ventilation: control of breathing

Question 1

why is alveolar ventilation rate adjusted?

Answer 1

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.

Question 2

what are the 4 major sites responsible for the adjustment of the alveolar ventilation rate?

Answer 2

1- respiratory control centre (source of central pattern generator)

2- central chemoreceptors

3- peripheral chemoreceptors

4- pulmonary mechanoreceptors

Question 3

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?

Answer 3

when the diaphragm contracts, the rib cage will automatically move up

Question 4

what will the section above the levels of the pons control?

Answer 4

the basic rhythm

Question 5

what happens if you cut off the section of the spinal cord below C3-C5?

Answer 5

the intercostal muscles will be paralysed

Question 6

what happens if you cut off the section below the medulla?

Answer 6

all breathing will stop.

Question 7

where will the most of the neurons for the dorsal respiratory group be located?

Answer 7

nucleus tractus soltarius

Question 8

what effect with 3 different transections (cuts) of the brain stem/spinal cord have on respiration?

Answer 8

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

Question 9

where are the respiratory centres located?

what do they do?

Answer 9

• 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

Question 10

what are the stimuli for the receptors?

Answer 10

oxygen level
carbon dioxide level
hydrogen ions.
CO2 plays the most significant role; significant hypercapnia can increase ventilation 10x.

Question 11

what are the 3 major respiratory groups that make up the respiratory centre?

Answer 11

1- pontine respirator group
2- dorsal (posterior) respiratory group
3- ventral (anterior) respirator group

Question 12

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?

Answer 12

• 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

Question 13

in the dorsal respiratory group, when it is performing its function, what can this ramp be altered by?

Answer 13

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)

Question 14

what 2 places will ventral respiratory group neurons be found?

Answer 14

1- nucleus ambiguus
2- nucleus retroambigualis

Question 15

what 2 things will the ventral respiratory group not take part in?

Answer 15

1- inactive during normal quite breathing
2- they don’t participate in basic rhythmical oscillation

Question 16

whatwill ventral respirator group take part in?

Answer 16

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)

Question 17

what are pneumotaxic and apneustic centres for?

Answer 17

they are modulating centres but are not essential for normal respiratory output.

Question 18

what is the difference in fiction between pneumotaxic and apneustic centres?

Answer 18

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.

Question 19

where are pneumotaxic centres located?

what is their primary function?

Answer 19

• pneumotaxic centres are located dorsally in the nucleus parabrachialis medials of upper pons.
• primary effect is to control switch -off point of inspiration (so controls filling phase of lung cycle)

Question 20

What is the ultimate goal of ventilation?

Answer 20

The ultimate goal of ventilation is to maintain proper levels of PO2, PCO2 & pH (H+)

Question 21

Where are central chemoreceptors located?

What 2 things do they detect?

Answer 21

Central chemoreceptors are located in the central respiratory centre in the medulla

2 things central chemoreceptors detect:
1) Hypercapnia (increased PCO2)
2) Acidosis (decreased pH)

Question 22

Where are peripheral
chemoreceptors located?

What 3 things do peripheral chemoreceptors detect?

Answer 22

Peripheral chemoreceptors are located in the carotid body at the bifurcation of the common carotid and aortic bodies in the aortic arch

3 things peripheral chemoreceptors detect:
1) Hypoxia (decreased PO2)
2) Hypercapnia (PCO2)
3) Acidosis (pH)

Question 23

How was the location of central chemoreceptors identified?

Where were chemosensitive neurons also found?

What are neurons in this area very sensitive to?

Answer 23

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)

Question 24

Where are chemosensitive neurones located?

what are the sensitive too?

what can cross the BBB?

Answer 24

• they are located bilateral beneath ventral surface of the medulla in the BBB
• they are very sensitive to hydrogen ions
• ions can’t move across the BBB but gases like O2 and CO2 can.

Question 25

what is the effect of when blood PCO2 increases?

Answer 25

when blood PCO2 increases, PCO2 can diffuse across the BBB, resulting in an increase in the PCO2 in the interstitial fluid of the medulla and CSF CO2 can then combine with H20 to form hydrogen ions by the action of carbonic anhydrase, this will decrease the pH.

Question 26

when there is a decrease in pH across the BBB what happens?

Answer 26

the central chemoreceptors will sense this decrease in pH and they will then increase firing to increase ventilation, eliminate CO2 faster and increase pH

Question 27

why can a rise in PCO2 cause a greater change in pH in CSF than blood?

Answer 27

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

Question 28

what does an increase in blood PCO2 cause?

Answer 28

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

Question 29

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?

