Chest & Upper Back : Human Anatomy
Spine
Stretching down the midline of the trunk from the base of the skull to the coccyx, the spine plays an extremely important role in our bodies as it supports the upper body’s weight; provides posture while allowing for movement and flexibility; and protects the spinal cord.
The spine, also known as the vertebral column or spinal column, is a column of 26 bones in an adult body – 24 separate vertebrae interspaced with cartilage, and then additionally the sacrum and coccyx Prior to adolescence, the spine consists of 33 bones because the sacrum’s five bones and the coccyx’s four do not fuse together until adolescence.
The vertebrae are named by the first letter of their region (cervical, thoracic, or lumbar) and with a number to indicate their position along the superior-inferior axis. For example, the fifth lumbar vertebra (which is most inferior one, located beneath the fourth lumbar vertebra) is called the L5 vertebra.
Each vertebra has several important parts: the body, vertebral foramen, spinous process, and transverse process.
- The body is the main weight-bearing region of a vertebra, making up the bulk of the bone’s mass.
- Extending from the body, the transverse processes are thin columns of bone that point out to the left and right sides of the body.
- The spinous process extends from the ends of the transverse processes in the posterior direction.
- Between the body, transverse processes and spinous process is thevertebral foramen, a hollow space that contains the spinal cord and meninges.
Between the vertebrae of the spine are thin regions of cartilage known as the intervertebral discs. Intervertebral discs are made of an outer shell known as the annulus fibrosus and a soft, pulpy region known as the nucleus pulposus in the middle.
- The annulus fibrosus is made of tough fibrocartilage that binds the vertebrae together but is flexible enough to allow for our movements.
- The inner nucleus pulposus acts as a shock absorber to support the body’s weight and prevent the vertebrae from painfully crashing into each other while under strain.
The vertebrae of the spine align so that their vertebral canals form a hollow, bony tube to protect the spinal cord from external damage and infection. Between the vertebrae are small spaces known as intervertebral canals that allow spinal nerves to exit the spinal cord and connect to the various regions of the body.
There are 5 major regions of the spine:- Cervical: The 7 vertebrae in the neck form the cervical region of the spine. Cervical vertebrae are the thinnest and most delicate vertebrae in the spine but offer great flexibility to the neck. The first cervical vertebra, C1, supports the skull and is named “atlas” after the Greek titan who held the Earth on his shoulders. The skull pivots on the atlas when moving up and down. The second cervical vertebra, C2, is also known as the “axis” because it allows the skull and atlas to rotate to the left and right.
- Thoracic: The 12 vertebrae in the chest region form the spine’s thoracic region. Thoracic vertebrae are larger and stronger than cervical vertebrae but are much less flexible. The spinous processes of the thoracic vertebrae point inferiorly to help lock the vertebrae together. A unique feature of the thoracic vertebrae is that each one forms joints with a pair of ribs to form the sturdy rib cage that protects the organs of the chest.
- Lumbar: The 5 vertebrae in the lower back form the lumbar region of the spine. Lumbar vertebrae are even larger and stronger than thoracic vertebrae, but are more flexible due to the lack of ribs in the lumbar region. All of the upper body’s weight bears down on the lumbar vertebrae, leading to many back problems in this region despite the size and strength of the vertebrae.
- Sacral: The sacral region of the spine contains only the sacrum, a single bone in the adult skeleton that is formed by the fusion of 5 smaller vertebrae during adolescence. The sacrum is a flat, triangular bone found in the lower back and wedged between the 2 hip bones.
- Coccygeal: The spine’s coccygeal region contains only the coccyx, a single bone in the adult skeleton that is formed by the fusion of 4 tiny vertebrae during adolescence. The coccyx is often referred to as the human tailbone, as this region is homologous to the tail bones of animals that have tails. In humans, the coccyx bears our body weight when sitting down and provides attachment points for muscles of the pelvic and gluteal regions. While most people have a coccyx made of 4 fused vertebrae, the coccyx may consist of as few as 3 or as many as 5 vertebrae. The length of the coccyx has no effect on the body’s function.
Anterior Longitudinal Ligament
The long green portions are Anterior Longitudinal Ligament
The anterior longitudinal ligament is a ligament that runs down the anterior surface of the spine. It traverses all of the vertebral bodies and intervertebral discs.
