ventilation: control of breathing Flashcards
why is alveolar ventilation rate adjusted?
alveolar ventilation rate is normally adjusted so that PO2 and PCO2 in the arterial blood are hardly altered even during heavy exercise and other respiratory stresses.
what are the 4 major sites responsible for the adjustment of the alveolar ventilation rate?
1- respiratory control centre (source of central pattern generator)
2- central chemoreceptors
3- peripheral chemoreceptors
4- pulmonary mechanoreceptors
What are the 2 primary muscles of inspiration?
What are the 4 secondary muscles of inspiration?
What are the 2 secondary muscles of expiration?
What are they each innervated by?
Where is the location of their motor neuron?
Where do cranial nerves originate?
when the diaphragm contracts, the rib cage will automatically move up
what will the section above the levels of the pons control?
the basic rhythm
what happens if you cut off the section of the spinal cord below C3-C5?
the intercostal muscles will be paralysed
what happens if you cut off the section below the medulla?
all breathing will stop.
where will the most of the neurons for the dorsal respiratory group be located?
nucleus tractus soltarius
what effect with 3 different transections (cuts) of the brain stem/spinal cord have on respiration?
1) Section below the level of the pons (ponto-medullary transection)
- The basic rhythm of respiration continues
- Integrated phrenic nerve activity remained
- Integrated CNX11 activity remained (accessory nerve)
2) Section the spinal cord below C3-C5
- The intercostal muscles are paralysed
- Internal and external intercostal muscles are innervated by thoracic spinal cord ventral horn
3) Section below the medulla (spino-medullary transection)
- All breathing ceases
- No integrated phrenic nerve activity
- Integrated CNX11 activity remained
- Although ventilation stops, respiratory activity continues in muscles innervated by motor neurons whose cell bodies reside in brain stem (i.e nostrils still flare etc)
- Suggests this area is an important aspect for normal breathing pattern
where are the respiratory centres located?
what do they do?
- medulla oblongata
- pons
- they will collect sensory information about O2 and CO2 levels in the blood and the determined signal will be sent to respiratory muscles which leads to alveolar ventilation
what are the stimuli for the receptors?
oxygen level
carbon dioxide level
hydrogen ions.
CO2 plays the most significant role; significant hypercapnia can increase ventilation 10x.
what are the 3 major respiratory groups that make up the respiratory centre?
1- pontine respirator group
2- dorsal (posterior) respiratory group
3- ventral (anterior) respirator group
where are most of the dorsal respiratory tracts located?
where do they receive sensory information from?
what is the job of the neurons in this group?
- most of the neuons will be located within the nucleus tracts solitaries
- receives information from the organs of thorax and abdomen
- neurons in this group emit repetitive bursts of inspiration neuronal action potential (the cause of these burns is unknown)
involves a respiratory ramp for 3 seconds
in the dorsal respiratory group, when it is performing its function, what can this ramp be altered by?
the ramp can be altered by:
- controlling rate of increase of ramp (heavy breathing), ramp increases rapidly so lungs fill rapidly
- controlling limiting point at which ramp suddenly stops (control rate of respiration)
what 2 places will ventral respiratory group neurons be found?
1- nucleus ambiguus
2- nucleus retroambigualis
what 2 things will the ventral respiratory group not take part in?
1- inactive during normal quite breathing
2- they don’t participate in basic rhythmical oscillation
whatwill ventral respirator group take part in?
1) During increased respiratory drive, ventral respiratory area contributes to extra respiratory drive
3) Especially important in providing powerful expiratory signals to abdominal muscles during heavy expiration (type of overdrive mechanism)
what are pneumotaxic and apneustic centres for?
they are modulating centres but are not essential for normal respiratory output.
what is the difference in fiction between pneumotaxic and apneustic centres?
Apneustic centres will stimulates inspiration by activating the dorsal respiratory group in the medulla.
It induces apneusis, a deep and prolonged inspiratory gasp followed by a pause and a brief expiration.
Pneumotaxic centres will inhibit inspiration, reduces tidal volume and regulates respiratory rate.
How was the location of central chemoreceptors identified?
Where were chemosensitive neurons also found?
What are neurons in this area very sensitive to?
Hans Loeschke, Marianne Schlafke and Robert Mitchell applied acidic solutions to particular areas.
When acid solution was applied to candidate regions near ventrolateral medulla, ventilation increased, meaning central chemoreceptors are located here.
Chemosensitive neurons have also been identified bilaterally beneath ventral surface of the medulla and in medullary raphe inside.
Neurons in these area very sensitive to H+ ions (which may be only important direct stimulus)
when there is a decrease in pH across the BBB what happens?
the central chemoreceptors will sense this decrease in pH and they will then increase firing to increase ventilation, eliminate CO2 faster and increase pH
why can a rise in PCO2 cause a greater change in pH in CSF than blood?
Because there is less protein in CSF than plasma a rise in PaCO2 can cause a larger effect on pH in CSF than in blood
what does an increase in blood PCO2 cause?
increases in blood PCO2 causes PCO2 to increase in interstitial fluid of medulla and CSF allowing CO2 to combine with H20 to form hydrogen ions by action of carbonic anhydrase
How do PO2 levels excite nerve endings?
What cells do bodies that contain chemoreceptors have?
What do they synapse on to?
What autonomic innervation does the carotid body have?
How low PO2 excites nerve endings is still largely unknown
Bodies that contain chemoreceptors have multiple highly characteristic glandular-like cells (Glomus cells – Type 1 cells)
Glomus cells synapse directly or indirectly with nerve endings
The carotid body has both sympathetic and parasympathetic innervation
what happens when chemoreceptors sense there is a decrease in arterial pH (metabolic acidosis)?
blood pH (7.25) and fixed PO2 (80 mmHg), firing rate of carotid sinus nerve is greater over all PCO2 values.
What is the final shared common pathways for the pathways of changing PO2, PCO2, and pH in the glomus cell of the carotid body?
How does this common pathway work?
The final shared common pathways for the pathways of changing PO2, PCO2, and pH in the glomus cell of the carotid body is the K+ channel in the glomus cell
All pathways lead to the K+ channel being blocked, which results in L-type voltage gated calcium channels opening
This causes the exocytosis of neurotransmitter towards the post-synaptic membrane of the afferent glossopharyngeal nerve, triggering an action potential
Where are rapidly adapting pulmonary stretch (Irritant) receptors located?
What are they responsible for?
Rapidly adapting pulmonary stretch (Irritant) receptors are located in nerve endings in the epithelium of trachea, bronchi, and bronchioles
These receptors are responsible for coughing and sneezing
summary control of respiration
Normal and abnormal respiratory patterns. Describe the following respiratory patterns:
- Eupnoea
- Sigh
- Inspiratory apneusis
- Vagal breathing
- Cheyne-Stokes respiration
- Ataxic breathing
What disease can some of them indicate?
Respiratory patterns:
1) Eupnoea
* normal breathing
2) Sigh
* larger than normal breath that occurs at regular intervals in normal subjects
3) Inspiratory Apneusis
* prolonged inspirations separated by brief expirations
4) Vagal breathing
* slow, deep inspirations due to vagal interruption
5) Cheyne-Stokes respiration
* Benign respiratory pattern.
* Cycles of gradual decrease in TV, followed by gradual increase in TV, then apnoea
* Suggests bilateral cortical disease, healthy people at high altitude
6) Ataxic breathing
* irregular inspirations, separated by long periods of apnoea
* Suggests medullary lesion
