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Muscles > Muscles > Flashcards

Muscles Flashcards

1
Q

Name the three types of muscle in the body

A

Cardiac, Smooth, Skeletal

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2
Q

Where is Smooth muscle found

A

walls of blood vessels and intestines

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3
Q

Where is Skeletal muscle found

A

attached to incompressible skeleton by tendons

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4
Q

Where is cardiac muscle found

A

exclusively in the heart

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5
Q

What does the phrase ‘antagonistic pair of muscles’ mean?

A

Muscles can only pull so they work in pairs to move bones around joints.

Pairs work in opposite directions: agonist contracts while antagonist is relaxed

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6
Q

Describe the 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 capillaries.

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7
Q

Describe the microscopic structure of skeletal muscle.

A

Myofibrils: site of contraction

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

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

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8
Q

Draw a diagram to show the ultrastructure of a myofibril

A

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9
Q

How does each band appear under an optical microscope

A

I-band: light

A-band: dark

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10
Q

How is muscle contraction stimulated?

A
  1. Neuromuscular junction: action potential = voltage-gated Ca2+ channels open
  2. Vesicles movie towards & fuse with presynaptic membrane
  3. Exocytosis of acetylcholine (ACh), which diffuses across synaptic cleft
  4. ACh binds to receptors on Na+ channel proteins on skeletal muscle cell membrane
  5. Influc of Na+ = depolarisation
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11
Q

Explain the role of Ca2+ ions in muscle contraction

A
  1. Action potential moves through T-tubules in the sarcoplasm = Ca2+ channels in sarcoplasmic reticulum open
  2. Ca2+ binds to troponin, triggering conformational change in tropomyosin
  3. Exposes binding sites on actin filaments so actinomyosin bridges can form
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12
Q

Outline the 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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13
Q

How does sliding filament action cause a myofibril to shorten?

A

Myosin heads flew in opposite directions = 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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14
Q

State 4 pieces of evidence that support the sliding filament theory.

A
  • H-zone narrows
  • I-band narrows
  • Z-lines get closer (sarcomere shortens)
  • A-zone remains same width (proves that myosin filaments do not shorten)
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15
Q

What happens during muscle relaxation?

A
  1. Ca2+ is actively transported back into endoplasmic reticulum
  2. Tropomyosin once again blocks actin binding site
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16
Q

Explain the role of phosphocreatine in muscle contraction.

A

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

17
Q

How could a student calculate the length of one sarcomere

A
  1. View thin slice of muscle under optical microscope
  2. Calibrate eyepiece graticule
  3. Measure distance from middle of one light band to middle of another
18
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

19
Q

Explain the 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

20
Q

Explain the structure and properties of slow-twitch muscle fibres

A
  • Glycogen store: many terminal ends can 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
21
Q

Explain the 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+
22
Q

What is a motor unit?

A

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

Muscles (2 decks)

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