Dr Archna Ghildiyal Associate Professor Department of Physiology KGMU Respiratory System

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 Cells- Spontaneous 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 Kim E. Barrett, Heddwen L. Brooks, Scott Boitano, Susan M. Barman.ed:23 rd Ganong’s Review of Medical Physiology:Mc Graw Hill student_files.htmlhttp://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