The respiratory centers in the brainstem control both involuntary and voluntary respiration. The medulla and pons are the primary centers, with the medulla containing groups that stimulate inspiration and expiration. The pons controls respiratory rate. Chemoreceptors in the brainstem and body sense pH in the blood and provide feedback to adjust ventilation. Proprioceptors in the lungs called stretch receptors trigger the Hering-Breuer reflex to prevent overinflation by inhibiting inspiration. This reflex can also cause the heart rate to briefly increase during inhalation in a phenomenon called sinus arrhythmia.

2. Presenter #01
Rahim Ullah
Reg. No : ZO220172036

4. The Respiratory Centers
 Involuntary respiration is controlled by the respiratory centers of the
upper brainstem (sometimes termed the lower brain, along with the
cerebellum).
 This region of the brain controls many involuntary and metabolic
functions besides the respiratory system, including certain aspects of
cardiovascular function and involuntary muscle movements (in the
cerebellum).

5.  The respiratory centers contain chemoreceptors that
detect pH levels in the blood and send signals to the
respiratory centers of the brain to adjust the
ventilation rate to change acidity by increasing or
decreasing the removal of carbon dioxide (since
carbon dioxide is linked to higher levels of hydrogen
ions in blood).
 There are also peripheral chemoreceptors in other
blood vessels that perform this function as well,
which include the aortic and carotid bodies.

6. The Medulla
 The medulla oblongata is the primary respiratory control center. Its main function is to
send signals to the muscles that control respiration to cause breathing to occur.
 There are two regions in the medulla that control respiration:
 The ventral respiratory group stimulates expiratory movements.
 The dorsal respiratory group stimulates inspiratory movements.
The medulla also controls the reflexes for nonrespiratory air movements, such as
coughing and sneezing reflexes, as well as other reflexes, like swallowing and vomiting.

7. The Pons
The pons is the other respiratory center and is located underneath the medulla. Its main function is to
control the rate or speed of involuntary respiration. It has two main functional regions that perform this
role:
 The apneustic center sends signals for inspiration for long and deep breaths. It controls the intensity of
breathing and is inhibited by the stretch receptors of the pulmonary muscles at maximum depth of
inspiration, or by signals from the pnuemotaxic center. It increases tidal volume.
 The pnuemotaxic center sends signals to inhibit inspiration that allows it to finely control the respiratory
rate. Its signals limit the activity of the phrenic nerve and inhibits the signals of the apneustic center. It
decreases tidal volume.
The apneustic and pnuemotaxic centers work against each other together to control the respiratory rate.

8. Neural Mechanisms (Cortex)
 The cerebral cortex of the brain controls voluntary respiration.
 Voluntary respiration is any type of respiration that is under conscious control.
 Voluntary respiration is important for the higher functions that involve air
supply, such as voice control or blowing out candles.
 Similarly to how involuntary respiration’s lower functions are controlled by
the lower brain, voluntary respiration’s higher functions are controlled by the
upper brain, namely parts of the cerebral cortex.

9. The Motor Cortex
 The primary motor cortex is the neural center for voluntary respiratory control. More broadly, the
motor cortex is responsible for initiating any voluntary muscular movement.
 The processes that drive its functions aren’t fully understood, but it works by sending signals to
the spinal cord, which sends signals to the muscles it controls, such as the diaphragm and the
accessory muscles for respiration. This neural pathway is called the ascending respiratory
pathway.
 Different parts of the cerebral cortex control different forms of voluntary respiration. Initiation of
the voluntary contraction and relaxation of the internal and external intercostal muscles takes
place in the superior portion of the primary motor cortex.

10.  The center for diaphragm control is posterior to the location of thoracic control
(within the superior portion of the primary motor cortex).
 The inferior portion of the primary motor cortex may be involved in controlled
exhalation.
 Activity has also been seen within the supplementary motor area and the
premotor cortex during voluntary respiration.
 This is most likely due to the focus and mental preparation of the voluntary
muscular movement that occurs when one decides to initiate that muscle
movement.

