Chapter 22 (4)

H+

Stimulates central chemoreceptors of brain stem

CO2

Most powerful factor in changing breathing

Hypothalamic controls

Act thru limbic system to modify rate & depth of respiration ex. breath holding that occurs in anger or gasping w/ pain Rise in body temp increases respiratory rate

Dorsal respiratory group (DRG)

Near root of cranial nerve IX Integrates input from peripheral stretch & chemoreceptors, sends info to VRG Influence & modify activity of VRG Smooth out transition b/w inspiration & expiration & vice versa Transmit impulses to VRG modify & fine-tune breathing rhythms during vocalization, sleep, exercise

Neural controls

Neurons in reticular formation of medulla & pons

Eupnea

Normal respiratory rate & rhythm (12-15 breaths per min)

O2

Not very significant factor in changing breathing

Ventral respiratory group (VRG)

Contains rhythm generators whose output drives respiration (where we start/originate our breath) Located in medulla

Expiratory neurons

Inhibit inhibitory neurons

Dorsal respiratory group (DRG)

Integrates peripheral sensory input & modifies the rhythms generated by VRG Located in medulla

Pontine respiratory centers

Interact w/ medullary respiratory centers to smooth respiratory pattern Located in pons

Low pH

High amount of hydrogen ions

Same irritant

Results in cough in trachea or bronchi or a sneeze in nasal cavity (can be dust, pathogens, etc)

Ventral respiratory group (VRG)

Rhythm-generating & integrative center Sets eupnea Its inspiratory neurons excite inspiratory muscles via phrenic (diaphragm) & intercostal nerves (external intercostals)

Rate

Determined by how long inspiratory center active

Cortical controls

Directs signals from cerebral motor cortex that bypass medullary controls ex. voluntary breath holding (brain stem reinstates breathing when blood CO2 critical)

Control of respiration

Involves higher brain centers, chemoreceptors & other reflexes

Generation of respiratory rhythm

1 hypothesis: Pacemaker neurons w/ intrinsic rhythmicity (automatically depolarizes) Most widely accepted hypothesis: Reciprocal inhibition of 2 sets of interconnected pacemaker neurons in medulla that generate rhythm

Depth & rate

Both modified in response to changing body demands (most important are changing levels of CO2, O2 & H+)

Hering-Breuer reflex

Can only get to certain amount of lung size Inflation reflex

Depth

Determined by how actively respiratory center stimulates respiratory muscles

High pH

Low amount of hydrogen ions

Respiratory centers

Medulla & pons

Receptors in bronchioles

Respond to irritants Communicate w/ respiratory centers via vagal nerve afferents Promote reflexive constriction of air passages

Hering-Breuer reflex

Stretch receptors in pleurae & airways stimulated by lung inflation Inhibitory signals to medullary respiratory centers end inhalation & allow expiration Acts as *protective response* more than normal regulatory mechanism

Partial pressure of O2

When excited, cause respiratory centers to increase ventilation (requires substantial drop to stimulate increased ventilation)