Rhythmogenesis of breathing

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Respiratory movements are controlled by the rhythmic activity of respiratory neurons in the medulla oblongata (elongated medulla). The course of rhythmogenesis is autonomous. However, it must be adapted to the needs of the organism (modification when working, speaking, swallowing, coughing, sneezing, etc.). The respiratory neurons receive information from peripheral receptors (sensors) and central structures.

  • Phases of respiratory control:
    • Inspirational phase:
      • The inhalation muscles are made to contract by nerve impulses.
    • Post-inspiration phase:
      • The neuronal activation of the inhalation muscles decreases. This enables passive exhalation.
    • Active expiratory phase:
      • In this phase the exhalation muscles are activated.

Respiratory rate

Breathing movements occur during the resting phase with a frequency of 10–20 breaths per minute. A breathing cycle lasts about 3–6 seconds. The inhalation phase takes 1–2.5 seconds and the exhalation phase 2–3.5 seconds.

Respiratory neurons

The breathing rhythm is created in a neural network of the medulla oblongata . These neurons are arranged as a ventral respiratory group (VRG) along the nucleus ambiguus .

Three neuron classes are connected here:

  • I neurons ( inspiratory neurons ):
    • They fire during the inhalation phase. According to the time of their activity, there are four types.
      • 1. Ramp I neurons
        • They fire throughout inspiration. Your activity grows "ramp-like".
      • 2. Pre-I neurons:
        • They fire just before and at the beginning of the inspiration.
      • 3. Early I neurons:
        • They fire during early inspiration.
      • 4. Late I neurons
        • They fire in the late stage of inspiration
  • PI neurons ( post-inspiratory neurons ):
    • You are active during the passive exhalation phase.
  • E neurons ( expiratory neurons ):
    • You discharge during the active exhalation phase.

Rhythmic activity

The ventral respiratory group (VRG) is driven by the spontaneously active reticular formation .

Disorders of the breathing rhythm

Disturbances occur with heart failure , pulmonary edema , fever , processes in the brain stem and with mental illnesses.

Kussmaul breathing
Deepened and accelerated breathing; first sign of acidosis (disturbance of the acid-base balance of the body, e.g. with coma diabeticum or kidney failure )
Cheyne-Stokes breathing
Periodic increase and decrease in breathing movements; to a lesser extent this is normal during sleep and while staying at high altitude. If it occurs more frequently, this can be an indication of the presence of a heart disease. Such a breathing disorder can also occur in the case of a stroke or poisoning (e.g. opiates ).
Flat breathing
Regular flattened breathing can be observed with concussion and demyelinating diseases .
Biot - or atactic breathing
Irregular breathing with periodic interruptions. Occurrence in brain injuries in the area of ​​the brain stem , meningitis and increased intracranial pressure
Apnea periods
Brief cessation of breathing;

In newborns this is physiological. Long-lasting dropouts can indicate a lack of energy supply to the brain stem , immature or pathological control mechanisms.

Gasping
Only occasional breathing movements. Serious sign of disorders in the respiratory network

inhalation

During inhalation, the activity of the Nn increases. phrenici and Nn. intercostales externi . This causes the diaphragm to contract and thus lower the dome of the diaphragm . At the same time, the external intercostal muscles expand the chest .

Post-inspiration

As soon as the contraction of the inspiratory intercostal muscles subsides, the exhalation phase begins. This begins passively. Now the glottis are narrowed. This is done by increasing the activation of the adductors of the larynx . The following muscles are involved:

Due to the narrowing of the air flow is slowed down during expiration and can by means of the vocal cords to the articulation ( phonation are used).

Active exhalation

The contraction of the expiratory intercostal muscles (Mm. Intercostalis interni) and the expiratory abdominal and lumbar muscles (Mm. Transversus and obliquus abdominis and M. quadratus lumborum) increases the pressure in the abdomen. This causes the dome of the diaphragm to rise . The resulting air flow is stronger and therefore more difficult to control. These muscle groups are rarely used when resting. If there is superficial rapid breathing (panting), the breathing rhythm consists of two phases of inspiration and post-inspiration.

Respiratory network

The breathing rhythm is created in the ventral respiratory group (VRG) of the medulla oblongata . Along the Nucl. ambiguus , the VRG forms a column of tissue. The breathing center is located in the Pre-Bötzinger complex . This is where the basic activity of the bronchial muscles occurs.

Network interconnection

The respiratory network is activated by inflows from the reticular activating system from the reticular formation . Connections to other respiratory neurons lead to excitatory and inhibitory postsynaptic potentials. In this way a periodic oscillation of the membrane potential develops .

The I-neurons, PI-neurons and E-neurons are connected downstream of the primary network. Some neurons have both inspiratory and post-inspiratory properties.

literature