Exam 3 Review:  Chapter 22:  ANS Control of Breathing

respiratory center - The series of paired and functionally related autonomic nuclei located bilaterally in the reticular formation of the brain stem; this control center consists of the medullary rhythmicity area (containing the dorsal respiratory group (DRG) (formerly the inspiratory area) and the ventral respiratory group (VRG) = (formerly the expiratory area) and the pontine respiratory center (formerly the pneumotaxic and the apneustic areas); these collections of neurons cooperate to regulate the rate and depth of breathing as an involuntary unconscious activity in response to the physiological needs of the body for O2 and CO2 exchange and for blood acid-base balance.

medullary rhythmicity area - A collection of neurons in the reticular formation within the medulla oblongata involved in establishing or modifying the pattern for breathing; within this area are two key components:  (1) the ventral respiratory group (VRG) (formerly the inspiratory area) which autorhythmically stimulates spontaneous ventilation, resting or tidal breathing (eupnea), and (2) the dorsal respiratory group (DRG) (formerly the expiratory area) which responds to situations beyond those of the resting or tidal breathing (eupnea) to alter the pattern for ventilation in response to the physiological needs of the body for O2 and CO2 exchange and for blood acid-base balance.

dorsal respiratory group (DRG) (formerly the inspiratory area) - The collection of motor neurons forming nuclei within the dorsal portion of the medullary rhythmicity area of the reticular formation within the medulla oblongata which are involved in altering the pattern for ventilation in response to the physiological needs of the body for O2 and CO2 exchange and for blood acid-base balance; these neurons stimulate neurons in the ventral respiratory group (VRG) to achieve those effects; they are responsive to sensory information from chemoreceptors and mechanoreceptors.

ventral respiratory group (VRG)  (formerly the expiratory area) - The collection of autorhythmic motor neurons forming nuclei within the ventral portion of the medullary rhythmicity area of the reticular formation within the medulla oblongata; this group contains both inspiratory and expiratory neurons; the inspiratory neurons stimulate the diaphragm and external intercostals for approximately 2 seconds to cause inspirations and then the antagonistic expiratory neurons fire for approximately 3 seconds to permit passive or stimulate active expirations; thereby inspiratory and expiratory neurons cooperate in a negative feedback control relationship, setting the basic rhythm of respiration (spontaneous ventilation, resting or tidal breathing (eupnea)); VRG neurons may be influenced by the dorsal respiratory group (DRG) for ventilations in situations other than eupnea.

pontine respiratory center (formerly pneumotaxic and apneustic areas) - A collection of neurons in the reticular formation within the pons which limit inspiratory duration by sending inhibitory signals to the medullary rhythmicity area reducing duration of inspiratory impulses causing shorter cycles which increases ventilation rate; these pontine respiratory neurons receive input from higher brain centers and peripheral receptors, and their output fine tunes the breathing rhythm during activities such as speaking, sleeping, or exercising.

cortical influences - The action of higher, "conscious" centers in the cerebral cortex which permit voluntary control of ventilation by interacting with and over-riding the autonomic centers in the medullary rhythmicity area; examples include the control of ventilation during speech and singing, as well as deliberate forceful inspirations, expirations, or attempts at breath holding; pain and certain emotional states may also influence the rate and depth of ventilation in this fashion.

central chemoreceptors - A sensory neuron located within the CNS, usually in the brain stem or hypothalamus, which responds to chemical stimuli; a type of enteroreceptor sensitive to concentration changes of a variety of molecules in the blood or cerebrospinal fluid.

