Week 10 - Control of respiration

Question 1

What is homeostasis?

Answer 1

The state of steady internal, chemical and physical conditions maintained by living systems

Question 2

What does ventilatory control involve?

Answer 2

Sensors
Afferent pathway
Respiratory control centre
Efferent nerve fibres
Spinal cord
Effectors

Question 3

What are the sensors in the ventilatory control centre and what do they do?

Answer 3

Peripheral chemoreceptors
Central chemoreceptors
Pulmonary mechanoreceptors

They detect change and things that need to be altered e.g. too much hyperventilation or hypoventilation, increase in CO2 or decrease in O2.

Question 4

What does the respiratory control centre consist of?

Answer 4

Medulla, pons

Question 5

What do the effectors in the ventilatory control centre consist of?

Answer 5

Respiratory muscles
Diaphragm

Question 6

What are chemoreceptors? (2 types)

Answer 6

Cell that responds to chemical compounds to give an impulse to a sensory nerve.

2 sets:
↳ Oxygen receptors which are in peripheral nervous system
↳ Carbon dioxide receptors which are found both peripherally and centrally

Question 7

What are mechanoreceptors?

Answer 7

Sensory receptors that respond to mechanical deformation of the receptor or surround tissue

Question 8

What are stretch receptors?

Answer 8

Respond to the stretching of muscles by giving impulses to the CNS

Question 9

What are proprioceptors?

Answer 9

Cells that monitor body changes brought about by muscular movement to give an impulse to the CNS to co-ordinate movement

Question 10

What are juxtacapillary receptors?

Answer 10

Cells that cause an increase in breathing rate as reflex response, thought to be involved in the sensation of dyspnea.

Question 11

What are nociceptors?

Answer 11

Cells that respond to a pain stimulus by giving impulses to the central nervous system

Question 12

Where are the medulla and pons found in the brain?

Answer 12

in the brain stem

Question 13

Definition of “nuclei” in neuroanatomy?

Answer 13

• Nucleus is a collection of neuronal cell bodies within the CNS
• The neurons in one nucleus usually have roughly similar connections + functions
• Nuclei are connected to other nuclei by tracts, the bundles (fascicles) of axons (nerve fibres) extending from the cell bodies

Question 14

What do chemoreceptors do?

Answer 14

Monitor blood gas tensions, PaCO2, PaO2 and pH, and help keep minute volume appropriate to the metabolic demands of the body.

Therefore, chemoreceptors respond to:
↳ hypercapnia (CO2 too high)
↳ hypoxia (O2 too low)
↳ acidosis (low pH)

The most important factor controlling the rate and depth of breathing is the effect of carbon dioxide on the central chemoreceptors.

Question 15

What are the respiratory control centres?

Answer 15

Areas of the brain and spinal cord involved in control of breathing

Question 16

What are the 4 respiratory control centres?

Answer 16

Pneumotaxic centre
Apneustic centre
Dorsal respiratory group (inspiratory)
Ventral respiratory group (expiratory)

Question 17

Where is the pneumotaxic centre located?

Answer 17

upper aspect of pons

Question 18

What is the function of the pneumotaxic centre?

Answer 18

→ Controls fine tuning of respiratory rate and depth
→ Sends signals inferiorly and can influence VRG and DRG
→ Inhibits inspiration, which allows for transition from inspiration to expiration
→ Decreases tidal volume

Transitioning occurs as a response to stimulus from peripheral receptors.

Question 19

Where is the apneustic centre located?

Answer 19

lower aspect of pons

Question 20

What is apeneusis?

Answer 20

Prolonged breathing

Question 21

What is the function of the apneustic centre?

Answer 21

→ Controls prolonged breathing
→ Receives peripheral stimulus from stretch receptors
→ Sends signals to the VRG + DRG to trigger inspiration
→ Increased tidal volume

Question 22

What would occur if the pneumotaxic centre is damaged?

