control of breathin Flashcards
what is the central control of breathing?
the brain stem
what occurs in the brainstem?
normal automatic control of breathing
what can override this + when?
the brain’ cortex when voluntary control is desired
what generates the respiratory rhythm?
medulla
what is the brainstem?
posterior part of the brain, continuous with the spinal cord
consists of the midbrain, pons and medulla oblongata of the hindbrain
experiment to deduce the various functions
sectioning of the brainstem above the respiratory centre of the medulla abolishes voluntary, cortical control of breathing but leaves normal rhythmicity intact
different groups of motor neurone in the brain
dorsal respiratory group and ventral respiratory group
explain dorsal respiratory group
motor neurones associated with initiating inspiration found in the ventrolateral region of the medulla
explain ventral respiratory group
upper motor neurones responsible for inspiration and expiration, found in the dorsomedial region of the medulla
what property do these cells have?
intrinsic periodic firing, where repetitive bursts of Abs are exhibited that correspond to the rhythm of the ventilatory cycle
what is the function of the pons?
fine tuning of the intrinsic respiratory rhythm created by the medulla
major output of nerves from the brain stem
phrenic nerves to the diaphragm
what other parts of the brain can alter breathing + when?
limbic system, hypothalamus during moments of rage and high emotional states
what considerations must the body consider when regulating breathing?
- want to breathe enough to ensure Hb gets close to full saturation
- don’t want to breathe more than is necessary, waste of effort
- want to regulate carbon dioxide quite carefully since variations in CO2 vary pH and small variations in pH can alter physiological function quite widely
what detects changes of pH in the blood?
chemoreceptors
Chemoreceptors definition
receptors that respond to a change in the chemical composition of the blood or fluid around it
two types of chemoreceptors
central and peripheral
where are the central chemoreceptors found?
anteriorly superficial to the medulla surface
what do the central chemoreceptors react to?
the composition of blood and the CSF
What is the major determinant of pH in the brain + why?
carbon dioxide, as the blood brain barrier is relatively impermeable to HCO3- and H+ whereas CO2 can diffuse easily.
when blood CO2 uses it diffuses into the CSF from cerebral blood vessels and liberates H+ ions that stimulate the chemoreceptors
CSF contains very little protein, so has a lower buffering capacity than the blood, so a change in pH of the CSF for a given PCO2 is much greater
how do central chemoreceptors respond to a fall in pH?
increase the frequency of action potentials in their afferent nerves, which regulate the activity of the medullary respiratory centre
this causes an increase in ventilatory rate and subsequent decrease in PCO2
what is the respiratory centre + location?
three major respiratory groups of neurones, two in the medulla and one in the pons
responsible for generating and maintaining the rhythm of respiration and also adjusting the homeostatic response to physiological changes
where are peripheral chemoreceptors located?
in the carotid bodies at the bifurcation of the common carotid arteries and in the aortic bodies above and below the aortic arch
what innervates the carotid bodies?
sinus nerve, a branch of the glossopharyngeal nerve IX cranial nerve
which body has mainly respiratory effects? + what does the other have?
carotid, aortic bodies mainly vascular effects
structure of the carotid body + functions
glomus type 1 cells- peripheral chemoreceptors derived from neural crest cells, release neurotransmitter such as ACh ATP and dopamine that trigger EPSPs in synapsed neurones leading to the respiratory centre
glomus type 2- resemble glial cells and act as supporting cells
responsible for all increases in ventilation that occurs in humans response to arterial hypoxemia
what do the carotid bodies detect?
sensitive to changes in PO2 in arterial blood, specifically decreases
action potential production in carotid bodies
decrease in oxygen partial pressure leads to the depolarosation of the cell membrane by blocking potassium currents
reduction in membrane potential opens voltage gated calcium channels which causes a rise in intracellular calcium concentration leading to the release of neurotransmitter containing vesicles
explain relay of the AP
feedback from the carotid body is sent to the cardiorespiratory centres in the medulla oblongata via afferent branches of the glossopharyngeal nerve
efferent fibres from the aortic body chemoreceptors are relayed by the vagus nerve
innervation of aortic bodies
vagus nerve X
stimuli of aortic bodies
decrease in PO2, increase in CO2
do not respond to changes in pH
when are the various receptors sensitive to concentrations of oxygen?
peripheral cells are relatively insensitive to changes in PO2 above 100mmHg, as shown by limited firing of the afferent nerves
below 100mmHg the firing rate greatly increases
at low CO2, the body does not really recognise the PO2
when are the various receptors sensitive to concentrations of carbon dioxide?
at high PO2 there is still a good CO2 response through central chemoreceptors
different degrees of importance of central vs peripheral chemoreceptors explained
less than 20% of the ventilatory response can be attributed to the peripheral chemoreceptors when there is an increase in CO2
however there is a more rapid response and so may be useful in matching ventilation to abrupt changes in PCO2
result of removing peripheral chemoreceptors
removing carotid bodies was a treatment for asthma
individuals may lose carotid bodies following vascular surgery
PAco2 will settle 0.5 kPa higher than normal
no sensitivity to hypoxia
animals without carotid bodies at altitude often become sick and die
effect of increased ventilation on alveolar pressures
PaO2 increased, PaCO2 decreased
where are pulmonary stretch receptors located?
lie within airway smooth muscle and discharge in response to distention of the lung
innervation of pulmonary stretch receptors
impulses travel in the vagus nerve via large myelinated fibres to the medulla and apneustic centre of the pons, resulting in the inhibition of inhalation
what is the main reflex that stimulates these receptors?
Herring-Breuer reflex
explain the Herring-Breuer reflex
describes the inhibition of inspiration as the lungs are stretched, with the receptors slowing respiratory frequency due to an increase in expiratory time
prevents the over inflation of the lung
what other functions of pulmonary stretch receptors?
determine the rate and depth of breathing where tidal volumes exceed 1L like in exercise
bronchodilation by relaxing smooth muscle
2 other receptors in lungs
irritant receptors and juxtacapillary receptors
explain irritant receptors
lie between the airway epithelial cells in the nasal mucosa
small myelinated fibres within vagus
respond to stretch and irritants within airways
reflex effects, cough, bronchoconstriction and tachypnoea
explain J receptors
they re the endings of non-myelinated C vagus fibres found in the lung interstitium
respond if the lungs become congested- stimulated by oedema, act as a visceral pain receptor
believed to be located in the alveolar walls close to the capillaries
responses include rapid, shallow breathing, apnea
innervation of bronchi
autonomic, from the pulmonary branches of the vagus nerve
upper airway obstruction definition
the blockage of any portion of the airway above the thoracic inlet
presentation of a patient with upper airway obstruction
drooling, swelling of face and tongue, wheezing, choking, unconsciousness,
lower airway obstruction definition
obstruction at the level of trachea, bronchi and bronchioles
consequences of obstruction
fatal in a matter of minutes
respiratory failure, arrhythmia and cardiac arrest
inflammation of airway walls or lung abscesses
relief of obstruction
removing foreign body, intubation below the body, tracheotomy and cricothyrotomy
how does foreign body aspiration occur?
body too large enters the trachea and becomes lodged
how does foreign body aspiration occur?
body too large enters the trachea and becomes lodged
body in mouth then strong inhalation makes it move into the trachea not the oesophagus
