Muscle

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Skeletal muscle

A skeletal muscle muscle consists of muscle fibres. One muscle fibre is approximatels 100 µm in diameter and consists of several nuclei and many mitochondria. Each muscle fibre contains myofibrils. These are approximately 1 µm in diameter.

The myofibril is organised in repeating units called sarcomeres. These contain thick and thin filaments. Muscle contraction occurs when the thin filaments slide along the thick filament by hydrolysing ATP [1] by what is known as the Sliding Filament Theory.

Contraction in a muscle cell is produced by an action potential travelling along a motor neurone and arriving at a Synapse. The voltage gradient causes voltage-gated calcium ion channels in the presynaptic neurone to open, triggering vesicles containing neurotransmitters, specifically acetylcholine, to travel towards the sarcolemma; fusing with the membrane and releasing acetylcholine into the synaptic cleft [2]. They diffuse across the cleft where they bind to specific receptors called nicotinic cholinergic receptors on the sarcolemma, where the depolarisation travels along the membrane and deep into the cell via T-tubules [3]. Therefore it allows the sarcoplasmic reticulum to become depolarised, releasing calcium ions and triggering muscle contraction to take place by the sliding filament theory [4].

References

  1. Berg J., Tymoczko J and Stryer L. (2001) Biochemistry, 5th edition, New York: WH Freeman.
  2. Bowness E, Braid K, Brazier J, Burrows C, Craig K, Gillham R, Towle J. (2009), A2-level Biology The Revision Guide Exam Board AQA, page 57-60, Newcastle-upon-Tyne: CGP books.
  3. Bowness E, Braid K, Brazier J, Burrows C, Craig K, Gillham R, Towle J. (2009), A2-level Biology The Revision Guide Exam Board AQA, page 57-60, Newcastle-upon-Tyne: CGP books.
  4. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008), Molecular Biology of The Cell, page 1028-1029, 5th edition, New York:Garland Science.
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