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1

The brain receives neural signals from chemoreceptors. What do these do with regards to regulation of breathing

Provide feedback on partial pressures of Oxygen, Co2 and pH. 

2

The brain receives neural signals from mechanreceptors. What do these do with regards to regulation of breathing

Provide feedback on mechanical status of lungs, chest wall and airways. 

3

Peripheral chemoreceptors, are small, highly vascularised bodies in regions of the aortic arch and carotid sinuses. Where is information from these chemoreceptors sent?

  • Signals from carotid sinuses are sent via the glossopharyngeal nerve 
  • Signals from the aortic arch are sent via the vagus nerve 
  • Signals from both of these is sent to the nucleus tractus solitarius 

4

The reduction in partial pressure of which gas activates peripheral chemoreceptors? 

oxygen 

5

When oxygen is reduced, the peripheral chemoreceptors feedback to the brainstem via , specifically the Nucelus tractus solitarius and cause what affect?

As partial pressure of oxygen decreases, INCREASE VENTILATION 

6

It is important to note that it takes for partial pressure of oxygen to drop to 60mmHG before what?

BEFORE rate of ventilation increases 

7

You also have central chemoreceptors found in the Medulla oblongata. These chemoreceptors are activated when there is an increase in partial pressure of what gas? What is the subsequent response?

Carbon dioxide 

Signals passed on to other neuronal clusters in the brainstem that cause an increase in ventilation in order to restore partial pressure of carbon dioxide. 

8

What are the central chemoreceptors measuring to detect partial pressure of CO2? 

CSF

9

Previously we said how it took a large drop in the partial pressure of oxygen in order to trigger increase/decrease the rate of breathing. How much carbon dioxide does it take to change the rate of breathing 

Very small changes 

10

Define mechanoreceptors and state their role in the respiratory system. 

  • Sensory receptors that detect changes in pressure, movement and touch 
  • In respiratory system, they detect movement of lung and chest wall 

11

Inflation of lungs (inspiration) activates lungs. Neural signals are sent via vagus nerve to Nucleus tractus solitarius. Ventilation is the Adjusted accordingly. 

Given that mechanoreceptors are found in airway smooth muscle and the airway epithelium, what are the possible responses? 

Essentially triggers termination of inspiration. 

12

What region of the meduall receives signals from the mechanoreceptors and peripheral chemoreceptors ?

Nuclear Tractus Soltarius 

13

Clusters of respiratory neurones in brainstem generate rhythm of breathing. This respiratory signal is sent to the respiratory muscles. They do this based in information provided by the Nucleus tractus solitarius. These rhymic generating neurones can be either INSPIRATORY OR EXIRATORY (i.e. they fire at different times) 

Brainstem neurones produce regular breathing. The signals go from the spinal cord to the phrenic nerve (goes to diaphragm). Other nerves exit from the throacic spinal cord which innervate the intercostal muscles. 

Groups of neurones involved 

Dorsal respiratory group (this is where nucleus tractus solitarius) - this receives sensory information from mechano and chemoreceptors Has mainly inspiratory neurones. 

Ventral respiratory group - these are the neurones that generate the rhythm of breathing. This done by controlling the muscles involved in breathing (diaphram and intercostal muscles) via motor neurones (dorsal respiratory group does NOT have motor neurones). Has mainly inspriatory and expiratory neurons. 

Pontine respiratory group - modules respiratory output 

 

Is also higher structures than input: Ceberal cortex for example. 

14

Summary 

15

Dorsal respiratory group of neurones has an important region called the nucleus tractus solitarius.  The NTS is the sensory termination of both the vagal and glossopharyngeal nerves; which collect sensory information from the peripheral chemoreceptors, baroreceptors and mechancoreceptors in the lung. 

The basic rhythm of respiration is generated mainly from the dorsal respiratory group. 

