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Biology A Level 2023 2 > Skeletal Muscles > Flashcards

Skeletal Muscles Flashcards

1
Q

name the 3 types of muscle in the body and where they are located

A
  • cardiac: exclusively in heart
  • smooth: walls of blood vessels and intestines
  • skeletal: attached to incompressible skeleton by tendons
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2
Q

what does phrase ‘antagonistic 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 relaxed

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3
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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4
Q

describe the microscopic structure of skeletal muscle

A

myofibrils: site of contraction

sarcoplasm: shared nuclei and cytoplasm with lots of mitochondria and endoplasmic reticulum

sarcolemma: fold inwards towards sarcoplasm to from transverse (T) tubules

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5
Q

what is the Z-line

A

boundary between sarcomeres

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6
Q

what is the I-band

A

only actin

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7
Q

what is the A-band

A

overlap of actin and myosin

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8
Q

what is the H-zone

A

only myosin

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9
Q

how does each band appear under an optical microscope

A

I-band is light
A-band is dark

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10
Q

how is muscle contraction stimulated

A
  1. neuromuscular junction: action potential = voltage gated Ca 2+ channels open
  2. vesicles move towards and 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. influx of Na+ = depolarisation
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11
Q

explain the role of Ca 2+ ions in muscle contraction

A
  1. action potential moves through T-tubules in the sarcoplasm = Ca 2+ channels in sarcoplasm reticulum open
  2. Ca 2+ 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 ‘sliding filament theory’

A
  1. myosin head with ADP attached forms cross bridge with actin
  2. power stroke: myosin head changes shape and 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 flex 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

4 pieces of evidence for sliding filament theory

A
  • H-zon 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. Ca 2+ 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

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 twitch muscle fibres found in the body

A

sites of sustained contraction e.g. calf muscle

19
Q

where are fast twitch muscle fibres found in the body

A

sites of short term, rapid, powerful contraction e.g. biceps

20
Q

role of slow twitch muscle fibres

A

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

21
Q

role of fast twitch muscle fibres

A

powerful short-term contraction; well-adapted to anaerobic respiration

22
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 and glucose
23
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 and release of Ca2+

Biology A Level 2023 2 (17 decks)

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