Lecture 8 = Craniovertebral Joints and Disarticulation

Question 1

What are the characteristics of the special vertebrae C1 and C2?

Answer 1

• C1 - atlas
  
  • supports the skull
  • no body
  • no spinous process
  • anterior arch and posterior arch
  • large lateral masses support the occipital condyles of the skull superiorly and articulate with the axis inferiorly
  • foramen transversarium located in the large transverse process
• C2- axis:
  
  • dens (aka odontoid process) located on the body’s superior surface
  • foramen transversarium located in the small transverse process
  • spinous process is large and bifid

Question 2

What are the craniovertebral joints?

Answer 2

I. Atlanto-occipital joint
- contributes to nodding movement (“yes”)
- allow for tilting of the head, side to side
II. Atlanto-axial joint
- contributes to rotation movement (“no”)
- the rotation is around the dens of the odontoid process
*both are synovial joints with no discs

Question 3

Tell me about the atlanto-axial joint

Answer 3

• articular surface is anterior arch of C1 and dens of C2
• synovial, pivot joint
• ROM: rotation (supplies 50% of cervical rotation)

Question 4

tell me about the atlanto-occipital joint

Answer 4

• articulation is at occipital condyles and superior/articular facets of C1
• synovial, condyloid joint
• ROM: flexion/extension joint - yes joint

Question 5

What are the dura mater and tectorial membrane?

Answer 5

Cranial vault is lined with periosteal dura mater
- continuous inferiorly into spinal column
Beneath this is the tectorial membrane
- a superior extension of the posterior longitudinal ligament
Beneath this are the craniovertebral joints and their deep ligaments
*b/c we are looking at and talking about interior surfaces, when we say beneath here we are actually talking about the next most superficial layer.
* these ligaments stabilize these joints (axiooccipital/atlantooccipital, etc
*the dura is continuous inferiorly along the length of the spinal cord

Question 6

What is the tectorial membrane?

Answer 6

• superficial to the dura mater is tectorial membrane - this is the most superficial layer after the dura
• adheres to periosteal layer of dura so is continuous to dura and continues beneath it
• this is the cranial extension of the posterior longitudinal ligaments across the atlanto-occipital joint (so once the posterior longitudinal ligament comes to the Atlanta-occipital joint, it’s now called the tectorial membrane and goes to to the cranium).
• posterior longitudinal ligament is inside the vertebral canal on the posterior surface of vertebral bodies
• behind the posterior longitudinal ligament are the vertebral bodies - that’s anterior

Question 7

What are the Anterior and Posterior longitudinal ligaments?

Answer 7

• These are both superficial to the dura
• posterior longitudinal ligament is on the posterior surface of the vertebral body and anterior longitudinal ligament is on the anterior surface of the vertebral bodies

Question 8

What is the anterior atlanto-occipital membrane?

Answer 8

• it’s the superior/cranial extension of anterior longitudinal ligament - on anterior surface of vertebral body - name changes past C2
• attaches to base of occipital bone superiorly at margin of foramen magnum
• covers anterior arch of atlas inferiorly
  
  • extends from anterior margin of foramen magnum to cover the anterior arch of C1 - the atlas

Question 9

What is the posterior atlanto-occipital membrane?

Answer 9

• posterior membrane found between atlas and occipital bone
• uppermost/cranial extension of ligament flavum - is on the opposite side (posterior) of anterior Atlanto-occipital membrane
  
  • fills in gaps between posterior vertebral arches
• these form parts of posterior wall of vertebral canal
• this is inside the canal on the dorsal. posterior surface of surface of vertebral body have the p. long lig. and on the anterior surface of the bodies are the a. long lig.

Question 10

What is ligamentum flava?

Answer 10

• this falls in gaps between the posterior vertebral arches
• p. long. ligament is anterior in the vertebral canal but is posterior to the surface of the vertebral bodies
• p. and a. long ligs. are named depending on their position in relation to the vertebral bodies.

Question 11

What are the deep ligaments?