11.  Note that voluntary respiratory nerve signals in the ascending respiratory
pathway can be overridden by chemoreceptor signals from involuntary
respiration.
 Additionally, other structures may override voluntary respiratory signals, such as
the activity of limbic center structures like the hypothalamus.
 During periods of perceived danger or emotional stress, signals from the
hypothalamus take over the respiratory signals and increase the respiratory rate
to facilitate the fight or flight response.

12. Presenter #02
Riaz Ullah
Reg. No : ZO220172037

13. Nerves Used in Respiration
 There are several nerves responsible for the muscular functions involved in respiration. There are
three types of important respiratory nerves:
 The phrenic nerves: The nerves that stimulate the activity of the diaphragm. They are composed of
two nerves, the right and left phrenic nerve, which pass through the right and left side of the heart
respectively. They are autonomic nerves.
 The vagus nerve: Innervates the diaphragm as well as movements in the larynx and pharynx. It
also provides parasympathetic stimulation for the heart and the digestive system. It is a major
autonomic nerve.
 The posterior thoracic nerves: These nerves stimulate the intercostal muscles located around the
pleura. They are considered to be part of a larger group of intercostal nerves that stimulate regions
across the thorax and abdomen. They are somatic nerves.

14.  These three types of nerves continue the signal of the ascending
respiratory pathway from the spinal cord to stimulate the muscles
that perform the movements needed for respiration.
 Damage to any of these three respiratory nerves can cause severe
problems, such as diaphragm paralysis if the phrenic nerves are
damaged.
 Less severe damage can cause irritation to the phrenic or vagus
nerves, which can result in hiccups.

15. Chemoreceptor Regulation of Breathing
 Chemoreceptors detect the levels of carbon dioxide in the blood by
monitoring the concentrations of hydrogen ions in the blood.
 Chemoreceptor regulation of breathing is a form of negative
feedback.
 The goal of this system is to keep the pH of the blood stream within
normal neutral ranges, around 7.35.

16. Chemoreceptors
 A chemoreceptor, also known as chemosensor, is a sensory receptor that transduces a chemical
signal into an action potential.
 The action potential is sent along nerve pathways to parts of the brain, which are the integrating
centers for this type of feedback.
 There are many types of chemoreceptors in the body, but only a few of them are involved in
respiration.
 The respiratory chemoreceptors work by sensing the pH of their environment through the
concentration of hydrogen ions.
 Because most carbon dioxide is converted to carbonic acid (and bicarbonate ) in the bloodstream,
chemoreceptors are able to use blood pH as a way to measure the carbon dioxide levels of the
bloodstream.

17. The main chemoreceptors involved in respiratory feedback are:
1. Central chemoreceptors:
 These are located on the ventrolateral surface of medulla oblongata and detect changes in the pH
of spinal fluid.
 They can be desensitized over time from chronic hypoxia (oxygen deficiency) and increased
carbon dioxide.
2. Peripheral chemoreceptors:
 These include the aortic body, which detects changes in blood oxygen and carbon dioxide, but not
pH, and the carotid body which detects all three.
 They do not desensitize, and have less of an impact on the respiratory rate compared to the central
chemoreceptors.

18. Chemoreceptor Negative Feedback
Negative feedback responses have three main components:
 The sensor, the integrating sensor, and the effector.
 For the respiratory rate, the chemoreceptors are the sensors for blood pH, the medulla
and pons form the integrating center, and the respiratory muscles are the effector.
 Consider a case in which a person is hyperventilating from an anxiety attack.
 Their increased ventilation rate will remove too much carbon dioxide from their body.
 Without that carbon dioxide, there will be less carbonic acid in blood, so the
concentration of hydrogen ions decreases and the pH of the blood rises, causing
alkalosis.

19.  In response, the chemoreceptors detect this change, and send a signal to the
medulla, which signals the respiratory muscles to decrease the ventilation rate so
carbon dioxide levels and pH can return to normal levels.
 There are several other examples in which chemoreceptor feedback applies.
 A person with severe diarrhea loses a lot of bicarbonate in the intestinal tract,
which decreases bicarbonate levels in the plasma.
 As bicarbonate levels decrease while hydrogen ion concentrations stays the same,
blood pH will decrease (as bicarbonate is a buffer) and become more acidic.

