Control of Respiration

Describe apneustic breathing

prolonged inspiratory spasms followed by short expiration.

Respiratory centres is made of several groups of neurons located bilaterally in medulla oblongata and pons. Name 4 major groups.

1. Dorsal Respiratory Group (DRG) - medulla 2. Ventral Respiratory Group (VRG) - medulla 3. Pneumotaxic center - pons 4. Apneustic centre - pons

State the location & function for each groups of respiratory centres respectively

1. Dorsal Respiratory Group (DRG): - medulla - responsible for inspiration (I neurons) 2. Ventral Respiratory Group (VRG): - medulla - both inspiration & expiration (I and E neurons) 3. Pneumotaxic center: - upper pons - sends inhibitory signals to DRG - controls rate & pattern of breathing 4. Apneustic centre - lower pons - send excitatory signals to DRG to prolong inspiration - inhibited by pneumotaxic centre

Define Biot's breathing

Periods, or "clusters", of rapid respirations of close to equal depth followed by regular periods of apnoea.

This respiratory centre sends inhibitory signals to DRG, switching off the ramp signals

Pneumotaxic center

Afferent vagus and glossopharyngeal nerve directly or through pontine centres control rate and pattern of respiration. True or False

True

State the changes in arterial pCO2 & alveolar pO2 during hypocapnia.

1. Arterial pCO2 falls from 40 to as low as 15 mm Hg 2. Alveolar pO2 rises to 120-140 mm Hg

Suggest 2 causes of obstructive sleep apnoea

1. Blockage of upper airway : Relaxation of muscles of pharynx , older, obese persons, nasal obstruction. 2. Disorders causing cessation of ventilatory drive during sleep e.g., stroke

Characterized by slowly waxing and waning respiration, every 40 to 60 seconds. State the type of periodic breathing

Cheyne-Stokes breathing

Suggest 3 stimulant of peripheral chemoreceptors

Decreased pO2 , increased pCO2 , increased [H+]

What happens when large amounts (>7%) PCo2 is markly elevated?

Depression of central nervous system: confusion, diminished sensory acuity, coma with respiratory depression and death

This respiratory group discharges spontaneously & rhythmically.

Dorsal respiratory group (DRG)

DRG is not stimulated during forced breathing. True or False

False.

Both carbon dioxide & H+ can penetrate the blood-brain barrier (BBB). True or False.

False. CO2 readily penetrates the blood-brain barrier BUT H+ cannot penetrate BBB. CO2 + H2O = H2CO3 = H+ + HCO3-

Both DRG & VRG involve in quiet respiration. True or False.

False. VRG do not fire during quiet respiration.

Hypercapnia occurs in --- while Hyperventilation results in ---

Hypercapnia occurs in hypoventilation while Hyperventilation results in hypocapnia.

What is the ramp signal?

In quiet breathing: 1. In DRG, the spontaneous nerve signals for respiration begins weakly and increase steadily (inspiration) for about 2 seconds. 2. Next, it ceases abruptly (expiration) for 3 seconds. 3. Then ramp signal again starts for next respiratory cycle.

Name the type of breathing occur in diabetic ketoacidosis

Kussmaul breathing, leading to hyperventilation, which decreases PaCO2 and fall in H+ concentration.

What is the Hering-Breuer inflation reflex?

Protective reflex when tidal volume exceeds 1.5 L. 1. Stimulated by inflation of lungs 2. Send impulses through vagus to DRG to switch off ramp signals' and stops further inspiration. 3. Switch from inspiration to expiration

State what happens to respiration when pneumotaxic centre is damaged in experimental animals?

Respiration becomes slow and deep. Due to control of apneustic centre is lost. Inhibition of DRG.

Rhythm and pattern of spontaneous breathing is generated in?

Respiratory center of the brain stem.

Efferents for inspiration originate from DRG to? Name 2 inspiratory muscles involved

Spinal motor neurons supplying inspiratory muscles 1. Diaphragm: Phrenic nerve originate from C2 - C4 spinal segments 2. External intercostal muscles: originate from upper thoracic segments

DRG along with Pre-Botzinger complex initiate respiration. True or False

True

Decreased PaO2 results in a more sensitive response to PaCO2. True or False.

True

Pre-Botzinger complex in medulla discharge rhythmically, to produce rhythmic discharges in phrenic motor neurons. True or False

True

VRG is only stimulated in forced breathing (high pulmonary ventilation). True or False

True. 1. When pulmonary ventilation is high, signals spill over to VRG stimulating I & E neurons causing powerful inspiration and expiration. 2. There is reciprocal innervation between the inspiratory and expiratory muscles. 3. Therefore when one contracts the other will relax.

CO2 is far more potent stimulus for ventilation as compared to O2. True or False

True. 1. pCO2 and ventilation is directly proportional till a limit. 2. When alveolar PCO2 is fixed at lower than normal values, there is no stimulation of ventilation by hypoxia until the alveolar PO2 falls below 60 mm Hg.

Central chemoreceptors can be stimulated by a rise of blood pCO2 but not by blood pH. True or False. Justify your answer.

True. Because H+ cannot penetrate the BBB.