Answer 11

• transverse ligament of the atlas
• cruciform (cruciate) ligament of the atlas
• alar (check) ligaments
• apical ligament of the dens (apical dental)
• ligaments are associated with the dens - C1 being stabilized with C2

Question 12

What is the transverse ligament of atlas?

Answer 12

• holds dens of axis (C2) tightly to anterior arch of atlas (C1) –> holds the dens in the articular facet
• very strong, dense CT, bow shaped ligament
• if there is a fracture, it happens at the base of the dens so we don’t get a good repair of that fracture
• clinical note: fractures of the dens usually occur at it’s base and often these fractures don’t reunite due to the position of the transverse ligament
  
  • can be fatal if we sever the spinal cord or spinal nerves

Question 13

What is the cruciform (cruciate) ligament?

Answer 13

• formed by transverse ligament of atlas and 2 bands
• superior long. band - attaches to foramen magnum base
• inferior long. band - attaches to dens of C2 post
• both bands (crura) vertically oriented. Thus, all 3 form a crucifix (cross)
• also help protect the dens at the joint

Question 14

What is the alar (check) ligament?

Answer 14

• strong paired ligaments nearly as thick as a pencil
• extends from dens to medial portions of occipital condyles
• “check” lateral rotation of skull/head
• are obliquely oriented deep to the cruciform lig.
• these limit our rotation and check the range of motions so it can only go so far
• owls don’t have this

Question 15

What is the apical ligament of dens?

Answer 15

• slender band ascending from apex of dens
• attaches to anterior margin of foramen magnum
• located deep to superior long. band of cruciform ligament
• functions together with the transverse ligament - holds the dens to the anterior arch of C1
• it comes off of top of the head of the dens and attaches to the anterior most form of the foramen magnum
• this helps keep C1 and C2 together
• alar and apical ligaments are small

Question 16

What are the neurovascular structures?

Answer 16

• internal jugular v. - emerges from jugular foramen
• internal carotid a. - enters carotid canal
• sympathetic trunk - gives rise to internal carotid plexus
• CN VII - emerges from stylomastoid foramen
• CNs IX, X, XI - emerge from jugular forament
• CN XII - emerges from hypoglossal canal

Question 17

What are some structural relationships?

Answer 17

• pharynx - hangs from pharyngeal tubercle like a drape of circular shower curtain from the base of the skill and is continuous with the oral cavity
• carotid sheath - located lateral and posterolateral to pharynx
• sympathetic trunk - located posteromedial to carotid sheath in the retropharyngeal space. sympathetics get into the skull via carotid sheath
• remember that all of the structures that we are talking about are prevertebral - anterior to the vertebral musculature

Question 18

What are the ganglia at base of skull?

Answer 18

• CN IX and X: each give rise to superior and inferior ganglia (sensory ganglia within the jugular foramen)
• sympathetic trunk: gives rise to superior cervical ganglion and sends off internal cervical ganglion and sends off internal carotid plexus (how we get sympathetics to the eye) (travels on ICA)

Question 19

What is the glossopharyngeal n. (CN IX)?

Answer 19

• travels with the stylopharyngeus m. (m. of pharynx) between the ICA and ECA
• CN IX runs along lateral side of stylopharyngeus m. and innervates it and then continues inferiorly and descends to the pharynx and back of tongue
• CN IX and X continue on as their main trunks of nerve after leaving the superior and inferior ganglia within the jugular foramen. They remain separate.

Question 20

What are the pharyngeal plexus of nerves?

Answer 20

• formed by union of pharyngeal branches of CN IX and CN X
• CN IX: primarily contributes sensory fibers to plexus and innervates stylopharyngeus m. so also have a motor component
• CN X: supplies motor innervation to most pharyngeal mm. and carries p-symp.
• symp. fibers from superior cervical ganglion

Question 21

What is the accessory nerve (CN XI)?

Answer 21

• runs immediately lateral to CN X at base of skull
• usually travels between ICA and IJV as it descends
• supplies the SCM and trapezius mm.
• the ventral roots are motor
• the Doral roots are sensory
• spinal portion of CN I has 2 foramen - this goes in and out of different foramen

Question 22

What is the hypoglossal n. (CN XII)

Answer 22

• emerges from hypoglossal canal
• runs inferior within submandibular triangle
• supplies mm. of tongue

Question 23

How can you remove the head from the body?

