Anatomy and Physiology II: Control of Respiration

Anatomy and Physiology II: Control of Respiration

• The respiratory center is located bilaterally in the medulla and pons.
• Three major centers regulate respiration: dorsal respiratory center, ventral respiratory center, and pneumotaxic center.
• The dorsal respiratory center controls inspiration.
• The ventral respiratory center controls both inspiration and expiration.
• The pneumotaxic center controls breathing rate and pattern.

Subtopics and Learning Outcomes

• Subtopic: Physiology of the respiratory system
• Learning Outcomes:
  • Describe the role of the respiratory center in respiration.
  • Explain the regulations of the respiratory center.
  • Discuss the nervous control on smooth muscle of the lungs.

Respiratory Center: Medullary Rhythmicity Area

• The function of the medullary rhythmicity area is to control the basic rhythm of respiration.
• During quiet breathing, inhalation lasts about 2 seconds and exhalation lasts about 3 seconds.
• Nerve impulses generated in the inspiratory area establish the basic breathing rhythm.
• The inspiratory area is active for about 2 seconds.
• The inspiratory area becomes inactive and the diaphragm and external intercostal muscles relax, causing exhalation for about 3 seconds.
• The cycle repeats.

Respiratory Center: Pneumotaxic Area

• The pneumotaxic area transmits inhibitory impulses to the inspiratory area.
• These impulses help turn off the inspiratory area before the lungs become overly full.
• The impulses shorten the duration of inhalation.
• Increased activity in the pneumotaxic area results in a more rapid breathing rate.

Respiratory Center: Apneustic Area

• This area sends stimulatory impulses to the inspiratory area to prolong inhalation.
• The result is a long, deep inhalation.
• When the pneumotaxic area is active, it overrides signals from the apneustic area.

Nerves Used in Respiration

• Phrenic nerves: Stimulate the diaphragm's activity.
• Vagus nerve: Innervates the diaphragm, larynx, and pharynx; provides parasympathetic stimulation for the heart and digestive system.
• Posterior thoracic nerves: Stimulate intercostal muscles. They're somatic nerves.

Regulation of Respiratory Center

• The basic rhythm of respiration is set and coordinated by the inspiratory area.
• This rhythm can be modified by inputs from other brain regions, peripheral nervous system receptors, and other factors.
• It is controlled by:
  • Cortical influences
  • Chemoreceptor regulation
  • Proprioceptor regulation
  • Inhalation reflex

Cortical Influences on Respiration

• The cerebral cortex has connections with the respiratory center.
• This allows for voluntary control over breathing patterns.
• We can voluntarily alter our breathing rate and pattern.
• We can even refuse to breathe for a short time.
• Voluntary control protects against water or irritating gases entering the lungs.

Chemoreceptor Regulation of Respiration

• Chemoreceptors monitor CO2, H+, and O2 levels, providing input to the respiratory center.
• Central chemoreceptors: Located in the medulla oblongata; respond to changes in H+ concentration or pCO2 in cerebrospinal fluid.
• Peripheral chemoreceptors: Located in the aortic and carotid bodies; respond to large decreases in arterial O2, respond to changes in H+, pCO2, or both, in the blood.
• CO2 diffuses into cells and combines with water to form carbonic acid. This breaks down into H+ and HCO3-.
• An increase in CO2 results in an increase in H+, and a decrease in CO2 results in a decrease in H+.

Proprioceptor Stimulation of Respiration

• Proprioceptors in muscles and joints are stimulated by exercise or pain.
• They send nerve impulses to the inspiratory area of the medulla oblongata, increasing respiratory effort.

The Inhalation Reflex

• Stretch-sensitive receptors (baroreceptors) in the bronchi and bronchioles respond to lung stretch during over-inflation.
• This triggers the vagus nerves to inhibit the inspiratory and apneustic areas, causing exhalation.
• The reflex prevents excessive lung inflation.

Other Influences on Respiration

• Limbic system stimulation: Anticipation of activity or emotional anxiety can increase breathing rate and depth.
• Temperature: Increased body temperature (fever, exercise) increases respiration rate.
• Pain: Sudden pain can cause brief apnea (cessation of breathing). Prolonged pain increases the rate of breathing.
• Stretching anal sphincter: Increases respiratory rate, sometimes used to stimulate in newborns or those who've stopped breathing.
• Irritation of airways: Coughing and sneezing occur in response to physical or chemical irritation of the pharynx or larynx causing temporary cessation of breathing.
• Blood pressure: Changes in blood pressure have a small but notable effect on the respiration rate : increased blood pressure decreases respiration rate, decreased blood pressure increases respiration rate.

Nervous Control on Smooth Muscle of the Lungs

• Exercise and the sympathetic branch of the autonomic nervous system cause the adrenal medulla to release epinephrine/norepinephrine, resulting in bronchodilation (relaxation of bronchiole smooth muscle).
• Lung ventilation is improved due to increased air reaching the alveoli.
• The parasympathetic branch and substances such as histamine cause bronchoconstriction (contraction of bronchiole smooth muscle).