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The Sliding Filament Theory
Transcript of The Sliding Filament Theory
Muscle fibers and Myofibrils
Skeletal muscle is composed of microscopic, individually specialised cells called muscle fibers , each muscle fiber is enclosed within a thin cell membrane called the sarcolemma, this fiber contains several nuclei and a cytoplasm called sarcoplasm
Inside each muscle fiber there are small cylindered shaped organelles called myofibrils which contain thin and thick filaments, actin and myosin along with two other proteins troponin and tropomyosin which are found in the actin filament.
The Sarcoplasmic reticulum and the Sarcomere
What is the sliding filament theory?
The sliding filament theory describes the mechanism that create contraction. Contraction is the process when the actin and myosin filaments interact , thus when the cross bridges attach and create the force that enables the actin filaments to slide towards the myosin filaments.
During muscle contraction the sarcomere shortens and the distance between the Z lines, shorten thus the overlap between actin and myosin increases. Muscles contract in order to move limbs or maintain correct body posture or position.
Bibliography( Harvard System)
Name of Book: Human anatomy and physiology
Name of Authors/ Writers: Robert Carola , John P Harley , Charles K Noback
Edition: International edition
Page numbers: 235-250
Name of Book: Fundamental of anatomy and physiology
Name of Author: Frederic Martini
Edition: Second edition
Page number: 297-308
Website for information:
vistited on the 31/03/2014
Websites for picture : http://mollythrodahl.wordpress.com/
Writer: Molly Throdahl
Visited on the 25/03/2014
Websites for picture: http://cyhsanatomy1.wikispaces.com/Sliding+Filament+Theory+of+Muscle+Contraction
Visited on the 25/03/2014
Website for picture:
As you can see in the diagram above , the sarcoplasmic reticulum is responsible for the release of calcium ions, which produces muscle contraction as well as muscle relaxation.
Around each myofibril there is what we call the sarcoplasmic reticulum which is composed of a network of tubes which release calcium ions that produce contraction.
A section of the myofibril , from one Z line to the other makes up the sarcomere, which is the fundamental unit of muscle contraction. A sarcomere is the one responsible for the muscle contraction. When a muscle contracts the sarcomere shortens, likewise when the muscle relaxes the sarcomere goes back to its original shape, extending further away
The Sliding Filament theory Process in steps
Firstly a signal is sent from central nervous system to the muscle via neurons
Calcium ions are then released by the sarcoplasmic reticulum, this then travel along the Tubules, were it finally arrives at the muscle fiber , to the myofibrils
Calcium ions then bind onto the troponin protein resulting in the actin filaments rotating and exposing the binding sites to the myosin heads.
The myosin head then attaches to the actin binding sites, this is also referred to as the cross bridge.
ADP also known as adenosine diphosphate is responsible for the force which creates the interaction between the actin and myosin filaments, this is referred to as the ‘power stroke’ whereby the actin filaments slide by the myosin filaments. This stroke results in the sarcomere shortening and contracting.
Adenosine triphosphate abbreviated as ATP is responsible for activating the myosin head
ATP is then required to detach the cross bridges from the actin filaments
Calcium ions then return back into the sarcoplasmic reticulum where they are stored. Tropomyosin returns to block the binding sites and
the actin filaments returns to its resting position causing the muscles to lengthen and relax into their normal position.
Troponin and Tropomyosin
Troponin and tropomysosin are situated in the actin filaments, both proteins have a very important role in assisting in both muscle contaction and muscle relaxation.
Tropomyosin blocks the actin binding sites from any further exposure to the myosin cross bridges.
Troponin does the complete opposite , it enables the attachment sites to be exposed to the myosin cross bridges.