Neural Control Of Breathing

Question 1

What happens if the pressure gradient between aveoli and capillary is too low

Answer 1

If this gradient is too low, gas exchange does not occur efficiently.

Question 2

Why is level of ventilation regulated

Answer 2

Breathing is done to ventilate the alveoli and the level of ventilation is regulated to meet varying
oxygen demand or carbon dioxide production. Ventilation is regulated by changing tidal volume and
breathing rate.

Question 3

Give examples of when ventilation is increased

Answer 3

Examples of when ventilation is increased is during exercise, emotional stimulus,
infections (sepsis that increases acid production by the body) and trauma.

Question 4

When do respiratory muscle contraction

Answer 4

There are different respiratory muscles that contract during breathing. They are initiated when
breathing is initiated.

Question 5

What types of muscles are respiratory muscles

Answer 5

Respiratory muscles are skeletal and require a neural input to contract.

Question 6

What diseases and injuries can effect breathing

Answer 6

Spinal cord injury (no signal initiating contraction), motor 
neuron disease (no signal initiating contraction) and muscular dystrophy (muscle not strong enough 
to perform function) can all affect the act of breathing.

Question 7

What happens during quiet breathing

Answer 7

During quiet breathing,
contraction and relaxation of the diaphragm provides enough force to move the thoracic cavity
(elastic recoil aids exhalation). During increased or forced ventilation, there are different respiratory
and accessory muscles involved in inspiration and expiration.

Question 8

What muscles are used in forced inspiration

Answer 8

External intercostals are respiratory
muscles involved in forced inspiration whilst pectorals, sternomastoid and scalene muscles are
accessory muscles involved in forced inspiration.

Question 9

What are respiratory mediators In forced expiration

Answer 9

Elastic recoil as well as internal intercostal muscles
are respiratory mediators of forced expiration whilst the abdominals are accessory muscles involved
in forced expiration.

Question 10

What do accessory muscles actually do

Answer 10

Accessory muscles do not have a primary role in breathing but help facilitate
forced breathing.

Question 11

How are different muscles initiated

Answer 11

The different muscles involved in breathing are initiated to contract and relax by different neural
signals. These signals originate from the brain and travel down via the spinal cord to neurons that
lead to the different target muscles. These signals are initiated at the brainstem of the brain.

Question 12

Describe the brainstem

Answer 12

In the
brainstem is a series of complex neural networks that function in tandem to interpret various inputs
and signals from around the body and initiate signals to the respiratory system that determines
breathing rate and depth of breathing in order to meet the metabolic demands of the body.

Question 13

How are signals sent in the brainstem and what is the name

Answer 13

These
signals are sent in a regular pattern to the different respiratory muscles controlling when they breath
in and out. This network in the brainstem that produces a breathing pattern is known as the central
pattern generator.

Question 14

What is the pattern generator dependant on - factors that effect it

Answer 14

This generator is based on information from central and peripheral
chemoreceptors

Question 15

What do chemoreceptors use to function- and where found

Answer 15

that give oxygen, carbon dioxide and hydrogen ion concentrations, receptors in
muscles and joints

Question 16

What receptors do lungs contain and function

Answer 16

stretch receptors in the lungs that indicate how inflated the lungs are as well as
irritant receptors in the lungs that detect different chemical irritants.

Question 17

What can the central pattern generator also receive

Answer 17

The central pattern generator
also receives signals from higher centres in the brain that influence breathing pattern through
emotional stimuli and other receptors that report back to the hypothalamus (e.g. response to stress
and pain), and voluntary control over breathing through the cerebral cortex.

Question 18

The central pattern generator
also receives signals from higher centres in the brain that influence breathing pattern through
emotional stimuli and other receptors that report back to the hypothalamus (e.g. response to stress
and pain), and voluntary control over breathing through the cerebral cortex.

Answer 18

The central pattern
generator uses the different inputs to check pH of the cerebral spinal fluid (usually measured through
carbon dioxide partial pressure), how much oxygen, carbon dioxide and hydrogen ions are in arterial
blood, lung volume and how stretched it is, and coordinates stimulation from higher emotional
centres of the brain and the ANS into the breathing pattern.

Question 19

What is the most important regulatory systems

Answer 19

One of the most important regulatory systems that regulate ventilation are the central and
peripheral chemoreceptors.

Question 20

What is the most prodominent chemoreceptors

Answer 20

Central respiratory chemoreceptors (CRC) are the more predominant of
the two types of chemoreceptors and they contribute to around 70% of the chemoreceptor influence
on breathing patterns.

