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231 > Lecture 11: Excitation-Contraction Coupling and the Cross-Bridge Cycle > Flashcards

Lecture 11: Excitation-Contraction Coupling and the Cross-Bridge Cycle Flashcards

1
Q

What is the name of the connective tissue that surrounds muscle fibres?

A

endomysium

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2
Q

What is the name of the connective tissue that surrounds that fasicle?

A

perimysium

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3
Q

What is the name of the connective tissue that surrounds the muscle?

A

epimysium

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4
Q

What is the purpose of the veins and capillaries surrounding the fasicles?

A

to supply the muscle fibres with O2 and nutrients

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5
Q

What is the purpose of the nerves that surround the muscle fibres?

A

to travel from the spinal cord to the muscle cells to innervate them

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6
Q

Where is Ca2+ stored in the muscle fibres?

A

in the sarcoplasmic reticulum

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7
Q

What is the purpose of the T-tubule?

A

to conduct the depolarisation into the muscle cell

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8
Q

What is the name of the skeletal muscle membrane?

A

sarcolemma

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9
Q

Where does the sarcoplasmic reticulum sit?

A

right next to the T-tubule

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10
Q

How does the AP that is conducted along the sarcolemma get inside the muscle cell?

A

via the T-tubule which propagates it inside the cell

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11
Q

What is the purpose of the mitochondria in the muscle fibre?

A

to generate ATP to be used for muscle contraction via the cross-bridge cycle

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12
Q

How does Ca2+ get into the SR?

A

it is actively pumped from the cytosol into the SR by a Ca2+ pump which requires ATP

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13
Q

How does the action potential get propagated along the sarcolemma?

A

via the opening of voltage gated ion channels which brings it into the muscle

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14
Q

What is the voltage sensor?

A

it is the dihydropyridine receptor which senses the action potential in the T-tubule and it relays it to the Ca2+ channel through physical coupling which opens the Ca2+ channel

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15
Q

What causes the Ca2+ channel to open?

A

when the voltage sensor senses the action potential and relays it to the channel through physical coupling

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16
Q

What is the name of the voltage sensor which opens the Ca2+ channel?

A

dyhydropyridine

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17
Q

What is the name of the Ca2+ channel?

A

ryanodine receptor

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18
Q

Which direction does Ca2+ flow when the ryanodine receptors open in the membrane of the SR?

A

out of the sarcoplasmic reticulum (into the cytosol)

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19
Q

What is the name of the Ca2+ pump which pumps Ca2+ back into the SR?

A

SERCA

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20
Q

What happens to the Ca2+ once it is in the cytosol?

A

it can interact with the actin

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21
Q

What happens if the Ca2+ stay high in the cytosol for too long?

A

the muscle contract for too long and there is continued force development

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22
Q

What is heat a biproduct of?

A

muscle activity (muscle contraction)

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23
Q

Why is heat a necessary biproduct?

A

because it maintains our body temperature

24
Q

How is heat produced?

A

through processes which generate ATP and use ATP

25
Q

Give an example of where heat is generated during a muscle contraction

A

when Ca2+ is pumped back into the SR via SERCA, SERCA hydrolyses ATP to ADP and phosphate to pump Ca2+ back into the sarcoplasmic reticulum and this generates heat. The production of new ATP also produces heat

26
Q

What is is called when the body temperature increases above normal?

A

hyperthermia

27
Q

What is it called when the body temperature decreases below normal?

A

hypothermia

28
Q

What can hyperthermia cause? Why is this?

A

it can lead to nausea, vomiting, headaches, confusion and death because many processes stop working

29
Q

What causes malignant hyperthermia?

A

mutations in ryanodine receptor or the dihydropyridine receptor (DHPR)

30
Q

What is malignant hyperthermia?

A

an autosomal dominant, life-threatening disease

31
Q

What triggers malignant hyperthermia?

A

volatile anaesthetics (ones that you inhale)

32
Q

What happens during malignant hyperthermia?

