444- Regulation of respiration. Respiratory centre and breathing rhythm. Chemical control of respiration. Reflex control of respiration. Effects of the cerebral cortex on respiration.

Respiratory centre

The area from which nerve impulses are sent is located in the brainstem and is referred to as the respiratory center.

in medulla oblongata and pons.

It is divided into three major parts:

- sensory signals into the respiratory centre from peripheral chemoreceptors,

baroreceptors and all types of receptors in the lungs

- the basic rhythm of respiration is generated mainly in the dorsal respiratory centre

The respiratory center consists of groups of neurons in the brain stem that are functionally divided into

three areas:

1. The medullary rhythmicity area in the medulla oblongata.- controls basic rhythm of respiration

2. The pneumotaxic area in the pons- helps to coordinate the transition between inspiration and

expiration, limits inspiration so expiration takes place

3. The apneustic area in the pons- stimulates inspiratory area to prolong inspiration, thus inhibiting

expiration

Chemical control of respiration

- Central chemoreceptors - in the medulla oblongata, highly sensitive to blood

concentration of CO2.

• Located in the medulla oblongata.

• Highly sensitive to changes in the partial pressure of CO₂ (pCO₂).

• CO₂ diffuses into the cerebrospinal fluid (CSF) and forms carbonic acid (H₂CO₃).

• Carbonic acid dissociates into hydrogen ions (H⁺) and bicarbonate (HCO₃⁻).

• Increased H⁺ concentration stimulates the chemosensitive area in the medulla.

• This leads to an increase in respiratory rate and depth to expel excess CO₂.

resulting in a strong increase in respiratory centre activities.

- Peripheral chemoreceptors - in the aortic body and common carotid arteries, sensitive to

changes in CO2 and O2 levels in blood.

- This mechanism responds when blood O2 drops too low. chemoreceptors transmit

nervous signals to the brain to help regulate respiratory activity.

• Peripheral chemoreceptors are located in the aortic bodies (in the aortic arch) and carotid bodies (in the common carotid arteries).

• They are sensitive to changes in:

  • Low O₂ levels (hypoxemia)

  • High CO₂ levels (hypercapnia)

  • Low blood pH (acidosis, often due to CO₂ buildup)

🧠 Respiratory Response:

• When O₂ levels drop too low, the chemoreceptors send signals to the respiratory centers in the brainstem (mainly the medulla oblongata).

• This increases the rate and depth of breathing (ventilation), helping bring in more oxygen and remove excess CO₂.

❤ Cardiovascular Response:

• Chemoreceptors can also stimulate vasomotor centers in the medulla.

• This leads to increased sympathetic nervous system activity, which causes:

  • Increased heart rate (tachycardia)

  • Vasoconstriction

• These changes raise blood pressure and improve oxygen delivery to tissues by increasing cardiac output and speeding up oxygen transport.

Reflex control of respiration

•This reflex prevents over-inflation of the lungs during breathing.

• It involves stretch (baroreceptors) receptors located in the walls of the bronchi and bronchioles.

• When the lungs expand excessively during inspiration, these stretch receptors are activated.

• They send inhibitory signals via the vagus nerve to the dorsal respiratory group (DRG) and the pneumotaxic centre in the brainstem.

• This causes inhibition of further inspiration, helping to terminate the inspiratory phase and protect the lungs from damage.

Effects of the cerebral cortex on respiration

• respiration can be affected by higher brain conditions such as emotional state via limbic system, or

temperature via hypothalamus or free will.

• Voluntary or conscious control of respiration is provided via the cerebral cortex, although

chemoreceptors are capable of overriding it

Eventually, rising CO₂ levels will stimulate involuntary breathing if voluntary control is prolonged (e.g., after holding breath too long).