Control of respiration

Question 1

what types of muscle are the diaphragm and intercostal muscles and what does this mean?

Answer 1

skeletal muscles

don’t contract unless stimulated by motor neurons

Question 2

destruction of respiratory motor neurons

Answer 2

destruction or disconnection between origin and respiratory muscles leads to paralysis of respiratory muscles and death - unless artificial respiration

Question 3

how is respiration initiated?

Answer 3

burst of action potentials in spinal motor neurons to inspiratory muscles
action potentials cease - inspiratory muscles relax, expiration occurs as elastic lungs recoil

Question 4

exercise and expiration

Answer 4

neurons to expiratory muscles (facilitate expiration) start firing during expiration

Question 5

control of neurons to respiratory muscles

Answer 5

medulla oblongata (medullary respiratory centre)
dorsal respiratory group (DRG)
ventral respiratory group (VRG)

Question 6

DRG neurons

Answer 6

primarily fire during inspiration
input to spinal motor neurons that activate respiratory muscles - diaphragm (phrenic nerve C3,4,5) and external intercostal muscles (intercostal nerves)

Question 7

VRG neurons

Answer 7

respiratory rhythm generated in pre-Boetzinger complex of neurons in upper VRG - pacemaker cells and neural network, acting together, sets basal respiratory rate

Question 8

expiratory neurons

Answer 8

most important when large increases in ventilation are required
expiratory muscles contract

Question 9

quiet breathing

Answer 9

respiratory rhythm generator activates inspiratory neurons in VRG - depolarise inspiratory spinal motor neurons - inspiratory muscles contract
stop firing, relax, passive expiration

Question 10

increases in breathing

Answer 10

inspiratory and expiratory neurons and muscles alternate in function

Question 11

pons location and function

Answer 11

above medulla oblongata
sends synaptic input to finetune output of medullary inspiratory neurons and helps terminate inspiration by inhibiting them

Question 12

apneustic centre

Answer 12

lower pons
finetunes output of medullary inspiratory neurons
terminates inspiration by inhibiting them

Question 13

pneumotaxic centre

Answer 13

upper pons
modulates activity of apneustic centre
smooths transition between inspiration and expiration

Question 14

synaptic input from higher areas of the brain

Answer 14

pattern of respiration is controlled voluntarily during speaking, diving, emotions and pain

Question 15

pulmonary stretch receptors

Answer 15

lie in airway smooth muscle layer

activated by large lung inflation

Question 16

Hering-Breuer reflex

Answer 16

action potentials in afferent nerve fibres from stretch receptors travel to brain and inhibit medullary activity - feedback from lungs helps terminate inspiration by inhibiting inspiratory nerves in the DRG
only in large tidal volumes

Question 17

sensitivity of medullary inspiratory neurons

Answer 17

sensitive to inhibition by drugs - barbituates and morphine. death by cessation of breathing

Question 18

peripheral chemoreceptors

Answer 18

high in neck at bifurcation of common carotid arteries (carotid bodies) and on the arch of aorta (aortic bodies). close to arterial baroreceptors and contact the arterial blood.
composed of specialised receptor cells stimulated by decrease in P02 and increase in [H+] and increased PCO2.
excitory input to inspiratory neurons.
predominant carotid input.

Question 19

central chemoreceptors

Answer 19

located in medulla.
excitatory synaptic input to medullary inspiratory neurons. #stimulated by increased PCO2 and increased [H+] of extracellular fluid.

Question 20

control of ventilation by P02

Answer 20

little increase in ventilation until O2 conc is reduced to 60mmHg - after this, there’s a large increase
mediated by peripheral chemoreceptors - increased rate of charging -> increased number of action potentials travelling up afferent nerve fibres and stimulating medullary inspiratory neurons

Question 21

increased CO2 consequences

Answer 21

increase in alveolar CO2 - diffusion gradient is reversed and arterial CO2 increases
~40mmHG+ arterial CO2 increases ventilation

Question 22

emphysema and CO2

Answer 22

causes people to retain CO2 - increase in arterial CO2

Question 23

decreased CO2

Answer 23

removes stimulus for ventilation - metabolically produced co2 accumulates and returns back to normal

Question 24

CO2 and H+

Answer 24

increased CO2 increases H+

affects peripheral and central chemoreceptors

Question 25

most important chemoreceptors in regulation of CO2

Answer 25

central - 70% of increased ventilation

Question 26

effects of increased co2 and decreased o2

Answer 26

potentiate each other’s effects - acute ventilatory response to combined co2 and o2 is greater than sum of individual responses

Question 27

other symptoms of high blood co2

Answer 27

severe headaches, restlessness, dulling or loss of conciousness

Question 28

retention of co2

Answer 28

respiratory acidosis

Question 29

excessive elimination of co2

Answer 29

respiratory alkalosis

Question 30

metabolic acidosis

Answer 30

increase in H+ not due to primary change in co2

Question 31

metabolic alkalosis

Answer 31

decrease in H+ not due to primary change in co2

Question 32

major chemoreceptors involved in altering ventilation in metabolic acidosis/alkalosis + example

Answer 32

peripheral chemoreceptors
addition of lactic acid to the blood (strenuous exercise) causes hyperventilation by mostly stimulation from peripheral chemoreceptors

Question 33

flow chart of change in H+ conc in blood

Answer 33

production of non co2 acid
increased arterial [H+]
increased firing of peripheral chemoreceptors
increased contraction of respiratory muscles
increaesed ventilation
decreased alveolar and arterial co2
return of arterial [H+] towards normal

Question 34

chemoreceptors and H+ conc

Answer 34

not involved much due to brain [H+] only increasing a small amount, as it penetrates the blood-brain barrier very slowly
co2 penetrates blood-brain barrier rapidly

Question 35

decrease of [H+]

Answer 35

ventilation is depressed due to decreased peripheral chemoreceptor output
e.g. loss from vomiting

Question 36

why is maintenance of normal arterial H+ necessary?

Answer 36

most enzymes of the body function best at physiological pH