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Sem 1 > 34. Muscle contraction > Flashcards

34. Muscle contraction Flashcards

1
Q

Describe skeletal muscle cells? (3pts)

A
  1. Very low cells with many nuclei
  2. Stripy patterns- the contractile proteins are arranged in a logical organised array,
  3. There is overlap of thick and thin filaments giving a dark band and overlap less giving a lighter band.
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2
Q

Describe cardiac muscles? (3pts)

A
  1. One nuclei
  2. Very stripey
  3. Cells are electrically coupled so there is smooth flow of electrical activity throughout the cardiac muscle.
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3
Q

Describe mono nucleated cells?

A

Do not have a striated pattern

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4
Q

Describe mono nucleated cells?

A

Do not have a striated pattern

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5
Q

Describe contractile proteins?

A

Contractile proteins do not become arranged into a logical organised pattern. They are more diffused within the muscle cell creating a network allowing the muscle cell to be rung out when it gets contracted.

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6
Q

Describe muscle contraction? (3pts)

A
  1. The interaction between actin and myosin
  2. It is fuelled by ATP- allows actin to be moved by myosin
  3. It is driven by a rise in CA2+

ATP hydrolysis alters myosin and allows structural movement of actin that produces shortening of the muscle cells.

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7
Q

Describe skeletal muscles? (5pts)

A
  1. Made up of a bundle of cells
  2. Each muscle fascicle is compromised of muscle fibres which are the individual muscle cells.
  3. This produces one cell called a myofibril.
  4. Within the muscle cell there are rod like structures which are the arrangement of the contractile proteins
  5. The overlap of thin and thick filaments give the skeletal muscle its stripey appearance and the two coloured bands.
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8
Q

How do muscles get their stripy appearance?

A

The overlap of thick and thin filaments give the skeletal muscle its stripy appearance and the two coloured bands.

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9
Q

What is the SR?

A

The sacroplasmic reticulum is a calcium store. It lies very close to the contractile proteins and it is a trigger for muscle contraction.

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10
Q

Describe thin filaments? (3pts)

A
  1. Made up of actin anchored at the 2 disc by alpha actin.
  2. Tropomyosin and troponin lie over the acton. Troponin have a calcium binding domain and a tropomyosin binding site.
  3. Actin consists of myosin binding sites. At rest these binding sites are covered by tropomyosin.
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11
Q

Describe thick filaments? (4pts)

A
  1. Compromised of globules called myosin which has a long tail and a dominant myosin head. The myosin head has the ability to hydrolyse ATP
  2. The myosin head is motile due to its flexible hinge
  3. At rest the myosin binding sites on actin are covered by tropomysoin
  4. When myosin binds to actin it moves the actin towards the centre.
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12
Q

Describe the contractile cycle? (6pts)

A
  1. Mysoin binds to actin
  2. Upon the release of ADP, power stroke occurs which is the movement of myosin from the right to the left. This will drag the bound actin with it.
  3. The myosin is in a low energy configuration and undergoes spatial movement.
  4. ATP binds to myosin which causes myosin to detach from actin
  5. The cross bridge dissociates
  6. The mysoin head hydrolyses the ATP to ADP leading to a high energy configuration which can interact with the next part of the actin.
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13
Q

What happens when an individual dies?

A

When an individual dies there is a rise in calcium in cells which leads to myosin and actin interaction. Stiffness occurs in muscles because there is no more ATP being generated. As a consequence the myosin cannot detach from the actin therefore remains in the myosin actin interacted state forever.

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14
Q

Describe what happens to calciium? (9pts)

A
  1. Tropomysin lies along the actin molecule and prevents myosin binding to actin
  2. Calcium ions are released from the SR and bind to troponin-C.
  3. Tropnin then has a higher affinity for tropomysoin.
  4. Troponin then removes the tripomysoin from the myosin binding sites on actin
  5. This allows actin to bind to myosiin.
  6. ATP dependant cross bridge cycling occurs-each myosin head cycles 5x per sec
  7. As the ADP is released power stroke occurs
  8. Upon the binding of ATP detachment occurs
  9. Hydrolysis leads to clocking of the myosin protein
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15
Q

Describe what happens to calciium? (9pts)

