Muscle (3.6.3) Flashcards

1
Q

What is a Skeletal Muscle also known as?

A

Striped / Striated Muscle

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2
Q

Why is a Skeletal Muscle also known as a Striped / Striated Muscle?

A

Due to its striped appearance when viewed under a microscope due to alternate light bands of protein filaments

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3
Q

What is a muscle attached to?

A

Bone

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4
Q

What stimulates a muscle to contract?

A

Nerves

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5
Q

What does a muscle act as?

A

Effector

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6
Q

What are 2 features of muscle fibres?

A
  • Multinucleate

* Many Mitochondria

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7
Q

Explain the Structure of Muscles:

A
  • Consists of cells, muscle fibres that are multinucleate and contain many mitochondria
  • Elongated with bundles of myofibrils
  • Sarcolemma = cell surface membrane, folded deeply into muscle fibre (t – tubules)
  • Sarcoplasm
  • Sarcoplasmic Reticulum containing Ca2+
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8
Q

What are the 2 protein filaments in Myofibrils?

A

1) Thick Filaments – Myosin

2) Thin Filaments - Actin

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9
Q

What line is Actin attracted to?

A

Z – Line

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10
Q

What is the part of the myofibril between 2 Z – lines called?

A

Sarcomere

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11
Q

What line is Myosin attracted to?

A

M – Line

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12
Q

What does the A – Band include?

A

This is where Myosin Filaments + Actin Filaments

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13
Q

What does the I – Band include?

A

Only Actin Filaments

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14
Q

What does the H – Band include?

A

Only Myosin Filaments

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15
Q

What Theory explains Muscle Contraction

A

Sliding Filament Theory

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16
Q

How are the Bands affected when a muscle contracts?

A
  • I Band is reduced as Actin slides between myosin
  • A Band remains the same as Myosin length is unchanged
  • H Zone is reduced as overlap between Actin + Myosin increases
  • Sarcomere is reduced in length
17
Q

What stops myosin heads from binding to Actin in a resting muscle?

A

The binding sites, in a resting muscle, will be blocked by a protein called Tropomyosin

18
Q

What causes the unblocking of myosin binding sites?

A

The release of Calcium ions as they cause Tropomysoin to change shape and expose the myosin binding sites on the Actin filament

19
Q

What causes the release of Calcium ions?

A

When an action potential spreads along the t-tubules

20
Q

Events for Each Myosin Head:

A
  • Myosin Head attaches to myosin binding site on Actin filaments forming actinomyosin bridge
  • Myosin head tilts in a rowing action, sliding actin filaments iver myosin filaments towards the centre of Sarcomere
  • ATP binds to the myosin head and causes it to release the actin filament
  • ATP hydrolase (in the head) hydrolyses ATP releasing energy which causes the myosin head to flip back into its original position
  • Cycle Repeats
21
Q

What happens when the action potentials stop arriving?

A
  • Calcium ions actively pumped back into Sarcoplasmic reticulum via Active transport – ATP needed)
  • Tropomyosin returns to original shape + myosin heads no longer attach to Acton filaments
  • The muscle remains in its contracted state as Action filaments only slide in 1 direction towards centre of Sarcomere.
22
Q

Why are the muscles described to work in antagonistic pairs?

A

As they work against an incompressible skeleton which means when 1 contracts, the other muscle in the pair relaxes

23
Q

When is energy needed in muscle contraction?

A
  • Movement of myosin heads (detach + return to original position)
  • Return of Ca2+ ions into Sarcoplasmic reticulum by active transport
24
Q

State 2 sources where Energy is supplied from?

A
  • ATP

* Phosphocreatine

25
Why must energy be supplied by another source?
This is because hydrolysis of ATP releases energy + ADP + Pi. Muscle fibres only store small quantities enough for 3-4 secs of muscle contractions and it takes 10 secs to generate ATP from anaerobic respiration, so it must be supplied by another source
26
Why is Phosphocreatine useful?
This is because Muscle fibres can store it; producing ATP rapidly
27
What is the formula to produce ATP using Phosphocreatine?
ADP + Phosphocreatine  ATP + Creatine
28
What happens with Phosphocreatine when muscle fibre stops contracting?
It is resynthesised
29
What are the 2 types of Muscle Fibre?
* Slow Twitch Fibres | * Fast Twitch Fibres
30
Explain the basic function of Slow twitch fibres
* Rely on ATP generated by aerobic respiration | * Contract slowly over long periods of time (standing, walking, balancing etc.)