Control of Respiration
Dr. Meg-angela Christi Amores
Control of Respiration
• Central
o Respiratory Center
o Bilaterally in the medulla oblangata and pons
1. Dorsal Respiratory Group – dorsal medulla
–
Mainly inspiration and rhythm of breathing
2. Ventral Respiratory Group – ventrolateral medulla
–
Either inspiration or expiration
3. Pneumotaxic Center – dorsal superior pons
–
Controls rate and pattern of breathing
Dorsal Respiratory Group
• Generates basic rhythm of respiration
• Operates on a “ramp” signal
• Begins weakly and increases steadily for about 2 seconds,
then ceases abruptly for next 3 secs.
• Turns off excitation of diaphram, allows elastic
recoil
• 2 ways of control:
1. Control of rate of increase of ramp signal
2. Control of limiting point at which ramp signal ceases
Pneumotaxic Center
• Control “switch off” point of inspiratory ramp
• If strong, inspiration is 0.5 seconds, filling
lungs only slightly
• Primary function is to limit inspiration
Ventral Respiratory Group
• Inactive during normal quiet respiration
• No participation in rhythm control
• Contributes to respiratory drive when
pulmonary ventilation increases
• Some neurons excite – inspire
• Other neurons excite – expire
• Useful in heavy breathing
Chemical Substances
• Oxygen
• No significant direct effect, instead, regulates
respiration on its effect on peripheral chemoreceptors
• Carbon Dioxide
• Potent indirect effect
• Excess concentration in blood acts directly on
respiratory center itself
• Hydrogen
• Excites sensory neurons in chemosensitive areas
• Cannot cross blood brain barrier
Control of Respiration
• Peripheral
– Chemoreceptors – special nervous chemical
receptors located in several areas outside brain
• Detects changes in oxygen concentration in blood
• Transmits nervous signals to the respiratory center to
the brain
• Mostly in Carotid bodies and Aortic bodies
– Decreased arterial O2 concentration in blood
– Increased CO2 and H ion concentration
Chemoreceptors
Factors that Affect Respiration
• Voluntary control
• One can
hyperventilate/hypoventilate
• Nervous pathway for voluntary
control passes directly from
cortex and down the corticospinal
tract, not through the respiratory
center
Factors that Affect Respiration
• Effect of Irritant receptors in Airways
• Epithelium in trachea, bronchi, bronchioles – sensitive
• Cause cough and sneeze
• Also cause bronchial constriction – as in BA and
Emphysema
Factors that Affect Respiration
• Function of lung “J” receptors
• Sensory nerve endings in alveolar walls, in juxtaposition to
pulmonary capillaries
• Excitation gives feeling of dyspnea
• Effect of brain edema
• Activity of respiratory center may be decreased or
inactivated by acute brain edema due to blockage of blood
supply
• Anesthesia
• Most prevalent cause of respiratory
depression and arrest
• Eg Na pentobarbital, morphine overdose
Abnormalities in Respiratory Control
• Periodic breathing
• (e.g. Cheyne-Stokes breathing)
• Waxing and waning respiration
• 40-60 seconds
– Due to:
1. Long delay of transport of blood carrying O2
–
As in severe heart failure
2. Increase negative feedback gain
–
Brain damage