8 - Breathlelssness and control of breathing (awake)

Question 1

What is the main functions of the respiratory muscles?

Answer 1

• maintenance of arterial PO2, PCO2 and pH (pH is probably the most important)
• defence of airways and lungs (coughing, sneezing)
• exercise: fight and flight
• speech
• control of intrathoracic and infra-abdominal pressures e.g. for defection, belching and vomiting

Question 2

What is TTOT?

Answer 2

duration of a single reparatory cycle (breath)
at rest —–> 4 seconds
(frequency = 60/TTOT, therefore frequency=4)

Question 3

What is VE?

Answer 3

Minute ventilation OR expired volume

Question 4

What do TI and TE stand for?

Answer 4

TI = inspiratory duration
TE = expiratory duration

TTOT = TI + TE

Question 5

What area of the brain is the voluntary centre of the control of breathing?

Answer 5

motor area of the cerebral cortex

Question 6

What nerves are involved in reflexes of breathing?

Answer 6

cranial nerves (fromt he brainstem not the spinal chord)

Question 7

Which nerve is involved in the sneeze reflex?

Answer 7

trigeminal nerve (V)
afferents detect irritants int he nerves and face

Question 8

Which nerve is involved in the gag reflex?

Answer 8

glossopharyngeal nerve (IX)
afferents detect irritants from the pharynx and larynx

Question 9

Which nerve is involved in the cough reflex?

Answer 9

vagus nerve (X)
afferents detect irritants from the bronchi and bronchioles

Question 10

Which nerve is involved in the Hering Breuer reflex?

Answer 10

vagus nerve (X)
(stops lungs overexpanding/signal to stop inspiration)
afferents detect stretch from the lungs

NOTE: there is also a detection of expansion from he chest wall and stretch or respiratory muscles via thoracic spinal chord

Question 11

How is breathing centrally controlled?

Name the specific complex that generates the respiratory rhythm

Answer 11

centrally controlled by a group of neurones in the medulla

- Pre-Botzinger complex is essential for generating the respiratory rhythm

Question 12

Describe the CNS control of breathing - what are the 2 centres that are used to control the amount that we breath?

Answer 12

• involuntary (metabolic) centre in the medulla

- voluntary/behavioural centre in the motor cortex

Question 13

Where does the behavioral/voluntary control lie in the motor homunculus?

Answer 13

between the hip and the trunk

Question 14

What 2 inputs into the metabolic centre allow it to keep parameters in the normal range?

Answer 14

• detection of H+ in nearby ECF

- chemoreceptors in carotid body detect H+, PCO2, PO2 in blood

Question 15

How can the lungs feedback on the metabolic centre?

Answer 15

• if they are being overworked (can become damaged)

- there is feedback from muscles and stretch of lungs to metabolic centre to stop inspiration

Question 16

Where do the following 5 systems/actions fit into the system?

• limbic system (survival responses)
• emotion (frontal cortex)
• sensory inputs (pain)
• the voluntary centre
• sneeze and cough reflexes

Answer 16

• limbic system, frontal cortex and sensory inputs act directly on the metabolic centre
• behavioural controller and sneeze/cough receptors act on the respiratory spinal motorneurones

Question 17

Where are the carotid bodies and what do they detect?

Answer 17

at the bifurcation of the common carotid artery in the neck

- detect H+, PCO2, PO2 in blood

Question 18

Are the chemoreceptors in the carotid bodies described as having a slow or rapid response?

Answer 18

rapid response

because changes occur rapidly in the carotid body as H+, CO2 and O2 can easily diffuse from the blood into it

Question 19

Is the detection of H+ in the ECF (by the metabolic centre) described as having a slow or rapid response?

Answer 19

Slow response

because it takes time for ECF acidity to change

Question 20

What are the factors that affect the response/sensitivity to CO2?

Answer 20

• Hypoxia (potentiates the response)
• Acidosis (potentiates the response)
  (since usually, blood acidity correlates with CO2 levels)

Question 21

What are the principle ions/molecules involved in acid bar balance and where are they controlled from?
Which of thee is a slow reaction and which a quick one?

Answer 21

• bicarbonate —–> kidneys (slow)

- CO2 —–> lungs (fast)