An Exploration Of The Ribcage
Our ribcage is a critically important structure in our body. Its protective role is likely obvious as it covers some of our vital organs. Our heart and lungs, the organs for two of our most essential functions, breathing and blood circulation, are found in the thorax and protected by our ribcage. But did you know that the ribs are also one of the places where red blood cells are produced in our body? In this article, we’ll explore the structure and function of the ribcage. Keep reading to learn more!
What structures make up the ribcage?
The ribcage makes up the bony container of our thorax, the section of our body above the abdomen, which our shoulder girdle rests on. There are multiple bones and a large number of muscles that cross our thorax at some point.
Bones
Twelve pairs of rib bones come together to create our ribcage. Each rib is composed of a bony section and a cartilaginous section, called the costal cartilage. More specifically, the bony portion of each rib includes several key sections:
- Rib head
- One or two articular facets
- Tubercle
- Neck
- Costal groove
The rib head is the end that connects with the spine and articulates with the vertebrae. The specific places on the rib bone where that connection to the vertebrae happens are called the articular facets. Most of the ribs have two articular facets. However, the first rib only has one. Each rib also has a tubercle, a bony protuberance where the costotransverse ligament attaches.
The rib neck is the section of the rib between the head and the tubercle. The length of the rib neck varies from rib to rib, and the eleventh and twelfth ribs do not have a neck at all. From the tubercle to the cartilaginous section is the main body of each rib. It’s called the rib shaft. Finally, each rib has a groove present along the bone called the costal groove. This is where the neurovascular bundle runs.
Types of rib connections
While the rib bones share many similarities, there are also a few differences between them. They are often grouped according to those differences. Based on the type of their connection to the sternum, the ribs are often grouped into true ribs, false ribs, and floating ribs. True ribs include ribs one through seven. They’re called true ribs because they connect directly to the sternum via an individual piece of costal cartilage.
Ribs eight through ten are called false ribs because their costal cartilage doesn’t connect directly to the sternum. Instead, the costal cartilage for each of these ribs connects to the costal cartilage for rib seven, which then indirectly connects those ribs to the sternum. Finally, ribs eleven and twelve are called floating ribs because they don’t attach to the sternum or any other bone on the ventral side of our body.
To form our ribcage, the rib bones attach to the spine on the dorsal (back) side of our body. And, with the exception of the floating ribs, the ribs attach to our sternum on the ventral side of our body. Our sternum has three main sections: the manubrium at the top, the body in the middle, and the small, pointy xiphoid process at the bottom.
Ribs one and two attach to the manubrium of the sternum. Ribs three through seven attach to the body of the sternum via their costal cartilage. Ribs eight, nine, and ten attach to a common costal cartilage that then attaches to the costal cartilage of rib seven to indirectly attach these ribs to the body of the sternum. The last two ribs, eleven and twelve, don’t attach to the sternum. Although the spine is not part of the ribcage, per se, it’s where each of the ribs attaches at their posterior end.
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Other important bones
Additionally, there are a couple of bones that have a particularly important relationship to the position of the ribcage. Those are the scapula and the clavicle. The scapula floats in a sea of muscle and connective tissue on the back of the ribcage. It does not have a true articulation with the ribcage, but the position of the ribcage is so influential on scapular position that sometimes that indirect connection is referred to as the scapulothoracic joint.
The clavicle is situated just a little superior and superficial to the first rib. It can articulate at a small connection with the first rib. It also articulates with the sternum at the sternoclavicular joint. In that way, movement at the clavicle is indirectly influenced by movement of the ribcage.
Joints in the ribcage
Several important types of joints allow the ribcage to have the kind of movement necessary for it to complete all of its functions. On our back, the ribs articulate with the vertebrae of the spine through costovertebral joints. The costovertebral joint is where the rib head articulates with the body of a vertebra above, the body of a vertebra below, and the vertebral disc in between those vertebrae. The exception to this is the first rib, which only attaches to one vertebra, T1.
On the front side, ribs one through seven articulate with the sternum at joints called sternocostal joints. Additionally, the first rib can articulate with the clavicle at a joint called the costoclavicular joint. Ribs eight, nine, and ten connect via cartilage with the seventh costal cartilage at what is called a costochondral joint. And of course, ribs eleven and twelve don’t attach onto anything on the front of our body, hence the term “floating ribs.”
Muscles that connect to the ribcage
Because the ribcage is so centrally located and is part of relating the pelvis below to the head above, many, many muscles attach to some point on the ribcage. However, some are more strongly related to the movement of the ribcage than others.
The muscles that are part of moving the ribcage in breathing include:
- Diaphragm
- Internal and external intercostals
- Levatores costarum
- Subcostales
- Innermost intercostals
- Scalenes
- Transversus thoracis
- Serratus posterior superior
- Serratus posterior inferior
Some of these are tiny deep muscles that make only a small contribution to the movement of the ribcage during breathing, so you may not have heard of them.
Other muscles that have a connection to the ribcage include:
- Subclavius
- Serratus anterior
- Deep spinal muscles
- Erector spinae
- Quadratus lumborum
- External and internal obliques
- Pectoralis minor
- Pectoralis major
- Rectus abdominis
- Latissimus dorsi
Functions of the ribcage
The ribs can also be grouped based on the other structures in the body that they’re connected to and most affected by. Tom Myers of Anatomy Trains groups the ribs into two neck ribs, three chest ribs, four abdominal ribs, and three pelvic ribs. Grouping the ribs in this way can give us a different perspective on the protective function of each section and how each section is affected by the movement of other connected structures and/or organs.
The scalene muscles attach to the first and second ribs, the neck ribs, so those ribs are affected by neck movement. The chest ribs, ribs three, four, and five, house our heart and lungs. Those ribs are in a relationship to those organs. The abdominal ribs, ribs six, seven, eight, and nine, shelter several organs, including our liver, pancreas, and stomach. This is also where our diaphragm is found. Finally, our pelvic ribs, ribs ten, eleven, and twelve, help protect our kidneys and adrenal glands.
Movement
The ribs articulate with the spine to allow a certain amount of movement. If those joints didn’t allow any movement at all, we would be more fragile and prone to injury and issues. Instead, we have a certain amount of movement at those joints that allows for more resiliency. We can do a certain amount of flexion/extension, side bending, and rotation (twisting) with our spine, and our ribs follow along with these movements until either the ribs themselves or the vertebrae bump into each other.
Protection and red blood cell production
Protection is one key function of our ribcage. It helps protect our heart, lungs, liver, pancreas, stomach, and kidneys, as well as the network of connective tissue and neurovascular connections between them. But, while the protective function of the ribcage might be familiar to you, our ribcage also has other roles to play. As adults, the flat bones of our ribcage are a significant location for the production of red blood cells.
Breathing
Probably the most significant function that our ribcage has its association with breathing. The movements of our ribcage are essential for making space for our breath and for creating the change in pressure that draws air in and pushes it out. The ribs do somewhat more specialized movements when we breathe. There are two main motions that happen at our rib cage that allow it to expand in three dimensions, up and out in the front and back, and out laterally from the sides. Those motions have names that describe the movements.
More space is created in our ribcage in the mediolateral direction when we experience what is called bucket-handle motion of the ribs during breathing. You could imagine that it looks something like the motion of a bucket handle going from a resting position against the bucket to a lifted position. That motion happens primarily at ribs seven through ten. The upper ribs also do what is referred to as a pump-handle motion. This movement is our ribcage expanding up and out from the front and back, like the motion of a pump handle from resting to lifted. In addition to the function of breathing itself, movement of the ribs during breathing results in small movements of the spine, which help hydrate our vertebral discs.