Respiration IV Flashcards
What is the BASIC respiratory rhythm pattern generated by?
How do we know this?
Centres in the MEDULLA
Know this because:
- Lesion between the medulla and the pons - maintain basic breathing pattern
- Lesion BELOW the level of the medulla - basic breathing rhythm is LOST
What MODIFIES the basic respiratory pattern?
Inputs from various regions of the brain
How can breathing be CONSCIOUSLY altered?
- Hyperventilating
- Breath holding
What are the 2 respiratory groups in the medulla?
1) DORSAL respiratory group
2) VENTRAL respiratory group
What does the dorsal respiratory group in the medulla control?
Inspiration
What does the ventral respiratory group in the medulla control?
FORCED inspiration and FORCED expiration
How does quiet EXPIRATION occur?
Passive process - elastic recoil
Where do the INSPIRATION outputs from the medulla go to?
1) Down the PHERNIC NERVE to control the diaphragm
2) Down the SPINAL NERVES to control the external intercostal muscles
Where do the EXPIRATION outputs from the medulla go from/to?
From: the VENTRAL RESPIRATORY GROUP
To:
- INTERNAL intercostal muscles
- ABDOMINAL muscles
What complex in the medulla controls the basic breathing pattern?
How do we know this?
PRE-BOTZINGER COMPLEX
Know this because:
The activity in the HYPOGLOSSAL nerve matches the Pre-Botzinger complex output
Where is the pre-botzinger complex present?
At the top of the ventral respiratory group
What 3 basic types of pattern output does the Pre-Botzinger complex generate?
1) Eupneic
2) Sigh
3) Gasp
What is a eupneic breathing pattern?
Basic, standard breathing
What happens to the activity of the Pre-Botzinger complex when there is a sigh?
Increase INTENSITY of spike rate
What does a sigh help with?
Gas exchange
What happens to the activity of the Pre-Botzinger complex when there is a gasp?
Short, rounded activity spike
When does a gasp occur?
When there is shortage of oxygen
What are the 2 main classes of neurons in the Pre-Botzinger complex?
1) Pacemaker cells
2) Non-pacemaker cells
What is the difference between pacemaker and non-pacemaker cells?
Pacemaker - able to generate their OWN rhythmic action potential
Non-pacemaker - NOT able to generate their own rhythmic action potential
Describe the activity of the pacemaker cells in the PB complex
1) Spiking phase - slow, background depolarisation called the SODIUM LEAK CURRENT
2) Reaches point where the membrane remains depolarised
3) Activation of a PERSISTANT SODIUM CURRENT
- Causes BURSTING phase of action potentials –> inspiration
4) Eventually, deactivation of the persistant sodium current
5) Repolarisaion back to normal membrane potential
6) No further inspirations until the activation of the persistant sodium current again
What is NALCN?
The sodium leak channel
What occurs in a mouse with NALCN KO?
No sodium leak - membrane is hyperpolarised:
- Breathing stops for 5 seconds, 5 times in one minute
- Very IRREGULAR breathing pattern
- Don’t survive past 24 hours
What does K+ do?
Determine the resting membrane potential through the K+ gradient across the membrane
What does increase in K+ cause?
What does this allow?
Depolarisation
More of a chance for the neuron to enter BURSTING activity
What does the transition to bursting activity depend upon?
2 different types of inward current:
1) Persistant sodium current (Inap)
2) CAN cation current (Ican)
What is the CAN cation current activated by?
When is the CAN cation current activated more?
Ca2+ influx
Activated more during the ‘sigh’ breathing pattern
What classes are the pacemaker cells split into?
2 classes:
1) Cadmium SENSITIVE
- Neurons relying on Ican for bursting
2) Cadmium INSENSITIVE
- Neurons relying on Inap for bursting
What alters the background depolarisation of the pacemaker cells?
What does this determine?
Altered by inhibitory and excitatory inputs on the neurons of the Pre-Botzinger
Determines when the neurons are in spiking phase or in bursting phase
What is hypoxia?
LACK of oxygen
What impact does hypoxia have on the Pre-Botzinger complex?
Normal breathing –> sighing –> gasping:
- Loss of the IPSCs on the Pre-Botzinger complex
- Loss of autonomous spiking neurons
- Loss of cadmium sensitive neurons
- Cadmium insensitive neurons remain
What are cadimium insensitive neurons responsible for?
The GASPING pattern of breathing
How does the dorsal respiratory group control quiet inspiration?
Sending signals to the inspiratory muscle
When is the dorsal respiratory group active?
Spontaneously active:
1) Period of ACTIVITY
- Activity in the PB sends signals to the DRG, activating it
2) Shuts OFF
- No signalling of the PB to the DRG
3) Period of activity again
What happens when the dorsal respiratory group is inactive?
Passive expiration
When is the VRG inactive?
During quiet respiration
When is the VRG active?
During FORCED inspiration/expiration (eg. exercise)
How do signals from the pons act on the PB?
What does it regulate?
Can have STIMULATORY or INHIBITORY impacts on the PB
To REGULATE the RATE and DEPTH of breathing
What are the centres in the pons that send signals to the PB?
1) Pneumotaxic centre
2) Apeneustic centre
What does the Pneumotaxic centre do?
INHIBITORY effect on the INSPIRATORY centre
- -> Reducing/shortening inspiration phase
- -> Shallower breathing (increase rate, reduce depth)
What does the Apneustic centre do?
STIMULATES the INSPIRATORY centre
- -> PROLONGS inspiration phase
- -> INCREASES DEPTH and REDUCES RATE
How is the breathing pattern determined?
- MANY inputs on the PB complex (inhibitory/excitatory)
- SUM of all the inputs determine the output of the PB (which controls the basic breathing pattern, gasping, sighing etc)
What is the Hering-Breuer reflex?
Describe this reflex
Negative feedback loop controlling the stretch of the lung:
- Stretch receptors in the lung send signals BACK to the medulla when the diaphragm contracts and the lungs INCREASE in volume
- Signal via the VAGUS NERVE to the INSPIRATORY centre
- -> SHUTS OFF inspiration, to prevent over-inflation of the lungs
What is the ‘inspiratory centre’?
The dorsal respiratory group
What do CENTRAL chemoreceptors do?
How?
Monitor conditions in the CEREBRO-SPINAL fluid such as CO2 and pH
Increase in CO2 –> acidification
Where are PERIPHERAL chemoreceptors located?
In the carotid body and the aortic arch
What do the peripheral chemoreceptors respond to?
Increase in Co2
Decrease in pH
Decrease in O2
What does the stimulation of the chemoreceptors cause?
Increase in ventilation