Question 21

Where are CRCS present

Answer 21

CRCs are present in the medulla, a structure present in the brainstem, and
indirectly monitor changes to arterial carbon dioxide levels by responding to changes in hydrogen ion
concentration within cerebrospinal fluid.

Question 22

Why do CRCS not actually react with h+ ions

Answer 22

This is because hydrogen ions cannot 
pass through the blood brain barrier as they are charged. The CRCs rather monitor the number of 
hydrogen ions that have been produced from carbon dioxide diffusing out from the blood into 
cerebrospinal fluid (can pass through the blood brain barrier as it is uncharged and a small gas) 
where it is then converted into carbonic acid and then dissociates into hydrogen ions.

Question 23

What mechanism do central chemoreceptors use

Answer 23

Central
chemoreceptors work by negative feedback in that they are only activated when the number of
hydrogen ions in cerebrospinal fluid is too high.

Question 24

What is the main aim for CRC

Answer 24

They initiate respiratory control centres in the

brainstem to increase ventilation rate to remove excess carbon dioxide.

Question 25

Where are peripheral chemoreceptors located

Answer 25

Peripheral chemoreceptors are located outside the central nervous system and are specifically
located within the aortic and carotid bodies.

Question 26

How are peripheral chemoreceptors activated

Answer 26

These chemoreceptors are activated by decreased levels
of oxygen, increased levels of carbon dioxide and acidaemia. They then signal to respiratory centres
in the brainstem (specifically the medulla) to increase ventilation by a negative feedback mechanism.
Both types of chemoreceptors work together to sense the metabolic demands of the body and
convey this information to respiratory centres in the brainstem.

Question 27

What does the brainstem do after receiving signal from chemoreceptors

Answer 27

The brainstem then interprets these

signals and decides the level of ventilation.

Question 28

What primarily drives ventilation rate

Answer 28

Ventilation rate is primarily driven by carbon dioxide levels in the body.
Oxygen levels have a certain effect on ventilation, however, there has
to be drastically low levels of oxygen for it to have a major influence on
ventilation.

Question 29

How can ventilation rate o2 vs carbon dioxide be observed

Answer 29

This can be seen experimentally by varying levels of oxygen
and carbon dioxide and seeing the effect on
ventilation (see right) . Carbon dioxide has a
linear relationship with ventilation whilst
oxygen has limited effect. The effect of
oxygen can only be seen to affect ventilation rates at hypoxic levels (see
left).

Question 30

What drive has a greater effect on ventilation

Answer 30

In general, hypercapnic drive has a much greater effect on ventilation
than hypoxic drive.

Question 31

What is sleep apnoea

Answer 31

Central sleep apnoea is an example where the generation of breathing patterns goes wrong. Sleep
apnoea is when individuals stop breathing for a short period of time during sleep (e.g. 30 seconds).
Sleep apnoea can be obstructive where the airways are blocked, or central where the cause is
problems in the brainstem (specifically the generation of signals that initiate breathing).

Question 32

What happens in central apnoea

Answer 32

In central
sleep apnoea, this can occur a number of times during ones sleep and this has a few negative
consequences. It causes tiredness and fatigue due to the fact the individual usually wakes up when
this occurs and mentally causes stress. Central sleep apnoea also pressures body metabolism (lack of
gas exchange) potentially causing cardiovascular complications and metabolic dysfunction.

Question 33

What is the cause of central sleep apnoea

Answer 33

The
causes of central sleep apnoea all stem from problems related to the function of the brainstem.
These include damage to the respiratory centres caused by stroke (in extreme cases, the person
actually dies) and drugs that supress neuronal activity (specifically overdoses on opioids). Injury or
congenital abnormalities (particularly in Ondine’s curse where a person breaths normally whilst
awake but stops breathing when asleep) also cause central sleep apnoea. Different environmental
conditions can also cause central sleep apnoea including

Question 34

What is Cheyene-stokes

Answer 34

high altitude that can cause Cheyne-Stokes
respiration. This is where there is a disbalance between the systems that work to inhibit and increase
ventilation. For example, at high altitude, the low partial pressure of oxygen causes hyper ventilation
where excess carbon dioxide is consequently removed. This increases blood pH and other receptors
detect this and respond by decreasing ventilation rates such that hypoxic levels of oxygen are
reached as breathing ceases for a period of time. The different receptors that contribute to
ventilation overcompensate for one another.