Control of respiration Practice Questions

Correct answer: Medullary respiratory center

The medullary respiratory center generates the basic rhythm of breathing. It includes dorsal and ventral respiratory groups that coordinate inspiration and expiration.

Correct answer: Quiet inspiration

The dorsal respiratory group is mainly involved in quiet inspiration. It integrates sensory input and drives the diaphragm via the phrenic nerve.

Correct answer: Pneumotaxic center

The pneumotaxic center limits inspiration by inhibiting inspiratory neurons. This helps regulate respiratory rate and pattern.

Correct answer: Cerebrospinal fluid pH

Central chemoreceptors respond to changes in cerebrospinal fluid pH. These changes reflect arterial carbon dioxide levels.

Correct answer: Increased arterial carbon dioxide

An increase in arterial carbon dioxide strongly stimulates ventilation. CO2 readily crosses the blood-brain barrier and affects central chemoreceptors.

Correct answer: Carotid and aortic bodies

Peripheral chemoreceptors are located in the carotid and aortic bodies. They respond primarily to changes in arterial oxygen tension.

Correct answer: Hypoxia

Peripheral chemoreceptors are most sensitive to hypoxia. A significant fall in arterial oxygen strongly increases their firing.

Correct answer: Forced breathing

The ventral respiratory group is recruited during forced breathing. It contributes to both active inspiration and expiration.

Correct answer: Hering-Breuer inflation reflex

The Hering-Breuer inflation reflex inhibits inspiration when the lungs are excessively stretched. It is mediated by vagal afferents.

Correct answer: Cerebral cortex

Voluntary control of breathing originates in the cerebral cortex. Cortical signals can override automatic respiratory centers temporarily.

Correct answer: Glossopharyngeal nerve

The glossopharyngeal nerve carries afferent signals from carotid body chemoreceptors. These signals influence respiratory centers.

Correct answer: Reduce carbon dioxide levels

In metabolic acidosis, ventilation increases to remove carbon dioxide. This helps compensate by reducing acidity.

Correct answer: High altitude acclimatization

In chronic high altitude exposure, sensitivity to CO2 decreases. Ventilation becomes more dependent on hypoxic drive.

Correct answer: Central chemoreceptor area

The central chemoreceptor area responds to increased CO2 by stimulating inspiratory neurons. This enhances ventilation.

Correct answer: Prolongs inspiration

The apneustic center prolongs inspiration. It is normally regulated by inhibitory input from the pneumotaxic center.

Correct answer: Increase in CSF pH

An increase in CSF pH reduces central chemoreceptor stimulation. This leads to a decrease in respiratory drive.

Correct answer: Neural input from motor cortex

At the onset of exercise, ventilation increases due to neural signals from the motor cortex. This occurs before chemical changes in blood gases.

Correct answer: Opioid overdose

Opioids depress medullary respiratory centers. This reduces respiratory rate and depth, potentially causing hypoventilation.

Correct answer: Slowly adapting stretch receptors

Slowly adapting stretch receptors respond to lung inflation. They help regulate the depth and timing of breathing.

Correct answer: Decrease in oxygen

Central chemoreceptors are relatively insensitive to oxygen levels. They primarily respond to CO2 and pH changes.

Correct answer: CO2 diffuses into the CSF, where it forms H+ ions that stimulate the receptors

While central chemoreceptors are highly sensitive to H+, these ions cannot easily cross the blood-brain barrier. Instead, CO2 diffuses into the CSF and brain interstitial fluid, where it reacts with water to form H+ ions that directly stimulate the receptors.

Correct answer: Stretch receptors in airway smooth muscle signalling via the vagus nerve

The Hering-Breuer reflex is initiated by pulmonary stretch receptors located in the smooth muscle of the bronchi and bronchioles. When the lungs overinflate, these receptors send inhibitory signals to the medullary respiratory centers via the vagus nerve to terminate inspiration.

