This document discusses control of breathing. It begins by defining breathing and respiration, noting that breathing is the process of inhaling and exhaling air while respiration involves cellular oxidation reactions. It then describes the mechanics of breathing, including inspiration driven by diaphragm and intercostal muscle contraction, and expiration triggered by relaxation of these muscles. The document outlines three levels of nervous control over breathing: primary control by the medulla oblongata in response to rising blood CO2 and H+ levels, secondary control via chemoreceptors responding to blood O2, and alveolar control through stretch receptors signaling full alveoli to the medulla.

1. Control Of Breathing
By- Anindya Jana
B. Pharm 2nd year

2. What Is Breathing?
Breathing is entrance and
exit of air into and out of
lungs.

3. Mechanics Of Breathing
Breathing, called ventilation consists of two phases :-
1st – Inspiration
2nd - Expiration
Inspiration
→ To increase temporarily the activity of
respiratory center causes:
● Contraction of the Diaphragm (downwards) and
intercostal muscle (up and outwards)
● This increase the volume of thoracic cavity and
decrease the pressure in the lungs.
● Air pressure is greater than the pressure in the
lungs and alveoli fill with air.

4. Expiration
→ Inhibition of respiratory center (due to full
alveoli) causes:-
● Relaxation of the intercostal muscle and the
diaphragm.
● This decrease the volume of the thoracic cavity
and increase the pressure in the lung.
● Air pressure is less than the pressure in the
lung so air is forced out of the lungs.

6. What is the difference between
breathing and respiration?
Generally, breathing and respiration are often
considered the same; however there is a big
difference in the meaning of the two.
Breathing is when you consistently breathing air in
and out. It is the process of taking in oxygen and
expelling carbon dioxide.
Respiration is a process in which the C-H bonds
(carbon-hydrogen bonds) in food are broken down
by oxidation reduction reactions and the energy is
transformed in to ATP

7. Control Of Breathing
●Breathing is under the control of the Autonomic
Nervous System. This means it is a involuntary
action.
An involuntary action is one which occurs without the
conscious choice of an organism.
●We can control the rate and depth of breathing
voluntarily.
→Nervous system includes :-
•Chemoreceptors (Sensitive to CO2 and H+)
•Respiratory center of Medulla Oblongata.
•Stretch Receptors in Alveoli.

8. Primary Nervous control
●When the CO2 and subsequently H+ concentration
in the blood increases, the activity of Medulla
Oblongata is temporarily increases.
The medulla oblongata is the most vital part of the brain because it is
the control center for breathing, blood pressure and heart beat among
other involuntary body functions under all unconscious control.
What happens to CO2 in the blood!!
CO2 + H2O ———→ H2CO3
Then,
H2CO3 ———→ H+ + HCO3
-
This is why CO2 level in the blood lead to an
increase in H+ level.

9. Secondary Nervous Control
●Chemoreceptors located in the carotid arteries and the
aorta respond O2 level in the blood.
A chemoreceptor, also known as chemo sensor, is
a sensory receptor that produce a chemical signal into
an action potential.
●When O2 level in the blood are low, a nerve impulse is
stimulate the respiratory center of medulla oblongata.

10. Alveolar Control
● The alveoli contain stretch receptors.
Stretch Receptors:
They are the mechanoreceptors responsive to various
organs and muscles, and are neurologically linked to
the medulla in the brain via afferent nerve fibers.
● When the alveoli are full, the stretch receptors sent a
signal to the respiratory center.
●This signal inhibits the respiratory center (negative
feedback).