respiration 3, control of breathing

What is the difference between the rhythmic beating of the heart and and the rhythmic cycles of inspiration and expiration?

• the heart that doesn’t need any neural input to initiate spontaneous beating of the heart

•  the skeletal muscle that coordinate contraction of the respiratory system do

what is the brain stem and what is it made out

• its what connects the spinal chord to the cerebrum and cerebellum 

• its made out of midbrain, pons an dmedulla oblongata

which neurones in the brain stem help with controllign breathing

• dorsal respiratory group - group of neurons that control muscle for inspiration

• pontine respiratory groups - help coordinate smooth repiratory rhythm

which neurons in the medulla oblongata control breathing

- the nucleus tractus solitarius (NTS) contains the dorsal respiratory group (DRG) of neurons which control muscles of inspiration

which nerves does the NTS receive sensory input from

C9 ad C10

how do the dorsal repiratory group controll muscles of inspiration

• the NTS whihc is what contaisn the DRG gets the sensory info from the peripheral echmo and mechano recpetors

• they are innervated from C9 and C10

• their output goes via the phrenic nerves to the diaphragm and via the intercostal nerves to the intercostal muscles

what does the pontine respiratory groups do

 provide tonic input to the medullary networks to coordinate a smooth respiratory rhythm

which neurones act as a pacemaker for the respiratory system?

• pre-Botzinger complex in the ventral respiratory group (VRG)
  

• has output to:

- muscles in inspiration/expiration

- to muscles of the pharynx, larynx and tongue to keep upper airways open

what happens during quite breathing

• 
  A few inspiratory neurons in the ventral respiratory group (VRG) fire spontaneously.

• This recruits more inspiratory neurons to fire in a positive feedback loop, increasing activation.

• As more neurons fire, more skeletal muscle fibres (e.g. diaphragm, external intercostals) are contracted, causing inspiration.

• At the end of inspiration, the inspiratory neurons stop firing.

• This causes the respiratory muscles to relax, leading to passive expiration.

• Expiration occurs due to the elastic recoil of the inspiratory muscles and elastic lung tissue

• not used in expiratory as not forced

what happens during forced breathing

1. VRG neurones are activated by a stimulus 

2. inspiratory neurones stimulate accesory muscles contraction e.g scalnes pectoralis major

3. accessory muscles contracting raises the sternum and upper ribs, increasing thoracic volume moving air out

4. expiratory neurones cause the contraction of the internal intercostal and abdominal muscles

5. nspiratory neurons are inhibited while expiratory neurons fire, preventing overlap.

how does CO2 affect ventialtion rate

• if the rate of CO2 productionby the cells exceeds the rate of CO2 removalby the lungs, arterial PCO2 increases, and ventilation is intensified to match CO2 removal to production

if CO2 high more repsiration

how does O2 influence ventilation

if too little o2 is present in arterial blood destined for the brain and other tissues, the rate and depth of breathing increases

how does PH affect ventilation

 A reduction in plasma pH or increased P_CO2 will activate the carotid and aortic glomus cells and increase ventilation.

what is the link between CO2 and pH

• if there is an increase in the amount of CO2, we get an increase conversion into H+ ions

• Increasing CO2, decreases pH levels (more acid)

Why is CO2 the main type of stimulus for changes in ventilation

• 
  Peripheral chemoreceptors (in carotid & aortic bodies) contain glomus cells.

• ↑ arterial CO₂ (↑PCO₂) → lowers plasma pH (forms carbonic acid).

• This activates glomus cells, triggering a reflex increase in ventilation.

• CO₂ changes cause a rapid and sensitive ventilatory response.

• O₂ levels must fall a lot more to below 60mmHgbefore a strong response occurs — so CO₂ is the main respiratory drive.

• Anything that increases PCO₂ or decreases pH → increases ventilation

what type of relfex is it that helos to keep the pO2 and pCO2 constant

haemostatic

What are the two types of chemoreceptors

1. central chemoreceptors: in the medulla - detect changes in CO2 conc in the cerebrospinal fluid

2. Peripheral chemoreceptors: in the carotid and aortic bodies - detect chnaged in pO2, pCO2 and pH of the plasma

How does the carotid body cells (peripheral chemoreceptor) respond to PO2 below 60 mmHg, high CO2 or low pH

1. K⁺ channels close → glomus cell depolarises.

2. Voltage-gated Ca²⁺ channels open → Ca²⁺ enters cell.

3. Neurotransmitter released → triggers action potentials in sensory neurons.

4. Signal sent to brainstem → increases ventilation.

how does the central chemorecptor monitor CO2 by responding to change in PH

1. CO₂ crosses blood–brain barrier → enters Cerebrospinal fluid.

2. CO₂ + H₂O → H⁺ + HCO₃⁻ (via carbonic anhydrase).

3. ↑ H⁺ in CSF activates central chemoreceptors in the medulla.

4. These receptors stimulate respiratory centres → increase rate & depth of ventilation.

5. More CO₂ is exhaled, restoring normal PCO₂ and pH.

how does plasma pH influence central chemoreceptors?

•  pH changes in the plasma do not usually influence the central chemoreceptors directly as H= annot pass into the blood brain barrier 

explain what these 3 graphs show

• PCO2 is more sensitive than PO2 in changing respiration

• the 2 similar graphs show that the impact on the volume respired is more for how then o2 as it increases

how does the body protect the respiratory tract from physical damage or injury with reflexes

1. Irritant detected – inhaled dust, smoke, or noxious gases stimulate irritant receptors in the airway mucosa.

2. Signal sent to CNS – receptors send impulses via sensory neurons (vagus nerve) to the integrating centres in the brainstem.

3. Reflex response – CNS activates parasympathetic neurons, which cause bronchoconstriction (narrowing of bronchioles) by contracting smooth muscle.

4. Purpose – limits further entry of harmful substances into the lungs.

5. Other protective reflexes – coughing and sneezing are also triggered by irritant receptors to expel particles.

explain the Hering-Breuer reflex

it stops overinflation of the lungs and limits the depth of inspiration 

1. During inspiration, lungs expand → stretch receptors in bronchi and bronchioles are activated.

2. Stretch receptors send signals via the vagus nerve to the respiratory centres in the brainstem.

3. Brainstem response: inhibits inspiratory neurons → terminates inspiration.

4. Result: prevents excessive lung expansion and protects lung tissue from damage.

what can the higher centres in the hypothalmus and cerebrum do

• it can alter the activity of the brainstem to change the ventilation rate and depth

• higher means physically higher than the brainstem

do respiratory reflexes or chemoreceptor reflexes overide and make the final outcome

chemoreceptor reflexes