Question

Explain the mechanism of neural control of respiration

Answer 1

Centre	Location	Effect on Respiration
Pneumotaxis centre	Dorsally in the nucleus parabrachialis of upper Pons	Increase Respiration rate by decreasing Inspiration time
Apneustic centre	Lower Pons	Prolonged Inspiratory ramps.
Dorsal root ganglion	Dorsomedial region of Medulla	Stimulation of Inspiration
Ventral root ganglion	Nucleus Ambigius rostrally,Nucleus retroambigius caudally	Remains inactive during quite /normal respiration,Increase Expiration during Exercise
Pre BOTC	Located on either side of Medulla ,Contain Pacemaker cells	Discahrges automatically causing inspiration by Phrenic nerve stimulation.

Pneumonic DIVE --DRG for Inspiration and VRG for expiration .

Mechanism of Neural control of Respiration .

1.Autonomic control Brainstem (Pons and upper Medulla)
2.Voluntary control - Cerebral cotex .

1)Pre Botzinger complex Pre BOTC -Known as pacemaker cells of respiration .
or, central pattern generator.

**Located on either side of the medulla between the nucleus ambiguus and the lateral reticular nucleus.

** These neurons discharge rhythmically, and they produce rhythmic discharges in phrenic motor neurons. Neurons in the pre-Bötzinger complex have neuro - kinin1 (NK1) and μ opioid receptors that are responsive to the neurotransmitter, substance P and opioids.

** In-vivo, substance P stimulates and opioids inhibit respiration. Depression of respiration is a side effect that limits the use of opioids in the treatment of pain.

**However, it is now known that 5HT4 receptors are present in the pre-Bötzinger complex and treatment with 5HT4 agonists blocks the inhibitory effect of opiates on respiration in experimental animals, without inhibiting their analgesic effect.

2)Dorsal and Ventral groups of respiratory neurons.

**Dorsal and ventral groups of respiratory neurons (DRG and VRG) are present in the medulla. However, lesions of these neurons do not abolish respiratory activity, and they apparently project to the pre-Bötzinger pacemaker neurons.

**DRG contains mainly I (inspiratory neurons) neurons and is part of the nucleus of the solitary tract (or nucleus tractus solitarius, NTS).

**The afferent input from arterial chemoreceptors and lung mechanoreceptor synapses on neurons in the NTS near the DRG.

**So, major function of DRG is integration of sensory information from respiratory system.

**VRG is a column of neurons that fire action potentials in phase with respiration.

**It includes neurons depolarizing during inspiration (I neurons) and expiration (E neurons).

**All of these respiratory centers are bilaterally symmetrical on the right and left sides of the brainstem.

3)PONTINE INFLUENCES

Modify pacemaker neurons, but not essential for respiration.

***Pneumotaxic- CenterControl rate of breathing.

*Located in the medial parabrachial and KöllikerFuse nuclei of the dorsolateral pons.

* Contains both E neurons and I.

*The normal function of the pneumotaxic center is unknown, but it may play a role in smooth switching between inspiration and expiration (“fine-tune” the breathing).

*A strong pneumotaxic signal can increase the rate of breathing 30–40 breaths per minute, whereas a weak pneumotaxic signal may reduce the rate to only 3–5 breaths per minute.

*** Apneustic Center- An area in the in caudal (lower part) pons, control depth of breathing by stimulating inspiratory neurons of pre-Bötzinger complex.

*The center is tonically active. This center may act as an integration site for afferent information.

* The specific group of neurons that function, as the apneustic center has not been identified.