Skeletal Muscles Flashcards

Topic 6.3

1
Q

Name 3 types of muscle in body & where they are located

A
  • Cardiac: exclusively found in heart.
  • Smooth: walls of blood vessels and intestines
  • Skeletal: attached to in-compressible skeleton to tendons
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2
Q

What does ‘antagonsitic pair of muscles’ mean?

A

Muscles can only pull, so they work in pairs to move bones around joints.
Pairs pull in opposite directions: agonist contracts while antagonist is relaxed

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3
Q

Describe gross structure of skeletal muscle

A

Muscle cells are fused together to form bundles of parallel muscle fibres (myofibrils)

Arrangement ensures there is no point of weakness between cells

Each bundle is surrounded by endomycium: loose connective tissue with many capilaries

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4
Q

Describe microscopic structure of skeletal muscle

A

Myofibrils: site of contraction

Sarcoplasm: shared nuclei and cytoplasm with lots of mitochondria & endoplasmic reticulum

Sarcolemma: folds inwards towards sarcoplasm to form transverse (T) tubules

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5
Q

How is muscle contraction stimulated?

A
  1. Neuromuscular junction: action potential = voltage-gated Ca+ channels open
  2. Vesicles move towards & fuse with presynaptic membrane.
  3. Exocytosis of acetlycholine (ACh), which diffuses across synaptic cleft.
  4. ACh binds to receptors on Na+ channel proteins on skeletal muscle cell membrane.
  5. Influx of Na+ = depolarisation
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6
Q

Explain role of Ca+ ions in muscle contraction

A
  1. Action potential moves through T-tubules in sarcoplasm= Ca+ channels in sarcoplasmic reticulum open.
  2. Ca+ binds to troponin, triggering conformational change in tropomyosin.
  3. Exposes binding site on actin filaments so actinomyosin bridges can form
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7
Q

Outline ‘sliding filament theory’

A
  1. Myosin head with ADP attached forms cross bridge with actin.
  2. Power stroke: myosin head changes shape & loses ADP, pulling actin over myosin.
  3. ATP attaches to myosin head, causing it to detach from actin.
  4. ATPase hydrolyses ATP -> ADP(+Pi) so myosin head can return to original position.
  5. Myosin head re-attaches to actin further along filament.
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8
Q

How does sliding filament action cause a myofibril to shorten?

A

Myosin heads flex in opposite direction = actin filaments are pulled towards each other

Distance between adjacent sarcomere Z lines shortens.

Sliding filament action occurs up to 100 times per second in multiple sarcomeres.

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9
Q

What happens during muscle relaxation?

A
  1. Ca+ is actively transported back into endoplasmic reticulum.
  2. Tropomyosin once again block actin binding site.
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10
Q

Role of phospho-creatine in muscle contraction

A

Phosphorylates ADP directly to ATP when oxygen for aerobic respiration is limited (e.g. during vigorous exercise)

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11
Q

Where are slow and fast-twitch muscle fibres found in the body?

A

Slow-twitch: sites of sustained contraction (e.g. calf muscle)
Fast-twitch: sites of short-term, rapid, powerful contraction (e.g. biceps)

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12
Q

Role of slow and fast-twitch muscle fibres

A

Slow-twitch: long-duration contraction; well-adapted to aerobic respiration to prevent lactate buildup

Fast-twitch: powerful short-term contraction; well-adapted to anaerobic respiration

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13
Q

Explain structure and properties of slow-twitch muscle fibres

A
  • Glycogen store: many terminal ends ca be hydrolysed to release glucose for respiration
  • Contain myoglobin: higher affinity for oxygen than haemoglobin at lower partial pressures.
  • Many mitochondria: aerobic respiration produces more ATP
  • Surrounded by many blood vessels: high supply of oxygen & glucose
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14
Q

Explain structure and properties of fast-twitch muscle fibres

A
  • Large store of phosphocreatine
  • More myosin filaments
  • Thicker myosin filaments
  • High concentration of enzymes involved in anaerobic respiration
  • Extensive sarcoplasmic reticulum: rapid uptake & release of Ca2+
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15
Q

What is a motor unit?

A

One motor unit supplies several muscle fibres, which act simultaneously as one functional unit

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