Is phrenic nerve activity associated with inhalation or exhalation?
Inhalation; phrenic stimulates the diaphragm to contract
What happens to the activity of the phrenic nerve during exhalation?
Stops stimulating the diaphragm
What happens to the diaphragm when the phrenic stops firing?
Diaphragm relaxes
Is breathing automatic or autonomic, and what does that mean?
Automatic, because diaphragm is a skeletal muscle, it is not under autonomic control
Additionally, phrenic nerve is a somatic motoneuron
Is phrenic nerve a somatic motoneuron or autonomic neuron?
Somatic motoneuron
Where does the phrenic exit?
Spinal cord
Where do the cell bodies of the phrenic nerve located?
C3-C5 of the spinal cord
Where does the axon of phrenic nerve terminate?
Diaphragm
True/False: diaphragm is a smooth muscle
False, it is a skeletal muscle
What is the phrenic nerve neural activity during exhalation?
No activity/ action potentials fired
Describe the phrenic nerve neural activity during inhalation:
Starts off with low in early inhalation, followed by moderate in middle inhalation and then high activity in late inhalation
True/False: Phrenic nerve fire rate oscillates with respiratory cycle
True
True/False: phrenic nerve firing frequency during inhalation is fast and furious
False, it is slow and steady
True/false: there is a sharp decline in the phrenic nerve firing rate graph during exhalation
True
Why is the phrenic nerve firing rate slow and steady?
Stimulate a slow and sustained diaphragm contraction, which leads to a slow and steady filling of lungs with air
What is the lung volume at the end of inspiration?
Volume plateaus because no more air flow
What is the air flow at the end of inhalation?
Zero
What would happen if the phrenic nerve simply fired at maximum rate during inhalation?
Forceful and abrupt gasps
What does the phrenic nerve firing rate over time graph look like when there is not slow and steady phrenic nerve firing?
No ramp
What is the most important regulator of the respiratory rhythm, aka- regulate the firing rate of phrenic nerve?
Dorsal respiratory group (DRG)
Where is the DRG located?
Dorsal portion of the medulla within nucleus of solitary tract (NTS)
What is the function of DRG?
Receives input to regulate breathing by controlling phrenic nerve’s firing rate
What type of neurons are found in the DRG?
Interneurons and pre-motor neurons
What does DRG stand for?
Dorsal respiratory group
Where does the DRG receives its sensory input from?
Vagus nerve
Glossopharyngeal nerve
True/False: DRG determines firing rate of the phrenic nerve during both inspiration and expiration
False; there is no phrenic activity in expiration, so inspiration ONLY
Which type of breathing, eupnea or hyperpnea, do DRG mainly play a role in?
Eupnea
During eupnea, which structure contributes to the firing rate of phrenic nerve?
Dorsal respiratory group (DRG)
True/False: DRG neurons have an intrinsic firing rate
True
Does DRG cause phrenic to ramp up or down during inhalation?
Ramp up, phrenic fires when DRG fires
DRG firing stops during which phase of respiration?
Exhalation
Where is the ventral respiratory group (VRG) located?
medulla
What neurons make up the VRG?
Interneurons and premotor neurons
What does VRG stand for?
Ventral respiratory group
True/False: VRG contributes to both inspiration AND expiration
True. Unlike DRG, VRG DOES contribute to both phases of respiration
When does VRG get activated?
When there is an increased demand for breathing – hyperpnea
Which structure is more active during hyperpnea?
Ventral respiratory group
What are the medullary structures that control breathing?
DRG
VRG
Where is pneumotaxic center located?
Dorsal region of the pons
What is the function of pneumotaxic center?
Stops the inhalation ramp – inhibiting DRG
Inhibit apneustic center
Where do the neurons in the pneumotaxic center innervate?
inhibitory neurons to DRG
how does the pneumotaxic center affect breathing when it is firing a lot? A little?
Decreases time spent in inhalation, lungs filled only partially when firing a lot
Increases time spent in inhalation and lungs fill with excess air when fires a little
Does tidal volume go up or down with pneumotaxic center firing a lot? A little?
Goes down
Goes up
Is respiratory cycle longer or shorter when pneumotaxic center fires a lot? A little?
Shorter
longer
What happens to respiratory rate when pneumotaxic center fires a lot? A little?
Respiratory rate increases, because respiratory cycle shortens
Respiratory decreases, because respiratory cycle lengthens
What is the apneustic center and what inhibits it?
