Respiratory Areas in the Brainstem

1
Respiratory Areas in the Brainstem

• Medullary respiratory center
• Dorsal groups stimulate the diaphragm
• Ventral groups stimulate the intercostal and
  abdominal muscles
• This section is especially sensitive during
  infancy, and the neurons can be destroyed if the
  infant is dropped and/or shaken violently. The
  result can be death due to "shaken baby syndrome
• Pontine (pneumotaxic) respiratory group
• Involved with switching between inspiration and
  expiration (fine tunes the breathing
  pattern-----there is a connection with medullary
  resp. center but precise function unknown)

2
Rhythmic Ventilation

• Starting inspiration
• Medullary respiratory center neurons are
  continuously active
• Center receives stimulation from receptors (that
  monitor blood gas levels) and simulation from
  parts of brain concerned with voluntary
  respiratory movements and emotion
• Combined input from all sources causes action
  potentials to stimulate respiratory muscles
• Increasing inspiration
• More and more neurons are activated (to stimulate
  respiratory muscles)
• Stopping inspiration
• Neurons stimulating the muscles of respiration
  also stimulate the neurons in the medullary
  respiratory center that are responsible stopping
  inspiration. They also receive input from
  pontine group and stretch receptors in lungs.
  Inhibitory neurons activated and relaxation of
  respiratory muscles results in expiration.
• Note although the medullary neurons establish
  the basic rate depth of breathing, their
  activities can be influenced by input from other
  parts of the brain by input from peripherally
  located receptors.

3
Rhythmic Ventilation

• Chemical control
• Carbon dioxide is major regulator, but indirectly
  through p H change
• Increase or decrease in pH can stimulate
  chemo-sensitive area, causing a greater rate and
  depth of respiration
• Oxygen levels in blood affect respiration when a
  50 or greater decrease from normal levels exists
• CO2.
• Hypercapnia too much CO2
• Hypocapnia lower than normal CO2

• Apnea. Cessation of breathing. Can be conscious
  decision, but eventually PCO2 levels increase to
  point that respiratory center overrides
• Hyperventilation. Causes decrease in blood PCO2
  level, which causes respiratory alkalosis (high
  blood pH). Fainting, leads to changes in the
  nervous system fires and leads to the paresthesia
  (pins needles)
• Cerebral (cerebral cortex)and limbic system.
  Respiration can be voluntarily controlled and
  modified by emotions (ex strong emotions can
  cause hyperventilation or produce the sobs
  gasps of crying)

4
Modifying Respiration
5
Chemical Control of Ventilation

• Chemoreceptors specialized neurons that respond
  to changes in chemicals in solution
• Central chemoreceptors chemosensitive area of
  the medulla oblongata connected to respiratory
  center
• Peripheral chemoreceptors carotid and aortic
  bodies. Connected to respiratory center by
  cranial nerves IX and X (9 10)
• Effect of pH chemosensitive area of medulla
  oblongata and carotid and aortic bodies respond
  to blood pH changes
• Chemosensitive areas respond indirectly through
  changes in carbon dioxide
• Carotid and aortic bodies respond directly to p H
  changes

6
Chemical Control of Ventilation

• Effect of carbon dioxide small change in carbon
  dioxide in blood triggers a large increase in
  rate and depth of respiration
• - ex an increase PCO2 of 5 mm Hg causes an
  increase in ventilation of 100.
• Hypercapnia greater-than-normal amount of carbon
  dioxide
• Hypocapnia lower-than-normal amount of carbon
  dioxide
• Chemosensitive area in medulla oblongata is more
  important for regulation of PCO2 and pH than the
  carotid aortic bodies (responsible for 15 -
  20 of response)
• During intense exercise, carotid aortic bodies
  respond more rapidly to changes in blood pH than
  does the chemosensitive area of medulla

7
Chemical Control of Ventilation

• Effect of oxygen carotid and aortic body
  chemoreceptors respond to decreased PO2 by
  increased stimulation of respiratory center to
  keep it active despite decreasing oxygen levels
  (50 or greater decrease----------bec. of
  oxygen-hemoglobin dissociation curve-------at any
  PO2 above 80 mm Hg nearly all of hemoglobin is
  saturated with oxygen)
• Hypoxia decrease in oxygen levels below normal
  values

8
Regulation of Blood pH and Gases
9
Hering-Breuer Reflex

• Limits the degree of inspiration and prevents
  overinflation of the lungs
• Depends on stretch receptors in the walls of
  bronchi bronchioles of the lung.
• It is an inhibitory influence on the respiratory
  center results in expiration. (as expiration
  proceeds, stretch receptors no longer stimulated)
  
• Infants
• Reflex plays a role in regulating basic rhythm of
  breathing and preventing overinflation of lungs
• Adults
• Reflex important only when tidal volume large as
  in exercise

10
Effect of Exercise on Ventilation

• Ventilation increases abruptly
• At onset of exercise
• Movement of limbs has strong influence (body
  movements stimulate proprioceptors in joints of
  the limbs)
• Learned component (after a period of training,
  the brain learns to match ventilation with the
  intensity of exercise)
• Ventilation increases gradually
• After immediate increase, gradual increase occurs
  (4-6 minutes it levels off)
• Anaerobic threshold highest level of exercise
  without causing significant change in blood pH.
  If exercise intensity is high enough to exceeded
  anaerobic threshold, lactic acid produced by
  skeletal muscles

11
Other Modifications of Ventilation

• Activation of touch, thermal and pain receptors
  affect respiratory center
• Sneeze reflex (initiated by irritants in the
  nasal cavity), cough reflex (initiated by
  irritants in the lungs)
• Increase in body temperature yields increase in
  ventilation

12
Respiratory Adaptations to Exercise

• Athletic training
• Vital capacity increases slightly residual
  volume decreases slightly
• At maximal exercise, tidal volume and minute
  ventilation increases
• Gas exchange between alveoli and blood increases
  at maximal exercise
• Alveolar ventilation increases
• Increased cardiovascular efficiency leads to
  greater blood flow through the lungs

13
Effects of Aging

• Vital capacity and maximum minute ventilation
  decrease (these changes are related to weakening
  of respiratory muscles decreased compliance of
  thoracic cage caused by stiffening of cartilage
  ribs)
• Residual volume and dead space increase
• Ability to remove mucus from respiratory
  passageways decreases
• Gas exchange across respiratory membrane is
  reduced