Lecture 33: Control of Respiration and Chemoreceptors Flashcards
Breathing occurs in what pattern
- Continuous, cyclical pattern
- Inspiratory muscles rhythmically contract
- Activities are accomplished automatically without conscious effort
Respiratory muscles require what to bring about contraction
nervous stimulation
Respiratory control centers are housed where and are responsible for what
in the brain stem
generating the rhythmic pattern of breathing
Three respiratory centers in the brain stem
- Medullary
- Apneustic
- Pneumotaxic
What is the primary control center for respiration in the brain
Medullary
Consists of cell bodies
Two clusters that the medullary respiratory center are composed of
- Dorsal
- inspiratory - Ventral respiratory
- expiratory
- Also composed of inspiratory neurons
- Dorsal respiratory group has connections to it
Inspiratory center of medullary purpose
-Controls basic rhythm for breathing by setting the frequency of breathing
Inspiratory center of medullary receives sensory input from
- Peripheral chemoreceptos via glossopharyngeal (CN IX) and vagus (CN X) nerves
- Mechanoreceptors in the lungs via vagus nerves
Inspiratory center sends motor output to…
and as a result…
- The diaphragm via the phrenic nerve, external intercostal muscles via the intercostal nerves
- As a result, respiration occurs because these muscles produce an increase in intrathoracic pressure and initiates the flows of air into the lungs
What muscles may be used for more vigorous respiration
Those connecting the sternum and the head
Ventral respiratory group is composed of inspiratory and expiratory neurons which remain inactive during
normal quiet breathing
Air is driven out of the lungs by
the reverse pressure gradient between the lungs and the atmosphere until the system reaches its equilibrium point again
Purpose of the ventral respiratory group
- Called into play as an overdrive mechanism when demands for ventilation are increased
- Esp important in active expiration
Pneumotaxic and apneustic centers are located
in the pons
Pneumotaxic and apneustic purpose
Exerts fine-tuning influences over medullary center to help produce normal, smooth, insp and exp
Pneumotaxic
Transmits inhibitory impulses to DRG that help turn off insp neurons, limiting duration of inspiration
Apneustic center
-Prevents inspiratory neurons from being switched off, providing extra boost to inspiratory drive
Pneumotaxic vs apneustic
Pneumotaxic is dominant over apneustic, helping to bring inspiration to a halt and allowing expiration to occur normally
Arterial blood gases are maintained within a normal range by
varying the magnitude of ventilation to match the needs of the body for O2 uptake and CO2 removal
Three chemical factors that increase ventilation
- An decrease in arterial PO2
- An increase in arterial PCO2
- An increase in H+ concentration
Two types of chemoreceptor that monitors ventilation
- Peripheral
2. Central
Where are peripheral chemoreceptors located
Carotid bodies and aortic bodies
What do peripheral chemoreceptors respond to
- Primarily to decreases in blood O2
- Less sensitive to increases in CO2 and decreases in blood pH
Peripheral chemoreceptors relay info about
Arterial PO2, PCO2, and H+ to medullary inspiratory center via cranial nerves IX and X
Most important responsibility for peripheral chemoreceptors
-Detect changes in arterial O2
Arterial PO2 must fall below ___ mm HG before peripheral chemoreceptors are activated
60
Central chemoreceptors link
changes in arterial PCO2 to compensatory adjustments in ventilation
Do central chemoreceptors monitor CO2 itself
Nope
What do central chemoreceptors monitor?
Changes in CO2-induced H+ concentration in the ECF of the brain that bathes them
Central chemoreceptors monitor what breathing
minute to minute
Central chemoreceptors are very sensitive to what?
Changes in the pH of the brain ECF
A decrease in pH of ECF leads to
increased breathing rate (hyperventilation)
A increase in pH of ECF leads to
a decrease in the breathing rate (hypoventilation)
Diabetes mellitus
-Excess of H+ keto acids in the circulation
Four “other” respiratory receptors
- Lung stretch receptors
- Joint and muscle receptors
- Irritant receptors
- J receptors
Lung stretch receptors
- Located in smooth muscle of airways
- When stimulated by lung distension, action potentials travel through afferent fibers to the medullary center and inhibit the inspiratory neurons
Hering-Breuer reflex
Negative feedback from highly stretched lungs prevents over-inflation
Proprioceptors (muscle and joint receptors)
-Increase breathing rate
Where are irritant (nocioreceptors) located
- Between epithelial cells lining airways
- Info travels to medulla and causes reflex constriction of bronchial smooth muscle and increase in breathing rate
J receptors are called
Juxtacapillary receptors
J receptors are located
In alveolar walls of near the capillaries
J receptor purpose
Engorgement of pulmonary capillaries with blood and increases in interstitial fluid volume activates these receptors to produce an increase in rate of breathing
Example of J receptor activation
In left-sided heart failure, blood backs up in pulmonary circulation. J receptors mediate change in breathing pattern, including rapid shallow breathing
