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MNSR > Lecture 9 > Flashcards

Lecture 9 Flashcards

1
Q

What is the name of the cell membrane that each muscle fibre enclosed in?

A

The sarcolemma

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2
Q

What is embedded in the sarcoplasmic matrix of a muscle fibre?

A

Myofibrils

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3
Q

What is the cytoplasmic matrix (cytoplasm) called in a muscle fibre?

A

sarcoplasm

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4
Q

What are the main components found in the sarcoplasm?

A
  • Cytosol
  • Transverse tubules (T-tubules)
  • Sarcoplasmic reticulum
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5
Q

What is cytosol?

A

Energy source for muscle

  • In muscle known as sarcoplasm
  • Rich in glycogen, ATP, Creatine Phosphate, glycolytic enzymes
  • Myofibrils comprise ⅔ the dry mass of the cells
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6
Q

What are T-tubules?

A

Transmit electrical signals to depolarise the muscle cells

  • Series of membranous folds extending from plasma membrane
  • Transmit electrical signal
  • Small gap to
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7
Q

What is the sarcoplasmic reticulum?

A

Stores the calcium

  • Flattened vesicles which surround each myofibril
  • Sequester (collect) calcium
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8
Q

What are the 2 main filamentous components of the sarcomere?

A
  • Actin (thin filaments)

- Myosin (thick filaments)

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9
Q

What is the sliding filament theory?

A
  • Contraction is due to the actin and myosin filaments sliding between each other
  • The force of contraction is caused by the movement of the cross-bridges
  • As contraction commences increased overlap between actin and myosin filaments
  • As the sarcomeres shorten the muscle fibres shorten
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10
Q

What happens to the A-band, I-band and H-zone during muscle contraction?

A
  • The A-band remains the same length
  • The I-band shortens
  • The H-zone is reduced or disappears
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11
Q

What are the 5 steps to the ratchet mechanism?

A
  1. Actin is uncovered through the binding of Ca2+ to troponin. The Myosin-ADP - Pi complex binds to actin
  2. This releases Pi, producing the powerstroke at the cross-bridge. The myosin head changes conformation
  3. Immediately another ATP molecule replaces ADP in the myosin head, binding to the actomyosin complex to form an A-M-ATP complex
  4. The actin is released. The myosin head reverts to the resting conformation
  5. ATP is hydrolysed to ADP – Pi; the resting state
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12
Q

What are the two types of muscle relaxants used in anaesthesia?

A

Depolarizing muscle relaxants and non-depolarizing muscle relaxants

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13
Q

Depolarizing muscle relaxants?

A

Cause contraction of the muscle once, but prevent further contractions
e.g. Suxamethonium

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14
Q

Non-depolarizing muscle relaxants?

A

Prevent muscle from contracting

e.g. Tubocurarine

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15
Q

What are anaesthetics used for?

A

Muscle relaxants

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16
Q

What are actin and myosin responsible for?

A

They’re the main proteins responsible for muscle movement (contraction)

17
Q

Myofibrils in striated muscle?

A

Divided into light and dark bands

  • I-band
  • A-band
  • Z-line
  • M-line
  • H-zone
18
Q

I-band?

A
  • Isotropic
  • Contain only actin thin filaments. This not concentrated area gives this band it’s light appearance
  • Facilitates the passage of light (light coloured)
  • Shortens during muscle contraction
19
Q

A-band

A
  • Anisotropic
  • Contains thick myosin filaments and thin actin filaments. This concentrated area gives this band it’s dark appearance
  • Avoids the passage of light (dark coloured)
  • Remains the same length during muscle contraction
20
Q

Z-line?

A
  • In the middle of the I-band

- A dark line

21
Q

What is the space between each Z-line?

A
  • The sarcomere

- The unit of contraction

22
Q

The sarcomere?

A
  • The unit of contraction
  • The space between each Z-line
  • Gives skeletal muscle the striated appearance under the light microscope
  • Made up of parallel and overlapping proteins, the location of which gives the dense (A-band) or light (I-band) appearance to the myofibril
23
Q

What are the three different components that the thin filament is made up of?

A
  • A double stranded F-actin protein molecule wound into a double helix,
  • A double stranded a-helical protein molecule tropomyosin, lying in the groove of the F-actin helix,
  • A third, troponin, consisting of 3 globular proteins (TnC, TnI, TnT) periodically attached to the tropomyosin strand
24
Q

What are the functions of tropomyosin and troponin?

A
  • Regulate actin

In the resting state the tropomyosin strands cover the myosin binding sites on actin
One of the troponin proteins (TnT) binds to the tropomyosin, (TnI) binds to F-actin, and (TnC) binds to Calcium (Ca2+) ions. When Ca2+ is released from the SR, it binds to TnC. This initiates the moving of tropomyosin from the myosin binding site. Myosin is now able to bind to actin.

25
Q

What are the 3 troponin proteins?

A

TnT, TnI and TnC

26
Q

Structure of myosin (thick filament)?

A
  • Made of polypeptides

- Consists of compact myosin heads and a long tail which is made of two a-helices

27
Q

What is most of the myosin tail called?

A
  • Light meromyosin
28
Q

What are myosin heads and part of the tail composed of?

A

Heavy meromyosin

29
Q

Where can myosin be found?

A

In the A-band of the sacromere

30
Q

Function of myosin head?

A
  • Each head acts as an enzyme binding to ATP and subsequently hydrolysing it (uses it to cause the contraction).
  • The myosin head stores energy in the form of ADP and Pi
31
Q

H-zone?

A

Is reduced or disappears during muscle contraction

32
Q

Why does the A-band remain the same length, but the I-band shortens during muscle contraction?

A

Bc the myosin in the A-band pulls the actin

33
Q

What chemical is released as the initial signal for muscle contraction?

A

Acetylcholine (ACh)

34
Q

What is a powerstroke?

A

A crossbridge action:

  • Attachment of myosin
  • ‘Contraction’ of myosin head
  • Breaking of actin/myosin interaction
  • Re-attachment further along the actin filament at the next active site

MNSR (12 decks)

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