Normal quiet breathing consists of active inspiration followed by passive expiration; when respiratory efforts are increased, active expiration also comes into play.
Brainstem neurones that control breathing can be divided into groups that regulate these three phases of the breathing cycle.
Neurones with a respiratory rhythm exist in a number of sites throughout the medulla. An important group of neurones that generate the respiratory rhythm can be found within a column known as the ventral respiratory column. Within this column one particular group of neurones, the pre-Bötzinger complex (preBötC), are essential for breathing, and are seen as the primary respiratory rhythm generator.
The older literature described a pontine pneumotaxic centre that could modify the rhythm and depth of breathing: recently it has been possible to identify which pontine neurones are involved.
Respiratory rhythm and tidal volume are increased when arterial pCO2 is elevated, a phenomenon that depends upon sensors known as the central chemoreceptors, which exist on the ventro-lateral surface of the medulla and are in close contact with the cerebrospinal fluid.
Key Words: Respiratory rhythm; respiratory neurones; central chemoreceptors; pneumotaxic centre
Image source: www.neurology.org
Neuroanatomy of the brainstem respiratory control network.
Brainstem Neurones with Respiratory Rhythms
The diagram shows the sites in the medulla and pons where neurones with respiratory rhythms are found.
The nucleus ambiguus (NA) and nucleus of the tractus solitarius (NTS) are involved in reflex functions, but are not primary rhythm generators.
The pontine nuclei that form the classical pneumotaxic centre are also not primary rhythm generators. Rhythmic breathing continues following destruction of the pons.
The ventral respiratory column or group (VRC) contains respiratory neurones known to be essential for the respiratory rhythm. This column can be subdivided into different components, and it is believed that one, in an area known as the pre-Bötzinger complex (preBötC), is the principal respiratory rhythm generator.
The other functional compartments of the VRC and some pontine respiratory neurones are involved in shaping the basic rhythm produced by preBötC.
The classical literature identified a pontine pneumotaxic centre that could modify the pattern or depth of breathing. Two groups of pontine respiratory neurones are found in the dorsolateral pontine parabrachial and Kölliker–Fuse nuclei, and these influence the shape and pattern of respiratory movements.
Respiratory rhythm and tidal volume are increased when arterial pCO2 is elevated. The primary central CO2 chemosensors are found on the ventral surface of the medulla oblongata, but other regions, such as the preBötC, may also contain chemoreceptors.