A
  1. Tropomysin lies along the actin molecule and prevents myosin binding to actin
  2. Calcium ions are released from the SR and bind to troponin-C.
  3. Tropnin then has a higher affinity for tropomysoin.
  4. Troponin then removes the tripomysoin from the myosin binding sites on actin
  5. This allows actin to bind to myosiin.
  6. ATP dependant cross bridge cycling occurs-each myosin head cycles 5x per sec
  7. As the ADP is released power stroke occurs
  8. Upon the binding of ATP detachment occurs
  9. Hydrolysis leads to clocking of the myosin protein
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16
Q

Describe a skeletal muscle fibre? (3pts)

A
  1. Many mitochondria as it is a ATP dependant process
  2. Contains sarcolemma which are holes at the beginning of the t tubule systems. T t tubules are an invagination of the membrane which takes information into the cell. They lie close to the SR.
  3. T tubules present in skeletal muscle cells and cardiac muscle cells.
17
Q

Describe skeletal muscle cells? (4pts)

A
  1. Skeletal muscle cells contain t tubules. They express nicotine acetylcholine receptors which are ligand gated ion channels activated by acetyl choline released from the motor nerves
  2. Activation of acetylcholine by the nicotine acetylcholine receptor will lead to an influx of sodium which produces a EJP (excitatory junction potential)
  3. This takes the membrane potential to a level where the voltage gated sodium channels are activated which creates a prominent action potential.
  4. The depolarisation is carried deep into the cell next to the SR which is a calcium store.
18
Q

Describe a dihydropyridine receptor? (5pts)

A
  1. T tubules have a dihydropyridine receptor which is an ion channel that does not pass calcium ions.
  2. At rest it physically interacts with the calcium release ions preventing calcium release.
  3. A molecular change occurs in the dihydropyridine receptor which removes the suppressive interaction with the calcium release channel.
  4. As a result there is pronounced calcium release which is sufficient enough to allow binding to troponin c, removal of tropomyosin and the interaction of myosin and actin.
  5. The loops of the dihydropyridine receptor inhibits the calcium release channels.
19
Q

Describe calcium ions in cardiac muscles? (4pts)

A
  1. In cardiac muscle there is a functional calcium ion channel within the t tubules
  2. Depolarisation opens this calcium ion channel
  3. This causes calcium ions to rise stimulating the RyR2 receptor
  4. This causes calcium induced calcium release which causes an influx of calcium
20
Q

Describe calcium ions in smooth muscle? (3pts)

A
  1. Smooth muscles have no t tubules and the filaments are in a regular array. They span the muscle cell like a network interacting with these faecal adhesion points
  2. Smooth muscle cells contain numerous calcium ion channel receptors which cause an increase in calcium and numerous g protein coupled receptors.
  3. IP3 releases calcium from the sarcoplasmic reticulum
21
Q

Describe the properties of smooth muscles? (6pts)

A
  1. Contain no troponin
  2. Tropomyosin does not interact with the myosin binding sites
  3. Myosin in smooth muscle is a different isoform than the skeletal muscle
  4. Has lower ATPASE activity
  5. Has a lower affinity for ATP- does not hydrolyse ATP well
  6. When calcium binds activation of myosin light chain kinase phosphorylates MLC at ser 19. This increases the ATPASE activity of the mysoin head. This then alters the structure of myosin.
22
Q

Describe Contractile mechanism? (4pts)

A
  1. There is an increase in calcium ions
  2. Calcium ions bind to calcium-calmodulin
  3. This stimulates myosin light chain kinase (MLCK)
  4. By phosphorylating myosin there is an increase in ATPASE activity which allows you to turn over ATP to hydrolyse it and to move the actin after the dissociation of ADP.
22
Q

Describe Contractile mechanism? (4pts)

A
  1. There is an increase in calcium ions
  2. Calcium ions bind to calcium-calmodulin
  3. This stimulates myosin light chain kinase (MLCK)
  4. By phosphorylating myosin there is an increase in ATPASE activity which allows you to turn over ATP to hydrolyse it and to move the actin after the dissociation of ADP.
23
Q

What is the contractile mechanism of skeletal and cardiac muscle?

A

Removal of tropomysoin

24
Q

What is the contractile mechanism of smooth muscle?

A

MLCK- myosin light chain kinase activation

Sem 1 (37 decks)

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