Sliding Filament Theory

The sliding filaments theory of muscle contraction was discovered in 1954 proposed that muscle contraction is an onset cyclic process which involves the sliding of filaments and the shortening of sarcomere. Striated muscles such as skeletal muscles contain a highly organised internal structure which allows these muscle to contract following the mechanism of sliding filament theory.

Skeletal muscle contraction requires an action potential which is an electric signal sent though motor neurones towards the muscle cells. This action potential originated for the central nervous system which travels down the alpha motor neurons and propagates though the lengths of the axon till neuron terminal is reached. As this impulse travels along the axon it

These ions diffuse into the sarcomere and bind onto troponin C which is located on the thin filaments of the myofibrils known as actin. The binding of ca2+ onto troponin results in a conformational change of tropomyosin, which normally obstructs the actin-myosin head binding site. The conational changes orientates the positioning of tropomyosin thus allowing the binding site to be exposed.

The thick filament of the myofibrils also known as myosin, consists of a head structure which poses ADP and inorganic phosphate. Myosin head bind tightly onto the actin at the binding site and forming a temporary cross-bridge. The formation of this cross bridge resulting in the phosphorylation of the ADP and inorganic phosphate in to ATP. This induces a power stroke movement of the myosin head creating a pulling force on the Z lines of the sarcomere and efficiently allowing the two filaments to slide over each other. The sliding of filaments causes the sarcomere to shorten and the skeletal muscle to

One of the most common form of dystrophy is Duchenne muscle dystrophy (DMD). DMD is characterised as an X-linked inherited mutation on the DMD gene which manifests rapidly causing muscular waste within the first 3 years of a child’s life. Recent study shows DMD is associated with an incidence of 1 to 3500 boys at birth (refernce).

Duchenne muscular dystrophy is said to be the most sever neuromuscular disorder which is caused by mutation mapped on dystrophin gene. Most of these mutation include either, frameshift, deletion, duplication or nonsense eventually leading to the loss of a functional protein. Dystrophin encodes for a 427kD protein that is naturally located in the inner surface of the sarcolemma and with high concertation at costameres. There have been several different mutation associated with this gene but disruption of this protein has always lead to muscle dystrophies. At early stages of the disease patient’s biopsies have shown both degeneration and regeneration of the myofibers indicating there is a balance between the cell death and regenerative process. However muscle fibres taken from older patients showed a reduction in the number of myofibers and far more adipose and connective tissues, clearly indicating that the progression of this disease is due