control of breathing

what is the basic pathway of neural control of breathing?

1) receptors collect information to be relayed to respiratory centres

2) signals sent down afferent fibres to central respiratory centres

3) signals sent down efferent fibres to the effectors which are respiratory muscles

what are examples of the receptors involved in breathing?

- central chemoreceptors

- peripheral chemoreceptors

- baroreceptors

- pulmonary stretch receptors

- cough or lung-irritant receptors

- J-receptors

- bronchial c fibres

where are peripheral chemoreceptors located?

- carotid bodies

- aortic bodies

what do peripheral chemoreceptors detect?

detect changes in partial pressure of oxygen (pO2) as arterial blood leaves the heart

what do peripheral chemoreceptors in aortic body send if low levels of oxygen are detected?

afferent impulses via vagus nerves to medulla oblongata and the pons in the brainstem

what are two examples of chemoreceptor cells?

- type I - glomus cells

- type II - sustentacular cells

what happens at the microscopic level of glomus cell when low pO2?

1) glomus cell detects low O2

2) inhibits K+ channels

3) depolarisation

4) opening of Ca2+ channels

5) Ca2+ influx

6) neurotransmitters released to synaptic cleft

7) neurotransmitters attach to afferent fibre receptors to stimulate afferent fibre to CNS

what do peripheral chemoreceptors in the carotid body send if low levels of oxygen are detected?

afferent impulses via glossopharyngeal nerves to medulla oblongata and pons in the brainstem

where are central chemoreceptors located?

very close to the medulla oblongata of brainstem

what do central chemoreceptors do?

detect changes in partial pressure of CO2 by the changes in the pH of cerebral spinal fluid (CSF)

what does the blood brain barrier (bbb) do?

separates the CSF from the blood

can H+ ions pass through BBB?

no

can CO2 pass through BBB

yes

what happens in terms of central chemoreceptors when there is an increase in CO2 in blood?

- more CO2 diffuses into CSF

- causes decrease in pH

- chemoreceptors detect this and ventilation is increased

what effects on ventilation do the stimulated chemoreceptors have?

- increased rate

- increased depth

where are baroreceptors located? (2)

- internal carotid arteries

- aortic arch

what do baroreceptors do?

detect changes in blood pressure

what do baroreceptors do if blood pressure is too high?

detect high bp - causes increase baroreceptor firing - causes decreased sympathetic activity

what do baroreceptors do if blood pressure is too low?

detect decrease in bp - decreases baroreceptor firing - causes increase in sympathetic activity

where are pulmonary stretch receptors found?

smooth muscle of airways

what do pulmonary stretch receptors respond to?

lung distension

what do pulmonary stretch receptors do if stimulated?

- inhibit inspiration

- stimulate expiration

where are cough or lung-irritant receptors found?

between airway epithelial cells

what stimulates cough or lung-irritant receptors?

- cigarette smoke

- noxious gases

- dust

- cold air

what do stimulated cough or lung-irritant receptors do?

cause bronchoconstriction and hyperpnea (taking deeper breaths)

where are J (juxtacapillary) receptors found?

alveolar walls close to capillaries

what stimulates j cells?

chemicals in pulmonary circulation

what do stimulated j cells do?

cause rapid shallow breathing

what are the two respiratory centres?

- medulla oblongata (primary centre)

- pons

where are the medulla oblongata and pons located?

brainstem

what are the two sections of the medulla?

- dorsal medulla

- ventral medulla

what is the dorsal medulla contain?

neurons responsible for inspiration

what does the ventral medulla contain?

neurons responsible for expiration

is the ventral medulla always used in expiration?

no, only for forceful expiration

what causes normal expiration?

inactivation of dorsal medulla causes:

- relaxation of diaphragm and external intercostal muscles

- elastic recoil

what controls the medulla (primary centre)?

pons

what are the 2 centres in the pons?

- apneustic centre

- pneumotaxic centre

aka the pontine respiratory group

where is the apneustic centre located?

lower pons

what does the apneustic centre do?

sends impulses to dorsal medulla to stimulate inspiration

where is the pneumotaxic centre located?

upper pons

what does the pneumotaxic centre do?

sends impulses to dorsal medulla to inhibit inspiration so expiration can take place

what happens after dorsal medulla is stimulated for inspiration?

inspiratory motor neurons send impulses to:

- external intercostals

- diaphragm

- scalene and sternomastoid (only in forced inhalation)

what happens after ventral medulla is stimulated for expiration?

expiratory motor neurons send impulses to:

- internal intercostals

- abdominal muscles

what happens in forced expiration?

pneumotaxic centre stimulates ventral respiratory group to stimulate FORCED expiration - contraction of internal intercostals and abdominal muscles

is breathing always under autonomic control?

no, it can be under voluntary control too

how can breathing sometimes be voluntary?

the cortex overrides the brainstem to a certain extent

what stimulates voluntary control of breathing?

emotional states e.g. fear

what system is triggered from emotional states?

limbic system

what will the limbic system trigger?

medulla oblongata and pons