A

The volatile anaesthetics interfere with the ryanodine receptor or the DHPR receptor with the mutations. These anaesthetics increase the function of these voltage sensors or Ca2+ channels causing a massive increase in the amount of Ca2+ released through the receptors. This excessive Ca2+ released from the SR store, there is muscle rigidity, spontaneous muscle contractions which leads to hyper-metabolic state because the Ca2+ has to be pumped back into the SR which uses ATP (which requires ATP production) which causes lots of heat

33
Q

In the autoimmune disease myasthenia gravis, a rapid and prolonged sequence of action potentials at the NMJ will initiate progressively weaker muscle contraction BECAUSE more ACh is released from the motor neuron during each successive action potential

A

the first statement is true and the second one is false

34
Q

Which is the thin filament, actin or myosin?

A

actin is the thin filament and myosin is the thick filament

35
Q

What does a single action potential tigger?

A

a twitch

a short period of force generation which lasts just a short period of time

36
Q

What two states can the myosin head be in?

A

flexed or energised (when it has ATP hydrolysed)

37
Q

What is Mg2+ important for?

A

ATP hydrolysis

38
Q

Describe the cross bridge cycling

A

the interaction between myosin and actin which generates force and allows these filaments to slide across each other

39
Q

What does the thin actin filament have?

A

tropomyosin and troponin associated with them

40
Q

What is tropomyosin?

A

This long thin beaded structure which runs across the entire length of actin which normally blocks the myosin binding sites

41
Q

Where are the myosin binding sites?

A

on the actin

these are normally hidden by tropomyosin

42
Q

What is troponin?

A

it is part of tropomyosin and it has a calcium binding site on it
troponin is the calcium sensor which senses calcium and causes a conformational change in tropomyosin to expose these myosin binding sites

43
Q

Describe myosin

A

there are heavy chains and light chains and two heads

44
Q

What are the two heads of myosin for?

A

both heads have both actin binding sites on the end of the head and ATP binding sites

45
Q

Why can’t myosin bind to actin under resting conditions? ie. low sarcoplasmic Ca2+ (Ca2+ inside the muscle cell not the sarcoplasmic reticulum)

A

because tropomyosin is blocking the myosin binding sites

46
Q

In order to get interaction between actin and myosin to generate skeletal muscle contraction, what needs to happen?

A

tropomyosin needs to be removed from the myosin binding sites

47
Q

When Ca2+ is released from the sarcoplasmic reticulum into the inside of the muscle cell, what happens?

A

Ca2+ binds to troponin which causes a conformational change which causes tropomyosin to move off the myosin binding sites which allows the myosin head to bind and engage with actin. This is cross bridge formation

48
Q

At the “end” of the cycle, where is ATP bound?

A

if ATP is available, it will bind the ATP binding sites on the myosin head

49
Q

When ATP binds to the ATP binding site on the myosin head, what happens (at the “end of the cycle)?

A

the myosin head can disengage/come off the actin

50
Q

What happens to the ATP when it is bound to the myosin head? What does this cause?

A

it is hydrolysed to ADP and phophate which energises the myosin head so it goes from a flexed position (relaxed) to an energised extended position

51
Q

Where so the ADP and Pi go when the myosin head is energised?

A

they stay on the myosin head

52
Q

If the myosin head is stimulated but there is no Ca2+ around, what happens?

A

the process stops here, there is no cross bridge formation because the myosin sites are blocked by tropomyosin

53
Q

When the myosin head binds to actin, in order to generate force, what has to happen?

A

the ADP and Pi are released which flexes the myosin head and force is generated

54
Q

To get repeating of the cycle after there has been force generated, what has to happen?

A

the myosin head needs to come off the actin so ATP binds

55
Q

The cross bridge cycle requires ATP. What happens when there is no ATP around?

A

the myosin head stays attached to the actin and so the muscle stays stiff (rigor mortis after death)

231 (41 decks)

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