Gwen Kennedy, Kia Witt, and Nicole Larson 19.4 Control of Breathing Gwen Kennedy, Kia Witt, and Nicole Larson

Respiratory Areas -groups of neurons in the brainstem which controls breathing -initiate impulses that travel on cranial and spinal nerves to breathing muscle. This causes inspiration and expiration -adjusts the rate and depth of breathing to meet cellular requirements for supply of oxygen and removal of carbon dioxide. Even during physical exercise -located throughout the pons and medulla oblongata

Respiratory Areas Medullary Respiratory Center -includes two bilateral group of neurons that extend throughout the length of the medulla oblongata 1. Ventral Respiratory Group -conducts the basic rhythm of breathing -maintains inspiration and expiration 2. Dorsal Respiratory Group -stimulates the inspiratory muscles, primarily the diaphragm -helps process sensory information related to the respiratory system. This can play a role in cardiopulmonary reflexes that affect respiratory rhythm

Partial Pressure -amount of pressure each gas contributes -gas molecules from the air may enter, or dissolve in liquid -partial pressure of a gas dissolved in a liquid equals the partial pressure of that gas in the air with which the liquid has equilibrated Factors Affecting Breathing -degree to which lung tissues are stretched -emotional state -level of physical activity -PO2 and PCO2 in body fluids

Factors Affecting Breathing -under normal circumstances, the main control of respiratory activity is NOT the level of oxygen in the blood -most blood oxygen is carried bound to the hemoglobin molecules in red blood cells -this large excess of oxygen “frees up” respiratory control from responding to blood oxygen levels -respiratory system responds to blood PCO2 and H+ concentration

Factors Affecting Breathing -chemoreceptors respond to PO2 and PCO2 1. Central Chemoreceptors -monitor the pH of the brain -located in the ventral portion of the medulla oblongata -responds to changes in blood pH, but only indirectly. H+ do not easily cross the blood-brain barrier, therefore do not have access to this area -CO2 can cross the blood-brain barrier -if PCO2 rises, CO2 diffuses into brain, combines with H2O to form H2CO3 CO2 + H2O  H2CO3

Factors Affecting Breathing 1. Central Chemoreceptors -H2CO3 ionizes, releasing H+ and HCO3- H2CO3  H+ + HCO3- -respond to the released H+ -breathing rate and tidal volume increase when a person inhales air rich in CO2 2. Peripheral Chemoreceptors -primarily sense changes in the blood -carotid and aortic bodies  walls of the carotid sinuses and aortic arch

Factors Affecting Breathing 2. Peripheral Chemoreceptors -well positioned to monitor oxygen that will reach the brain and the rest of the body -decreasing PO2 stimulates peripheral receptors, send impulses to respiratory center, breathing rate and tidal volume rises, increasing alveolar ventilation -changes in blood pH stimulates carotid and aortic bodies

Factors Affecting Breathing 2. Peripheral Chemoreceptors Example -lactic acid production may threaten to lower pH -if this occurs, peripheral chemoreceptors signal respiratory centers to increase alveolar ventilation -stimulating respiratory centers to exhale more CO2, stabilizing blood pH in the presence of excess lactic acid -kidneys eliminate the extra H+ and blood CO2 returns to normal

Chef  diaphragm muscles Bouillon CO2 Water O2 Rat Central Chemoreceptor Stew blood Straw blood-brain barrier Probe Peripheral Chemoreceptor Hair nerves

Factors Affecting Breathing 3. Inflation Reflex (Hering-Breuer reflex) -helps regulate the depth of breathing -occurs when stretch receptors in the visceral pleura, bronchioles, and alveoli are stimulated as lung tissues are stretched -emotional upset or strong sensory stimulation may alter the normal breathing pattern -gasping and rapid breathing are familiar responses to fear, shock, or even stepping into a cold shower -we can alter our breathing pattern consciously or stop it for a short time

Rx - Sleep Apnea -condition that causes one to momentarily stop breathing while asleep -obstructive sleep apnea (most common) is caused by the relaxation of the throat and tongue tissue, blocking the airway -central sleep apnea (less common) is caused by a problem in the respiratory control centers

Rx - Sudden Infant Death Syndrome -condition in which an otherwise healthy infant less than one years of age dies unexpectedly -can only be ruled SIDS after an autopsy determines no apparent cause of death -majority of cases occur while the baby is asleep -may occur because of a problem with a baby’s respiratory control centers

Rx - Hyperventilation -rapid, deep breathing that lowers the blood CO2 concentration below normal -after hyperventilation, it takes longer for blood CO2 concentration to override the conscious effort for breath control; can allow a person to hold their breath for longer -can also occur in times of emotional distress -can cause dizziness or fainting by lowering CO2 concentration which increases blood pH and causes vasoconstriction of blood vessels in the brain, resulting in loss of consciousness

Rx – COPD (Chronic Obstructive Pulmonary Disease -group of lung diseases that block airflow and make it difficult to breathe -caused by a long-term exposure to irritating gases or particulate matter….cigarette smoke -people with COPD are at an increased risk of developing heart disease, lung cancer and other similar conditions

Midbrain Fourth Ventricle Pontine respiratory Group Pons Medulla Oblongata Medullary Respiratory Center Ventral Respiratory Group Dorsal Respiratory Group Internal (expiratory) intercostal muscles External (inspiratory) intercostal muscles Diaphragm