what causes us to breathe

[Phee]

What actually causes us to start breathing, an increase in blood carbon dioxide levels or a decrease in blood oxygen levels?

[Poison]

Aren't they basically the same?

[MrMistery]

He/She is asking what stimulates the pathway. I am rather curious myself since i did not come across this info anywhere...

[Poison]

I couldn't think of any logical explanation too.

[MrMistery]

It is not a logic question, it is a question of cellular pathways and biochemistry

[Poison]

yes, but increase of CO2 means decrease of O2. So which one stimulates...

[victor]

breathing is under the control of autonom nerve. When the cells and Tissues lack of oxygen, they send a chemical signals to the nervous system and 'autonom'ically, we're forced to take a breath.
Beside, there're also many other factors which get involved in this mechanism like inhibotors, pH, CO2-O2 equilibrium, etc.

[MrMistery]

That is what the user is asking, a very interesting question: What stimulates that nerve impulse? Excess CO2 or/and lack of O2? Of course they happen at the same time but which one works as a stimulus? My guess is just like yours victor: lack of O2. However, i have no reference to prove my theory

[sdekivit]

yes, but increase of CO2 means decrease of O2. So which one stimulates...

the both regulate different things

--> High alveolar pCO2 cause bronchioles to dilate and high alveolar pO2 cause alveolar capillaries to dilate.

[Poison]

I learned something new. Good.
But maybe the exact answer should be: both

[victor]

My hypothesis said that it's related with the pH of the interestial fluid..excess of CO2 means little bit acidic blood plasm and I can think that's the time when signals should be transducted..

[MrMistery]

LOL... I understood the question in a different way. When you hold your breath, what is the thing that gets your breathing muscles started? Is it excess CO2 or a lack of oxygen?