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Second Year - Biomedical Sciences BS22001 > Lecture 4 - Excitation-Contraction Coupling > Flashcards

Lecture 4 - Excitation-Contraction Coupling Flashcards

1
Q

Characteristics of skeletal muscle

A

Striated, multiple nuclei and an abundance of mitochondria

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2
Q

Characteristics of a skeletal muscle cell

A

Relatively large, elongated and cylindrical in shape

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3
Q

Why are multiple mitochondria required in skeletal muscle

A

As the muscle has high energy demands

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4
Q

What are the muscle fibres formed by during embryonic development

A

Fused myoblasts

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5
Q

What are the specialised contractile elements within skeletal muscles

A

Myofibrils

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6
Q

What does each myofibril consist of

A

Thick and thin filaments

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7
Q

What protein makes up the thick filaments

A

Myosin

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8
Q

What protein makes up the thin filaments

A

Actin

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9
Q

What are the different areas a myofibril can be split into

A

A band, I band, Z line, M line and the H zone

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10
Q

What is the A band composed of

A

A stacked set of thick filaments and the thin filaments that overlap

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11
Q

In what area(s) of the myofibril are the thick filaments found

A

The A band

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12
Q

What is the lighter area within the A band known as

A

The H zone

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13
Q

What causes the lighter portion within the A band

A

It is the point where the thin filaments do not overlap with the thick

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14
Q

What holds the thick filaments together

A

A system of supporting proteins

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15
Q

The proteins that hold the thick filaments together form the

A

M line

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16
Q

What is the I band composed of

A

The portions of the thin filaments that don’t overlap with the thick filaments

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17
Q

What is the dense vertical line present in the I band called

A

The Z line

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18
Q

What is the area between two Z lines called

A

A sarcomere

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19
Q

What is the functional unit of skeletal muscle

A

The sarcomere

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20
Q

What is the Z line

A

Flat, cytoskeletal discs that connect the thin filaments

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21
Q

What is the smallest functional unit that can undergo contraction

A

A sarcomere

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22
Q

If a muscle is to grow, how does it do this

A

By adding new sarcomeres onto the ends of the myofibrils

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23
Q

What is excitation-contraction coupling

A

How the muscle converts an electrical stimulus, action potential, into a mechanical response, contraction

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24
Q

What cycle brings about contraction

A

The cross-bridge cycle

25
Q

What are the two main proteins involved in the cross bridge cycle

A

Actin and myosin

26
Q

The cross bridge interactions cause

A

The sliding filament mechanism

27
Q

Why is calcium so important

A

As it is the link between excitation and contraction

28
Q

The release of what stimulates skeletal muscle to contract

A

Acetylcholine

29
Q

Where is acetylcholine released

A

The neuromuscular junction

30
Q

What does the binding of ACh cause

A

A change in the membrane permeability which results in an action potential being fired

31
Q

What are the two important membranous structures that help to ensure conduction of the AP over the whole muscle

A

The transverse (T) tubules and the sarcoplasmic reticulum (SR)

32
Q

Within the muscle where are T tubules found

A

At the junction between the A band and the I band

33
Q

Where do the T tubules run from

A

The muscle cell membrane into the central portion on the muscle fibre

34
Q

What does the presence of an AP in the T tubules cause

A

A change in permeability of the sarcoplasmic reticulum

35
Q

What is the sarcoplasmic reticulum (SR)

A

A modified endoplasmic reticulum that consists of a fine network of interconnected membrane enclosed compartments surrounding each myofibril

36
Q

What are the sac like regions at the ends of the SR known as

A

The lateral sacs (terminal cisternae)

37
Q

What is stored within the lateral sacs

A

Ca2+

38
Q

What does the spread of an AP down a T tubule trigger

A

The release of Ca2+ from the SR (lateral sacs) into the cytosol

39
Q

What serves as Ca2+ release channels

A

Foot proteins

40
Q

What are foot proteins also known as

A

Ryanodine receptors

41
Q

WHat are the foot proteins made up of

A

Four subunits

42
Q

What is ryanodine

A

A plant chemical that holds open the calcium release channels

43
Q

What are the T tubule receptors made up of

A

Four subunits

44
Q

What is another name for T tubule receptors

A

Dihydropyridine receptors

45
Q

What effect does the drug dihydropyridine have on T tubule receptors

A

It blocks them

46
Q

What type of sensors are the dihydropyridine receptors

A

Voltage-gated

47
Q

What occurs to the ryanodine receptors when an AP is propagated down the T tubule

A

The local depolarisation causes the receptors to open

48
Q

Opening of the Ca2+ channel in direct contact with the T tubule causes what

A

The other half of the receptors that aren’t connected to the T tubule to open

49
Q

Once all the receptors are opened what happens

A

Calcium is released into the cytosol

50
Q

During the cross-brigde cycle what does the released Ca2+ cause

A

For the binding sites on actin to be exposed

51
Q

When the binding sites of actin are exposed, what does this signal the beginning of

A

The cross bridge cycle

52
Q

What is unique about the APs of cardiac muscle

A

The exhibit a prolonged positive phase accompanied by a prolonged period of contraction

53
Q

The AP of cardiac muscle has a characteristic shape due to

A

The plateau phase

54
Q

What happens during the plateau phase of a cardiac muscle AP

A

Calcium is constantly entering the muscle cells

55
Q

Where does the calcium, required for contraction, in cardiac muscle come form

A

The external environment

56
Q

What is activated to allow calcium to move from the external environment into the cardiac muscle cells

A

The activation of L-type Ca2+ channels

57
Q

What does the entry of the Ca2+ from the external environment cause

A

The release of more Ca2+ from the sarcoplasmic reticulum

58
Q

What leads to cross bridge cycling and contraction within cardiac muscle

A

Ca2+ induced Ca2+ release

59
Q

What causes variation in cross bridge activity

A

The amount of cystolic Ca2+ present

Second Year - Biomedical Sciences BS22001 (28 decks)

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