The Nervous System & Its Signals to Breathe
The respiratory centre of the brain regulates involuntary breathing so that the concentration of O2 and CO2 remain constant. There are three stimuli that affect the respiratory centre
- CO2 in the blood stream: affects the respiratory centre
directly. Though a lack of oxygen will also affect the centre, it is more
sensitive to carbon dioxide.
- response of the chemoreceptors: located in two centres, the carotid
and aortic bodies, just above the heart, the chemoreceptors respond to the
chemical makeup of the bloodstream as it flows through minute arteries coming
off the major blood vessels. When the CO2 level rises to a certain
level, it sends a signal to the brain, which in turns sends a signal to
the diaphragm and to the intercostals. Once the inspiration is completed,
the O2 level rises, and the muscles relax. The CO2
laden air is pushed out of the lungs by passive forces, and the process
begins again, happening about 12 times a minute for our whole lives.
- activity of the stretch receptors: located in the lung tissue,
bronchial tree and the visceral pleura, these respond to the amount of stretch
in the lung tissue. When the lungs are relaxed (deflated), few impulses
from the stretch receptors are sent to inspiratory centre of the brain.
When they are expanded, impulses are relayed at high-frequency to the expiratory
centre of the brain, which inhibit the inhalation process. Overexpansion
of the lungs is also inhibited by receptors located in the bronchioles.
When the receptors are relaxed, the signals are inhibited, allowing the
inhalation process to begin again.
Back to Respiration
More on the Nervous System
Speech and Hearing Science : Anatomy and Physiology
by Willard R. Zemlin
Check out Chapter 5, The Nervous System and in particular, pages 401 - 404.