Control of Breathing

Question 1

What are the four main sites of regulation of alveolar ventilation

Answer 1

• Respiratory control centre, - Central chemoreceptors, - Peripheral chemoreceptors, - Pulmonary mechanoreceptors

Question 2

Where are the respiratory ‘centres’ located?

Answer 2

Medulla oblongata and pons

Question 3

Describe the features of the dorsal respiratory group

Answer 3

It is compose of inspiratory neurons located within the nucleus tractus solitarius. The DRG controls the basic rhythm of breathing by sending impulses to the motor nerves of diaphragm and external intercostal muscles. It involves a respiratory ramp for two seconds followed by cessation for 3 secs.

Question 4

Describe features of the ventral respiratory group

Answer 4

Contains both inspiratory and expiratory neurons, they are primarily active in exercise and stress. The VRG sends inspiratory impulses to laryngeal and pharyngeal muscles muscles, diaphragm and external intercostal muscles. Other VRG neurons send expiratory signals to abdominal muscles and internal intercostals.

Question 5

What is the pneumotaxic centre and its effects?

Answer 5

It is a modulatory centre located dorsally in nucleus parabrachialis medialis of upper pons. It sends inhibitory signals to the inspiratory centre of the medulla so controls filling phase of lung cycle.

Question 6

What detects hypercapnia, acidosis and hypoxia?

Answer 6

Hypercapnia and acidosis - Central respiratory centre as well as chemoreceptors in carotid and aortic bodies. Hypoxia - Chemoreceptors carotid and aortic bodies.

Question 7

Where are chemosensitive areas located?

Answer 7

Bilaterally beneath ventral surface of the medulla.

Question 8

Describe what the neurons in the chemosensitive areas are sensitive to?

Answer 8

Hydrogen ions.

Question 9

Describe how hydrogen ions reach the CNS

Answer 9

Hydrogen ions do not pass the BBB very well but carbon dioxide does. When there is an increase in blood PCOs, there will be an increase in the interstitial fluid of the medulla and CSF too. CO2 combines with H2O to form hydrogen ions by the action of carbonic anhydrase. This means high levels of CO2 lead to more activation which increases the respiratory rate.

Question 10

Describe the cells of carotid and aortic bodies

Answer 10

They have multiple highly characteristic glandular-like cells (glomus cells) which synapse directly or indirectly with nerve endings. They can detect changes in partial pressure

Question 11

What happens when the carotid body senses decreased arterial PO2?

Answer 11

There will be low PO2 but normal PCO2 and pH so the rate of firing of carotid sinus nerve increases.

Question 12

What happens when the carotid body senses an increase in arterial PCO

Answer 12

Increase in firing rate of the carotid sinus nerve

Question 13

What occurs if there is a decrease in arterial pH?

Answer 13

There is increased sensitivity so firing rate of carotid sinus nerve is greater over all PCO2 values.

Question 14

What is the common effect that these different chemical properties have on glomus cells?

Answer 14

Inhibition of potassium channels which results in an increase in intracellular calcium levels, this leads to exocytosis of neurotransmitters.

Question 15

Name the two other inputs that the respiratory system receives information?

Answer 15

• Stretch and chemical irritant receptors, - Higher CNS centres that contol non-respiratory activity

Question 16

Describe the inputs to the medulla which affect respiratory output

Answer 16

• Slowly adapting pulmonary stretch receptors (prevent over-inflation) - Rapidly adapting pulmonary (irritant) receptors (responsible for coughing and sneezing) . - C-fibre receptors (J Receptors) (they respond to chemical and mechanical stimuli, it induces aponea)

Question 17

Briefly describe the cough reflex

Answer 17

• Nerve endings activated by irritation of trachea or bronchi. - The response has three phases: - Preparatory, Compressive (glottis forced closed by vagal efferent activity, foced expiration against closed glottis) and expulsive phase (glottis opens and trapped air expelled at high speed by contraction of internal IC and abdo muscles). - Result is to dislodge mucus covering airways to carry irritant away.

Question 18

Describe what types of actions are controlled by higher brain activity

Answer 18

Voluntary hyperventilation, Breath0holding, speaking, singing, whistling or playing musical instruments.

Question 19

Draw this

Answer 19

cool