Control of Resp.

Question 1

name the 3 resp. centers located in the medulla oblongota

Answer 1

• DRG: dorsal resp. group
  
  • neurons active during inspiration
  • output via the phrenic/intercostal nerves
• VRG: ventral resp. group
  
  • neurons active with normal insp. and active exp.
• PRG: Pontine resp. group
  
  • tonic input to medulla to control smooth resp. rhythm

Question 2

describe ramp activity

Answer 2

• latent period - after expiration - then a ramp pattern develops
  
  • there is an increase in APs and concomitant increase in diaphragm muscle tone
  • the APs reach a crescendo; maximal diaphragm muscle tone
  • the APs then cease and the diaphragm relaxes

Question 3

name the important centers in the CNS

Answer 3

• cerebrum: voluntary control
• medulla oblongota: site of dorsal resp. center and ventral resp. center; generate the basic rhythmic pattern of breathing
• pons: apneustic and pneumotaxic centers can modulate the basic pattern of the medulla but are not essential
• emotional responses: limbic system and hypothalamus (anxiety, rage, fear)

Question 4

describe the pulmonary stretch receptors

Answer 4

• lie in the smooth muscle layer of the airways
• fire in proportionate response to the transmural pressure
• continue to fire in the continued presence of stretch, adapting slowly
• cause an excitation of the inspiratory offswitch and prolongs expiration

Question 5

describe the irritant receptors

Answer 5

• located in the airway epithelium
• respond to touch or noxious substances (smoke, particles)
• stimulated by histamines, serotonins and prostaglandins (activated during inflammation)
• lung edema also stimulates these receptors
• stimulation results in coughing/gasping

Question 6

describe J receptors

Answer 6

• juxtapulmonary capillary receptors (aka C-fiber endings)
• alveolar and bronchial groups
• alveolar C-fibers fire in response to lung injury, overinflation, pulmonary edema, pulmonary embolism–but are not sensitive to inflammatory mediators
• bronchial C-fibers are sensitive to inflammatory mediators
• stimulation of bronchial C fibers:
  
  • rapid shallow breathing
  • bronchoconstriction
  • airway secretion
  • cardiovascular depression (hypotension and bradycardia)

Question 7

describe proprioceptors

Answer 7

• present in joints, tendons and muscle
  
  • inform the brain of the position of the body through the reception of tension

Question 8

describe the central chemoreceptors

Answer 8

• located in the ventral surface of the medulla
• responds to a change in the PCO2 and pH of the CSF
• CSF is separated from the blood by the BBB–which is largely impermeable to H+ and HCO3-
  
  • metabolic acidosis or alkalosis has little effect of CSF pH
• the BBB is very permeable to O2 and CO2; therefore PCO2 has a strong effect on CSF pH

Question 9

describe the peripheral chemoreceptors

Answer 9

• located in the carotid and aortic bodies
• detect changes in PCO2, PO2 and pH
• carotid body: small sensory organ at the bifurcation of the carotid artery
  
  • afferents feed CNS via the glosso-pharyngeal nerves
• aortic bodies: multiple bodies along aorta
  
  • afferents feed CNS via vagus nerve
• Glomus cells: site of chemoreception

Question 10

describe the glomus cells

Answer 10

• decreased PO2: depolarizes glomus cell and stimulates afferents to the CNS
• increased PCO2 in the cells causes acidification which also causes depolarization
• H+ causes acid loading into the cell which causes depol.