16

FROM TEXTBOOK - Describe respiratory centres in medulla oblongata 

  • Respiratory rhytmicity centres of the medulla oblongata - Dorsal respiratory group and ventral respiratory group 
  • DORSAL RHYTHMIC GROUP functions in every respiratory cycle
    • Controls neurons that controls lower motor neurons innervating the external intercostal muscles and diaphragm 
  • The VENTRAL RHYTMIC GROUP functions during forced breathing - it has an expiratory and inspiratory - controls lower motor neurones which innervate the muscles involved in active inhalation and exhalation
    • RECIPROCAL INHIBITION OCCURS  - WHEREBY THE EXPIRATORY CENTRE IS ACTIVE WHILST THE INHALATION CENTRE IS INACTIVE AND VICE-VERSA - ENSURES RIGHT MUSCLES CONTRACT AT RIGHT TIME  
  • Basic patterning of respiration is thought to be governed by a pacemaker cells, but what group of cells this is exactly has not been clarified 

17

Describe the interplay between the DRG and VRG in quiet breathing and forced breathing 

Quiet breathing

  • Activity in the DRG increases over a period of around 2 seconds, stimulating the inspiratory muscles - this is where inhalation takes place 
  • After 2 seconds, the DRG neurons become inactive, and remain so for 3 seconds, allowing the inspiratory muscles to RELAX 

Forced breathing

  • Increases in responses from chemoreceptors and baroreceptors feedsback to the DRG and stimulates the VRG to activate accessory muscles involved in inhalation 
  • Then, DRG inspiratory and VRG inspiratory centres are inhibited, whilst the EXCITATORY CENTRE OF VRG IS ACTIVATED 

 

18

Textbook: The Apneustic and Pnemotaxic centres of the PONS

 

  • These are centres of the PONS that regulate the depth and rate of respiration in response to sensory stimuli  from other centres in the brain 
  • Apneustic centre provdies constant stimulation to the dorsal respiratory group - apneustic is all about the length of INSPIRATION
  • An increase in  pneumoatic centres output inhibit the apneustic centres and promote passive or active exhalation 
    • DECREASE in pneuotaxic centre output slows the respiratory pace but increases the depth of respiration - SINCE INHALATION IS LONGER AND BIGGER BREATHS CAN BE TAKEN 
  • In some cases, the inhibitory output of the pneumotaxic centres is damaged by a stoke, meaning there is nothing there to inhibit the apneustic centres and inhalation periods can be 10-20 seconds long 

 

 

BEAR IN MIND THAT THE DRG AND VRG ARE THEREFORE GETTING INPUT FROM THE PONS, AS  WELL AS THE CHEMO AND MECHANORECEPTORS - ALL CONTRIBUTE TO BREATHING RATE  - STUDY DIAGRAM CAREFULLY BELOW 

IN SUMMARY 

  • Pneumotaxic centres establish the rate of breathing 
  • An increase in pneumotaxic output increases the rate of breathing by shortening the duration of inhalatoin 
  • A decrease in pneumotaxic output decreases the rate of breathing but increases by allowing for LONGER inhalation (since apneustic centre is more active as it is less inhibited by pneumotaxic) 

19

Volunatry control of respiration 

  • activity of the cerebra cortex has an indirect effect on the respiratory centres
  • Conscious thought, tied to emotions, can affect the respiratory rate 
  • Emotional states can cause bronchodilatoin and increase respiratory rate, whilst parasymapthetic has opposite effect 
  • Higher centres can also control that same lowor motor neurnes that are controlled by DRG and VRG 
    • THIS IS IMPORTANT IN THINGS LIKE SINGING WHERE YOU BREATHING RATE IS GOING TO BE COMPLETELY DIFFERENT
  • Higher centres can also have an inhibitory effect of apneustic centres and on the DRG and VRG - THIS IS IMPORTANT WHEN YOU HOLD YOUR BREATH 
  • YOU CAN ONLY HOLD YOUR BREATH - AS CHEMORECEPTOR REFLEX ARE EXTREMELY POWERFUL AND YOU CANNOT CONCIOUSLEY SUPPRESS THEM 

20

Which cranial nerve monitors chemoreceptors in the aortic arch?

Vagus

21

Which cranial nerve monitors chemoreceptors at the carotid bodies near the carotid sinus 

Glossopharyngeal nerve 

22