Correct answer: 60 mmHg

Peripheral chemoreceptors have a non-linear response to oxygen. They show relatively little activity until arterial PO2 drops below approximately 60 mmHg, at which point the ventilatory drive increases sharply to compensate for hypoxia.

Correct answer: Type I (glomus) sensor cells

Type I glomus cells contain oxygen-sensitive potassium channels. Under hypoxic conditions, these channels close, causing cell depolarization, calcium influx, and the release of neurotransmitters that stimulate the afferent nerve.

Correct answer: Pneumotaxic center

The pneumotaxic center, located in the upper pons, sends inhibitory signals to the inspiratory area to limit the duration of inspiration. By doing so, it effectively increases the respiratory rate and prevents over-expansion of the lungs.

Correct answer: Feed-forward drive from the cerebral cortex and limb and joint proprioceptors

The initial rapid rise in ventilation during exercise is mediated by neural factors, including motor impulses from the cerebral cortex (anticipatory) and sensory input from proprioceptors in moving limbs. This ensures oxygen delivery and CO2 removal match the increased metabolic demand instantly.

Correct answer: Arterial PO2 remains normal, so peripheral chemoreceptors are not stimulated

Peripheral chemoreceptors respond to the partial pressure of dissolved oxygen (PO2), not the total oxygen content or hemoglobin saturation. In CO poisoning, PO2 remains normal while oxygen content is low, so the 'hypoxic drive' is never triggered.

Correct answer: Pulmonary capillary congestion or edema, causing rapid shallow breathing

J-receptors are stimulated by engorgement of pulmonary capillaries or accumulation of interstitial fluid (edema). Their activation leads to a sensation of dyspnea and a reflex pattern of rapid, shallow breathing.

Correct answer: Respiratory drive may depend on hypoxic drive due to blunted CO2 sensitivity

In chronic hypercapnia, central chemoreceptors become desensitized to CO2. The respiratory drive then shifts to the peripheral chemoreceptors (hypoxic drive); providing too much oxygen can remove this stimulus, leading to respiratory depression.

Correct answer: It acts as the pacemaker for the respiratory rhythm

Located in the upper part of the ventral respiratory group, the Pre-Bötzinger complex contains spontaneously firing neurons. It is widely considered the primary site of respiratory rhythm generation in the brainstem.

Correct answer: Vagus nerve (CN X)

While the carotid bodies send signals via the glossopharyngeal nerve (Hering's nerve), the aortic bodies utilize the vagus nerve to communicate with the nucleus tractus solitarius in the medulla.

Correct answer: Providing inspiratory drive by stimulating the diaphragm

The DRG consists mainly of inspiratory neurons. During quiet breathing, it provides the repetitive 'ramp' signal to the phrenic nerve to cause diaphragmatic contraction and inspiration.

Correct answer: A decrease in arterial PO2

Central chemoreceptors are shielded by the blood-brain barrier and respond primarily to CO2-induced H+ changes in the CSF. Peripheral chemoreceptors are unique in their ability to respond to arterial hypoxia (low PO2) and arterial pH changes.

Correct answer: It prolongs inspiration, leading to deep, gasping breaths

The apneustic center has an excitatory effect on the inspiratory area of the medulla. If not inhibited by the pneumotaxic center or vagal lung stretch signals, it causes prolonged inspiratory gasps, a condition known as apneusis.

Correct answer: Breathing would continue but become irregular and gasping

The basic rhythm is generated in the medulla, but the pons (pneumotaxic and apneustic centers) is required to smooth the transition between inspiration and expiration. Without the pons, the medullary rhythm is irregular and inefficient.

Correct answer: Irritant receptors

Irritant receptors are found between airway epithelial cells. When stimulated by mechanical or chemical irritants, they trigger protective reflexes like coughing, sneezing, and bronchoconstriction.

Correct answer: Arterial PCO2

While low oxygen eventually contributes, the irresistible urge to breathe during a breath-hold is primarily driven by the accumulation of arterial CO2, which stimulates both central and peripheral chemoreceptors.