 

peripheral chemoreceptors - A sensory neuron located outside the CNS, usually in the wall of a blood vessel (e.g., the aortic body, the carotid body, the juxtaglomerular apparatus) which responds to chemical stimuli; a type of enteroreceptor sensitive to concentration changes of a variety of molecules in the blood or other body fluids.

carotid body - A group of peripheral chemoreceptors located near the bifurcations of the carotid arteries which monitor changes in the oxygen and CO2 content and pH of the blood and rely that sensory information to the hypothalmus and brain stem to help them control cardiovascular and respiratory functions; other cells in the carotid body respond to blood temperature and to certain chemicals, e.g., nicotine and cyanide.

aortic body - A group of peripheral chemoreceptors located in the arch of the aorta which monitor changes in the oxygen and CO2 content and pH of the blood and rely that sensory information to the hypothalmus and brain stem to help them control cardiovascular and respiratory functions.

baroreceptors - A type of mechanoreceptor; a specialized sensory end organ or sensory neuron which responds to mechanical stimuli such as tension (stretching) in the wall of a blood vessel or other tubular organ; important sensors in the regulation of blood pressure.

inflation reflex - A relatively rapid and predictable motor response by the skeletal muscles responsible for ventilation which occurs when stretch receptors in the visceral pleura, bronchioles, and alveoli are stimulated by being stretched; the motor response helps regulate the depth of breathing; over-stretching causes apnea, bronchodilation, increased heart rate and peripheral vasoconstriction.

Chemoreceptor Control of Breathing


Describe:

3. The control of respiration (ventilation) by the respiratory center of the brain.
 
The ventral respiratory group (VRG) and the dorsal respiratory group (DRG) within the medullary rhythmicity area cooperate to establish the pattern for spontaneous ventilation and basal rate of ventilation which may be adjusted by impulses from related respiratory control centers in the pons; the ventral respiratory group (VRG) contains both inspiratory and expiratory neurons; the autorythmic inspiratory neurons stimulate the diaphragm and external intercostals for approximately 2 seconds to cause inspirations and then the antagonistic expiratory neurons fire for approximately 3 seconds to permit passive or stimulate active expirations; thereby inspiratory and expiratory neurons cooperate in a negative feedback control relationship, setting the basic rhythm of respiration (spontaneous ventilation, resting or tidal breathing (eupnea)); the dorsal respiratory group (DRG) neurons are involved in altering the pattern for ventilation in response to the physiological needs of the body for O2 and CO2 exchange and for blood acid-base balance; these neurons stimulate neurons in the ventral respiratory group (VRG) to achieve those effects; they are responsive to sensory information from chemoreceptors and mechanoreceptors.


4. The cortical, chemical, and neural influences on the respiratory center of the brain.
 
Cortical Influences voluntary controls:  conscious decisions to change the rate and depth of breathing associated with speaking, singing, coughing, etc.
Chemical Influences changing levels of oxygen, carbon dioxide, hydrogen ion and bicarbonate ion in the blood are detected and this visceral sensory information is routed to the hypothalamus and medulla where it stimulates or inhibits the action of components of the respiratory center of the brain
Neural Influences (a) the medullary rhythmicity center with its authorythmic inspiratory and expiratory neurons sets the basal ventilation rate adjusted to the level of activity and metabolic demands of the body at any given moment

(b) the pontine respiratory center neurons limit inspiratory duration by sending inhibitory signals to the medullary rhythmicity area reducing duration of inspiratory impulses causing shorter cycles which increases ventilation rate; these pontine respiratory neurons receive input from higher brain centers and peripheral receptors, and their output fine tunes the breathing rhythm during activities such as speaking, sleeping, or exercising.

(c)  proprioceptive stretch receptors in the lungs, pleura, and thoracic wall convey information about the degree of the filling of the lungs and overfilling will cause a reflex decrease in the strength of inspirations

Sketch and label:

5. The negative feedback pathway illustrating how the respiratory center of the brain that controls breathing by as a function of oxygen, carbon dioxide, and acidity levels of the blood.

Increased pO2, decreased pCO2, and a drop in [H+]* (alkalosis) all interact to discourage ventilation to retain more CO2 and, therefore, to restore normal CO2 levels.

Decreased pO2, increased pCO2, and a rise in [H+]* (acidosis) all interact to encourage ventilation to blow off more CO2 and, therefore, to restore normal CO2 levels.

[*Note:  CO2 levels and acidity levels are directly proportional; when one rises the other rises, and vice versa.]