Transcript LECTURE8 - King George's Medical University

Respiratory System
Dr Archna Ghildiyal
Associate Professor
Department of Physiology
KGMU
LECTURE:8
Contents
• Regulation of Respiration: Neural
• Group of Neurons controlling
Respiration
• Breathing rhythm: Ramp Signals
• Lung Receptors
Learning Objectives
• NeuralControl of Respiration :
- Automatic
-Voluntary
• I & E Neurones
• Inspiratory “Ramp” Signal
• Pre-Botzinger Complex
• Lung Receptors
Neural Control of Respiration
Breathing
• Automatic/Spontaneous
• Voluntary
Neural control of Respiration
Groups of Neurons in the
Respiratory Center
In medulla
• Dorsal respiratory group
• Ventral respiratory group
In Pons
• Pneumotaxic center
• Apneustic Center?
Dorsal Respiratory Group(DRG)
• Most neurons located within NTS, some in
adjacent reticular substance of medulla
• Normal quiet breathing: Repititive
Inspiratory signals from DRG
Controls
• Inspiration
• Respiratory rhythm
Inspiratory “Ramp” Signals
• Rhythmical Inspiratory discharge from
DRG
• Nervous signal that is transmitted to the
inspiratory muscles, mainly the diaphragm
• Begins weakly & increases steadily for
about 2 secs in normal respiration
(inspiration)
• Then ceases abruptly for approx next 3
secs (expiration)
Control of Inspiratory Ramp
1.Control of the rate of increase of the ramp
signal rate of ramp signal - ramp
increases rapidly - fills the lungs rapidly
2.Control of the limiting point at which the
ramp suddenly ceases
• Usual method for controlling the rate of
respiration; shortens the duration of
Inspiration & Expiration(frequency of
respiration )
Contd…
Stopping the Ramp

Shortens the rate of inspiration and
expiration

Increasing the frequency of
respiration
Pneumotaxic center
(upper pons)
• Located dorsally in upper pons,in
N.parabrachialis
• Sends continual inhibitory impulses to
inspiratory center
• Ramp controls stopping point of DRG
• Inhibits I neurons
• Switch breathing from inspiration to
expiration
Contd…
• As impulse frequency rises: Faster
and Shallower Breathing
• Damage to Pneumotaxic center :
Results in increased depth of
inspiration
Ventral respiratory group(VRG)
• Located in ventrolateral part of
medulla,in N.ambigues &
N.retroambigues
• Functions in both Inspiration &
Expiration
• Remain inactive during normal quite
respiration
Contd…
• Act as Overdrive mechanism (as in
heavy exercise)
• Powerful expiratory signals to internal
intercostal & abdominal muscles
Pre-Bötzinger Complex
• Cluster of interneurons in the
ventrolateral medulla of
the Brainstem
• Contains Pace maker CellsSpontaneous Breathing
Apneustic Center (Lower Pons)
• Role not clear
• Stimulation causes Apneusis( pause
at full inspiration)
• Integrates inspiratory cut-off
information
Mechanism of Rhythmic
Ventilation
–Medullary respiratory center neurons
are continuously active
(spontaneous/automatic breathing)
–Combined input from all sources
(receptors,brain) causes action
potentials to stimulate respiratory
muscles
To Increase Inspiration
More and more neurons get activated
To Stop Inspiration
Neurons receive input from pontine group and
stretch receptors in lungs
Inhibitory neurons activated , cause
Inspiratory switch-off ,
Start of expiration
Effect: Relaxation of Inspiratory muscles
Voluntary control
• Provided via the Cerebral Cortex
• Modulate the activity of controlling centers
in the medulla and pons
• Allow the rate and depth of respiration to
be controlled
• During speaking, laughing, crying, eating,
defecating, coughing, and sneezing
Contd…
• Chemoreceptor reflex is capable of
overriding it.
• Conscious control of respiratory neuronal
networks in the reticular formation can
effect other basic functions regulated by
the brainstem(Yogic exercises)
Contd…
• Stimulation of the reticular activating
system of the brainstem
(RAS):Stimulates Ventilation
• Sleep: Ventilation
Peripheral receptors
• Chemoreceptors
• Pulmonary irritant receptors-on
stimulation cause
coughing,sneezing,bronchial
constriction
• Lung “J Receptors”
• Hering-Breuer inflation reflex
Lung “J Receptors”
• Indian Physiologist Prof A S Paintal
• Location:Sensory nerve endings in
alveolar walls in juxtaposition to pulmonary
capillaries
• Stimulus: Severe exercise, Engorged
capillaries,Pulmonary oedema
• Effect:Tachypnea,Hypotention,Bradycardia
J-Reflex
• Stimulation (severe exercise)

• Inhibition of gama motor neurons
supplying muscle spindle

• Muscle Tone

• Muscle Weakness & Stoppage of Exercise
Hering- Breuer Inflation Reflex
• Protective reflex
• Lung inflation signals limit inspiration
• Stretch Receptors: In Muscular Walls Of
Bronchi & Bronchioles
• Active when Tidal volume > 1.5 liters/breath
• Inspiratory ramp :“Switches off”
References
• John E. Hall.Guyton & Hall Text book of
Medical Physiology. A south Asian ed:
New Delhi: Elsevier.2013.p. 364-373
• Kim E. Barrett, Heddwen L. Brooks, Scott
Boitano, Susan M. Barman.ed:23rd
Ganong’s Review of Medical
Physiology:Mc Graw Hill
• http://meded.ucsd.edu/ifp/jwest/resp_phys/
student_files.html
Question:1
Respiratory control centers are
located in the :
A) Midbrain and Medulla
B) Medulla and Pons
C) Pons and Midbrain
D) Upper Spinal Cord and Medulla
Question:2
Damage to Pneumotaxic center
results in:
A) Decreased depth of Inspiration
B) Increased depth of Inspiration
C) Increased depth of Expiration
D) Decreased depth of Expiration
Question:3
Stimulation of the reticular activating system of
the brainstem (RAS) plays what role in
ventilation?
A) Stimulates ventilation
B) Inhibits ventilation
C) Stimulates inhalation but inhibits exhalation
(apneustic breathing)
D) Stimulates exhalation but inhibits inhalation
Question:4
Destruction of which part abolishes
automatic respiration?
A) Pre-Botzinger complex
B) Ventral group of respiratory neurons
C) Dorsal group of respiratory neurons
D) Section at the inferior border of the
pons
Question:5
Which of the following statement is true?
A) Hering Breuer inflation reflex respond to
lung distension by increasing frequency of
respiration.
B) Irritant receptors respond to noxious
gases by reflex bronchodilatation
C) J receptors respond to pulmonary
capillary congestion by rapid shallow
breathing
D) DRG neurons initiate expiration
Answers
1-B
2-B
3- A
4- A
5-C