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)