3.6.3 Skeletal muscles Flashcards

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1
Q

Antagonistic pairs

A

Agonist - contracting muscle

Antagonist - relaxing muscle

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2
Q

Sarcolemma

A

Cell membrane of muscle fibres

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3
Q

Sarcoplasm

A

Cytoplasm of muscle fibres containing many mitochondria

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4
Q

Sarcoplasmic reticulum

A

network of internal membranes throughout the sarcoplasm to store and release Ca2+ needed for contraction

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5
Q

Myofibril

A

Contains 2 types of protein filaments arranged in overlapping units - sarcomeres
Myosin (thick) and actin (thin)

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6
Q

Features of muscle fibres (cell)

A
  • specialised elongated fused cells
  • have many nuclei so can make proteins easily at any point along their length
  • have many mitochondria to provide ATP for muscle contraction
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7
Q

Myofibril structure

A
  • Myosin - thick protein filament
  • Actin - thin protein filament
  • I band actin only
  • H zone myosin only
  • A band - actin and myosin
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8
Q

How does the sarcomere change during muscle contraction?

A

Filaments slide over each other

  • A band never changes length
  • Sarcomere shortens (z lines closer)
  • H zone shortens
  • I band shortens
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9
Q

Uses of ATP in muscle contraction

A
  1. required for movement of myosin heads (that causes actin filaments to slide)
  2. Breaks actin-myosin cross bridge
  3. For active transport of Ca2+ back into reticulum (if no ATP muscle wouldn’t relax)
  4. Mitochondria generate ATP by respiration
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10
Q

What causes muscle fatigue?

A

lactic acid build up

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11
Q

Sliding filament theory

A
  1. Sarcolemma is depolarised, causing Ca2+ channels to open
  2. Ca2+ diffuse from sarcoplasmic reticulum into sarcoplasm into myofibril
  3. Ca2+ binds to troponin causing it to change shape
  4. This causes tropomyosin to move and expose the myosin binding site on actin
  5. Myosin heads bind, forming actin myosin cross bridges
  6. Ca2+ activates ATP hydrolase in the head - ATP hydrolysed into ADP and Pi releasing energy
  7. Energy causes myosin head to bend, pulling the actin with it
  8. ATP binds to head, breaking cross bridge, myosin head attaches to actin further along
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12
Q

How is energy provided for contraction by

  1. Aerobic respiration
  2. Anaerobic respiration
  3. ATP-Phosphocreatine system
A
  1. Most ATP generated by oxidative phosphorylation in mitochondria (requires O2)
  2. ATP made rapidly by glycolysis
  3. ATP made by phosphorylating ADP with phosphate from phosphocreatine

ADP + Phosphocreatine (Pi) -> ATP + Creatine

PCr system in anaerobic and alactic

PCr stores inside cells, generates ATP rapidly but runs out after a few seconds

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13
Q

Slow twitch muscle fibres

A
  • slow less powerful contractions over long time period
  • aerobic (uses oxygen as final e- acceptor) so less fatigue as no lactic acid
  • for endurance work pr maintaining posture
  • Large store of oxygen in myoglobin, lots of mitochondria, lots of blood vessels (short diffusion distance)
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14
Q

Fast twitch muscle fibres

A
  • fast powerful contractions
  • sprint work
  • anaerobic respiration producing lactic acid so muscles become fatigued quickly
  • less myoglobin, mitochondria and blood vessels (no O2 needed)
  • more phosphocreatine to supply ATP
  • larger glycogen stores - for glycolysis
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15
Q

Function of myoglobin

A
  • binds to oxygen in muscles
  • very high affinity for oxygen
  • unloads oxygen when partial pressure is low
  • acting as a store for oxygen
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