- Being short of breath - Unpleasant conscious awareness of difficulty breathing

Control of Breathing Flashcards by Georgie French

Why is breathing a unique behaviour?

It is continuous from birth to death

- It occurs spontaneously - does not need conscious thought unless there is a problem

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What is breathing modulated by?

Reflexes - coughing 
Volitional control - Breath hold 
Vocalisation - singing 
Emotional events - crying 
- Physiological challenges - Sleep, exercise

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What must neural control of breathing do?

Establish autonomic rhythm: breathing happens without conscious thought
Respond to metabolic demands
Respond to mechanical changes: change in posture
Range of episodic non-ventilatory behaviours: speaking, sniffling, eating

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What is Eupnea?

Normal rhythmic breathing

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What is Dyspnea?

Being short of breath

- Unpleasant conscious awareness of difficulty breathing

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What are respiratory related neurons?

Array of interconnected neurons

- Fire more action potentials during the respiratory cycle

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What are central pattern generators?

Brainstem (medulla oblongata)

- Independently generate respiratory rhythm

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What are respiratory motor neurons?

Innervate respiratory muscles

- Axons via the phrenic nerve innervate the diaphragm

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What does the frequency of respiratory central pattern generators change?

The strength of drive from central and peripheral receptors
Change in both depth and frequency of ventilation

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What do chemoreceptors provide feedback on in the respiratory system (to the brain)?

On the PO2, PCO2 and pH

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What do mechanoreceptors provide feedback on in the respiratory system (to the brain)?

Mechanical status of the lungs, chest wall and airways

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What does neural signals sent to respiratory muscles do?

They produce rhythmic breathing movements e.g. diaphragm and intercostals

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What does neural signals sent to upper airway muscles do?

e. g. laryngeal, pharyngeal and tongue

- Produce reflexes to keep airways patent (clear, prevent obstruction) e.g. cough, gag, sneeze

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What are chemoreceptors?

Sensory receptors that detect chemical changes in the surrounding environment

In the respiratory system chemoreceptors detect changes in PO2, PCO2 and pH of the blood
decreases in O2 - hypoxia
decreases in CO2 - hypercapnia

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What are peripheral chemoreceptors?

Small, highly vascularised bodies in the region of the aortic arch and carotid sinuses
Information is sent via the glossopharyngeal and vagus nerve to the nucleus in the brain stem (NTS)

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What is the name of the nucleus in the brainstem?

Nucleus Tractus Solitarius

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What do peripheral chemoreceptors respond to?

Decreases in Po2 - hypoxia

Reduction in arterial PO2
Peripheral chemoreceptors stimulated
Neural signals sent from carotid and aortic bodies to NTS in the brainstem
Ventilation increases to restore PO2 levels

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Below wat arterial PO2 (mmHg) is there progressive hyperventilation?

60 mmHg

The hypotoxic response originates in the carotid and aortic bodies in peripheral chemoreceptors. What do they play little part in?

The moment to moment control of breathing

What are central chemoreceptors?

Clusters of neurons in the brainstem that are activated when PCO2 is increased (hypercapnia) or pH is decreased

What is the process of the function of central chemoreceptors when there is an increase in arterial PCO2?

Central chemoreceptors are stimulated
Signals processed and information is passed on to neuronal clusters in the brainstem involved in generating breathing
Ventilation increases to restore PCO2 levels

What effect does very small changes in PCO2 have on ventilation?

Large effects

Where do hypercapnic responses originate and what major roles do they play?

Originate in central chemoreceptors in the brainstem

- Plays major role in moment to moment control of breathing

What are mechanoreceptors?

Sensory receptors that detect changes in pressure, movement and touch
In the respiratory system mechanoreceptors detect movement of the lungs and chest wall
e. g. during inspiration mechanoreceptors detect inflation of lungs and movement of the chest

Inflation of the lungs activated mechanoreceptors. What nerve are neural signals sent to the NTS in the brainstem via and what is the result of this?

- Signals sent via vagus nerve | - Ventilation is adjusted accordingly

What are mechanosensory signals essential in doing?

- Adapting and adjusting breathing | - Integrating respiratory pattern with their movements e.g. posture and locomotion

Where does the NTS in the brainstem receive information from?

- Mechanoreceptors and peripheral chemoreceptors | - This information is processed in the brainstem by respiratory neurons

What cluster of respiratory neurons in the brainstem generate the rhythm of breathing?

- Central pattern generator neurons | - The rhythmic signal is sent to the respiratory muscles

When are inspiratory neurons active?

During inspiration

When are expiratory neurons active?

During expiration

Rhythm generating neurons are a bilateral cluster of neurones found on both sides of the brain-stem. What kind of properties do they have?

Rhythm generating properties

Where does the phrenic nerve exit the spinal cord and what does it innervate?

- Exits at cervical spinal cord at level 3-5 | - Innervates the diaphragm

What do nerves exiting the thoracic spinal cord innervate in relation to respiration?

Innervates intercostal muscles (a group of muscles found between the ribs which are responsible for helping form and maintain the cavity produced by the ribs, and assisting with the expansion and contraction during breathing

What are the functions of the dorsal respiratory group and where are the found?

- Found in and around NTS - Are mainly inspiratory neurons - Receives sensory info: chemoreceptors and mechanoreceptors via CNXI and CNX - Integration of sensory info from the respiratory system

What are the functions of the ventral respiratory group?

- Both inspiratory and expiratory neurons - Contains motor neurons - Contains regions which may be the respiratory Central pattern generators

What is the function of pontine respiratory group?

Modulates respiratory output

Where is volitional and emotional modulation of breathing found?

Higher centres in the brain stem

What is a homunculus?

The distorted figure of a human superimposed on an illustration of the surface of the brain; used to demonstrate those portions of the body supplied by the various motor and sensory cortical regions

What are the voluntary actions that alter airflow?

- Breath holding - Speaking - Singing *control is precise and not absolute (breath holding is overridden by ventilatory drive from chemoreceptors)

Where do the voluntary actions that alter airflow originate in?

The cerebral cortex

What are the 2 main mechanisms for motor control from the cerebral cortex?

- Cortical neurons send axons to the brainstem | - Cortical premotor neurons send axons to motor neurons which control the muscles of respiration

What do chemoreceptors detect?

Changes in PO2, PCO2 and pH in blood, send neural signals to NTS

What do mechanoreceptors detect?

Mechanical changes in lung and chest wall, send neural signals to NTS

Where are respiratory rhythm generating neurons located?

In the brainstem