Apneustic center exerts excitatory influence on DRG, pneumotaxic center inhibits it so inspiratory drive decreases as a result and DRG stops the phrenic ramp
How does the pneumotaxic center stop the phrenic nerve ramp?
Direct inhibition of DRG
Indirect inhibition of dorsal respiratory group via the apneustic center
Where is the apneustic center located?
Lower pons
What is the function of apneustic center?
Excited the DRG, and increase inspiratory drive
What happens with over stimulation of the apneustic center?
Prolonged inhalations and brief exhalations
Damage to what region of the nervous system likely results in apneustic breathing?
Central nervous system i.e. head trauma or stroke
Describe what apneustic breathing is?
Prolonged inhalations and brief exhalations
Inspiratory pauses
What are the pontine structure that control breathing?
Pneumotaxic center (upper pons)
Apneustic center (lower pons)
Does the cerebral cortex directly innervates DRG?
No
Is cerebral cortex under voluntary or involuntary control of breathing?
Voluntary
Which structure does the cerebral cortex projects to control the diaphragm?
Phrenic nerve
What are the blood gas consequences for hyperventilation?
More oxygen enters blood as a result of increase partial pressure O2 in alveoli
More CO2 leaves the blood as PCO2 alveoli go down
What are the blood gas consequences for hypoventilation?
Less oxygen enters blood
Less carbon dioxide leaves blood
Where are central chemoreceptors located?
Ventral surface of medulla
Where do central chemoreceptors synapse on?
DRG
Where are peripheral chemoreceptors located?
Carotid and aortic bodies
Which is most sensitive to H+, central or peripheral chemoreceptors?
Central chemoreceptors
Which is most sensitive to Oxygen, central or peripheral chemoreceptors?
Peripheral chemoreceptors
True/False: carbon dioxide can also activate central chemoreceptors along with H+
True
True/False: carbon dioxide and H+ can also activate peripheral chemoreceptors along with oxygen
True
Does activation of the peripheral and central chemoreceptors increase or decrease respiratory rate and minute ventilation (Ve)?
Increase
Which of these can cross the blood-brain barrier: H+, CO2?
CO2
High or low pH and high or low CO2 would increase the discharge frequency of central receptors?
Low pH (High [H+])
High carbon dioxide
True/False: Increased rate of breathing is associated with decreased pH and increased CO2
True
True/False: central chemoreceptors are also stimulated by oxygen
False, central chemoreceptors do not respond to O2, only peripheral
Peripheral chemoreceptors are always exposed to arterial or venous blood?
Arterial
Peripheral chemoreceptors mainly sense O2 or CO2 levels of arterial blood?
Arterial oxygen levels mainly, some arterial CO2 and H+ concentration
What levels of O2, CO2 and pH would increase the discharge of frequency of peripheral chemoreceptors?
Low arterial O2
High CO2
Low pH (high H+)
True/false: decreased blood pH would lead to increased rate of breathing
True
True/False: carotid body firing rate decreases when arterial PO2 drops from 100 mmHg to 60 mmHg
False; carotid body firing (a peripheral chemoreceptor) would increase firing rate when there is a drop in arterial O2 pressure – think: low O2, you need more O2 so breathe more
Which is the most important signaling molecule during hypoxia?
ATP
Describe the hypoxia intracellular response:
Hypoxia closes K+ channel in carotid bodies
K+ channel closing leads to DEPOLARIZTATION of those cells, thereby opening Ca2+ VG channels, letting calcium in
Ca2+ promotes release of NT: ATP, Ach, dopamine
Which structures/ receptors directly carry signal to DRG?
Apneustic center
Peripheral chemoreceptors
Central chemoreceptors
Lung stretch receptors
Muscle and joint receptor
What structure(s) directly inhibit DRG?
Pneumostaxic center
What type of receptors are lung stretch receptors?
Mechanoreceptors
Where are lung stretch receptors located?
Bronchi and bronchioles
How are lung stretch receptors activated?
When lungs become overstretched
What happens when lung stretch receptors are activated?
Stimulate vagus which then carries the signal to the DRG to switch OFF the inspiratory ramp
What is the purpose of the lung stretch receptors?
Prevent lungs from getting overstretched by switching off the inspiratory ramp of DRG
What is the name of the reflex that switches off the inspiratory ramp after lung stretch receptor is activated?
Hering-Breuer reflex
What type of receptors are muscle and joint receptors? Where are they found?
Mechanoreceptors
Found in skeletal muscles and joints
When are muscle and joint receptors activated?
During exercise
What happens when muscle and joint recpeotrs are activated?
Synapse on DRG that leads to increase in respiratory rate and depth
