All muscles of the respiration
Inhalation muscles (inspiration muscles) Exhalation muscles (expiration muscles)
- Diaphragm (diaphragm) = most important breathing muscle
- Musculi intercostales externi (external intercostal muscles)
- Musculi levatores costarum (rib lifter)
- Scalene muscle
- Serratus posterior superior muscle
- Musculus serratus anterior (front saw muscle)
- Musculus rectus abdominis (straight abdominal muscle)
- Musculi intercostales interni et intimi (internal intercostal muscles)
- Abdominal Muscles
- Posterior inferior serratus muscle
- Musculus retractor costae
- Transversus thoracis muscle
- Subcostal muscle
- Chest wall
- Dermal artery (aorta)
- Superior vena cava
The bronchial musculature has a kind of control function for the distribution of breathing air to the individual sections. It is usually arranged spirally around the airways and is particularly numerous in the small and medium-sized bronchi. This makes sense because the walls have less cartilage with increasing distance from the neck and thus their diameter can be changed much more strongly by contractions.
In the bronchial tubes, where a lot of air is supposed to enter, the muscles relax and the diameter of the bronchi widens. In the opposite case, tensing of the muscles results in a reduced diameter and thus less ventilation of the lung section. The bronchial muscles play a greater, though not necessarily intended, role when breathing out.
If the musculature is tense and thus the diameter of the bronchial tube is narrow, it is possible that not enough air can escape from the alveoli during the phase of exhalation. Now during the next inhalation, more air is added, which cannot flow out sufficiently during the next breath. This mechanism is called obstructive (=occlusive) lung dysfunction.
In the long run, the affected alveoli literally empty out – in this case it is called pulmonary emphysema. Now one can of course ask oneself why during inhalation more air enters the lungs than can escape during exhalation. The reason is the following: During inhalation, there is negative pressure in the lungs, which naturally also expands the bronchial tubes.
Exhalation is triggered by an overpressure in the lungs – this overpressure also compresses the airways. The bronchial musculature is of the so-called smooth muscle type. This means that it works without conscious control but receives its impulses from the vegetative (autonomous) nervous system.
The two parts of the vegetative nervous system (sympathetic nervous system (short: sympathetic nervous system) – parasympathetic nervous system (short: parasympathetic nervous system)) have a nonsensical effect. As is the case with all connections between nerves and muscles, the respective effect at the muscle is mediated by proteins of the cell membrane (receptors), which can convert the signal of the nerves into muscle excitation or relaxation by changing their shape. During stress and physical work, the sympathetic nervous system sends a signal for relaxation of the bronchial musculature and thus for a widening of the airways (bronchodilatation).
This is mediated by so-called beta-2 receptors, which are located on the cell membrane of the muscle cells. In cases of shortness of breath (dyspnoea), caused by increased tension of the bronchial muscles, special drugs (beta-2 sympathomimetics) are given which lead to an alleviation of the symptoms, as they imitate the effect of the sympathetic nervous system on the receptors (mimetic = imitate). The parasympathetic nervous system, which is active during rest and sleep, leads to muscle tension and thus to a narrowing of the airways (bronchoconstriction).
There are other substances that can cause bronchial muscle tension, the most important being histamine. This histamine is secreted by special defence cells (so-called mast cells) in the course of an allergic reaction. The amount of histamine is usually so large that the muscles tense up. This makes breathing dangerously difficult for the patient. This condition is known as an asthmatic attack (asthma attack).