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Semester 2 Molecular Medicine > Excitation coupling in cardiac and skeletal muscle > Flashcards

Excitation coupling in cardiac and skeletal muscle Flashcards

1
Q

In the neuromuscular junction, what is the name of the receptors found on the skeletal muscle fibre and what is its role?

A

Nicotinic receptor
• Acetylcholine receptor
• Primary receptor in the muscle for motor nerve-muscle communication

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2
Q

What is the latent period?

A

The lag onset of the action potential- the time taken for the muscle to contract from the peak action potential

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3
Q

Describe the stages of depolarisation

A
  1. Somatic motor neurone releases Acetylcholine at neuromuscular junction
  2. Net entry of Na+ through Acetylcholine receptor channel initiates a muscle action potential
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4
Q

What is the role of the transverse tubule?

A
  • the action potential is propagated from the end plate along the surface of the muscle fibre and then does into the fibre down the T tubule membrane
  • The depolarisation of the T tubule membrane is signalled to the membrane of the terminal cisternae (SR)
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5
Q

What 2 compartments are calcium recycled between?(intracellularly)

A
  • Sarcoplasmic reticulum/ terminal cisternae

* Cytoplasm

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6
Q

What are the two junctional foot proteins?

A
  • Dihydropyridine receptor protein (DHPR)

* Ryanoidine receptor protein (RYR)

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7
Q

Describe the Dihydropyridine receptor protein

A
  • L type voltage gated calcium channel

* Located in the T tubule membrane

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8
Q

Describe the Ryanodine receptor protein

A

• Calcium release channel in the sarcoplasmic reticulum

main calcium channel in th SR

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9
Q

Describe the stages of mechanical coupling in the muscle fibre and how this causes contraction

A
  1. Membrane depolarisation opens the L type Ca2+ channel (DHPR)
  2. Mechanical coupling between the DHPR and RYR channel cause the RYR channel to open
  3. Ca2+ exits the sarcoplasmic reticulum and activates troponin C, leading to muscle contraction
    (4. Ca2+ entering the cell via the DHPR channels can also activate the RYR release channels but this is not essential in skeletal muscle contraction)
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10
Q

Describe what happens after the action potential in a t tubule has caused the conformation of the DHP receptor to be altered (up to cross bridges forming)

A
  • The DHP receptor opens Ca2+ release channels (RYR) in the sarcoplasmic reticulum and Ca2+ enters the cytoplasm
  • Ca2+ binds to troponin allowing strong actin-myosin binding
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11
Q

What is Dantrolene and what is it used to treat?

A

A spasmolytic drug thought to work on the ryanodine receptor that acts as a skeletal muscle relaxant (it may reduce the calcium release)
• Used to treat: (sarcoplasmic reticulum)
• Malignant hyperthermia

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12
Q

What is Nifedipine and what is it used to treat?

A
  • A Dihydropyridine blocker- blocks voltage gated Ca2+ channels
  • Used to treat: (smooth muscle)
  • Hypertension
  • Migrane
  • Atherosclerosis
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13
Q

What is malignant hypothermia?

A

Pharmocogenetic disorder of skeletal muscle
• It is the result of a severe reaction to commonly used anaesthetics and depolarising muscle relaxants
• First manifestations of malignant hypothermia occur in the operating room
• It is fatal if left untreated

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14
Q

What are the symptoms of malignant hypothermia?

A
  • Muscle rigidity
  • High fever
  • Increased acid levels in blood and other tissues
  • Rapid heart rate
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15
Q

What is the underlying mechanism of Malignant hypothermia?

A

A point mutation in the gene coding for RyR1

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16
Q

What is and what is the role of SERCA?

A
  • Sarcoplasmic Endoplasmic reticulum calcium ATPase
  • Works against the gradient to force calcium back into the stores (into the SR) by hydrolysing ATP (2 Ca2+ ions per molecule ATP) (activated by the increase in intracellular calcium concentration)
  • Therefore decreases the concentration of calcium ions in the cytoplasm
17
Q

At around what level of Ca2+ does the muscle relax?

A

Less than 10-7 M

18
Q

What is the role of calsequestrin

A

• Stores calcium at high concentrations in the terminal cisternae to establish a concentration gradient from the SR to the cytoplasm

19
Q

What is calsequestrin?

A
  • A calcium binding protein

* Molecular Weight 44000

20
Q

How many calcium ions can bind per molecule of calsequestrin?

A

43

21
Q

Aside from appearance (striations, nuclei) how do cardiac muscle cells differ from skeletal muscle cells?

A
  • Unstable resting potential

* Undergo automatic rhythmical depolarisation

22
Q

What is the Parasympathetic neurotransmitter of cardiac muscle, what is its action and innervation?

A
  • Acetylcholine
  • Slows the rate of contraction
  • Localised to pacemakers
23
Q

What is the Sympathetic neurotransmitter of cardiac muscle, what is its action and innervation?

A
  • Noradrenaline
  • Increases rate and strength of contractions
  • Diffuse
24
Q

What calcium concentration ultimately leads to the force generation in cardiac muscle?

A

10-5 M

25
Q

What is the resting potential of cardiac muscle?

A

-90mV

26
Q

How does the shape of a cardiac muscle action potential graph differ to that of skeletal muscle

A

In a cardiac muscle action potential graph, there is:
• A more rapid depolarisation
• A plateau period
• Then a repolarisation

27
Q

What is the resting potential of skeletal muscle?

A

-70mV

28
Q

What is the threshold potential of skeletal muscle?

A

-55mV

29
Q

What is the ratio of Na+ to Ca2+ of exchange in the sarcolemmal membrane?

A

3:1

30
Q

What is excitation contraction coupling?

A

Describes the series of events between the excitation of the muscle fibre membrane and the onset of contraction

31
Q

Why do we get a latent period?

A

To bring the impulse deep into the muscle fibre

32
Q

What is the t tubule?

A

An invagination of the plasma membrane

33
Q

In which regions of the heart are the pacemaker cells?

A
  • The sino-atrial node

* Atrio-ventricular node

34
Q

What, regarding depolarisation, is special about pacemaker cells?

A

They always depolarise to the threshold

35
Q

What percentages of calcium required for muscle contraction come from each receptor?

A
  • 25% from DHPR

* 75% from RYR

Semester 2 Molecular Medicine (27 decks)

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