control of breathing

Question 1

involuntary ventilation
- where in the brain are the respiratory muscle groups controlled
- 2 areas in the respiratory rhythmic centre and what they do

Answer 1

• brainstem
• the ventral respiratory group (VRG) controls forced expiration (Abdominals), and the dorsal respiratory group (DRG) controls inspiration (diphragm, ext intercostals) via inspiratory and expiratory motor neurons

Question 2

voluntary ventilation
- examples of voluntary ventilation
- what two centres important in voluntary ventilation

Answer 2

• Hyperventilation, Breath holding, Speaking, swallowing, eating
• The pneumotaxic centre (upper pons)
  (modulates the)
• Apneustic centre (lower pons)
  (which inhibits the)
• Respiratory rhythmicity centre

Question 3

Protective involuntary interruption of respiratory rhythm
- function of slowly adapting pulmonary stretch receptors
- function of rapidly adapting pulmonary stretch receptors

Answer 3

• located in airway smooth muscle, activated when TV close to physical limitations of lung tissue expansion, and prevents damage by initiating inhibition of inspiration (Hering-Breuer reflex)
• receptors in the trachea and large airway, respond to stimuli that shouldn’t be entering the airways, eg. cigarette smoke, inhaled particles and cold air, by initiating reflexes such as coughing and sneezing by causing bronchoconstriction.

Question 4

what creates the ventilatory drive
- 2 types of peripheral chemoreceptor and what they respond to
- peripheral chemoreceptor response to low o2 levels
- what do central chemoreceptors respond to and where are they
- how does co2 indirectly stim receptors

Answer 4

• carotid and aortic chemoreceptors
• main stimulus is PaO2, secondary co2 and h+
• sensed in membrane of chemoreceptors, k+ Channels close, causing depolarisation, vg ca2+ channels open, calcium enters releasing neurotransmitter from vesicles, AP in sensory neurone sends signal to brain stem appropriate for that level of o2
• changes in PaCO2 (through changes in concentration of H+), in the medulla
• co2 reacts with water producing bicarbonate ions and h+ ions, central chemoreceptors stimmed by increase in h+ in the brain extra cellular fluid

Question 5

control of breathing by po2
- what receptors does it affect
- when does ventilation start to increase

Answer 5

• Reduced levels of arterial oxygen affect peripheral chemoreceptors
• only after arterial oxygen reaches a value of ~60 mmHg

Question 6

control of breathing by pco2 (pH)
- when does it exert its effects
- what receptors does it affect

Answer 6

• during smaller deviations from normal arterial values
• peripheral and central chemoreceptors but mainly central

Question 7

phases of increased ventilation during steady state exercise
- phase 1,
- phase 2 and 3

Answer 7

• rapid increase (controlled by neural mechanisms)
• phase 2 more gradual until steady state achieved (phase 3) (chemical stimuli giving feedback loops to fine tune)