Neural Control of Blood O2, heart rate, and BP

What happens to blood pH when CO2 levels increase

decreases :p

What is the chemo reflex

How our NS adjusts breathing & HR in response to changes in blood chemistry

• breath rate and HR increase when blood O2 levels are low and CO2 levels are high (i.e. when blood pH is low acidic)

What part of the brain is the “master” regulator of breathing? And how?

The medulla

• neurons in medulla receive input about blood oxygen.

• neurons in the medulla respiratory control center (MRCC) work together to as the central pattern generator (CPG) for breathing: neurons that rhythmically fire without repairing rhythmic sensory input.

What are the steps of the chemoreflex?

1. Changes in cardiovascular activity due to low blood oxygen levels

2. MRCC senses increased blood acidity

3. MRCC integrates signals, increases firing frequency

4. Phrenic nerve firing rate increases

5. Breathing rate increases

6. As this operates as a negative feedback loop, the breathing rate increases stops this entire flow

Where does the chemoreflex happen

At the carotid body, found at the common carotid arteries where they bifurcate (highly vascularized collection of cells that sense changes in blood pH, CO2, and O2)

What is the globus cells role in the chemoreflex?

• It releases NTs when blood pH is low, CO2 is high, and O2 is low

• Then relays that info to the gloospharyngeal nerve (CNIX

Walk through the steps of the chemoreflex for breathing

• glomus cells become depolarized → excitation of glossopharyngeal nerve [CNIX]

• CN IX → nucleus of the solitary tract (NTS) → retrotrapezoid nucleus in the ventral medulla → respiratory CPGs (central pattern generators which are constant firing

• Leads to speeding up of resp. CPGs and then the animal breathes more deeply & rapidly

What does the medullary cardiovascular control center [MCCC] consist of and do?

Consists of separate neurons in medulla for regulating heart rate

• MCCC neurons receive input from glomus cells about blood oxygenation

• Therefore if blood ox decreases, the MCC activates sympathetic NS

What are the functions of baroreceptors?

Specialized endings (found on the carotid sinus near the carotid body and aortic arch) on sensory parts of cranial nerves that detect blood vessel stretching

• Cause increased neuronal firing when BP increase

How the baroreceptors decrease HR look at diagram

• increase in BP → increase baroreceptor firing

• CN IX & X → nucleus tractus solitarius → nucleus ambiguous

• (PARASYMPATHETIC) efferent CN X (vagus nerve) axons trigger the released ACh which the decreases HR

What about sympathetic regulation of heart rate?

• increase in BP → baroreceptor firing → Nucleus of the solitary tract neurons

• NTS → excites the caudal ventrolateral medulla [cVLM] constraining GABAergic neurons

• cVLM inhibits rostral VLM

• rVLM no longer excite preganglionic neurons in spinal cord

• preganglionic neurons release less ACh onto postganglionic neurons which release less NE → suppress NE release on the heart (prevents increase in HR) from symp NS

BASICALLY:

• decrease NE released decreased HR

• With increasing baroreceptor firing there is suppression of sympathetic branch

• The opposite of this would be the decrease in BP leads to decrease baroreceptor firing then decreases firing of GABAergic cVLMand disinhibits rVLM

• more NE released increase heart rate