Define periodic breathing

Uneven respiratory rhythms involving alternate apnoea & hyperventilation

Central chemoreceptors are highly sensitive to --- in brain

[H+]

Suggest the potent stimulus of central chemoreceptors

carbon dioxide

Stimulatory effect of H+ and CO2 on respiration is ---.

additive

Name the origin for spontaneous breathing

pre-Bötzinger complex (pre-BÖTC). DRG and VRG neurons project to pre-BOTC.

Each carotid body and aortic body contains islands of --- cells & --- cells surrounded by fenestrated sinusoidal capillaries.

type 1 (glomus) cells & type 2 (supportive) cells.

2 mechanisms of Cheyne-Stokes breathing (periodic breathing)

1. Delay in transport of blood from lungs to brain as in cardiac failure. 2. Increased negative feedback gain in respiratory control areas.

Name one substance that blocks the inhibitory effect of opioids on respiration, without inhibiting their analgesic effect

5-HT4 agonists

Stretch receptors present at the walls of large conducting airways. Name the reflex involved.

HERING-BREUER REFLEX

Suggest 2 types of stimuli affecting respiratory centers

1. Chemical control - CO2 ( via CSF and brain-interstitial fluid [H+ ] ) - O2 and H+ via carotid and aortic bodies) 2. Non-chemical control - Vagal afferents from receptor in airways and lungs - Afferents from pons, hypothalamus, limbic system - Afferents from proprioceptors - Afferents from baroreceptors

Describe 3 effects of hypoxia on glomus cells of peripheral chemoreceptors (carotid body & aortic body)

1. Closure of K+ channels (depolarisation of cells) 2. Influx of calcium ion, Ca2+ 3. Release of dopamine which excites the nerve endings through the D2 receptors

Suggest 2 causes of Cheyne-Stokes breathing

1. Congestive heart failure. 2. Uraemia 3. Strokes, traumatic brain injuries, brain tumors, carbon dioxide poisoning, metabolic encephalopathy 4. After hyperventilaton ; During sleep

State one difference between DRG & VRG

1. DRG involves in inspiration (I neurons) only while VRG involves in both inspiration & expiration (I & E neurons). 2. VRG do not fire in quiet respiration.

Suggest 2 causes of Biot's breathing

1. Damage or pressure to medulla oblongata : stroke, trauma 2. Prolonged opioid abuse

Describe Hering-Breuer deflation reflex

1. Increases inspiratory muscle activity on large lung deflation. 2. Switch from expiration to inspiration.

State 2 types of receptor in respiratory control system

1. Mechanoreceptors 2. Chemoreceptors

DRG receives afferents from? receives impulses from?

1. NTS receives afferents of IXth and Xth Cranial nerve. 2. DRG receives impulses from peripheral chemoreceptors, baroreceptors and various receptors of lungs.

List 4 sensory signals which control the rate & depth of breathing

1. Peripheral chemoreceptors 2. Bronchial and alveolar receptors (stretch receptors) 3. Muscle proprioceptors (exercise) 4. Impulses from higher centers: hypothalamus, and limbic system (emotion) 5. Baroreceptors: When blood pressure falls, the respiratory rate increases 6. Irritating physical or chemical stimuli in the nasal cavity, larynx, or bronchial tree. 7. Impulses from Viscera: contraction of respiratory muscles occur during deglutition, vomiting, defecation. 8. Pain and temperature: acute pain causes apnoea and hyperventilation. Fever is associated with hyperventilation.

State 2 types of chemoreceptors with their respective location.

1. Peripheral chemoreceptors: Carotid bodies - glossopharyngeal nerve (CN IX) Aortic bodies - vagus nerve (CN X) 2. Central chemoreceptors/ chemosensitive area : located bilaterally beneath the ventral surface of medulla.

State 2 regulations responsible by respiratory neurons

1. Regulate respiratory muscle activity 2. Rate and depth of breathing (ventilation)

In vivo study of Pre-Botzinger complex, state 2 substances that stimulate & inhibits respiration respectively.

1. Substance P stimulates respiration. 2. Opioids inhibits respiration.

Suggest 2 effects of hypocapnoea

1. Vasoconstriction Cerebral blood flow reduced leads to ischemia - lightheadedness, dizziness, and paraesthesias 2. Increases cardiac output 3. Respiratory alkalosis Reabsorption of HCO3- decreased Plasma Ca2+ level falls - Carpopedal spasm (tetany)

Describe events in periodic breathing

1. When an individual breaths as deep as possible and as fast as possible, pO2 rises and pCO2 falls appreciably which limits duration of hyperventilation. 2. Wash out of CO2 will fail to stimulate central chemoreceptors and breathing stops completely (apnoea). 3. During apnoea, pO2 falls and pCO2 builds up -hyperventilation 3. Thus there will be alternative hyperventilation and apnoea repeated (periodic breathing) for a few cycles before regular breathing is resumed.

1. A strong Pneumotaxic signal does what? 2. A weak Pneumotaxic signal does what?

1. can increase rate of breathing to 30 - 40/min. 2. can decrease the respiratory rate to 3 - 5 / min.

Respiratory activity is highly sensitive to changes of?

1. carbon dioxide 2. oxygen 3. pH

The rate of breathing can be controlled by the pneumotaxic center by? Name 2

1. controlling the rate of signal generation 2. controlling the duration of signals (switch off)