15.1.11

Sliding Filament Theory Contraction

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Sliding Filament Theory

The sliding filament theory explains how muscle contraction is coordinated in myofibrils. An overview of the steps involved are:

Depolarisation of the sarcolemma

Depolarisation of the sarcolemma

  • Muscle contraction is initiated when an action potential arrives at the muscle cells.
  • The action potential depolarises the sarcolemma.
Contraction of the sarcomeres

Contraction of the sarcomeres

  • Depolarisation of the sarcolemma causes the myosin and actin filaments to slide over each other.
  • The sliding movement causes the sarcomeres to contract.
Muscle contraction

Muscle contraction

  • There are multiple sarcomeres along the length of myofibrils.
  • As many sarcomeres contract simultaneously, the muscle fibres contract.
  • Contraction of the muscle fibres causes the whole muscle to contract.
Muscle relaxation

Muscle relaxation

  • After the muscle has contracted, the sarcomeres relax.
  • The filaments slide back over each other and the muscle relaxes.

Myosin Heads

The Sliding Filament Theory takes place due to globular heads on myosin filaments. The globular heads allow myosin and actin filaments to bind together and slide past each other.

Globular head

Globular head

  • Myosin filaments have globular heads.
  • Globular heads can move back and forth.
  • The movement of the globular heads is what allows actin and myosin filaments to slide past each other in muscle contraction.
Binding sites

Binding sites

  • There are two binding sites on every myosin head:
    • One site can bind to actin.
    • One site can bind to ATP.
  • There is also a binding site for the myosin heads on actin filaments. This is called the actin-myosin binding site.
Tropomyosin

Tropomyosin

  • Tropomyosin is a protein that is located on actin filaments.
  • Tropomyosin plays an important role in muscle contraction because it blocks the actin-myosin binding site when muscle fibres are at rest.
  • When muscle fibres are stimulated, the tropomyosin protein is moved so that myosin heads can bind to the actin-myosin binding site.
  • When actin and myosin bind, they can slide past each other to cause muscle contraction.
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1

Cell Structure

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Cell Structure

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Water

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Enzymes

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Transport in Plants

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Transport in Plants

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Gas Exchange System

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Photosynthesis

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14

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Homeostasis

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The Kidney

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14.3

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Blood Glucose Concentration

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Homeostasis in Plants

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15

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Control & Coordination in Mammals

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Control & Co-Ordination in Plants

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16

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16.3

Gene Control

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17

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Variation

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Natural & Artificial Selection

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Evolution

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Biodiversity

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19

Genetic Technology (A2 Only)

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Manipulating Genomes

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Genetic Technology Applied to Medicine

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Practice questions on Sliding Filament Theory Contraction

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Stages in Sliding Filament TheoryPut in order
  2. 2
    What causes the myosin and actin filaments to slide over each other?Multiple choice
  3. 3
    Which of these do NOT bind to myosin heads?Multiple choice
  4. 4
    Which of the following statements about myosin heads are true?True / false
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Skeletal Muscle

Sliding Filament Theory Contraction 2