Answer 22

• DRG + VRG would only receive signals from apeneustic centre.
• It cannot inhibit transition from inspiration to expiration and undergoes prolonged inspiration.
• Also known as apneustic breathing.

Question 23

Where is the dorsal respiratory group located?

Answer 23

Located medially in aspect within the medulla

Question 24

What is the function of the dorsal respiratory group?

Answer 24

→ Receives peripheral stimulus signals from the stretch receptors, proprioceptors, juxtacapillary receptors, and both central and peripheral chemoreceptors.
→ Sends signals to external intercostals and diaphragm to cause inspiration.

Question 25

Where is the ventral respiratory group located?

Answer 25

Anterior aspect of the medulla

Question 26

What is the function of the ventral respiratory group?

Answer 26

→ Controls expiration via sending expiratory signals

• VRG - stimulates expiratory movements
• DRG - stimulates inspiratory movements

Question 27

Key points about central chemoreceptors?

Answer 27

→ 80% of drive for ventilation as a result of their stimulation
→ When inactivated, respiration ceases
→ Readily depressed by drugs

Question 28

Location of central chemoreceptors?

Answer 28

• In the brainstem on the ventrolateral surface of the medulla.
• Anatomically separate from medullary respiratory control centre.

Question 29

What are central chemoreceptors sensitive to?

Answer 29

• Respond to hydrogen ion concentration within surrounding brain tissue and cerebrospinal fluid as well as low partial pressure of O2.

→ Raised hydrogen ion conc. = increased ventilation
→ Lowered hydrogen ion conc. = decreased ventilation

Question 30

What is the function of the central chemoreceptors? (how do they achieve homeostasis)

Answer 30

→ Increase in pCO2 levels leads to increased carbonic acid in CSF
→ Leads to increase in protons in CSF
→ Central chemoreceptors are stimulated, leads to increased ventilation and increase in blood pH (bringing it back to a normal level)

Question 31

Key points about peripheral chemoreceptors?

Answer 31

Stimulation of peripheral chemoreceptors has both cardiovascular and respiratory effects.

Cartoid bodies have a greater influence on respiration.

Question 32

Where are peripheral chemoreceptors located?

Answer 32

Around carotoid sinus and aortic arch

Question 33

What are the peripheral receptors sensitive to?

Answer 33

PaO2
PaCO2
pH
Blood flow
Temperature

Question 34

What do the carotid bodies do?

Answer 34

(2 types = type i , type ii)
→ Rich blood supply to the carotid bodies - (blood flow per mass of tissue far exceeds that to the brain) - venous blood flow, therefore remains saturated with oxygen.

→ Believed that type i (glomus) cells are activated by hypoxia and release transmitter substances that stimulate afferents to the brainstem

Question 35

Stimuli that increase breathing rate and depth?

Answer 35

• Voluntary hyperventilation controlled by cerebral cortex and anticipation of activity by stimulation of limbic system
• Increase in arterial blood pCO2 above 40mmHg (causes increase in H+) detected by peripheral and central chemoreceptors.
• Decrease in arterial blood pO2 from 105mmHg to 50mmHg
• Increased activity of proprioceptors
• Increase in body temp.
• Prolonged pain
• Decrease in blood pressure
• Stretching of anal sphincter

Question 36

Stimuli that decrease breathing rate and depth?

Answer 36

• Voluntary hypoventilation controlled by cerebral cortex
• Decrease in arterial blood pCO2 below 40mmHg (causes a decrease in H+) detected by peripheral and central chemoreceptors.
• Decrease in arterial blood pCO2, below 50 mmHg
• Decreased activity of proprioceptors
• Decrease in body temp. , sudden cold stimulus
• Severe pain (causes apnea)
• Increased blood pressure
• Irritation of pharynx or larynx by touch or chemicals (brief apnea followed by coughing/sneezing)

Question 37

What is apnea?

Answer 37

breathing repeatedly stops and starts