20.  In cases of acidosis, feedback will increase ventilation to remove more
carbon dioxide to reduce the hydrogen ion concentration.
 Conversely, vomiting removes hydrogen ions from the body (as the
stomach contents are acidic), which will cause decreased ventilation to
correct alkalosis.
 Chemoreceptor feedback also adjusts for oxygen levels to prevent
hypoxia, though only the peripheral chemoreceptors sense oxygen
levels.

21.  In cases where oxygen intake is too low,
feedback increases ventilation to increase
oxygen intake.
 A more detailed example would be that if
a person breathes through a long tube
(such as a snorkeling mask) and has
increased amounts of dead space,
feedback will increase ventilation.

22. Presenter #03
Rifat Ullah
Reg. No : ZO220172038

23. Proprioceptor Regulation of Breathing
 The Hering–Breuer inflation reflex prevents overinflation of the lungs.
 The lungs are a highly elastic organ capable of expanding to a much larger
volume during inflation.
 While the volume of the lungs is proportional to the pressure of the pleural
cavity as it expands and contracts during breathing, there is a risk of over-
inflation of the lungs if inspiration becomes too deep for too long.
 Physiological mechanisms exist to prevent over-inflation of the lungs.

24. The Hering–Bauer Reflex
 The Hering–Breuer reflex (also called the inflation reflex) is triggered to prevent
over-inflation of the lungs.
 There are many stretch receptors in the lungs, particularly within the pleura and
the smooth muscles of the bronchi and bronchioles, that activate when the lungs
have inflated to their ideal maximum point.

25.  These stretch receptors are mechanoreceptors, which are a type of
sensory receptor that specifically detects mechanical pressure,
distortion, and stretch, and are found in many parts of the human
body, especially the lungs, stomach, and skin.
 They do not detect fine-touch information like most sensory
receptors in the human body, but they do create a feeling of tension
or fullness when activated, especially in the lungs or stomach.

26.  When the lungs are inflated to their maximum volume during
inspiration, the pulmonary stretch receptors send an action potential
signal to the medulla and pons in the brain through the vagus nerve.
 The pneumotaxic center of the pons sends signals to inhibit the
apneustic center of the pons, so it doesn’t activate the inspiratory area
(the dorsal medulla), and the inspiratory signals that are sent to the
diaphragm and accessory muscles stop.
 This is called the inflation reflex.

27.  As inspiration stops, expiration begins and the lung begins
to deflate.
 As the lungs deflate the stretch receptors are deactivated
(and compression receptors called proprioreceptors may be
activated) so the inhibitory signals stop and inhalation can
begin again—this is called the deflation reflex.
 Early physiologists believed this reflex played a major role
in establishing the rate and depth of breathing in humans.

28.  While this may be true for most animals, it is not the case
for most adult humans at rest.
 However, the reflex may determine the breathing rate and
depth in newborns and in adult humans when tidal volume
is more than 1 L, such as when exercising.
 Additionally, people with emphysema have an impaired
Hering–Bauer reflex due to a loss of pulmonary stretch
receptors from the destruction of lung tissue, so their lungs
can over-inflate as well as collapse, which contributes to
shortness of breath.

29. Sinus Arrhythmia
 As the Hering–Bauer reflex uses the vagus nerve as its neural
pathway, it also has a few cardiovascular system effects
because the vagus nerve also innervates the heart.
 During stretch receptor activation, the inhibitory signal that
travels through the vagus nerve is also sent to the sinus-atrial
node of the heart.
 Its stimulation causes a short-term increase in resting heart
rate, which is called tachycardia.

30.  The heart rate returns to normal during expiration when the
stretch receptors are deactivated.
 When this process is cyclical it is called a sinus arrhythmia,
which is a generally normal physiological phenomenon in
which there is short-term tachycardia during inspiration.
 Sinus arryhthmias do not occur in everyone, and are more
common in youth.
 The sensitivity of the sinus-atrial node to the inflation reflex is
lost over time, so sinus arryhthmias are less common in older
people.