INTRODUCTION
• It is a complex neural mechanism which is modified by the following
1) Respiratory reflexes
2) Chemical mechanisms
REGULATION OF RESPIRATION
1. Neural mechanism
2.Chemical mechanism
Nervous Regulatory Mechanism involves the following :
Automatic Control
Voluntary Control
NERVOUS MECHANISM
•Dual control
• Automatic control
• Voluntary control
It is a involuntary function , which can be influenced voluntarily.
Functional significance
•Involuntary control allows us to breathe without our consciousness and is essential for life.
• Voluntary control facilitates acts like talking, singing, breath holding etc.
RESPIRATORY CENTERS
•Group of neurons are nothing but group of neurons located bilaterally in brainstem.
•Depending on location, they are of two groups :
- Medullary Respiratory Centre
- Pontine Respiratory Centre
•Medullary respiratory centers include two groups of neurons :
1.DRG : Dorsal respiratory group of neurons
2. VRG : Ventral respiratory group of neurons
II. Pontine centers includes two centres :
1. Pneumotaxic center
2. Apneustic center
MEDULLARY CENTERS :
1) Dorsal Respiratory Group of Neurons ( DRG )
•Situation : diffusely situated in NTS, in upper part of medulla oblongata .
•Inspiratory neurons.
•Autorhythmic property
• Generate Inspiratory Ramp
Functions of DRG :
• Generates basic rhythm of respiration.
• Rhythmicaly discharge of impulses (action potentials).
Electrophysiology
•Inspiratory ramp
•In DRG ,
•There is steady increase in amplitude of action potential for 2 seconds during which inspiration occurs.
•Then they stop abruptly for 3 seconds.
• During this period expiration occurs.
• Again inspiratory ramp reappears and cycle is repeated.
•Significance :
•Steady increase in lung volume during inspiration
2) Ventral Respiratory Group of Neurons ( VRG )
Location : Medulla oblongata anterior and lateral to NTS and it contains both inspiratory and expiratory neurons.
Functions of VRG :
Voluntary control.
Normally, they are inactive, when active stimulate both inspiratory and expiratory muscles.
Pontine Respiratory Centers
In pons, two respiratory centers:
•Pneumotaxic center
•Apneustic center
* They modulate rhythm generated in medullary respiratory centers
* They are not essential for normal respiration
Pneumotaxic Center
•Location : It located in upper pons
•Function :
It acts indirectly through apneustic center
↓
inhibitis medullary respiratory centers, particularly DRG
↓
stops inspiration & starts expiration .
•It increases respiratory rate by decreasing duration of inspiration.
Apneustic Center
•Location : It is located in lower pons
•Function
* It acts on DRG and increases depth of inspiration.
PRE BROTZINGER COMPLEX :
Until recently, it was thought that DRG generate basic rhythm of breathing
It is now known that it is generated by a neurons called Pre-Brotzinger complex.They have pacemaker activity.
They are located near upper end of medullary respiratory centre.
Role of Reticular Activating System in respiration :
•It stimulates the respiratory centres .
•During sleep, it’s activity decreases, therefore ventilation decreases and there is slight increase in PCO2 .
Role of Limbic system in respiration :
•During emotional reactions , stimulation of limbic system increases respiration
Neural regulation : Reflex mechanism , it contains three main components
1) Afferent Pathway
2) Respiratory Center
3) Efferent Pathway
•Afferent Pathway
Impulses from receptors are carried by glossopharyngeal & vagus nerves.
Respiratory centers receive impulses and modulates movements of thoracic cage and lungs through efferent pathway.
•Efferent Pathway
Starts from respiratory centers and terminate in anterior horn cells of cervical and thoracic segments of spinal cord .
From here Phrenic nerve and intercostal nerve arises
1.Phrenic nerve (C3 - C5) supplies diaphragm
2. Intercostal nerve (T1 - T11) supplies external intercostal muscles.
Vagus nerve also contains some efferent fibers
Various connections of Respiratory Centers :
Afferent impulses to respiratory centres come from
• Higher centres
• Non-chemical receptors
• Chemical receptors
• FROM HIGHER CENTRES
1. Cerebral cortex
2. Limbic system
FROM NON-CHEMICAL RECEPTORS
1. Receptors of Lungs: Hering-Breuer Reflex
2. 'J' Receptors of Lungs
3. Irritant Receptors of Lungs
4. Chest wall stretch receptors
5.Proprioceptors
6. Thermoreceptors
7.Pain Receptors
FROM CHEMICAL RECEPTORS
1. Chemoreceptors (central & periferal)
2. Baroreceptors
FROM HIGHER CENTRES
•1. Cerebral cortex
Normally, breathing is an involuntary process and occurs automatically. However, respiratory muscles being skeletal muscle, can also be controlled voluntarily.
Originates from neocortex and ends on spinal cord, bypassing medullary centres through Corticobulbar and Corticospinal tracts
It is involved in activities like talking, singing and breath holding etc
2. Limbic system
•It gets afferents from pain pathways.
•Pain and emotional stimuli increases rate and depth of breathing.
HERING -BREUER REFLEX
•Protective reflex
•Keeps respiration within physiological limits.
It has two types of reflexes :
a. Hering-Breuer Inflation Reflex
b. Hering-Breuer deflation Reflex
a .Hering-Breuer Inflation Reflex
Inspiration
↓
Tidal volume more than > 1 lit
↓
Stretching of lungs
↓
Stimulation of stretch receptors in air passage
↓
Impulses through vagal afferents
↓
Inhibition of DRG
↓
Inhibition of inspiration
b) Hering-Breuer deflation Reflex
Periodically ↑ lung compliance
↓
collapse of small alveoli
↓
stimulates irritant receptors
↓
this reflex acts as opens up alveoli
Impulses from 'J' Receptors of Lungs :
•It was discovered by an Indian Physiologist AS Paintal in 1954.
•Location : wall of the alveoli ,near pulmonary capillaries.
Receptors : sensory nerve endings of vagus.
•Stimulus :
• Increase in content of interstitial fluid between capillary endothelium and alveolar epithelium like,
i. Over inflation of lungs
ii. Pulmonary congestion
iii. Microembolism in pulmonary capillaries etc
•Response :
•Apnea followed by hyperventilation, bradycardia, hypotension and weakness of skeletal muscles.
Impulses from Irritant Receptors :
•Located below mucosa of entire respiratory tract.
•Stimulated by smoke, noxious gases, particulate matter in inspired air etc.
•These initiate many reflexes:
i. Sneezing reflex
ii. Deglutition reflex
iii. Cough reflex
iv. Bronchoconstriction
Impulses from stretch receptors
Increase in mechanical load on respiratory muscle
↓
Stimulates muscle spindle of inter costal muscle
↓
Afferent impulses through intercostals nerves
↓
Stimulates neighbouring
Intercostal muscle (intercostals to intercostal reflex) and
Diaphragm
Impulses from Proprioceptors
•They are present in joints, tendons and muscles.
•Stimulated during exercise & send impulses to cerebral cortex through somatic nerves.
•It causes hyperventilation by stimulating medullary respiratory centers.
Impulses from Thermo receptors
•These receptors are stimulated by a change in body temperature.
• Two types:
Cold receptors
Warm receptors
•When warm receptors are stimulated ,impulses are carried by somatic nerves to cerebral cortex .
•It stimulates respiratory centres to produce hyperventilation.
•So some amount of heat is lost in expired air.
Impulses from Pain Receptors
•Whenever they are stimulated, impulses are carried by somatic nerves to cerebral cortex.
•It stimulates respiratory centers and causes hyperventilation.
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