M6(2) Ventilation Control

respiratory control center

controls breathing and depth — 3 highly integrative levels of control for respiration

1. central controller

2. distribution/synchronization of respiratory motor output

3. sensory input

contains the Medullary Respiratory Center (in medulla oblongata)

central controller

generates the basic rhythm of breathing automatically, without conscious effort.

• contains groups of neurons that alternate stimulation between inspiratory and expiratory muscles.

• example: The dorsal respiratory group (DRG) controls inspiration, while the ventral respiratory group (VRG) helps regulate forced breathing

distribution/synchronization of respiratory motor output

coordinates the activity of respiratory muscles (like the diaphragm and intercostals) so that inhalation and exhalation happen smoothly and efficiently

sensory input

modulates and adjusts breathing based on feedback from sensors throughout body

• chemoreceptors

• mechanorecepetors

chemoreceptors

detect CO2, O2, and pH levels

• feeds input to respiratory control center

• peripheral vs central

mechanoreceptors

senses stretch and deformation in lungs and airways

• feeds input to respiratory control center

inspiratory neurons

governs normal respiration via diaphragm + external intercostal muscles

• self-limited (naturally shuts itself off after a period)

• inhibited by expiratory neurons

expiratory neurons

inhibits inspiratory neurons when active to allow exhalation

• as expiration proceeds, inspiratory center becomes progressively less inhibited

humoral factors

chemical signals in blood that provide feedback to respiratory control center

• variations in PO2, PCO2, pH, temperature monitored

• sensory units (central and peripheral chemoreceptors sends signals to adjust ventilation and maintain blood chemistry within narrow limits)

humoral feedback

• humoral feedback is dominant at rest (main regulator of breathing)

  • mainly CO2

peripheral chemoreceptors

aortic arch and carotid bodies

• detects changes in PaO2, PaCO2, pH

• monitors blood supplying the brain

central chemoreceptors

medulla

• detects changes in PaCO2, pH

• monitors cerebrospinal fluid

ventilatory response to O2

the increase in ventilation that occurs when arterial oxygen (PaO₂) drops below a certain level

• ventilation remains relatively stable until PaO2 falls below 60 mmHg

  • ventilation inc sharply — relationship is nonlinear because Hb is highly saturated at normal PaO2 (body doesn’t need to ventilate more until O2 levels drop significantly)

hypoxic threshold

arterial oxygen level (PaO₂) below which the body increases breathing in response to hypoxia

ventilatory response to CO2

the increase in ventilation that occurs in response to elevated arterial CO2 (PaCO2)

• primary driver of ventilation at rest

• Linear relationship: Ventilation increases proportionally with PaCO₂

neural feedback

neural feedback is dominant during exercise (main regulator of breathing)

• duration and intensity of inspiratory cycle: hypothalamic control

• feedforward

  • neural

  • mechanical

• feedback

  • mechanical

  • chemical

feedforward

mechanisms that are anticipatory signals that inc ventilation in advance of changes in blood gases

• neural / central command

• mechanoreceptors

neural / central command

sends a signal to the respiratory center parallel to initiation of movement (inc ventilation)

• the most important as it sets the initial set-point for ventilation (target level of blood gases, mainly CO₂ and O₂)

mechanoreceptors

type III afferents located in muscles and joints

• detects mechanical activity and provides fine-tuning for ventilation based on muscle activity

feedback

mechanisms that adjust ventilation in response to changes in blood gases/mechanical activity

• chemoreceptors

• mechanoreceptors

chemoreceptors feedback

includes peripheral and central chemoreceptors

• detect changes in PaO2, PaCO2, and pH in blood (peripheral)

• detect changes in PaCO2 and pH in CSF (central

sends signals to adjust ventilation within narrow limits

mechanoreceptors feedback

type III afferents in muscles and joints

• detects mechanical activity and provides fine-tuning for ventilation based on muscle activity

pulmonary stretch receptors

• detect lung inflation and prevent over-inflation

fine tunes breathing to match mechanical demands

ventilation threshold

point during exercise when ventilation rises disproportionately to oxygen consumption (VO₂)

• reflects lactate accumulation and subsequent inc CO2 production

• signals respiratory system to inc ventilation rapidly