chemoreception and breathing

Question 1

what is locked in syndrome?

Answer 1

• patient with a brainstem stroke
• unable to move voluntarily (except eyes)
• regular breathing pattern driven by metabolic system
• they exhibit no voluntary control of breathing

Question 2

when do we consciously and unconsciously control breathing ?

Answer 2

• conscious control is during laughing, coughing and exercise this is controlled by the cerebral cortex (behaviour)
• unconscious control is exhibited via the medulla is primitive in response to the rate of metabolism (PaCO2 levels)

Question 3

list the 3 phases of the breathing cycle

Answer 3

I–> diaphragm contracts -> ramp like -> no activity of the internal intercostal nerves

Post I phase–>inspiratory neurones fire in a decremental way to allow inspiration to be carefully regulated back down to an expiratory position

Expiratory phase -> internal intercostal nerve fibres are activated

Question 4

mechanoreceptors detect?

chemoreceptors detect ?

Answer 4

are deformed by stretch and mechanical stimuli and allow for the efficiency of breathing patterns

detect concentrations in PaCo2 and PaO2 and allow for minute ventilation to match the rate metabolism ]]

Question 5

where are peripheral chemoreceptors located?

Answer 5

• sensory receptors located in carotid bodies (GP) and aortic bodies (V)

Question 6

what do chemoreceptors sense?

Answer 6

• regulation of blood gas and acid-base formation

- respond to pa02 and pH

Question 7

where do afferents from the aortic bodies and the carotid bodies travel to?

Answer 7

• convergence at the NTS

- share the same afferents as the carotid sinus and aortic sinuses (BRs)

Question 8

carotid bodies are composed of what cell type?

Answer 8

glomus cells

• detect low PaO2–> activated in response to hypoxia –> secretion of NT onto the GP adjacent –> AP fired to the NTS
• richly vascularised
• surrounded by glial cells
• 3-5 G Cells per unit

Question 9

underline the chemotransduction process in glomus cells

Answer 9

• stimulated by hypoxia
• detected by O2 sensor–> low P02-> closure of K channels–> increased vM –> depolarisation–> opening of VGCC–> increased Ca influx–> neurosecretion (ATP, DA) onto GPN–> AP fired to NTS

Question 10

how is 02 sensed?

Answer 10

• less 02 enters complex 4
• cell detect low 02 by monitoring changes in AMP/ATP ratio
• determines activation of AMPK (LBK1)
• -> AMPK inhibits TASK channels/ BK
• increased Vm==> ca influx leading to neurosecretion

Question 11

carotid bodies can also respond to?

Answer 11

• CO levels

Question 12

carotid bodies contribute to?

Answer 12

• all of the ventilatory response to a change in Po2
  (Hypoxia)
• via metabolic acidosis (pH)
  20% of the response to CO2

Question 13

where are the central carotid bodies located?

Answer 13

the VRG and DRG (involved in breathing rhythm generation) contain cells that detect blood CO2 and pH

• rostral, intermediate and caudal areas
• located on other side of the BBB (close to ventral side of brain)

Question 14

summarise some key concepts about the central chemoreceptors

Answer 14

• lies 0.2mm from ventral surface
• generates 80% of VE response to CO2
• inhibited by hypoxia

(hypoxia stimulates peripheral)

• slower response as opposed to rapid by peripheral R
• unresponsive to metabolic acidosis or alkalosis (H cannot pass through BBB)

Question 15

list some of the identified chemosensitive sites within the brain

Answer 15

• retrotrapezoid nucleus
• solitary tract nucleus
• midline raphe nuclei
• glial cells?

Question 16

outline the transduction method

Answer 16

• unknown exactly
• similar to peripheral
• TASK channels inhibited by low pH leading to depol of the cell
• CO2 passively diffuses across BBB–> binds with H20–> Hco3–> H+ produced and sensed by cells

Question 17

why do we have both central and peripheral chemoreceptors ??

Answer 17

• peripheral senes Pao2 and H+ ions (20%) –> acid/base homeostasis (rapid shorter lasting)
• > quick rapid change in VE
• central R detect PaCo2 (80%) via H+ ion but not Pa02 levels (slower but more prolonged response) –> most of steady state response
• > continued slower increase in VE

Question 18

higher cortical areas can?

Answer 18

• bypass these brainstem-medullary areas to some extent until the body needs to breathe again due to elevated metabolic rate (sensed by cehmoR)