Respiration 2

Question 1

Explain how the pulmonary stretch receptors work

Answer 1

• Found in the upper airways
• Project via the vagus nerve to the NTS
• 2nd order neurons for this reflex are located in the NTS
• These afferents synapse onto neurons in the NTS that are GABergic (are inhibitory)
• These synapse onto inspiratory cells so that inspiration is reduced
• This will lead to a decrease in inspiratory time and frequency

Question 2

Activation of PSRs leads to. . .

Answer 2

a termination of inspiration & a slowing of respiratory rhythm by ACTIVATION of post-I

1. prolongation of expiration
2. inhibition of inspiration
3. slowing of respiratory rhythm

Question 3

Identify the effects on the respiratory neurons following activation of PSRs to produce the response in breathing observed.

Answer 3

• excite post-inspiratory neurons
• inibit augmenting expiratory (or late E) neurons
• inhibit inspiratory neurons
• inhibit pre-inspiratory neurons

Question 4

What is the Hering-Breuer Reflex?

Answer 4

• activated by pulmonary stretch receptors
• found in smooth muscle in lungs; slowly adapting receptors

Question 5

When are pulmonary stretch receptors activated?

Answer 5

• either by electrical stimulation
• inflating lungs and holding it to a particular pressure

Increased sensory activity of the pulmonary-stretch lung afferents (via the vagus nerve) results in inhibition of the central inspiratory drive and thus inhibition of inspiration and initiation of expiration.

Question 6

Blood vessels are surrounded by glomus cells (type I) & glial-like unsheathing cells (type II).

Answer 6

1. When glomus cells detect hypoxia, this causes depolarization of cell membrane
2. e.g. inhibiton of K+ channels which causes membrane depolarization
3. This activates voltage-gated calcium channels
4. Causes vesicular release of ATP (neurotransmitter)
5. Released ATP activates P2X2 receptor
6. This generates a depolarization at these afferents
7. This increases the activity of these afferents up to 2nd order neurons
8. At the same time, ATP binds to local P2Y receptors on the type II cells
9. This also causes depolarization of type II cells which causes release of ATP
10. This then perpetuates excitation within the system

P2X2 = ionotropic
P2Y receptors = GPCRs

Question 7

Peripheral chemoreceptors are also sensitive to hypercapnia

Answer 7

High CO2 levels (along with low O2)

They are also sensitive to low pH in the blood

Question 8

Central chemoreceptors respond to. . .

Answer 8

high CO2 in the cerebrospinal fluid

Question 9

Glomus cells / type I cells in the carotid body respond to hypoxia and hypercapnia, and transmit their signal via paracrine actions to the . . .

Answer 9

glossopharyngeal nerve

Question 10

Explain how peripheral chemoreceptors respond to changes in oxygen levels

Answer 10

There are two main areas - the carotid body (collection of cells) and the aortic body

Carotid bodies send afferents via glossopharyngeal nerve (IX) while the aortic bodies send them via the vagus nerve (X)

Both terminate in the NTS which is where the 2nd order neurons are

Some exit to the spinal cord & via symapthetic NS synapse onto the heart

Others exit via vagus nerve and synapse at the heart

Question 11

What does an activation of central chemoreceptors do?

Answer 11

These chemoreceptors are believed to be found in the RTN (retrotrapezoid nucleus)

They lead to an INCREASE in respiration and an INCREASE in sympathetic activity

Question 12

What happens if CO2 is too high in the blood?

Answer 12

H+ ions will activate:
VMS astrocytes, TASK-2 (ionotropic) & GPR4 (GPCR)

VMS astrocytes –> release ATP –> activates the RTN neuron -> increases breathing

TASK-2 & GPR4 -> activates RTN neuron –> increases breathing

GPR4 also –> inhibits K+ leak channels –> membrane potential increases