Correct answer: Cerebral cortex

Voluntary control of breathing originates in the motor cortex of the cerebral cortex. Impulses travel down the corticospinal tracts to the respiratory neurons in the spinal cord, bypassing the autonomic centers in the brainstem.

Correct answer: Increased ventilation to 'blow off' CO2 and raise blood pH

Peripheral chemoreceptors detect the increased H+ concentration in the blood. The resulting increase in ventilation (Kussmaul breathing) reduces PCO2, which helps shift the equilibrium of the bicarbonate buffer system to increase blood pH toward normal.

Correct answer: The curve shifts right, showing decreased sensitivity

During sleep, the respiratory center becomes less sensitive to CO2, causing the arterial PCO2 to rise slightly (about 3-4 mmHg). This rightward shift is why breathing is more likely to become irregular or periodic during sleep.

Correct answer: Glossopharyngeal nerve

The glossopharyngeal nerve (cranial nerve IX) transmits sensory input from the carotid bodies to the medulla. These receptors detect changes in oxygen, carbon dioxide, and pH.

Correct answer: Pulmonary stretch receptors

Pulmonary stretch receptors in the airways detect lung inflation and send signals via the vagus nerve to inhibit further inspiration.

Correct answer: 60 mmHg

Peripheral chemoreceptors respond strongly when PO2 drops below about 60 mmHg. This triggers an increase in ventilation.

Correct answer: Glomus cells

Glomus (Type I) cells detect hypoxia by closing oxygen-sensitive potassium channels, leading to depolarization and neurotransmitter release.

Correct answer: Pneumotaxic center

The pneumotaxic center in the upper pons limits inspiration duration, helping regulate respiratory rate and tidal volume.

Correct answer: Neural signals from motor cortex

Feedforward signals from the motor cortex and proprioceptors stimulate ventilation at the onset of exercise before blood gas changes occur.

Correct answer: Normal arterial PO2

In CO poisoning, arterial PO2 remains normal despite reduced oxygen content, so peripheral chemoreceptors are not strongly stimulated.

Correct answer: Increased interstitial fluid

J receptors respond to pulmonary congestion and edema, leading to rapid shallow breathing.

Correct answer: Oxygen levels

In chronic hypercapnia, central chemoreceptors adapt, making hypoxia the main driver of ventilation via peripheral chemoreceptors.

Correct answer: Generating respiratory rhythm

The Pre-Bötzinger complex in the medulla is the primary site for generating the basic rhythm of breathing.

Correct answer: CSF pH changes

Central chemoreceptors respond to changes in CSF pH, which reflect arterial CO2 levels, making them sensitive to hypercapnia.

Correct answer: Quiet breathing inspiration

The dorsal respiratory group generates the basic inspiratory rhythm during quiet breathing.

Correct answer: Low oxygen levels

Peripheral chemoreceptors are the only receptors that directly sense decreases in arterial oxygen levels.

Correct answer: Prolonged inspiration

The apneustic center promotes prolonged inspiration, leading to deep, sustained breaths if unopposed.

Correct answer: Loss of respiratory rhythm

Severing connections between the pons and medulla disrupts respiratory control, leading to loss of coordinated breathing.

Correct answer: Irritant receptors

Irritant receptors in the airways respond to dust, smoke, and mucus, triggering the cough reflex.

Correct answer: High carbon dioxide levels

Rising CO2 levels stimulate central chemoreceptors, creating the urge to breathe and ending voluntary breath-holding.

Correct answer: Cerebral cortex

The cerebral cortex allows conscious control over breathing, such as during speech or breath-holding.

Correct answer: Decrease CO2 levels

In metabolic acidosis, increased ventilation reduces CO2, helping to raise pH toward normal.

Correct answer: Decreases sensitivity

During sleep, the sensitivity of respiratory centers to CO2 decreases, resulting in reduced ventilatory response.