Rib Cage

The rib cage in terms of vertebrate anatomy is a basketlike skeletal structure that forms the chest, or thorax, and is made up of the ribs and their corresponding attachments to the breastbone or the sternum and the vertebral column. The rib cage surrounds the lungs and the heart that serves as an important means of bony protection for these vital organs. 

Rib Cage Information

Ribs are described depending on the location and the connection with the breastbone. All ribs present are attached to the thoracic vertebrae posteriorly and are numbered accordingly from one to twelve. Ribs that joined directly with the breastbone are called true ribs, whereas those that are not connected directly are termed false ribs. The false ribs include the floating ribs that are not attached to the sternum at all.

Total ribs in human body consist of the 12 thoracic vertebrae and the 24 ribs, in addition to the breastbone or sternum. With each succeeding rib, from the uppermost, the curvature of the rib cage has vast opening. The rib cage is semi rigid but can be expanded to have ability to increase in size. The small joints that are present between the ribs and the vertebrae can permit a gliding motion of the ribs on the vertebrae while breathing and during other activities.

• The rib pairs that are directly or indirectly attached to the sternum describe the terms true ribs and false ribs.

• The first seven rib pairs are known as the fixed or vertebrosternal ribs that are the true ribs as they are connected directly to the sternum; the next five pairs (eighth to twelfth) are the false ribs. 

• The false ribs include both vertebral ribs and vertebrochondral ribs. That consists of three pairs of vertebrochondral ribs (eighth to tenth) that connect indirectly to the sternum via the costal cartilages of the ribs above them.

Parts of the Rib Cage

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• Each of the ribs consists of a neck, head, and shaft. 

• All the ribs are attached to the thoracic vertebrae posteriorly. All the numbers are matched to the vertebrae they are from one to twelve, from the top to the bottom. 

• The head of the rib is the end part that is closer to the vertebra with which it articulates. 

• The neck is the flattened part that extends from the head laterally. 

• The neck is about 3 cm long. Its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface is rough that provides attachment to the ligament of the neck. 

• The upper border represents a rough crest for the attachment of the anterior costotransverse ligament and the lower border is rounded.

• On the posterior surface at the neck are the tubercles that consist of an articular and a non-articular portion. 

• The lower one is the articular portion which is more medial and presents a small and oval surface for the articulation with the transverse costal facet that is present to the end of the transverse process of the lower of the two vertebrae that are connected to the head. 

• The non-articular portion is a rough elevation which provides attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper ribs than in the lower ribs.

• The angle of a rib also called coastal angle and a prominent line in this area is a little in front of the tubercle. 

• The prominent line is directed downward and laterally that provides attachment to a tendon of the iliocostalis muscle. At this point, the rib is twisted on its long axis and is bent in two directions.

• The distance present from the second to the tenth ribs in between the angle and the tubercle is greater. The area present in between the angle and the tubercle is rounded, rough, and irregular, and provides attachment to the longissimus Dorsi muscle.

Ribcage: Bones

The first rib is broad and flat and is the most curved one and the shortest of all the ribsit, its surfaces are to the upward and downward, and its borders are to the inward and outward.

The second rib is the second uppermost rib in humans or the second most frontal rib in that animals that walk on four limbs. The second rib is defined as a true rib in humans as it is connected with the sternum in between the costal cartilage anteriorly. The second rib is connected posteriorly with the vertebral column by the second thoracic vertebra. The second rib has a very similar curvature and much longer than the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex and looks upward and outward; near the middle of it is a rough eminence for the origin of the lower part of the first and posterior scalene is attached behind and above this. The internal surface is smooth, concave and is directed downward and a little inward: on its posterior part there is a short coastal groove between the ridge of the internal surface and inferior border of the rib. Second rib protects the intercostal space that includes the intercostal veins, intercostal arteries, and intercostal nerves.

The ninth rib is at the same level as that of the first lumbar vertebra in the front part. This level is called the transpyloric plane.

The tenth rib attaches directly to the body of the T10 vertebra. Due to the direct attachment, vertebra T10 has a complete costal facet on its body.

The eleventh and twelfth ribs are called the floating ribs that have a single articular facet on the head, which is of rather large size. They have no necks or tubercles and are pointed at their anterior ends. The eleventh rib has a slight angle and a shallow coastal groove where it lacks in the twelfth rib. The twelfth rib is much shorter than the eleventh rib, and the head is inclined downwards.

Function:

The human rib cage acts as a component of the human respiratory system. It encloses the thoracic cavity that contains the lungs. An inhalation occurs when the muscular diaphragm present at the floor of the thoracic cavity contracts and flattens, while the contraction of intercostal muscles lifts the rib cage up and out.

The expansion of the thoracic cavity is driven in three planes they are:

• The vertical

• The anteroposterior

• The transverse

The vertical plane is extended by the help of the contracting diaphragm and the abdominal muscles relaxs to accommodate the downward pressure that is supplied to the abdominal viscera by the contracting diaphragm. The greater extension can be achieved by the diaphragm itself moving down rather than flattening of domes. The second plane is expanded by a movement known as the 'pump handle’ to the anteroposterior region.

The circumference of the normal adult human rib cage during inhalation expands by 3 to 5 cm.