Respiratory: Physiology - Control of Respiration Flashcards
(39 cards)
What is the major rhythm generator of breathing?
The Medulla
In brain damage, where would the injury have to be to affect normal ventilation?
- Normal ventilation is retained if the section above the medulla is affected but ventilation ceases if the section below the medulla is affected
What group of neurons in the medulla is responsible for the breathing rhythm?
The pre-botzinger complex
These neurons display pacemaker activity; they are located near the upper end of the medullary respiratory centre
Where is the pre-botzinger complex located?
Located near the upper end of the medullary respiratory centre
What gives rise to inspiration?
- Dorsal respiratory neurones fire to cause inspiration
- Fire leads to contraction of inspiratory muscles leading to inspiration
- When firing stops, the passive process of expiration begins
What occurs during inspiration?
- Diaphragm descends on contraction
- This increases the verticle dimensions of the thoracic cavity
- Contraction of the external intercostal muscles elevates the ribs and the sternum
- This enlarges the thoracic cavity from front to back and from side to side
How does active expiration occur?
Increased firing of dorsal neurones which excites a second group of neurones known as the ventral neurones; this excites the internal intercostals, abdominals etc. leading to forceful expiration
What neuron group are considered part of the medullary respiratory center?
Dorsal respiratory group
Ventral respiratory group
Pre-botzinger complex
What neuron group are considered part of Pons respiratory center?
Pneumotaxic center
Apneustic center
Is expiration a passive or an active process?
Passive
When are the ventral neurons of the pons not activated?
Not in normal breathing
Activated during hyperventilation
What modifies the rhythm set up by the medulla?
The pons respiratory centre
Where is the Pneumotaxic centre located?
In the Pons
What does stimulation of the pneumotaxic centre result in?
Termination of Inspiration
When is the pneumotaxic centre stimulated?
It is stimulated when the dorsal respiratory neurones fire
What occurs if the Pneumotaxic centre is unable to be stimulated?
Breathing is prolonged inspiratory gasps Brief expiration (Apneusis)
What does apneusis mean?
Abnormal breathing - characterised by prolonged breathing
What does the Apneustic centre impulses result in?
- Impulses from neurones in the Apneusitc centre excite the inspiratory area of the medulla
- This results in prolonged inspiration
What stimuli affect the respiratory centres?
- Higher brain centres
- Stretch receptors
- Juxtapulmonary receptors
- Joint receptors
- Barorecptors
- Central chemoreceptors
Describe how pulmonary stretch receptors work?
These are activated during inspiration, afferent discharge inhibits inspiration – Hering-Bruer reflex (guard against hyperinflation)
They are unlikely to switch off inspiration during the normal respiratory cycle as they are only activated at large volumes, 1L + tidal volumes
They may be important in new born babies
They may prevent over-inflation of lungs during hard exercise
Describe how joint receptors work?
Impulses from moving limbs reflex increase breathing
Probably contribute to the increased ventilation during exercise
What factors increase ventilation during exercise?
- Reflexes originating from body movement
- Adrenaline release
- Impulses from the cerebral cortex
- Increase in body temperature
- Later; accumulation of CO2 and H+ generated by active muscles
Describe the ventilatory response to exercise, in terms of ventilation over time ?
- Within seconds of starting exercise, ventilation will increase, then level out momentarily (I) before then gradually increasing (II) to reach a plateau (III)
- As soon as exercise ceases, ventilation will drop a little very suddenly, then gradually decrease over a longer period of time
- It is thought to be due to a combination of neural and chemical stimuli that we get such a response to exercise
Describe how the cough reflex is set up?
- Vital part of body defence mechanisms
- Activated by irritation of airways or tight airways (e.g. asthma)
- Centre in the medulla
- Afferent discharge stimulates: short intake of breath, followed by closure of the larynx, then contraction of abdominal muscles (increases intra-alveolar pressure), and finally opening of the larynx and expulsion of air at a high speed
