The scalene muscles are the three pairs of muscles that extend from the ribs to the sides of the neck. The three muscles are individually called the scalenus anterior, the scalenus medius and the scalenus posterior. The muscles serve to elevate the first and second ribs and control the turning of the neck. The brachial plexus and the subclavian artery are found between the anterior and medius scalene muscles.
The scalenus anterior muscle is the most important of the scalene muscles, and runs down from the vertebrae to the first rib. The first rib is the highest one in position on the body. The scalenus anterior muscle lifts the rib when the neck is fixed in position to aid breathing. The muscle is also responsible for bending the neck forward and aids in rotating the neck. The scalenus anterior muscle is on the left hand side of the neck.
The scalenus medius is another of the three pairs of scalene muscles, and performs similar functions to the scalenus anterior. The muscle is responsible for lifting the ribs during inhalation, and connects to the first rib, just behind the subclavian artery. The muscle runs up to the neck vertebrae at a slight diagonal angle, and sits behind the roots of the brachial plexus and the subclavian artery. This muscle is also responsible for turning the neck, and is located on the right hand side of it.
The scalenus posterior muscle is the smallest of the scalene muscles, and is located on the right hand side of the neck. This muscle performs similar functions to the other two, raising the ribs during inhalation and helping with the rotation of the neck, and it is also used to tilt the neck. The scalenus posterior usually connects to the second rib, but has been known to also reach to the third rib. It connects to the outer surface of the rib. The scalenus posterior muscle isn’t always present in humans, and has even been known to be fused to the scalenus medius muscle, which occupies the same side of the neck.
Where the brachial plexus and subclavian artery run between the scalene muscles is called the scalene hiatus. This region is technically referred to as the scaleotracheal fossa. The subcalvian vein and the phrenic nerve also pass by the anterior scalene where it meets the first rib.