Rectus capitis posterior minor muscle

The rectus capitis posterior minor (or rectus capitis posticus minor) is a muscle in the upper back part of the neck. It is one of the suboccipital muscles. Its inferior attachment is at the posterior arch of atlas; its superior attachment is onto the occipital bone at and below the inferior nuchal line. The muscle is innervated by the suboccipital nerve (the posterior ramus of first cervical spinal nerve). The muscle acts as a weak extensor of the head.

Anatomy
The rectus capitis posterior major muscle is one of the suboccipital muscles.

The muscle extends vertically superior-ward from its inferiro attachment to its superior attachment.  The muscle becomes broader superiorly. 

Attachments
The inferior attachment is (by a narrow tendon) onto the posterior tubercle  of the posterior arch of atlas. 

Its superior attachment is onto the medial portion of the inferior nuchal line  and the external surface of the occipital bone inferior to it  (between this line superiorly and the foramen magnum inferiorly ).

The muscle usually also additionally attaches onto the posterior atlantooccipital membrane (which is in turn attached onto adjacent dura mater of the spinal canal). 

Innervation
The muscle receives motor innervation from the suboccipital nerve (the posterior ramus of cervical spinal nerve C1). 

Variation
The muscle of either side may be doubled (along its length). 

Actions/movements
The muscle is a weak  extensor of the head. 

The synergists are the rectus capitis posterior major and the obliquus capitis superior.

Role in headache
Connective tissue bridges were noted at the atlanto-occipital joint between the rectus capitis posterior minor (RCPm) muscle and the dorsal spinal dura. Similar connective tissue connections of the rectus capitis posterior major have been reported recently as well. The perpendicular arrangement of these fibers appears to restrict dural movement toward the spinal cord. The ligamentum nuchae was found to be continuous with the posterior cervical spinal dura and the lateral portion of the occipital bone. Anatomic structures innervated by cervical nerves C1-C3 have the potential to cause headache pain. Included are the joint complexes of the upper three cervical segments, the dura mater, and spinal cord.

The dura-muscular (myodural) and dura-ligamentous connections in the upper cervical spine and occipital areas may provide anatomic and physiologic answers to the cause of the cervicogenic headache. The level of strain at which RCPm muscle fibers began to tear as a result of overstretching has been estimated to be 30%. This would be expected to put them at risk of injury during whiplash-type distortions when the occipitoatlantal (OA) joint is flexed upon impact. Tearing of the muscle fibers would result in fatty infiltration (FI) that would be expected to impact the functional relationship between the RCPm muscles and the pain sensitive spinal dura. While FI and/or a reduction in the cross sectional area (CSA) of active muscle would not be expected to be the direct cause of chronic headache, it is known that muscle pathology will result in functional deficits. Pathologies in RCPm muscles in conjunction with the myodural bridge can compromise the normal functional relationship between the RCPm and the pain sensitive dura mater and result in referred head and neck pain. This could help to explain manipulation's efficacy in the treatment of cervicogenic headache.