Neural Control Of Breathing Flashcards
What happens if the pressure gradient between aveoli and capillary is too low
If this gradient is too low, gas exchange does not occur efficiently.
Why is level of ventilation regulated
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.
Give examples of when ventilation is increased
Examples of when ventilation is increased is during exercise, emotional stimulus,
infections (sepsis that increases acid production by the body) and trauma.
When do respiratory muscle contraction
There are different respiratory muscles that contract during breathing. They are initiated when
breathing is initiated.
What types of muscles are respiratory muscles
Respiratory muscles are skeletal and require a neural input to contract.
What diseases and injuries can effect breathing
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.
What happens during quiet breathing
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.
What muscles are used in forced inspiration
External intercostals are respiratory
muscles involved in forced inspiration whilst pectorals, sternomastoid and scalene muscles are
accessory muscles involved in forced inspiration.
What are respiratory mediators In forced expiration
Elastic recoil as well as internal intercostal muscles
are respiratory mediators of forced expiration whilst the abdominals are accessory muscles involved
in forced expiration.
What do accessory muscles actually do
Accessory muscles do not have a primary role in breathing but help facilitate
forced breathing.
How are different muscles initiated
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.
Describe the brainstem
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.
How are signals sent in the brainstem and what is the name
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.
What is the pattern generator dependant on - factors that effect it
This generator is based on information from central and peripheral
chemoreceptors
What do chemoreceptors use to function- and where found
that give oxygen, carbon dioxide and hydrogen ion concentrations, receptors in
muscles and joints
What receptors do lungs contain and function
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.
What can the central pattern generator also receive
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.
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.
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.
What is the most important regulatory systems
One of the most important regulatory systems that regulate ventilation are the central and
peripheral chemoreceptors.
What is the most prodominent chemoreceptors
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.
Where are CRCS present
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.
Why do CRCS not actually react with h+ ions
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.
What mechanism do central chemoreceptors use
Central
chemoreceptors work by negative feedback in that they are only activated when the number of
hydrogen ions in cerebrospinal fluid is too high.
What is the main aim for CRC
They initiate respiratory control centres in the
brainstem to increase ventilation rate to remove excess carbon dioxide.
Where are peripheral chemoreceptors located
Peripheral chemoreceptors are located outside the central nervous system and are specifically
located within the aortic and carotid bodies.
How are peripheral chemoreceptors activated
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.
What does the brainstem do after receiving signal from chemoreceptors
The brainstem then interprets these
signals and decides the level of ventilation.
What primarily drives ventilation rate
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.
How can ventilation rate o2 vs carbon dioxide be observed
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).
What drive has a greater effect on ventilation
In general, hypercapnic drive has a much greater effect on ventilation
than hypoxic drive.
What is sleep apnoea
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).
What happens in central apnoea
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.
What is the cause of central sleep apnoea
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
What is Cheyene-stokes
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.
