INTERCOSTAL SPACES

The intercostal space is the space lying between two costae (ribs and their costal cartilages) there are about 11 intercostal space and they contain.

1.                 Intercostal muscles.

2.                 Intercostal nerve, artery, and vein.

3.                 Lymphatic vessel.

INTERCOSTAL MUSCLES:

Are made up of layers:

1.                 An External layer which comprises the external intercostal muscle and membrane.

2.                 A middle layer made up of internal intercostal muscle and its membrane.

3.                 An inner most layer which is made up of innermost intercostal muscle also known as intercostal intimi, the transverse thoracic and the subcostalis muscle.

EXTERNAL INTERCOSTAL MUSCLE

Origin: It arises from the lower border of the rib above and runs downward to be inserted into the upper border of the rib below. The fibers run downward and forward corresponding with the pathway of the movement of the hand into the pocket.

Action: Elevation of the rib.

Nerve Supply: They are supplied by intercoastal nerve 1 – 11 each for each space.

INTERNAL INTERCOSTAL MUSCLE

Arises from the costal groove of the rib above inserted into the upper border of the rib below and its fibers are running diagonally downward and backward in opposite direction to the external intercostal muscle.

Nerve supply: Intercoastal nerve 1 – 11 each nerve for its corresponding space.

Action: it depresses the rib in forceful respiration.

INNERMOST INTERCOSTAL MUSCLE

It is more or less functionally part of the internal intercostal muscle. Its fibers run in the same direction as the fibers of the internal intercostal muscle, and it is separated from the internal intercostal muscle by the intercostal vessels. It arises from the posterior part of the costal groove.

Intercostal vessels lies between the inner most intercostal muscle and internal intercostal muscle.

The inner most intercostal muscle sometimes extends from its space to other spaces. It does not have intercostal membrane. It is only limited to the lateral wall of the thorax.

Subcostalis it cross more than one space, they are much more developed at the upper spaces.

Transverse thoracis muscle, it arises from the posterior surface of the xiphoid process and the posterior surface of the lower part of the body of the sternum It then fans out to be inserted into the 6^th,5^th, 4^th, 3^rd and 2^nd rib, and the corresponding costal cartilage. It is supplied by the T2 – T6 intercostal nerves.

TYPICAL INTERCOSTAL NERVE must have:

1.       Lateral cutaneous nerve which divides into anterior and posterior ramus.

2.       Anterior cutaneous nerve which divides into medial and lateral cutaneous branch.

3.       It must lie within the intercostal space.

4.       It must supply structure within its space.

CLASSIFICATION OF INTERCOSTALNERVE

·        Intercostal nerve 1 and 2 are atypical because they give off a greater branch that forms part of the brachial plexus. They also give off cutaneous contribution to the upper limb. Intercostal nerve two has lateral cutaneous nerve but lack anterior and posterior rami, the lateral cutaneous branch is known as intercostobrachial nerve.

·        Intercostal nerves 3 to 6 are typical intercostal nerves with all the basic features.

·        Intercostal nerves T7 to T11 have all the features of typical intercostal nerve with the exception that they all cross their corresponding spaces to supply the anterior abdominal wall.

A TYPICAL INTERCOSTAL SPACE

This is a space that contains a typical nerve, rib and vertebra. The spaces between the 3^rd – 5^th ribs are typical spaces. Within each space lie one posterior intercostal artery and two anterior intercostal arteries, making 11 posterior intercostal arteries and 22 anterior intercostal arteries in the eleven intercostal spaces.