Control of Breathing

Question 1

Regarding the respiratory centre:

The respiratory centre is mainly within the pons

Answer 1

False. The PRG was historically thought to be the main central pattern generator with an alternating activity of apneustic and pneumotaxic centres. Now the PRG’s function is believed to mainly involve fine-tuning respiration, with the DRG and VRG, both residing in the medulla, as the sites of the respiratory centre.

Question 2

Regarding the respiratory centre:

The DRG neurones largely control inspiratory muscles on the same side of the body

Answer 2

False. Although the DRG is responsible for control of inspiratory muscles, its output decussates to the opposite side of the spinal cord and hence controls muscles on the opposite side of the body.

Question 3

Regarding the respiratory centre:

The DRG is found near the nucleus of the tractus solitarius

Answer 3

True. The nucleus of the tractus solitarius is near the floor of the 4th ventricle at the level of the inferior colliculus.

Question 4

Regarding the respiratory centre:

The VRG is composed of four major nuclei

Answer 4

True. These are the Botzinger Complex, nuclei para-ambigualis, retro-ambigualis, and nucleus ambiguus.

Question 5

Regarding the respiratory centre:

Sensory input to the respiratory centre inputs mainly via the VRG

Answer 5

False. Almost all sensory information inputs via the DRG.

Question 6

Regarding the respiratory centre:

The nucleus ambiguus controls airway dilators

Answer 6

True. This is an elongated nucleus in the medulla oblongata that gives rise to the motor fibres of the glossopharyngeal, vagus, and accessory nerves supplying striated muscle of the larynx and pharynx.

Question 7

Regarding central chemoreceptors:

They are located within the ventral respiratory group of neurones

Answer 7

False. The central chemoreceptors are some 200 μm below the antero-lateral (ventral) surface of the brainstem. They are anatomically distinct from the VRG.

Question 8

Regarding central chemoreceptors:

There is a caudal and rostral zone of receptors

Answer 8

True. There are two zones of central chemoreceptors, with the anterior inferior cerebellar artery separating them.

Question 9

Regarding central chemoreceptors:

They respond to brain CO2

Answer 9

False. The central chemoreceptors respond to blood PCO2, but the actual mechanism is through a response to brain H+ ions. CO2 crosses the blood brain barrier and then hydrates to carbonic acid, which in turn is in equilibrium with H+ and HCO3-.

Question 10

Regarding central chemoreceptors:

They generate 60% of the minute ventilation response to CO2 in air

Answer 10

False. The central chemoreceptors generate 80% of the response to CO2 in air.

Question 11

Regarding central chemoreceptors:

They have a slow time constant

Answer 11

True. They have a slow time constant taking 1-3 minutes to respond to changes in PaCO2. Breath-to-breath variation is mediated by the peripheral CO2 response.

Question 12

Regarding central chemoreceptors:

Factors such as drugs, age, and state of consciousness can influence their sensitivity to CO2

Answer 12

True

Question 13

Regarding peripheral chemoreceptors:

There are two sets, the aortic bodies being the most important in the control of breathing

Answer 13

False. There are indeed two sets - the carotid and aortic bodies. However, it is the carotid bodies which are the most important of the peripheral chemoreceptors.

Question 14

Regarding peripheral chemoreceptors:

The aortic bodies respond to pH

Answer 14

False. The aortic bodies do not respond to pH.

Question 15

Regarding peripheral chemoreceptors:

The carotid bodies are innervated by C.IX, the glossopharyngeal nerve

Answer 15

True. The glossopharyngeal nerve (sinus branch) supplies the carotid bodies.

Question 16

Regarding peripheral chemoreceptors:

They are the main receptors responsible for the increased respiration in response to hypoxaemia

Answer 16

True

Question 17

Regarding peripheral chemoreceptors:

They stimulate respiration in response to a fall in blood pressure

Answer 17

True. This is believed to be due to a form of stagnant hypoxia.

Question 18

Regarding peripheral chemoreceptors:

The aortic bodies respond to the partial pressure of oxygen alone

Answer 18

False. The aortic bodies respond to PaCO2 and also to the actual content of oxygen, i.e. they would be affected by the level of haemoglobin, in addition to partial pressure of oxygen.

Question 19

Regarding control of respiration:

At a normal PO2, there is a 15-20 L/min rise in minute ventilation per kPa rise in PaCO2

Answer 19

True. At normal PO2, there is a linear rise in ventilatory response to a rise in PaCO2.

Question 20

Regarding control of respiration:

J-receptors are implicated in the dyspnoea of pulmonary oedema

Answer 20

True. J-receptors respond to noxious stimuli within the pulmonary capillaries, and are probably responsible for augmenting the tachypnoea and dyspnoea of pulmonary oedema.

Question 21

Regarding control of respiration:

The responses to PO2 and PCO2 are additive

Answer 21

False. The responses to both a fall in PO2 and a rise in PCO2 are synergistic.

Question 22

Regarding control of respiration:

The Hering-Breuer reflex is important in adult humans

Answer 22

False. The Hering-Breuer reflex is very strong in some animals. It is probably relevant in neonates, but in adults it is of little physiological relevance.

Question 23

Regarding control of respiration:

The increased ventilation seen during strenuous exercise is explained by a rise in PaCO2

Answer 23

False. Much of the response to exercise is probably anticipatory, or comes from receptors within the musculoskeletal system.