Download CONTROL OF RESPIRATION

CONTROL OF RESPIRATION
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Control Of Respiration
• Respiratory process is involuntary process, but
under voluntary control as we can stop
breathing.
• Respiratory center is in the brain stem. It
causes rhythmic breathing pattern of
inspiration and expiration.
• Inspiratory and Expiratory muscles are skeletal
muscles and contract only when stimulated by
their nerve supply.
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Neural Control Of Respiration
1. Center that generate inspiration and
expiration.
2. Factors that regulate rate and depth of
respiration .
3. Factors modifying the respiratory activity
(voluntary eg.Speech or involuntary eg.
Cough or sneeze)
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Respiratory Centers
 In Medulla
- Inspiratory center(Dorsal respiratory group)
- Expiratory center (Ventral respiratory group)
These are neuronal cells that provide output to
respiratory muscles for inspiration and expiration.
 In Pons
- Pneumotaxic center – upper pons
- Apneustic center – lower pons
Pontine Center influence the output from medullary
centers.
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Respiratory Centers
• Inspiratory and Expiratory neurons in the
medullary center.
• We are breathing rhythmically in and out
during quiet breathing because of alternate
contraction and relaxation of inspiratory
muscles [diaphragm and External-intercostal
muscles] supplied by phrenic nerve [C345],
and intercostal nerves .
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Respiratory Centers
• Order comes from medullary center to spinal
cord motor neuron cell bodies [anterior horn
cells].
• When these motor neurons are activated,
they stimulate the inspiratory muscles leading
to inspiration.
• When these neurons are not firing, the
inspiratory muscles relax and expiration takes
place.
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Respiratory Centers
‘Summary’
• Inspiratory center [DRG] – Inspiration
(Pre-Botzinger complex, generates respiratory rhythm)
• Expiratory center [VRG] – used during active/ forced
Expiration
• Pneumotaxic center – acts on inspiratory center to
limit duration of inspiration,therefore regulates
inspiration and letting expiration to occur normally.
• Apneustic center – causes Apneusis [deep inspiration].
Apneusis occurs in certain severe type of brain
damage.
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Hering-Breur reflex
• Over inflation of lungs is prevented by this
reflex
• Pul. stretch receptors in airways are
stimulated by stretching of lungs by large tidal
volume.
• Action potential from these receptors go to
medullary center and inhibit insp. Neurons.
• Insp. is cut down & lung is prevented from
over inflation.
Chemical Control Of Breathing
• Chemical factors which affect the ventilation
are
-PO2
-PCO2
-H+ ion
• Their effect is mediated via respiratory
chemoreceptor.
• We will study chemoreceptors first .
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CHEMORECEPTORS
• There are two types of Chemoreceptors
1. Peripheral Chemoreceptors
2. Central Chemoreceptors
Peripheral Chemoreceptors
• Peripheral Chemoreceptors are Carotid bodies & Aortic
bodies.
Carotid Bodies
• Carotid body is present near the carotid artery bifurcation
on each side.
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They contain cells which can sense the level of PO2,
PCO2 , H+ ion.
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Peripheral Chemoreceptors
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Carotid bodies [cont]
Carotid body sends impulse to respiratory center
in medulla via IX cranial nerve [glassophyrangeal].
Aortic bodies
These receptors are situated in the aortic arch .
They also sense the O2, CO2, and H+ ion changes
in the blood.
Aortic body sends impulse to respiratory center
in medulla via X cranial nerve [vagus].
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Central Chemoreceptors
• They are located in the medulla near the
respiratory center .
• These central chemoreceptors monitor the
effect of PO2, PCO2 , and H+ ion.
• When CO2 increases, we get:
CO2 + H2O  H+ + HCO3• Increased H+ directly stimulates the central
chemoreceptors.
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‘Summary’
• Decreased PO2, increased PCO2, increased H+ ion
concentration in arterial blood stimulates Peripheral
Chemoreceptors. Most important stimulating factor is
decreased PO2 on peripheral chemoreceptors.
• Increased PCO2 in the arterial blood and increased H+
ion in the brain ECF strongly stimulates the central
chemoreceptors and dominant control of ventilation.
-Decreased PO2 in the arterial blood – depresses the
central chemoreceptors.
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What You Should Know From This
Lecture
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Neural Control of Respiration
Name of Respiratory centers in the Brain stem
Chemical Control of Breathing
Peripheral Chemoreceptors
Central Chemoreceptors
Effect of decreased PO2, increased PCO2 and H+
on Peripheral and Central Chemoreceptors