How the Lungs Work How Your Body Controls Breathing

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The body’s muscles and nervous system help control your breathing. 

The lungs are like sponges; they cannot get bigger on their own. Muscles in your chest and abdomen tighten or contract to create a slight vacuum around the lungs. This causes air to flow in. When you exhale, the muscles relax and the lungs deflate on their own, much like an elastic balloon will deflate if left open to the air. 

Your breathing muscles include:  

• The diaphragm: This dome-shaped muscle below your lungs separates the chest cavity from the abdominal cavity. The diaphragm is the main muscle used for breathing. 
• The muscles between your ribs: Called intercostal muscles, these muscles play a role in breathing during physical activity. 
• Abdominal muscles: You use these muscles to help you breathe out when you are breathing fast, such as during physical activity. 
• The muscles of the face, mouth, and pharynx: These control the lips, tongue, soft palate, and other structures to help with breathing. The pharynx is the part of the throat right behind the mouth. Problems with any of these muscles can narrow the airway, make it more difficult to breathe, and contribute to sleep apnea. 
• Muscles in the neck and collarbone area: You use these muscles to help you breathe in. 

Damage to the nerves in the upper spinal cord can interfere with the movement of your diaphragm and other muscles in your chest, neck, and abdomen. This can happen due to a spinal cord injury, a stroke, or a degenerative disease that affects the muscles, such as muscular dystrophy that causes muscle weakness or muscle loss. The damage can cause respiratory failure. Ventilator support or oxygen therapy may be necessary to maintain oxygen levels in the body and protect the organs from damage. 

Your breathing usually does not require any thought, because it is controlled by the autonomic nervous system, also called the involuntary nervous system. 

• The  parasympathetic system  slows your breathing rate. It causes your bronchial tubes to narrow and the pulmonary blood vessels to widen. 
• The  sympathetic system  increases your breathing rate. It makes your bronchial tubes widen and the pulmonary blood vessels narrow. 

Your breathing changes depending on how active you are and the condition of the air around you. For example, you need to breathe more often when you do physical activity. At times, you can control your breathing pattern, such as when you hold your breath or sing. 

To help adjust your breathing to changing needs, your body has sensors that send signals to the breathing centers in the brain. 

• Sensors in the airways detect lung irritants. The sensors can trigger sneezing or coughing. In people who have asthma, the sensors may cause the muscles around the airways in the lungs to contract. This makes the airways smaller. 
• Sensors in the brain and near blood vessels detect carbon dioxide and oxygen levels in your blood. 
• Sensors in your joints and muscles detect the movement of your arms or legs. These sensors may play a role in increasing your breathing rate when you are physically active. 

In central sleep apnea, the brain temporarily stops sending signals to the muscles needed to breathe.