Respiratory center summary midbrain upper pons inhibits inspiration

Respiratory center summary midbrain (upper pons) – inhibits inspiration pneumotaxic center Apneustic center (lower pons) – to promote inspiration pons medulla Cause the basic respirarory rhythm Spinal cord transfer for brain and respiratory muscle hypothesis of three –lever of respiratory center

PBKF neurons

dorsal respiratory group ventral respiratory group

Two respiratory nuclei in medulla oblongata Inspiratory center (dorsal respiratory group, DRG) • inspiratory neuron • more frequently they fire, more deeply you inhale，longer duration they fire, breath is prolonged, slow rate Expiratory center (ventral respiratory group, VRG) expiratory neuron, inspiratory neuron involved in forced expiration mainly

pond PBKF neurons dorsal respiratory group ventral respiratory group Spinal cord

hypothesis of basic rhythm—— pacesetter cell theory pneumotaxic center Central inspiratory activity generator inspiratory nueron Inspiratory muscle motor nueron PBKF neurons Inspiratory off swithch mechanism

Rhythmic Ventilation (Inspiratory Off Switch) • Starting inspiration – Medullary respiratory center neurons are continuously active (spontaneous) – Center receives stimulation from receptors and brain concerned with voluntary respiratory movements and emotion – Combined input from all sources causes action potentials to stimulate respiratory muscles

• Increasing inspiration –More and more neurons are activated • Stopping inspiration –Neurons receive input from pontine group and stretch receptors in lungs. –Inhibitory neurons activated and relaxation of respiratory muscles results in expiration. –Inspiratory off swithch.

3. Higher Respiratory Centers regulate the activity of the more primitive control centers in the medulla and pons. Allow the rate and depth of respiration to be controlled voluntarily. During speaking, laughing, crying, eating, defecating, coughing, and sneezing. ….

deflation

Hering-Breuer Reflex or Pulmonary Stretch Reflex • Including pulmonary inflation reflex and pulmonary deflation reflex • Receptor: Slowly adapting stretch receptors (SARs) in bronchial airways. • Afferent: vagus nerve

Significance of Hering-Breuer reflex – Terminate inspiration timely. – enhance inspiration/expiration transition， increase respiratory frequency. • Normal adults. Receptors are not activated at end normal tidal volumes. – Become Important in Chronic obstructive lung diseases when lungs are more distended. • Infants. Probably help terminate normal inspiration. – Become Important during exercise when tidal volume is increased.

Chemoreceptor Reflex Two Kinds of Chemoreceptors • Central Chemoreceptors – Responsive to increased H+ in CSF(cerebrospinal fluid) or local extracellular fluid • Peripheral Chemoreceptors – Responsive to decreased arterial PO 2 – Responsive to increased arterial PCO 2 – Responsive to increased H+ ion concentration.

Peripheral Chemoreceptors R：Carotid bodies • Aortic bodies adequate stimulus: PO 2 PCO 2 H+ exciting of breath depth and frequency Of breath pulmonary ventilation –glossopharyn –vagus

Carbon Dioxide, Oxygen and p. H Influence Ventilation (through peripheral receptor) • Peripheral chemoreceptors sensitive to PO 2, PCO 2 and p. H • Receptors are activated by increase in PCO 2 or decrease in PO 2 and p. H • Send APs through sensory neurons to the brain • Sensory info is integrated within the medulla • Respiratory centers respond by sending efferent signals through somatic motor neurons to the skeletal muscles • Ventilation is increased (decreased)

Central Chemoreceptor Location Rostral Medulla Caudal Medulla Ventral Surface of the medulla

The sensor neurons are especially excited by H+ H+ are the only direct stimulus for these sensor neurons.

Carbon Dioxide • Indirect effects – through p. H as seen previously • Direct effects – CO 2 may directly stimulate peripheral chemoreceptors and trigger ventilation more quickly than central chemoreceptors • If the PCO 2 is too high, the respiratory center will be inhibited.

• CO 2 easily crosses blood-brain barrier • , in CSF the CO 2 reacts with water and releases H+, • central chemoreceptors strongly stimulate inspiratory center arterial Blood –brain barrier Central Chemoreceptor Carbonic anhydrase

arterial Central Chemoreceptor peripheral Chemoreceptor

arterial Central Chemoreceptor peripheral Chemoreceptor

arterial Central Chemoreceptor peripheral Chemoreceptor 80% 20%

Effects of Hydrogen Ions Increasing H+ or decreasing PH can faster respiration. It is the effective stimulator to chemoreceptor. Pathway of H+ regulating respiration a. H+ in blood increases—excites peripheral chemoreceptor mainly b. H+ in cerebrospinal Fluid increases-excites central chemoreceptor

Oxygen • character • 1)Hypoxia stimulation act through peripheral chemoreceptor. If the inputing of peripheral chemoreceptor is cut, the stimulation effect disappear. • 2)The direct effect of hypoxia to center is inhibition. • 3)hypoxia ：PO 2< 80 mm. Hg ventilation volume increase is been awareness.

• The pathway of hypoxia regulating respiration: • The main pathway is acting directly on peripheral chemoreceptor and inputting impulse. Respiration center is excited. • Chronic hypoxemia, PO 2 < 60 mm. Hg, can significantly stimulate ventilation – emphysema, pneumonia – high altitudes after several days

Brief summary Central Chemoreceptor peripheral Chemoreceptor

Overall Response to. Pco 2, Po 2 and p. H