Answer 23

• craniovertebral joints: logical sites for removal
• all ligaments holding joints together must be severed
• retropharyngeal space: logical plane for separation (of head and viscera from vertebral column)- plane between buccopharyngeal and alar fascia
  
  • contains loose fibrous tissue easily separated

Question 24

What is the retropharyngeal space?

Answer 24

• located between buccopharyngeal fascia and alar fascia
• extends from base of skull to superior mediastinum
• easily accessed posterior to carotid sheaths
• this space has an inferior limit called the superior mediastinum which goes down to the bifurcation of the trachea

Question 25

What are the structures of the prevertebral region?

Answer 25

• sympathetic trunks
• CNs IX, X, XI, and XII of the neck
• cervical spinal nn. - cervical plexus nerves
• vertebral vessels
• pharyngeal plexuses of vv. and nn.
• deep cervical fascial layers

Question 26

What are the cranial nerves of the prevertebral region?

Answer 26

I. CN IX - most anterior and travels to posterior tongue and pharynx
II. CN X - found centrally in carotid sheath and travels into thorax
III. CN XI - most posterior and travels to SCM and trapezius
IV. CN XII - moves laterally and travels to tongue

Question 27

What are the cervical nerves of the prevertebral region?

Answer 27

(C1-C8)

• C1-C4: cervical plexus; posterior to longus capitis/colli mm.
• C3-C5: form phrenic nn,; descends anterior to anterior scalene mm.
• C5-C8: forms brachial plexus; runs between anterior and middle scalene mm.

Question 28

What are the cervical plexus?

Answer 28

• nerve network formed by ventral rami of C1-C4
  
  • there are sensory and motor contributions/components
• the cervical and brachial plexuses emerge between the anterior and middle scalene muscles
  
  • the cervical plexus appears more superiorly and the brachial plexus appears more inferiorly.

Question 29

What is the ansa cervicalis?

Answer 29

• it’s the cervical plexus formed by a superior limb, C1 fibers associated with the hypoglossal nerve and an inferior limb formed by C2 and C3 so C1-C3.
• the ansa cervicali provides motor fibers to the infrahyoid strap muscles and more motor branches and sensory to phrenic n.
• C1 branches - travel along the hypoglossal n. and innervate the geniohyoid m. and the thyrohyoid m.
• C1-C2 motor branches innervate anterior and lateral rectus capitis and longs capitis and colli muscles
• C3 motor branches to the longs capitis and Colli and levator scapulae muscles
• C4 motor branches to longus capitis and colli, levator scapulae and middle scalene muscles
• phrenic n. (C3-4-5, keep me breathing and alive) - has a motor and sensory component

Question 30

What is the phrenic nerve?

Answer 30

• is the sole motor innervation to the diaphragm
• it’s 30% sensory to the diaphragm
• irritation to both the superior and inferior surfaces of the central part of the diaphragm is carried by sensory fibers in the phrenic nerve.
• irritation to the superior and inferior surfaces of the peripheral portions off this is carried by the intercostal nn.
• so phrenic n. innervate the center potion of the diaphragm while the intercostal nn. innervate the peripheral portions.

Question 31

What are the vertebral vessels?

Answer 31

I. vertebral a.: arises from subclavian a.
II. vertebral v.: drains into brachiocephalic v. and also travel with the artery
* arise in the sub occipital triangle and form plexuses
* the plexuses descend thru transverse foramina
* continue to receive intervertebral and muscular vv. along path
* ultimately drain into brachiocepahilic vv.
-both located anterior to cervical spinal nn.
-both enter transverse foramina of C6 and above

Question 32

What are the pharyngeal plexus of veins?

Answer 32

• 2 pharyngeal plexuses of vv.
• external plexus: forms outside of pharyngobasilar fascia
• internal plexus: between pharyngobasilar fascia and constrictor mm.
• both drain into pterygoid plexus of vv. and IJV at angle of mandible and multiple inferior branches