Respiratory 8

Question 1

Which nerves innovate the skeletal muscles of inspiration?

Answer 1

• phrenic nerves

- intercostal nerves

Question 2

How is ventilation controlled subconsciously, and where does this occur?

Answer 2

Via respiratory centres that reside in the pons and medulla.

Question 3

What would be the outcome if the spinal cord was severed above C3-C5? Why?

Answer 3

• death
• the spinal cord would have been severed above the origins of the phrenic nerve and therefore there would be no means of breathing.

Question 4

Would paralysis to the thoracic region affect breathing?

Answer 4

No, as long as the diaphragm is intact.

Question 5

Describe the action of respiratory centres.

Answer 5

They set an automatic rhythm of breathing through coordinating the firing of smooth and repetitive bursts of action potentials.

Question 6

Name the four main stimuli that alter respiratory function.

Answer 6

• emotion (via the limbic system)
• voluntary override (via higher centres in the brain)
• mechanosensory input from the thorax (stretch reflex)
• chemical composition of the blood (changes in pH etc)

Question 7

Which stimulus that alters respiratory function is most significant?

Answer 7

Chemical composition.

Question 8

What does the ventral respiratory group of neurons innovate?

Answer 8

• tongue
• pharynx
• larynx
• expiratory muscles

Question 9

What does the dorsal respiratory group of neurons innovate?

Answer 9

• inspiratory muscles

Question 10

Name the two types of chemoreceptors.

Answer 10

• central

- peripheral

Question 11

Where are central chemoreceptors found?

Answer 11

The medulla.

Question 12

Where are peripheral chemoreceptors found?

Answer 12

The carotid and aortic bodies.

Question 13

Describe the primary ventilatory drive.

Answer 13

The response of central chemoreceptors to hydrogen ion concentration in the CSF around the brain.

Question 14

What drives the increase in hydrogen ion concentration?

Answer 14

Raised arterial partial pressure of carbon dioxide (hypercapnea)

Question 15

What would be the response from central chemoreceptors to an increase in hydrogen ion concentration?

Answer 15

An increase in the rate of ventilation to ‘blow off’ more carbon dioxide.
This drives the equilibrium to the left, utilising more hydrogen to form more carbon dioxide.

Question 16

Describe secondary ventilatory drive.

Answer 16

The response of peripheral chemoreceptors to changes in arterial partial pressure of oxygen and hydrogen ion concentration of the plasma.

Question 17

What would be the response of peripheral chemoreceptors to a fall in arterial partial pressure of oxygen to 50mmHg?

Answer 17

A stimulation of ventilation.

Question 18

What effect would a chronic lung disease have on central chemoreceptors?

Answer 18

• ‘blunted’ or desensitised central chemoreceptors
• this occurs if patients have been exposed to high levels of carbon dioxide for a long time.
• it shifts the body to hypoxic drive, where the rate of ventilation is controlled primarily by peripheral chemoreceptors.

Question 19

What will happen to the ventilation rate if plasma pH increases?

Answer 19

• alkalosis will occur
• ventilation will be inhibited
• hypoventilation will retain carbon dioxide and drive the equilibrium to the right

Question 20

What will happen to the ventilation rate if plasma pH decreases?

Answer 20

• acidosis will occur
• ventilation will be stimulated
• hyperventilation will blow off carbon dioxide and drive the equilibrium to the left

Question 21

Can voluntary control over respiration overcome involuntary stimuli?

Answer 21

No.

Involuntary stimuli such as partial pressure of carbon dioxide and hydrogen ion concentration cannot be over-ridden.

Question 22

Name three common drugs that affect respiratory centres.

Answer 22

• barbiturates
• most gaseous anaesthetics
• nitrous oxide