CRANIOVERTEBRAL JOINTS

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I. CRANIOVERTEBRAL JOINTS

 

A. Atlanto‑occipital joint: joint between atlas (vertebra C1) and occipital bone; 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 spinal cord; some prevent excessive movement; some are extensions of ligaments of spinal column (Atlas Figs. 4.38, 4.39; Snell Fig. 12‑4)

 

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 (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 cervical vertebrae 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 the joint, driving the dens into the medulla, resulting in instantaneous death; in inaccurate hanging, the knot is placed behind other cervical joints, resulting in flexion of the neck, prolonged agony and death by strangulation; amateurs should not attempt hanging people.

 

5. Alar ligament ‑ "check" ligament extending laterally from dens to occipital bone; prevents excessive rotation of head.

 

II. PREVERTEBRAL MUSCLES (Atlas Fig. 8.24) ‑ located anterior to cervical vertebrae.

 

MUSCLE

ORIGIN

INSERTION

ACTION

NERVE

Longus colli

Vertebra transverse processes lower cervical

Vertebra - bodies of upper cervical

Flex neck

Cervical ventral rami

Longus capitis

Vertebra transverse processes C3-C6

Occipital bone

Flex head

Cervical ventral rami

Rectus capitis anterior

Atlas

Occipital bone

Flex head

Cervical ventral rami

Rectus capitis lateralis

Atlas transverse process

Occipital bone

Flex head

Cervical ventral rami

 

Note: Colli means neck in Latin.

 

III. PHARYNX ‑ a fibromuscular tube which forms superior end of both respiratory and digestive tubes continuous inferiorly with trachea and esophagus, anteriorly with oral and nasal cavities. (Atlas Figs. 8.28. page 767)

 

A. Layers (from internal to external): correspond to layers of GI tract: 1. mucosa = epithelial lining; 2. submucosa = connective tissue layer; 3. muscular layer composed of inner circular and outer longitudinal layers, muscles listed below ; 4. adventitia = Buccopharyngeal fascia = part of Pretracheal fascia of neck.

 

B. Location ‑ Extends from base of skull superiorly to level of cricoid cartilage inferiorly; posterior to nasal cavity, oral cavity, and larynx; anterior to vertebrae C1 to C6; medial to carotid sheath and cranial nerves 9‑12.

 

C. Circular muscles of pharynx ‑ (Snell Figs. 11‑76) overlap each other somewhat; Function; constrict pharynx during swallowing to propel food inferiorly into esophagus and aid in closing off nasal from oral pharynx by contacting soft palate; All constrictors insert to Pharyngeal raphe which is a median fibrous band on posterior aspect of pharynx.

 

 

 

 

 

 

 

 

 

 

 

Circular Muscles of Pharynx

MUSCLE

ORIGIN

INSERTION

ACTION

NERVE

Superior Constrictor

Pterygomandibular raphe - continuous anteriorly with buccinator muscle

Pharyngeal raphe

Constrict pharynx

X

Middle Constrictor

Hyoid bone

Pharyngeal raphe

Constrict pharynx

X

Inferior Constrictor

Thyroid and cricoid cartilages

Pharyngeal raphe

Constrict pharynx

X

 

D. Gaps between constrictor muscles ‑ allow vessels, nerves, and muscles to pass into the interior of the pharynx. (Snell Figs. 11‑76, 11-77)

 

1. Gap between superior constrictor and base of skull ‑ passage of auditory tube into pharynx and levator veli palatini muscle.

 

2. Gap between superior and middle constrictors: passage of stylopharyngeus muscle and glossopharyngeal nerve.

 

3. Gap between middle and inferior constrictor muscles: for passage of Internal laryngeal nerve and Superior laryngeal artery.

 

E. Longitudinal muscles of pharynx ‑ three muscles located mostly internal to pharynx which fuse with circular muscles when they insert. (Atlas Figs. 8.28, 8.29)

 

Longitudinal Muscles of Pharynx

MUSCLE

ORIGIN

INSERTION

ACTION

NERVE

Stylopharyngeus

Temporal bone - styloid process

Thyroid cartilage

Raises pharynx and pulls wall laterally

IX

Palatopharyngeus

Soft palate - palatine aponeurosis

Thyroid cartilage

Raises pharynx and pulls down soft palate

X

Salpingopharyngeus

Auditory tube

Thyroid cartilage

Raises pharynx

X

 

F. Divisions of pharynx ‑ location relative to nasal and oral cavities and larynx.

 

1. Nasopharynx ‑

 

a. Location ‑ superior to soft palate and posterior to nasal cavity, anterior to occipital bone ; superior border is body of sphenoid;

 

b. Contents ‑ 1) pharyngeal tonsil (lymphoid tissue in submucosa of roof and posterior wall of nasopharynx); 2) opening of auditory tube

 

Note: Adenoids: enlargement of pharyngeal tonsil common in children; enlarged pharyngeal tonsils can interfere with breathing.

 

2. Oropharynx (Snell Fig. 11‑78)

 

a. Location ‑ Superior boundary :soft palate; inferior boundary: upper border of epiglottis; located posterior to palatoglossal arch

 

Note: palatoglossal arch is mucosal fold covering palatoglossus muscle; forms boundary between oral cavity and oropharynx

 

b. Contents ‑ 1) Palatine tonsils ;2) Glossoepiglottic folds ‑ folds of mucosa from posterior tongue to epiglottis; there is one Medial glossoepiglottic fold and two Lateral folds

 

Note: Valleculae (L. for little ditches) are two depressions of mucous membrane between Medial and Lateral Glossoepiglottic folds; food or foreign objects can lodge in valleculae (Snell Fig. 11-78)

 

3. Laryngopharynx

 

a. Location ‑ between upper border of epiglottis superiorly and lower border of cricoid cartilage inferiorly; communicates inferiorly with esophagus and anteriorly with larynx.

 

b. Contents ‑ 1) Piriform recess ‑ deep trench in mucous membrane in anterolateral wall of laryngopharynx, lateral to laryngeal inlet.(Atlas Fig. 8.29A)

Note: Foreign bodies can lodge in piriform recesses.

 

G. Innervation ‑ Motor (SVE) ‑ all muscles of pharynx are innervated by the Pharyngeal branch of Vagus (X) except stylopharyngeus which is innervated by the Glossopharyngeal nerve (IX); Sensory (GVA)nasopharynx is mostly innervated by Facial nerve (VII); oropharynx by Glossopharyngeal (IX) and laryngopharynx by Vagus (X).

 

H. Blood supply and lymphatics ‑ Arteries from Ascending Pharyngeal, Facial, Maxillary and Lingual arteries; Veins drain to pharyngeal plexus which drains to Internal Jugular; Lymphatics to Deep Cervical nodes.