Overview.
Direct phosphorylation.
Glycolysis.
Aerobic respiration.
Oxygen debt.
The muscles in the body, help us to engage in all physical activity.
It is the skeletal muscles which are involved in all kinds of activities,
like standing, sitting, walking, lifting, stretching, playing, etc..
There are about 650 skeletal muscles.
All these muscles, are mapped in the cortical homunculus in the brain.
The brain co-ordinates all these muscles to perform physical activity.
When the person is playing football,
the brain is constantly sending command signals, to different muscles.
All the skeletal muscles expend energy to perform work.
Other muscles tissue, like those present in the heart, lungs, gut, etc. work autonomously.
These muscles tissues, also expend energy, throughout the day, even when resting.
Energy is a basic requirement of muscles.
This energy is generated, in more than one way, in muscles.
All muscles cells generate ATP.
Muscles have a short term store of energy in the form of creatine phosphate.
Creatine phosphate is generated from ATP.
It can regenerate ATP when required.
In muscle cells which use ATP rapidly creatine phosphate, acts as a reservoir of energy.
Creatine is synthesised in the liver, and transported to the muscles via the blood stream.
Through phosphorylation creatine becomes creatine phosphate.
Creatine phosphate can anaerobically donate a phosphate group to ADP to form ATP.
This ATP can be used, for about the first fifteen seconds of intense muscle activity.
When muscles are resting, excess ATP can be used to create creatine phosphate.
ATP plus creatine generates creatine phosphate plus ADP.
This creatine phosphate is stored as a quick energy storage.
This process does not require oxygen.
Muscles use this energy, typically to kick start activity.
They then move on to other processes, to create energy for more continuous work.
Glucose is absorbed by the cells, with the aid of insulin.
Glycolysis is the process by which glucose is converted to lactic acid,
and energy in the form of ATP.
This is an anaerobic process.
Lactic acid, is a waste product, which contributes to muscle fatigue.
If enough oxygen is not present during strenuous exercise, lactic acid is produced.
This form of energy creation is useful, only for about a minute.
The excess of lactic acid build up causes muscles to fatigue.
Muscles are also capable, of storing a small amount of glycogen.
This glycogen can be used as a store for glucose.
Energy can be created from this glucose, through glycolysis.
The muscles in athletes, learn to store more glycogen.
The most important factor, in this process is the presence of oxygen.
In this case glucose is broken down to pyruvate.
This pyruvate enters the Krebs cycle.
Energy in the form of ATP is created.
Carbon dioxide and water are by products.
About 95% of the ATP required by muscles, is produced by aerobic respiration.
Aerobic respiration takes place in the mitochondria.
Amino acids and fatty acids, can also be metabolised through aerobic respiration, to produce ATP.
When we engage in strenuous activities, we may notice,
that we breathe fast, even after the activity is completed.
This is because the body apart from aerobic respiration,
has also exhausted the other metabolic pathways,
of direct phosphorylation, and glycolysis.
The muscles are in a state of oxygen debt.
After the activity the body continuous to draw extra oxygen, by fast breathing,
to restore these other short term pathways.
Oxygen is used to form oxymyoglobin.
Oxymyoglobin is the oxygen binding protein, found in muscle cells.
Creatine is converted into creatine phosphate.
Lactic acid is converted into glucose or glycogen.
This ensures that future short term needs of energy,
will be readily met, by the relevant metabolic processes.
This is the process of repaying the oxygen debt.