Role of Medullary Centers

Rhythmic discharge of inspiratory impulses

Dorsal respiratory group of neurons are responsible for the normal rhythm of respiration. These neurons maintain the normal rhythm of respiration by discharging impulses (action potentials) rhythmically. These impulses are transmitted to respiratory muscles by phrenic and intercostal nerves.

Inspiratory ramp

Inspiratory ramp is the pattern of impulse discharge from dorsal respiratory group of neurons. These impulses are characterized by steady increase in amplitude of the action potential. Impulse discharge from these neurons is not sudden and it is also not uniform.

Inspiratory ramp signals

To start with, the amplitude of action potential is low. It is due to the activation of only few neurons. Later, more and more neurons are activated, leading to gradual increase in the amplitude of action potential in a ramp fashion. Impulses of this type discharged from dorsal group of neurons are called inspiratory ramp signals. Ramp signals are not produced continuously but only for a period of 2 seconds, during which inspiration occurs. After 2 seconds, ramp signals stop abruptly and do not appear for another 3 seconds. Switching off the ramp signals causes expiration. At the end of 3 seconds, inspriatory ramp signals reappear in the same pattern and the cycle is repeated. Normally, during inspiration, dorsal respiratory

group neurons inhibit expiratory neurons of ventral group. During expiration, the expiratory neurons

inhibit the dorsal group neurons. Thus, the medullary respiratory centers control each other.

Significance of inspiratory ramp signals

Significance of inspiratory ramp signals is that there is a slow and steady inspiration, so that the filling of lungs with air is also steady.

Role of Pontine Centers

Pontine respiratory centers regulate the medullary centers. Apneustic center accelerates the activity of

dorsal group of neurons and the stimulation of this center causes prolonged inspiration.

Pneumotaxic center inhibits the apneustic center and restricts the duration of inspiration.

Pre-Bötzinger Complex

Pre-Bötzinger complex (pre-BötC) is an additional respiratory center found in animals. It is formed by a

group of neurons called pacemaker neurons, located in the ventrolateral part of medulla. Pacemaker neurons generate the rhythmic respiratory impulses. Medullary centers send nerve fibers into this complex. Exact functioning mechanism of this complex is not known.


Peripheral chemoreceptors are the chemoreceptors present in carotid and aortic region.

Mechanism of Action

Hypoxia is the most potent stimulant for peripheral chemoreceptors. It is because of the presence of oxygen sensitive potassium channels in the glomus cells of peripheral chemoreceptors. Hypoxia causes closure of oxygen sensitive potassium channels and prevents potassium efflux. This leads to depolarization of glomus cells (receptor potential) and generation of action potentials in nerve

ending. These impulses pass through aortic and Hering nerves and excite the dorsal group of neurons. Dorsal group of neurons in turn, send excitatory impulses to respiratory muscles, resulting in increased ventilation. This provides enough oxygen and rectifies the lack of oxygen.

In addition to hypoxia, peripheral chemoreceptors are also stimulated by hypercapnea and increased

hydrogen ion concentration. However, the sensitivity of peripheral chemoreceptors to hypercapnea and

increased hydrogen ion concentration is mild.

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