Sliding filament theory

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Physical Education - Sliding filament theory

Sliding filament theory

For contraction [1] to occur, a nerve impulse must be sent from the brain.
Down at the motor end plate, calcium ions are released which effectively
act as a power switch. This power switch activates the crossbridges (which
connect thick and thin filaments).

ATP energises the crossbridges, which allows a pulling action to occur,
resulting in the thin filaments sliding over the thick filaments. This
occurs all down the length of the fibre (at each sarcomere [2]), and the
result is a contraction [3] of the muscle.

What happens to each of the following when a muscle contracts?

* Actin [4] - thin filaments: slide over the thick filaments; whether
they slide toward or away from one another depends on whether it is a
concentric or eccentric contraction [5]

* Myosin [6] - thick filaments; do not move under contraction [7]

* - oar-like structures that are attached to the thick (myosin [8])
filaments. These structures reach out and are attracted to the thin (actin
[9]) filaments. When contraction [10] occurs, these oar-like structures
drag the thin filaments in toward the centre of the sarcomere and the
muscle contracts (concentric contraction [11])

* - distance between the z-line [12] and the edge of the A band

* - the gap between the thin filaments before contraction. The H zone
disappears upon full contraction

* - the length of the thick filament

Make sure you have a good look at a diagram of the sliding filaments
(actin): one is on the previous page. It is quite possible that a question
with a diagram will be used in the exam.

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Links:
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[1] http://alison.com/#
[2] http://alison.com/#
[3] http://alison.com/#
[4] http://alison.com/#
[5] http://alison.com/#
[6] http://alison.com/#
[7] http://alison.com/#
[8] http://alison.com/#
[9] http://alison.com/#
[10] http://alison.com/#
[11] http://alison.com/#
[12] http://alison.com/#