The ligament is thick and slightly more narrow over the vertebral bodies and thinner but slightly wider over the intervertebral discs which is much less pronounced than that seen in the posterior longitudinal ligament. The ligament actually has three layers: superficial, intermediate and deep. The superficial layer traverses 3 – 4 vertebrae, the intermediate layer covers 2 – 3 and the deep layer is only between individual vertebrae.
Intertransverse Ligaments
The intertransverse ligaments are ligaments that are placed between the transverse processes of the spine.
In the cervical region they consist of a few irregular, scattered fibers that are often replaced by muscles. In thethoracic region they are rounded cords intimately connected with the deep muscles of the back. In the lumbarregion they are thin and membranous.
#The intertransverse ligaments often blend with intertransverse muscles.
#The function of the intertransverse ligaments is to limit lateral flexion of the spine.
Posterior Ligament
The posterior ligament is a ligament of the foot located at the heel.
Radiate Ligaments
The radiate ligaments connect the front portion of the head of each rib with the side of the bodies of two vertebrae and the intervertebral fibrocartilage between them. The radiate sternocostal ligaments (sometimes called the sternocostal ligaments) are made up of broad and thin membranous bands that radiate from the ventral and dorsal surfaces of the sternal ends of the cartilages of the true ribs to the front and back surfaces of the sternum (breastbone).
Supraspinous Ligament
The supraspinous ligament, or supraspinal ligament, is a strong, fibrous cord that connects together the apices of the spinous processes of the seventh cervical vertebra to the sacrum; at the point of attachment to the tips of the spinous process, fibrocartilage is developed in the ligament. It is thicker and broader in the lumbar (lower back) than in the thoracic region (chest), and intimately blended, in both places, with the neighboring fascia (tissue).
Articular Capsule
An articular capsule (or joint capsule) is an envelope surrounding a synovial joint.
Each capsule consists of two layers:
On the inside of the capsule, articular cartilage covers the end surfaces of the bones that articulate within that joint.
The outer layer is highly innervated by the same nerves which perforate through the adjacent muscles associated with the joint.
Costal Cartilage
The costal cartilages are bars of hyaline cartilage which serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax. Costal cartilage is only found at the anterior ends of the ribs.
The first seven pairs are connected with the sternum; the next three are each articulated with the lower border of the cartilage of the preceding rib; the last two have pointed extremities, which end in the wall of the abdomen.
Like the ribs, the costal cartilages vary in their length, breadth, and direction.
They increase in length from the first to the seventh, then gradually decrease to the twelfth.
Their breadth, as well as that of the intervals between them, diminishes from the first to the last. They are broad at their attachments to the ribs, and taper toward their sternal extremities, excepting the first two, which are of the same breadth throughout, and the sixth, seventh, and eighth, which are enlarged where their margins are in contact.
They also vary in direction: the first descends a little, the second is horizontal, the third ascends slightly, while the others are angular, following the course of the ribs for a short distance, and then ascending to the sternum or preceding cartilage.
True Ribs
The first seven pairs of rib bones (beginning at the top of the sternum) are called "true ribs." They connect to the spine (by ligaments) at the back, and connect to the sternum by costal cartilage in the front. Costal cartilage is elastic and allows the ribcage to expand during respiration.
False Ribs
One of the last five pairs of ribs. A rib is said to be false if it does not attach to the sternum (the breastbone). The upper three false ribs connect to the costal cartilages of the ribs just above them. The last two false ribs usually have no ventral attachment to anchor them in front and so are called floating, fluctuating, or vertebral ribs.
Sternum
The sternum (from Greek στέρνον, sternon, "chest"; plural "sternums" or "sterna") or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax (chest). It connects to the rib bones via cartilage, forming the anterior section of the rib cage with them, and thus helps to protect the lungs, heart and major blood vessels from physical trauma. Although it is fused, the sternum can be sub-divided into three regions: the manubrium, the body, and the xiphoid process.
The sternum is an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. The superior end supports the clavicles (collarbones), and its margins articulate with the cartilages of the first seven pairs of ribs. Its top is also connected to the sternocleidomastoid muscle. It consists of three main parts, listed superior to inferior:
In its natural position, the inclination of the bone is oblique from above, downward and forward. It is slightly convex in front and concave behind; broad above, shaped like a "T", becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. Its average length in the adult is about 17 cm, and is rather longer in the male than in the female.
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