S4 L2 Neural and Chemical control of breathing

Question 1

Reminder:

• Nerve that supplies the diaphragm (and it’s nerve roots)
• Intercostal muscles responsible for inhalation and exhalation?

Answer 1

Diaphragm nerve: Phrenic nerve - from C3, C4, C5

Expiration - Mainly a passive process, by elastic recoil of lungs and chest wall, inner and innermost internal muscles
Inspiration - External intercostal muscles, diaphragm

Question 2

How is breathing controlled? (where in the brain and name of it) ___ ___ ___
What does the ____ ____ ____ control?
What can it be likened to (analogy)?
How many times does it make the inhalatory intercostal muscles contract a minute? (if not exercing, not pathology…)
Sensory inputs to the ____ ____ ___?
Where is the ____ ____ ____?

Answer 2

Respiratory Pattern Generator

Question 3

Inputs to the RPG
- State 3…

Answer 3

Question 4

RPG:
- 2 connections from RPG to ‘two things’ (oppose each other)

Answer 4

ignore blue lines in the diagram

Question 5

RPG
- How to stop both the inspiratory and expiratory neurones being switched on at the same time?

Answer 5

Question 6

3 nerves from Inspiratory and Expiratory neurones

Answer 6

Phrenic nerve to diaphragm
Motor neurones to external intercostal muscles
Motor neurones going to internal and innermost intercostal muscles

purple in digram and light green (ignore the rest)

Question 7

Everything just gone through: inputs to the RPG, inspiratory and expiratory neurones, motor nerves is part of what type of control?

Answer 7

Involuntary:
Somatic but regulated by inputs from autonomic system. (Intercostal muscles are skeletal muscles)

Question 8

Voluntary part of this system, what does this mean?

What condition is the voluntary part of this system affected in?

Answer 8

Blue in the diagram

Condition - Ondine’s curse: Patient lose ability to regulate breathing involuntarily, can only breath voluntarily. Constantly have to be thinking about breathing! Sleep - will forget to tell the body to breath - so have to be ventilated during sleeping

Question 9

Summary of whole system

Answer 9

Question 10

Summary:

• What is included in buffer system
• What are compensatory mechanisms?

Answer 10

Question 11

Summary:
Link between - Sensors, Respiratory pattern generator, effectors

Answer 11

Question 12

Chemical Control of Ventilation:
RPG must respond in changes of needs and production of pO2, pCO2, pH

• What does ventilation need to accomodate for?
• Peripheral chemoreceptors sense? how long take to respond?
• Central chemoreceptors sense? how long take to respond?

Answer 12

Accomodate for:
– Maintain adequate oxygen status
– Adjust respirations for changing metabolic status/needs reflected by altered PO2, PCO2, pH (remember that pH is a measure of hydrogen ion concentration – inverse relationship – as H+ levels go up, pH goes down

Peripheral chemoreceptors:
Sense pO2, pCO2 and pH levels (but dominantely, pO2)
Respond in seconds

Central chemoreceptors:
pH and pCO2
Respond in hours

Question 13

Reminder of the carbonic acid - bicarbonate buffer system, and which organs affect it?

Answer 13

Question 14

Peripheral chemoreceptors: location, don’t confuse with…, sensitive too…, major function of them…
- Carotid bodies

• Aortic bodies

Answer 14

Question 15

Peripheral chemoreceptors and pH

• What happens
• HH equation

Aside:

• What happens in hyperventilation?
• What happens in a panic attack?

Answer 15

Question 16

Summary of Peripheral chemoreceptors:

• 2
• Sensory innervation…
• Most sensitive to changes in…
• Time take to respond?

Answer 16

Question 17

Central chemoreceptors:

• Location?
• Sense what?
• What can’t they sense?

Answer 17

• Central chemoreceptors
– Specialised neurons located on BRAIN side of Blood Brain Barrier (BBB) -bathed in CSF
– BBB = endothelial cells of blood vessels in brain surrounded by pericytes and foot processes (end feet) of astrocytes to create a highly selective permeability barrier
• Sense increases in arterial PCO2 and—much more slowly—decreases in arterial pH, but not arterial PO2
• When blood-gas parameters nearly normal central chemoreceptors are the primary source of feedback to the brainstem respiratory centres for needed adjustments
• If PCO2 increases suddenly then ventilation increases rapidly - augmenting minute ventilationocesses (end feet) of astrocytes to create a highly selective permeability barrier
• Sense increases in arterial PCO2 and—much more slowly—decreases in arterial pH, but not arterial PO2
• When blood-gas parameters nearly normal central chemoreceptors are the primary source of feedback to the brainstem respiratory centres for needed adjustments
• If PCO2 increases suddenly then ventilation increases rapidly - augmenting minute ventilation

Question 18

How do chemoreceptors work?

Answer 18

BBB seperates central chemoreceptors in the medulla from arterial blood

BBB has a low permeability to ions such as H+ and HCO3-, but high permeability to small molecules like CO2

Question 19

Central chemoreceptors and chronic hypercapnia e.g. long-term COPD
- 2 methods of compensation for this

Answer 19

Question 20

Hypoxaemia (low pO2), Hypercapnia (high pCO2), and Acidosis (low pH), all cause increase in ventilation, which should then cause the following changes in the body..

Can over-oxygenating a patient with COPD (for example) be bad?

Look at PP for some example Q - really helpful

Answer 20

Bad to over-oxygenate: in theory for healthy person it would be fine as can breath carbon dioxide out, but in COPD cant breath the carbon dioxide out as easily, so carbon dioxde stay her in the blood, causing acidity

Question 21

GW Q:

• How does CO poisoning affect oxygen in the blood?
• For someone with COPD, giving them too much oxygen can be bad because…

Answer 21

How does CO poisoning affect oxygen in the blood?
​CO poisoning affects HB levels of O2 and NOT paO2
The peripheral chemoreceptors are only detecting paO2 which would appear normal

COPD:
Lead to high CO2, which is more dangerous than having slightly reduced oxygen levels