Breathing Anatomy
To understand how breathing can influence movement, we have to understand the anatomy and mechanics of breathing. On the surface, it seems like a simple task. Our chest expands as we breathe in, and contracts as we breathe out. But to really understand it, we have to look a little bit deeper.
We will start at our thorax, where we have 12 vertebrae with 12 associated ribs that will combine to cartilage along the front of our body joining at our sternum. Within our thorax we have two lungs, but they are not created equal. Our right lung has three lobes, and our left has two. This is largely because your heart sits towards the left side of your chest (in what is called your pericardial cavity). Our mouth and airway combine to our trachea, which divides into our left and right bronchi, which will further divide into smaller and smaller divisions until they form tiny air sacs called alveoli, where gas exchange actually occurs. Looking at it as a whole, it looks like an upside down tree.
Next, we have to understand how we move air. It starts with the primary muscles of respiration (breathing): your diaphragm; intercostal muscles; scalenes, and; abdominals. Your diaphragm is a dome or umbrella shaped muscle that attaches from your lumbar spine to your lower ribs (ribs 7-12). Like your lungs, your diaphragm is asymmetrical. The right half of your diaphragm is more domed while the left is flatter. This is partly because we have a 3 pound liver sitting below our right diaphragm pushing it upward, and because our heart is sitting on top of our left diaphragm, pushing it downward (we will dive more into this asymmetry in a later post). Our intercostal muscles are small bands of muscles that go in between each rib from front to back, and they help to raise or lower each rib (depending on which intercostal muscle we are talking about). Our scalenes are a group of three muscles that attach from our cervical spine, to our first and second ribs. Our abdominal muscles (rectus abdominis, internal and external obliques, and transverse abdominus) attach from our lower rib cage and sternum, to our pelvis. These are the muscles that will primarily move our rib cage, although any muscle that is attached to our rib cage (and some that are not) can assist with moving our rib cage if needed.
During inspiration, our diaphragm contracts and the dome of our diaphragm descends. This presses down onto our internal organs and raises our ribs. As it does this, our abdominal muscles contract slightly to make sure that our organs don’t go forward and out. This is a key point: your diaphragm has to have something to push against in order to work correctly. Your abdominals make sure that things stay in place to allow your diaphragm to push against that something. As the breath continues and our ribs continue to raise, our intercostal muscle will contract to further raise our ribs, and if the breath is deep enough our scalenes will contract to lift our upper rib cage. As our ribs expand, our lungs expand as well and this pulls air into our lungs.
During passive exhalation our diaphragm and intercostal muscle will relax, and the tension through our thorax and associated muscles will return our rib cage to its starting position and push air out. During forceful exhalation,the same action occurs but our abdominal muscles are going to actively engage to “push” the air out faster so that we can expel waste products and get to the next breath sooner.
So there you have it. One full breath cycle and the muscles and structures that have allowed us to do that. In the next post we will talk about what happens to that air that is going into and out of our lungs because that is what really matters.