CRANIOVERTEBRAL JOINTS AND SUBOCCIPITAL REGION © 2019zillmusom

I. CRANIOVERTEBRAL JOINTS - specializations of joints between vertebrae

A. Atlanto-occipital joint: joint between (vertebra C1) and ; movements - flexion - extension of the neck (nodding the head in "yes" movement).

B. Atlanto-axial joint: joint between atlas (C1) and axis (C2); movement: rotation of atlas on axis (shaking head in "no" movement)

C. Ligaments of joint - stabilize joints and protect medulla and ; some prevent excessive movement; some are extensions of ligaments of spinal column

1. Anterior Atlanto-Occipital membrane = extension of anterior longitudinal ligament - extends from atlas to occipital bone

2. Membrana Tectoria = extension of posterior longitudinal ligament of spinal column - extends from axis to occipital bone, posterior to cruciate ligament.

3. Posterior Atlanto-Occipital membrane = extension of ligamenta flava - extends from atlas to occipital bone

4. Cruciate (cruciform or cross) ligament - composed of 1) Transverse ligament of atlas - transverse band within vertebral canal which is attached to inner side of atlas; holds dens of axis against inner aspect of anterior arch of atlas; 2) Superior and inferior bands - upper and lower extensions from transverse ligament of atlas to occipital bone superiorly and to body of the axis inferiorly.

Clinical note: Tear of Cruciate ligament of atlas can allow dens to be driven into spinal cord (resulting in quadriplegia) or medulla (resulting in death).

Morbid note: Hanging someone: most have articular facets that permit extension-flexion and rotational movements; the joint between the atlas and axis however is specialized and permits only rotational movement; in accurate hanging, a large knot is placed posterior to the joint between the atlas and the axis and the weight of the body forcibly flexes or extends (depending on position) the joint, typically fracturing C2, resulting in instantaneous death; in inaccurate hanging, the knot is placed behind other cervical joints, resulting in death by strangulation; Hangman’s fractures occur after trauma, often as hyperextension injuries in automobile accidents or falls in elderly and C2 fracture. 5. Alar ligament - "check" ligament extending laterally from dens to occipital bone; prevents excessive rotation of head.

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II. SUBOCCIPITAL REGION - - bounded by muscles; inferiorly by obliquus capitis inferior, medially by rectus capitis posterior major, laterally by obliquus capitis superior.

SUBOCCIPITAL MUSCLES MUSCLE ORIGIN INSERTION ACTION

Rectus Capitis Vertebra - axis Occipital bone Extends head, Suboccipital n. (dorsal Posterior Major (C2) rotates in ramus of C1) unilateral action

Rectus Capitis Vertebra - atlas Occipital bone; Extends head Suboccipital n. (dorsal Posterior Minor (C1) Dura mater ramus of C1)

Obliquus Capitis Vertebra - axis Vertebra - atlas Rotates head Suboccipital n. (dorsal Inferior (C2) (C1) ramus of C1)

Obliquus Capitis Vertebra - atlas Occipital bone Extends head Suboccipital n. (dorsal Superior (C1) ramus of C1)

A.

1. Suboccipital nerve - dorsal ramus of C1 ; motor to suboccipital region. 2. - dorsal ramus of C2 spinal nerve; sensory to skin of back of head and neck.

B. Arteries

1. Occipital artery - branch of External Carotid artery; pierces fascia of Trapezius muscle to supply back of head and suboccipital region. 2. - ascends neck through foramina transversaria of vertebrae C1-C6 and enters skull through ; passes through suboccipital triangle.

III. INNERVATION OF DURA AND ANATOMY OF HEADACHE

A. Headache = pain in any region of the head 1. Complex because diverse causes: ex. vascular, meningeal, muscular 2. Structures sensitive to pain: scalp, air sinuses, meninges, arteries and veins 3. Neural tissue is Insensitive: brain parenchyma (nerve cells, glia; except small part of midbrain)

2 B. Sensory Innervation of Dura: from recurrent branches of nerves that enter cranial cavity

1.Trigeminal: branches of V1, V2 and V3 (ex. nervous spinosus); 2. Also: (Vagus), Upper cervical spinal nerves

Clinical Note: Insertion of Rectus Capitis Posterior Minor to Dura may form anatomical basis for relief of tension headaches by neck massage.

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