Scalenus posterior muscle
Musculus scalenus posterior
Scalenus posterior, the least and deepest of the scalene muscles, runs from the lower cervical vertebrae to the second rib.
At a glance
- English
- Scalenus posterior muscle
- Latin (TA2)
- Musculus scalenus posterior
- System
- Muscle
- Region
- Neck
- Side
- Paired, left and right
About the scalenus posterior muscle
Scalenus posterior lies at the back of the scalene group in the side of the neck, tucked behind scalenus medius and partly hidden by it. It is the least bulky and most deeply set of the scalenes, and in some people its fibres merge with those of scalenus medius so that the two are hard to separate.
The muscle begins as two or three small tendons from the back tubercles of the lowest cervical transverse processes, usually C4 or C5 to C6. These join into a slim belly that descends behind scalenus medius and ends as a thin tendon on the outer face of the second rib, just posterior to the tubercle for serratus anterior.
Because it crosses over the first rib to reach the second, it is the only scalene that acts directly on the second rib. With the neck fixed it lifts that rib, so it helps to expand the upper chest when breathing is deep or forced; scalenes and sternocleidomastoid are the main accessory muscles of inspiration. With the ribs fixed it tilts the cervical spine towards its own side, and acting together the two sides help to steady the cervical spine.
Clinically scalenus posterior matters less than its neighbours, since the arm's nerve plexus and the subclavian artery emerge in front of scalenus medius, well away from it. It can still contribute to stiffness and referred pain in the neck and shoulder, and it is examined with the rest of the group when tight lateral neck muscles are suspected of narrowing the thoracic outlet.
Attachments, action and supply
- Origin
- Back tubercles on the C4 to C6 transverse processes, by two or three tendons.
- Insertion
- Outer face of the second rib, posterior to the serratus anterior tubercle.
- Action
- Raises the second rib in forced breathing; flexes the neck laterally towards its own side when the ribs are fixed.
- Nerve supply
- Ventral rami of the lower cervical spinal nerves, C5 to C7 (often given as C6 to C8).
- Blood supply
- Ascending cervical branch of the inferior thyroid artery and the superficial cervical branch of the transverse cervical artery.
Anthromica
See the scalenus posterior muscle where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
