Lecture 19 - Physiological control of breathing Flashcards Preview

1060 Human form and function > Lecture 19 - Physiological control of breathing > Flashcards

Flashcards in Lecture 19 - Physiological control of breathing Deck (19):

What initiates and controls breathing in a healthy person?


The AUTONOMIC nervous system


Breathing is a RHYTHMIC activity


During inspiration:

Respiratory muscles contract

During normal expiration:

Respiratory muscle relax and lungs empty primarily through elastic recoil


All respiratory muscles (diaphragm, intercostals, abdominals) are skeletal in origin and therefore require neural input for stimulation




Which nerve stimulates the Diaphragm and where does it originate from?


The main respiratory muscle, the DIAPHRAGM is stimulated by the PHRENIC nerve

Phrenic nerve originates from brain stem between cervical vertebrae C2 and C5



What happens to the basic rythm of breathing if the brain is sectioned above the pons?


It is unaffected.

This confirms that direct communication with higher brain centres is not necessary



What happens to the rhythm of breathing if the spinal cord is sectioned below the outflow of the phrenic nerves at C5? 


The diaphragm is unaffected but intercostals are paralysed. Breathing is regular



What happens to breathing if you section the lower portion of the medulla?


It stops all breathing.


This shows that initiation and regulation of breathing occurs in the medulla



Where does the  initiation and regulation of breathing occur?


In the medulla



What and where is the DRG?


Dorsal Respiratory Group (DRG)

Situated in the medulla one on either side.


DRG contains inspiratory neurones

These demonstrate rhythmic activity

and stimulate inspiratory muscles

DRG also receives afferent inputs from lung receptors via the vagus nerve




What and where is the VRG?


Ventral Respiratory Group (VRG)

Situated in the medulla one on either side.


VRG contains neurons with a degree of spontaneous rhythmic electrical pacemaker activity


VRG contains neurons that stimulate respiratory muscles to initiate:

Inspiration = Inspiratory neurons


Expiration = Expiratory neurons


VRG also receives inputs from DRG and central chemoreceptors




What forms the Central Respiratory Rhythm Generator?


The Dorsal Respiratory Group (DRG) and the Ventral Respiratory Group (VRG)



What effect does sectioning the pons have in the rhythm of breathing?


Sectioning the Pons does not alter basic rhythmicity but affects breath duration



What role does the Pons have in regulating breathing?


Two regions of the pons receive inputs from cerebrum and

hypothalamus and feed them into the medullary respiratory centre:

pneumotaxic centre

Inhibits the DRG to promote expiration, thus altering breathing rate

apneustic centre

Stimulates the DRG to promote inspiration, thus increasing breath duration

These two areas antagonise each other


Key point: the pons offers a fine-tuning of the basic rhytmicity generated in the medulla




Hypothalamus mediates response to changes in ??





Limbic system mediates response to changes in ???


emotional state



Lung receptor: irritant receptors how do they work





Metabolism by tissues results in ??


CO2 production

O2 consumption

H+ production (ie a reduction in pH).


Changes in these parameters provide very important stimuli that affect ventilation. The most important of these is PCO2



Which receptors detect PCO2,PO2 and pH ?



Central chemoreceptors present in medulla. Detect [H+] and

PCO2 (80% of response to PCO2)

Peripheral chemoreceptors present in carotid and aortic bodies. Detect PO2, PCO2 and [H+] (20% of response to PCO2)





Where are the central and peripheral chemoreceptors located?


Located on the ventrolateral surface of medulla, near the entry of the vagus and glosso-pharyngeal nerves



Where are peripheral chemoreceptors located?


In the aortic and carotid bodies



Carotid body contains 2 types of cells, which ?


Glomus and sheath


Glomus cells respond to decrease PO2, increase PCO2 and [H+]. Main O2 sensing cells in respiration.

Upon activation release dopamine at nerve junction.