Answer 29

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

Question 30

what are the sensory organs for monitoring arterial blood oxygen and carbon dioxide levels?

Answer 30

carotid and aortic bodies

Question 31

what are type I cells? (Glomus cells)

Answer 31

these have neuronal phenotype and are. the primary site of sensory transduction in the carotid and aortic bodies.

Question 32

what 3 things can peripheral chemoreceptors of the carotid body sense a change in?

Answer 32

1- senses decreased arterial PO2 2- can sense increases in arterial PCO2 3- can sense decreases in arterial pH (eg metabolic acidosis)

Question 33

what happens when chemoreceptors sense a decrease in arterial PO2?

Answer 33

- a low PO2, but normal PCO2 and pH - this will increase the firing rate of carotid sinus nerve - at normal values of PCO2 and pH a decrease of PO2 causes progressive increase in firing.

Question 34

what happens when an increase in arterial PCO2 is sensed by the chemoreceptors?

Answer 34

- an increased PCO2 at a fixed blood pH 97.45) and a fixed PO2 (80mmHg) produces graded increases in firing rate of carotid sinus.

Question 35

what happens when chemoreceptors sense there is a decrease in arterial pH (metabolic acidosis)?

Answer 35

blood pH (7.25) and fixed PO2 (80 mmHg), firing rate of carotid sinus nerve is greater over all PCO2 values.

Question 36

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?

Answer 36

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

Question 37

What 2 other sources does the respiratory system receive input from? What are 3 examples of stretch and chemical/irritant receptors?

Answer 37

2 other sources the respiratory system receives input from: 1) Stretch and chemical/irritant receptors 2) Higher CNS centres that control non-respiratory activity 3 examples of stretch and chemical/irritant receptors 1) Slowly adapting pulmonary stretch receptors 2) Rapidly adapting pulmonary stretch (Irritant) receptors 3) C-fibre receptors (J Receptors)

Question 38

What reflex are slowly adapting pulmonary stretch receptors involved in? What does this reflex help in doing? In humans, when is this reflex activated? Where are slowly adapting pulmonary stretch receptors located?

Answer 38

Slowly adapting pulmonary stretch receptors are involved in the Hering-Breuer reflex (1868) This reflex helps to prevent over-inflation of the lungs The stretch receptors are located in muscular portions of walls of bronchi and bronchioles. They will send signals through vagal nerves and DRG neurons when the lungs are over stretched. the feedback response initiated that 'swtiches off' inspiratory ramp In humans, this reflex is not activated until tidal volume increases to about 3 times normal (i.e. 1.5L / breath) Slowly adapting pulmonary stretch receptors are located in muscular portions of walls of bronchi and bronchioles

Question 39

What are the 2 steps in the Hering-Breuer reflex?

Answer 39

2 steps in the Hering Breuer reflex: 1) Send signals through vagal nerves (CNX) to DRG neurons when lungs overstretched – 2) Feedback response initiated that ‘switches off ‘inspiratory ramp

Question 40

Where are rapidly adapting pulmonary stretch (Irritant) receptors located? What are they responsible for?

Answer 40

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

Question 41

How are cough reflexes activated? What does this result in?

Answer 41

The cough reflex is activated when nerve endings of vagus and/or visceral afferent fibres are activated by irritation of the trachea or bronchi This results in action potentials travelling to medulla and spinal cord respectively

Question 42

what are the 3 phases of the cough response?

Answer 42

3 phases of the response: 1) Preparatory inspiration 2) Compressive phase * Glottis closed by vagal efferent activity * Forced expiration against a closed glottis * Pressure increases 3) Expulsive phase * Glottis suddenly opens and trapped air is expelled at high speed by contraction of internal intercostals and abdominal muscles The aim of this response is to dislodge mucous covering airways and carry irritant away to mouth, where is can be coughed out or swallowed

Question 43

summary control of respiration

Answer 43

Question 44

describe where the rapidly adapting pulmonary stretch (irritant) receptors? what are the responsible for?

Answer 44

- epithelium of trachea, bronchi and bronchioles contain sensory nerve endings, pulmonary irritant receptors - these are responsible for coughing and sneezing.

Question 45

where are they located (C fibres)? what are C fibres (J receptors) responsible for?

Answer 45

- there are receptors in alveoli and conducting airways close to capillaries - they respond to chemical and mechanical stimuli - they will be stimulated during conditions like pulmonary oedema, congestion, pneumonia, also from endogenous chemical such a histamine - induces shallow breathing, bronchoconstriction and mucus secretion.

Question 46

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?

Answer 46

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