control of breathin

Question 1

what is the central control of breathing?

Answer 1

the brain stem

Question 2

what occurs in the brainstem?

Answer 2

normal automatic control of breathing

Question 3

what can override this + when?

Answer 3

the brain’ cortex when voluntary control is desired

Question 4

what generates the respiratory rhythm?

Answer 4

medulla

Question 5

what is the brainstem?

Answer 5

posterior part of the brain, continuous with the spinal cord

consists of the midbrain, pons and medulla oblongata of the hindbrain

Question 6

experiment to deduce the various functions

Answer 6

sectioning of the brainstem above the respiratory centre of the medulla abolishes voluntary, cortical control of breathing but leaves normal rhythmicity intact

Question 7

different groups of motor neurone in the brain

Answer 7

dorsal respiratory group and ventral respiratory group

Question 8

explain dorsal respiratory group

Answer 8

motor neurones associated with initiating inspiration found in the ventrolateral region of the medulla

Question 9

explain ventral respiratory group

Answer 9

upper motor neurones responsible for inspiration and expiration, found in the dorsomedial region of the medulla

Question 10

what property do these cells have?

Answer 10

intrinsic periodic firing, where repetitive bursts of Abs are exhibited that correspond to the rhythm of the ventilatory cycle

Question 11

what is the function of the pons?

Answer 11

fine tuning of the intrinsic respiratory rhythm created by the medulla

Question 12

major output of nerves from the brain stem

Answer 12

phrenic nerves to the diaphragm

Question 13

what other parts of the brain can alter breathing + when?

Answer 13

limbic system, hypothalamus during moments of rage and high emotional states

Question 14

what considerations must the body consider when regulating breathing?

Answer 14

1. want to breathe enough to ensure Hb gets close to full saturation
2. don’t want to breathe more than is necessary, waste of effort
3. want to regulate carbon dioxide quite carefully since variations in CO2 vary pH and small variations in pH can alter physiological function quite widely

Question 15

what detects changes of pH in the blood?

Answer 15

chemoreceptors

Question 16

Chemoreceptors definition

Answer 16

receptors that respond to a change in the chemical composition of the blood or fluid around it

Question 17

two types of chemoreceptors

Answer 17

central and peripheral

Question 18

where are the central chemoreceptors found?

Answer 18

anteriorly superficial to the medulla surface

Question 19

what do the central chemoreceptors react to?

Answer 19

the composition of blood and the CSF

Question 20

What is the major determinant of pH in the brain + why?

Answer 20

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

Question 21

how do central chemoreceptors respond to a fall in pH?

Answer 21

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

Question 22

what is the respiratory centre + location?

Answer 22

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

Question 23

where are peripheral chemoreceptors located?

Answer 23

in the carotid bodies at the bifurcation of the common carotid arteries and in the aortic bodies above and below the aortic arch

Question 24

what innervates the carotid bodies?

Answer 24

sinus nerve, a branch of the glossopharyngeal nerve IX cranial nerve

Question 25

which body has mainly respiratory effects? + what does the other have?

Answer 25

carotid, aortic bodies mainly vascular effects

Question 26

structure of the carotid body + functions

Answer 26

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

Question 27

what do the carotid bodies detect?

Answer 27

sensitive to changes in PO2 in arterial blood, specifically decreases

Question 28

action potential production in carotid bodies

Answer 28

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

Question 29

explain relay of the AP

Answer 29

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

Question 30

innervation of aortic bodies

Answer 30

vagus nerve X

Question 31

stimuli of aortic bodies

Answer 31

decrease in PO2, increase in CO2 do not respond to changes in pH

Question 32

when are the various receptors sensitive to concentrations of oxygen?

Answer 32

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

Question 33

when are the various receptors sensitive to concentrations of carbon dioxide?

Answer 33

at high PO2 there is still a good CO2 response through central chemoreceptors

Question 34

different degrees of importance of central vs peripheral chemoreceptors explained

Answer 34

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

Question 35

result of removing peripheral chemoreceptors

Answer 35

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

Question 36

effect of increased ventilation on alveolar pressures

Answer 36

PaO2 increased, PaCO2 decreased

Question 37

where are pulmonary stretch receptors located?

Answer 37

lie within airway smooth muscle and discharge in response to distention of the lung

Question 38

innervation of pulmonary stretch receptors

Answer 38

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

Question 39

what is the main reflex that stimulates these receptors?

Answer 39

Herring-Breuer reflex

Question 40

explain the Herring-Breuer reflex

Answer 40

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

Question 41

what other functions of pulmonary stretch receptors?

Answer 41

determine the rate and depth of breathing where tidal volumes exceed 1L like in exercise bronchodilation by relaxing smooth muscle

Question 42

2 other receptors in lungs

Answer 42

irritant receptors and juxtacapillary receptors

Question 43

explain irritant receptors

Answer 43

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

Question 44

explain J receptors

Answer 44

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

Question 45

innervation of bronchi

Answer 45

autonomic, from the pulmonary branches of the vagus nerve

Question 46

upper airway obstruction definition

Answer 46

the blockage of any portion of the airway above the thoracic inlet

Question 47

presentation of a patient with upper airway obstruction

Answer 47

drooling, swelling of face and tongue, wheezing, choking, unconsciousness,

Question 48

lower airway obstruction definition

Answer 48

obstruction at the level of trachea, bronchi and bronchioles

Question 49

consequences of obstruction

Answer 49

fatal in a matter of minutes respiratory failure, arrhythmia and cardiac arrest inflammation of airway walls or lung abscesses

Question 50

relief of obstruction

Answer 50

removing foreign body, intubation below the body, tracheotomy and cricothyrotomy

Question 51

how does foreign body aspiration occur?

Answer 51

body too large enters the trachea and becomes lodged

Question 52

how does foreign body aspiration occur?

Answer 52

body too large enters the trachea and becomes lodged body in mouth then strong inhalation makes it move into the trachea not the oesophagus