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Pharmacology & Physiology 1 > Contractile Mechanisms > Flashcards

Contractile Mechanisms Flashcards

1
Q

What are the 3 types of muscle in the human body?

A
  • Smooth
  • Skeletal
  • Cardiac
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2
Q

Outline how smooth muscle contraction occurs

A
  1. IP₃ binds to its receptor
  2. Induces Ca2+ release
  3. Ca2+ channels also open bringing in even more Ca2+
  4. Calmodulin activates myosin light chain kinase
  5. myosin phosphorylated at light chain (regulatory area)
    Ser19
  6. Increases ATPase activity of myosin head
  7. Allows actin-myosin binding
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3
Q

List features that all 3 muscle type contractions share

A
  • All 3 involve the Sarcoplasmic reticulum (some more
    than others)
  • All require ATP hydrolysis to activate myosin head
  • All 3 involve the binding of actin and myosin filaments
  • All 3 have Ca2+ sensors involved (troponin in cardiac /
    skeletal, calmodulin in smooth)
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4
Q

Explain how muscle contraction is initiated

A
  1. Depolarisation initiated at nAchR creating kink in
    membrane
  2. Maintained by Na+ channels in synapse
  3. Spreads into t tubules via sarcolemma (DHSR)
  4. Voltage sensing ryanodine on SR Ca2+ channels open
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5
Q

Compare and contrast Ca2+ channels and DHPs

A

Both are blocked by Dihydropyridines

Ca2+ allow ions through, DHP can’t conduct ions

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6
Q

How is the secondary messenger IP₃ formed?

A

Inositol triophosphate produced via cleavage of PIP₂ by Phospholipase C

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7
Q

Which receptors enable contraction in skeletal muscle?

A

The physical interaction between DHP and RyR - create Ca2+ influx in skeletal muscle

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8
Q

What is calmodulin?

A

Ca2+ sensor that moderates calcium (instead of troponin) activates myosin light chain kinase

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9
Q

Explain what happens when Cardiac muscles are activated

A
  1. Depolarisation causes voltage gated Ca2+ channels to
    open
  2. Influx of Ca2+ down t tubules into cardiac cells
  3. Calcium induced Calcium release occurs (CIRC)
  4. Ryanodine receptors opened due to increase in Ca2+
    on their external surface
  5. causes contraction of cardiac muscles
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10
Q

How is muscle contraction in smooth muscle deactivated?

A

Myosin light chain phosphatase dephosphorylates the myosin

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11
Q

What is meant by a contraction?

A

The interaction of actn and myosin fuelled by ATP and driven by a rise in [Ca2+]

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12
Q

How do cardiac muscles enable a Ca2+ influx for contraction?

A

CICR (calcium induced calcium release) promoted by the opening of Ca2+ channels

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13
Q

How are actin filaments arranged in skeletal muscle?

A

Tropomyosin forms long thin threads wound around actin filaments

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14
Q

Describe how smooth muscle contraction differs from cardiac and skeletal muscle contraction

A

Smooth muscle differs because

  • contractile proteins not in regular array
  • not a tubule system
  • has a less developed Sarcoplasmic reticulum (SR)
  • Contractions sustained for long periods
  • myofilaments connect with dense bodies
  • caldesmon and calponin instead of troponin
  • Different form of myosin (MYHII)
  • Lower ATPase activity - lower ATP affinity
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15
Q

Where in the body is skeletal muscle found?

A
  • bicep
  • calf
  • thigh
  • diaphragm
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16
Q

How does smooth muscle relaxation occur?

A
  1. [Ca2+] drops
  2. Myosin light chain kinase becomes inactive
  3. Myosing light chain Phosphatase dephosphorylates
    Ser19
  4. lowers ATP affinity of myosin head
  5. Acto-myosin complex remains for latch phase before
    relaxing
17
Q

Explain what happens when skeletal muscle contracts

A

Contraction in skeletal muscle is the removal of a supressant protein tropomyosin

18
Q

What are DSHR and DHP?

A

Dyhydropyridine proteins are volatge sensing receptors that physically interact with Ca2+
channels
They are ion channels that don’t conduct ions
They are blocked by dihydropyridines that are well known calcium channel blockers

19
Q

How often does a crossbridge cycle occur during contraction?

A

Each myosin head cycles approximately 5 times per second

20
Q

How is skeletal muscle organised?

A

In bands with the M (myosin) line in the middle
and Z disks at the end of each sarcomere
The A band represents the entire myosin length with remains unchanged during contraction
The H band consists of myosin only
The I band is actin filaments only

21
Q

How does depolarisation cause tropomyosin to unblock actin-myosin binding sites?

A

Depolarisation -> Na+ influx -> DHSR -> Ryanodine cause Ca2+ influx
Ca2+ diffuses along T tubules
Binds to troponin -> pulling away tropomyosin
Unblocking crossbridge binding site

22
Q

Compare and contrast skeletal and smooth muscle contraction

A

Smooth Muscle

  • Has greater shortening of muscle
  • Slower contraction speed
  • Greater force generation
  • Sustained contraction (latch phase)

Skeletal muscle requires more energy than smooth muscle

23
Q

Where is smooth muscle in the body?

A
  • arteries
  • gut
  • reproductive organs
  • bladder
24
Q

Describe the components of the structure of skeletal muscle

A

A muscle fillacious is made of muscle fibres composed of myofibrils that are made up out of myofilaments

25
Q

Explain the role of Ca2+ in muscle contraction

A

When [Ca2+] increased due to influx, Ca2+ binds to troponin C

  • causes removal of suppressive tropomyosin
  • allows actin to interact with primed myosin
  • ATP dependent crossbridge cycling occurs
26
Q

Describe the structure of Actin filaments

A

Actin is the thinner globular protein, arranged into long chains that are twisted around one another, forming a helical strand

27
Q

Which muscle contractions require an influx of Ca2+?

A

Cardiac and Smooth muscle

28
Q

Name the 2 muscle types that contract using a t tubule network

A

Skeletal muscle and Cardiac Muscle

29
Q

Describe the structures of skeletal and cardiac muscles

A

Transverse tubules interact with the sarcoplasmic reticulum of muscle cells

30
Q

Outline how actin and myosin interact to cause muscle contraction in skeletal muscle

A
  1. ATP hydrolysed by ATPase in myosin head => ADP +
    myosin
  2. Causes myosin head to move and bind to actin
    filament
  3. Actin pulled along by myosin head, releasing ADP
  4. New ATP molecule hydrolysed
  5. Myosin head detaches to form new cross bridge
    • > repeat cycle
31
Q

Describe how the structure of myosin enables contraction to occur

A

Myosin head is complementary to both ATP and actin filaments

32
Q

What are transverse tubules?

A

aka T tubules are cell membranes that extend deep into the cell interiors

33
Q

What is rigormortis?

A

Permanent cell contraction due to lack of new ATP molecule production => myosin head never released from actin filaments; muscles permanently contracted til ATP runs out

34
Q

Describe the structure of myosin filaments

A

Myosin filaments line up in a thick bundle appearing as the darker filaments in striated muscles

Pharmacology & Physiology 1 (9 decks)

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