As you can see in the photo, the scalene root is divided into anterior, middle, and posterior. The scalene has slightly different attachments for the anterior, middle, and posterior fibres but, Functionality is a simpler muscle than you think.
It is anatomically and clinically important when talking about the neck, as it is in direct contact with the cervical vertebrae. The scalene can be a bit confusing because it has three fibres rather than a complex functional anatomy.
First, let's look at the anterior scalene muscle fibers. The anterior scalene muscle attaches to the upper surface of the first rib and the inner surface of the scalene tubercle from the tuberosity anterior to the transverse processes of the third to sixth cervical vertebrae.
To summarise, the first rib from the front of the cervical vertebrae 3-6 transverse processes. On the other hand, the main function of the anterior scalene is the elevation of the first and second ribs. It also has functions in neck flexion, lateral bending, and ipsilateral rotation of the head.
Secondly, the middle scalene muscle is between the anterior and posterior scalene muscles and then starting at the back of the cervical vertebrae 2-7 transverse processes and attaching to the upper surface of the first rib. The middle scalene has the same functionality as the anterior scalene.
Finally, the posterior scalene is the most dorsal, beginning at the posterior aspect of cervical vertebrae 5-7 transverse processes and ending at the outer surface of the second rib. The functions of the posterior scalene are the elevation of the first and second ribs and the lateral bending of the head and neck, and the ipsilateral rotation of the head.
However, scalene does much more than just movements. For example, the scalene acts as a protective muscle for the cervical spine and as a respiratory support muscle. The reason the first and second ribs are elevated in all scalene functions is also related to their role as respiratory support muscles.
Also, because the pathway between the fibres of the scalene is the pathway of the ‘brachial plexus’, shortening or stiffness of the scalene can be associated with neurological symptoms such as extreme pain, paresthesia, or tingling.