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Fundamentals of Physiology > L3: Muscle Cell Function > Flashcards

L3: Muscle Cell Function Flashcards

• Describe the basic structure of cardiac, skeletal and smooth muscle. • Describe how the membrane potential changes in different muscle types and it’s role in triggering contraction. • Recognise the central role of Ca in muscle contraction. Describe the process by which changes in membrane potential elevate Ca and trigger contraction in cardiac, skeletal and smooth muscle – the process of excitation-contraction coupling.

1
Q

What is a myocyte?

A

‘The Muscle Cell’
- Smallest subunit of muscular tissues & organs throughout the body

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2
Q

Structure of the cardiac muscle

A

Striated, branched & contains many mitochondria, involuntary contraction

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3
Q

Function of the muscle myocyte

A

Contraction

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4
Q

What are sarcomeres?

A

Basic unit of muscle fibre composed of actin + myosin

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5
Q

Structure skeletal muscle

A

Unbranched, striated, voluntary contraction

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6
Q

Structure of smooth muscle?

A

Spindle shaped, involuntary contraction

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7
Q

What does smooth muscle consists of?

A

Thick & thin filaments that are not arranged into sarcomeres; resulting in a non-striated pattern

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8
Q

What is a sarcomere?

A

Basic unit of muscle fibre; composed of actin & myosin

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9
Q

Length of sarcomere?

A

Distance between 2 adjacent Z lines

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10
Q

Which filaments are thin?

A

ACTIN

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11
Q

Which filaments are thick?

A

MYOSIN

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12
Q

What are T-tubules?

A

Voltage-gated calcium channels

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13
Q

What is a sarcolemma?

A

Plasma membrane of muscle cell

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14
Q

What happens in neuronal action potential?

A

Na+ moves into the cell causing depolarisation, K+ moves out of cell causing repolarisation

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15
Q

What happens during a refractory period?

A

Period where ion channels have not returned to closed state, so another AP cannot be initiated

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16
Q

What is a relative refractory period?

A

Na+ channels are ready to go, but the membrane potential is too negative, so a bigger depolarisation is needed

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17
Q

When would the cardiac action potential be triggered?

A

If theres a wave of excitation that spreads across the heart from the sino-atrial (SA) node

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18
Q

What do long refractory periods prevent?

A

Tetany (involuntary muscle contractions)

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19
Q

Define temporal summation

A

One heartbeat builds on another beat

20
Q

Why is the ability to tetanise skeletal muscle important?

A

Allows us to maintain a contraction, allow the heart to fill with blood & contract again

21
Q

Benefit of the twitch in cardiac muscle?

A

Forces the heart to contract & relax as it cannot tetanise

22
Q

2 important purposes of long duration AP

A

1) prevents tetany
2) prevents us getting extra beats where we don’t want them

23
Q

How is an action potential triggered in a skeletal muscle?

A

Triggered by activation of motor neurone, excitation initiated in the neuromuscular junction

24
Q

What channels drive the action potential in smooth muscle excitation?

A

Time-dependent channels

25
Q

What is graded depolarisation?

A

Steady change in the membrane potential

26
Q

What channels drive the graded depolarisation in smooth muscle excitation?

A

Time-dependent channels

27
Q

Examples of time-independent channels

A

Voltage-gated
Ligand gated

28
Q

What does the excitation contraction coupling describe?

A

Rapid communication between events occurring in the plasma membrane, leading to a contraction

29
Q

What element links excitation to contraction?

A

Calcium

30
Q

Role of calcium in the excitation contraction coupling

A

Production of wave of contraction out of the wave of excitation

31
Q

How do T-tubules respond to AP?

A

Opening the channels to allow Ca to enter

32
Q

How is the contraction of individual myocytes coordinated in cardiac muscle?

A

Propagation wave of depolarisation of myocyte cell membranes (sarcolemma)

33
Q

How does T-tubules (voltage-gated channels) respond to AP?

A

Opening and allowing calcium to enter the cell

34
Q

Where does the calcium diffuse across when it enters the cell?

A

Very small space between the T-tubule & the sarcoplasmic reticulum - the dyadic cleft

35
Q

What are ryanodine receptors?

A

Ion channels that open in presence of Ca & release Ca from the sarcoplasmic reticulum

36
Q

What does Ca bind to when it is elevated in the dyadic cleft?

A

Binds to ryanodine receptor

37
Q

Name of process when Ca binds to ryanodine receptor

A

Calcium induced calcium release

38
Q

What does the elevated Ca bind to in the myocyte?

A

Calcium-binding proteins like troponin & calmodulin

39
Q

What is troponin?

A

Contractile protein

40
Q

What is calmodulin?

A

Signalling protein

41
Q

What is initiated as a result of Ca binding to troponin?

A

Myofilament contraction

42
Q

How is Ca administered into the network sarcoplasmic reticulum?

A

SERCA (sarcoplasmic & endoplasmic reticulum calcium ATPase)

43
Q

Which pump brings relaxation by elevated Ca concentration being reversed when Ca is taken back into the SR?

A

SERCA

44
Q

What is the primary mechanism for removing Ca from the cytoplasm?

A

SERCA

45
Q

Which protein regulates SERCA?

A

Phospholamban

Fundamentals of Physiology (11 decks)

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