Mechanism of muscle contraction

The sliding filament Theory

• The way that muscles actually contract and shorten is a theory called the sliding filament theory

• This theory involves the movement of the microscopic thin (actin) and thick (myosin) filaments

the Sliding Filament Theory

• In this theory we need to look at the relationship between the actin filament and the myosin filament

• These filaments are going to work together in order to cause the contraction

the Sliding Filament Theory

• All over the thick filaments there are small heads that protrude from the body of the filament called myosin heads

• They myosin heads will attach themselves to binding sites on the thin actin filament.

the Sliding Filament Theory

• The binding sites are exposed and activated when calcium ions are present

• This allows myosin to bind temporarily to the actin filament

• The myosin then acts as oars to “row” in the thin filament

Energy for Muscle Contraction

• Muscles always need energy for muscle contraction

• Muscles can only use energy stored in the form ATP (Adenosinetriphosphate)

• Muscles only store 4-6 seconds worth of ATP therefore ATP needs to me made constantly

ATP creation

• There are three ways in which ATP is created in the body

• Direct Phosphorylation of ADP

• Aerobic respiration

• Anaerobic respiration

Direct Phosphorylation of ADP

• The body can directly Phosphorylate ADP into ATP

• This means that ADP and Creatine phosphate come together to set off a reaction that will create ATP and Creatine

Aerobic Respiration

• Aerobic respiration is how ATP is generated through cellular respiration in the presence of oxygen

• Aerobic respiration involves glycolysis, the Krebs cycle, and the electron transport chain.

Anaerobic respiration

• The human body can also get ATP from Anaerobic Respiration

• The method of Anaerobic Respiration is the fermentation of lactic acid

Muscle Fatigue

• If we exercise our muscles strenuously for a long time, muscle fatigue will occur.

• A muscle will become fatigued when it is unable to contract even though it is still be stimulated

Muscle fatigue

• Without rest an active muscle begins to tire and contracts more weakly until lit finally ceases reacting and stops contracting.

• This is believed to be from the oxygen debt that occurs during prolonged muscle activity.

Oxygen Debt• The oxygen debt is what happens when a person is not able to take in oxygen fast enough to keep up with the muscles when they are working hard.

• The oxygen debt will cause lactic acid to build up from anaerobic respiration and the muscles supply of ATP will dwindle.