body diameter, dendritic trees, axons and conduction velocity of slow motor units

A

Small cell body diameter
Small dendritic trees
Thinnest axons
Slowest conduction velocity

56
Q

Describe the cell body diameter, dendritic trees, axons and conduction velocity of FR and FF motor units

A

Larger cell body diameter
Larger dendritic trees
Thicker axons
Faster conduction velocity

57
Q

How does myoglobin content differ in slow, FR, FF motor units

A

Slow: high
FR: high
FF: low

58
Q

How does colour differ in S, FR, FF motor units?

A

S: red
FR: pink
FF: white

59
Q

How does aerobic capacity differ in S, FR, FF motor units?

A

S: high
FR: moderate
FF: low

60
Q

How does anaerobic capacity differ in S, FR and FF motor units?

A

S: low
FR: high
FF: high

61
Q

Out of S, FR and FF motor units, which one has the lowest tension generated?

A

S

62
Q

What are the 2 ways the brain regulates muscle force?

A

Recruitment and rate coding

63
Q

Describe recruitment as a method of regulating muscle force by the brain

A

Motor units are not randomly recruited, there is and order
Smaller units are recruited first (slow twitch units)
As more force is needed, more units are recruited allowing fine control under which low level force is needed

64
Q

Describe rate coding as a method of regulating muscle force by the brain

A

Motor units can fire at a range of frequencies, slow units fore at lower frequencies
As firing rate increases, force produced by the unit increases
Summation is when units fire at a frequency that is too high to allow muscles to relax between action potentials

65
Q

What is summation (in reference to motor units)

A

When during rate coding motor units fire at a frequency thats too high to allow muscles to relax between action potentials

66
Q

What is it called when a muscle wastes away?

A

Atrophy

67
Q

What are motor unit and fibre characteristics dependant on?

A

The nerve which innervates them

68
Q

What effects do neurons have on the muscle they innervate?

A

Its characteristics eg how fast it contracts and with what force

69
Q

What are the 3 types of muscle contraction?

A

Concentric
Eccentric
Isometric

70
Q

What is concentric muscle contraction?

A

When a load is overcome and the muscle is shorten (with the load being pulled towards you)

71
Q

What is isometric muscle contraction?

A

When a muscle is contracting and attempting to pull a load towards the body but is unable to and the load stays in the same place

72
Q

What is eccentric muscle contraction?

A

When force is generated but the muscle gets longer eg someone places a heavy book in your hand and you dont let it fall but it stretches your hand

73
Q

Out of eccentric and concentric muscle contraction, which can generate more force?

A

Eccentric

74
Q

What motor units/muscle fibres can undergo a change in properties?

A

FF to FR is most common

75
Q

What can rarely cause a change from slow to fast muscle fibres?

A

Severe deconditioning
Spinal chord injury
Microgravity during space flight

76
Q

What motor units does ageing cause a loss of?

A

Slow and fast but preferentially fast

BRS Y1 (52 decks)

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