Energy Systems

There are 3 energy systems that provide necessary supplies of energy for muscle contractions.

The Alactic System

This involves the anaerobic, rapid regeneration of ATP through an energy-rich compound existing in the body called Creatine Phosphate (Phosphocreatine). Creatine Phosphate is broken down in the sarcoplasm of the muscle cell. This is assisted by the enzyme Creatine kinase (Creatine Kinase is stimulated by the increase in free Phosphates; resulting from the breakdown of ATP into ADP). Once ATP is broken down, it must be resynthesized (which requires energy itself). It is a coupled reaction.

Features

*Lasts 8 - 12 seconds of maximum effort

Downsides

*Limited in the muscle

*Causes fatigue and subsequently lowers the ability to sustain ATP resynthesis

The Lactic Acid System

Once Creatine Phosphate is depleted, ATP is then resynthesized from glycogen. Carbohydrates and starch are stored as glycogen in the muscles and the liver. Glycogen must be converted to

Glucose-6-phosphate to provide energy for ATP resynthesis. This process requires one molecule of ATP. This process is called Anaerobic Glycolysis since conducted without oxygen.

Features

*Lasts 10 seconds - 3 minutes (peaks at 1 minute)

*Releases 5% of energy from the glycogen molecule

*Quick

*Lactic acid increases from 1 mmol/kg - 25 mmol/kg

Downsides

*Lactic acid produced prevents further glycogen breakdown

Aerobic System

This is 18 times greater than the Anaerobic System. It takes 3 minutes to release the remaining 95% of energy from the glycogen molecule. Glucose molecules are then broken down in the mitochondria. In the anaerobic system, lactic acid is produced; however, since oxygen is present, lactic acid becomes pyruvate during low intensity exercise. Pyruvate is then turned into Acetyl-Coenzyme-A, which is then combined with Oxaloacetic acid. These reactions begin the Kreb’s Cycle.

Features

*Lasts indefinetly as long oxygen is available

*The breakdown of 1 glycogen molecule will resynthesize 38 ATP molecules:

2 —>Anaerobic Glycolysis

2—->Kreb’s Cycle

34—>Active Transport/ Electron Transport System

Downsides

Used for endurance or long term activities only

Muscle Contractions

A motor unit is a group of muscle fibres that are innervated by a single motor neuron. A motor unit contracts when the neuron fires an electrical signal that reaches the muscle fibres which contracts and causes movement.

Action Potential

A wave of electrical activity that travels down a neuron. It is caused by an opening and closing of ion channels (sodium, potassium, calcium). In muscle fibres, action potentials are responsible for stimulating muscle contractions as they release calcium ions from the sarcoplasmic reticulum.

Sliding Filament Theory

It states that the thick myosin filament in muscles slide past the thin-acting filament, causing the muscle to shorten (contract).