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Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
Anatomy cervical vertebra
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Anatomy cervical vertebra

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  • 1. 2-20. ATYPICAL VERTEBRAEAtypical vertebrae (figure 2-20) are those vertebraewhose structure is highlymodified by function and position. They consist of thefirst cervical vertebra (C-1) oratlas, the second cervical vertebra (C-2) or axis, thesacrum, and the coccyx.a. The Atlas. (1) The first cervical vertebra (C-1) is named the atlasbecause it supportsthe head (figure 2-20A). It is characterized by theabsence of both body and spinousprocess and consists of an anterior and posterior arch,two lateral masses, and avertebral foramen. The anterior surface of the anteriorarch presents a slight projection,the anterior tubercle. The posterior surface is marked bya dental facet for articulation
  • 2. with the dens or odontoid process of the axis. On thesuperior surface are two groovesfor the vertebral arteries. (2) The morphology of the atlas affords freedom ofmovement of the skull.The body of the atlas is transferred to the axis (secondcervical vertebra) where itbecomes the dens (odontoid process), which articulateswith the dental facet (facet forodontoid) of the anterior arch of the atlas, thus makingpossible the rotary movements ofthe skull. The superior articular surfaces of the atlas areconcave for reception of thecondyles of the occipital bones, permitting flexion,extension, and hyperextensions ofthe skull. b. The Axis. The second cervical vertebra (C-2) is namedthe axis, or
  • 3. epistropheus, because it forms the pivot upon which theatlas rotates when the head isturned from side to side (figure 2-20B). The axis differsprimarily from a typical vertebraby the presence of a tooth like projection, called the densor odontoid process, whichrises perpendicularly from the upper surface of the body.On its anterior surface, thedens presents an oval facet for articulation with thedental facet on the anterior arch ofthe atlas. On its posterior surface is a shallow groovethat receives the transverseligament of this articulation. The relationship of the atlasand axis to the skull is shownin figure 2-21A. Other spinal articulations are also c. TheSacrum. In the adult, the sacrum (figure 2-20C) is a singlebone formedby the fusion of the five sacral segments. It is a largewedge-shaped (triangular) bone
  • 4. situated in the lower part of the vertebral column and atthe upper and back part of thepelvic cavity where it is wedged between the twohipbones. Its base is directed upwardand its apex is directed downward. In the center, thebase presents the kidney-shapedbody; behind this is the superior opening of the sacralcanal, which is bounded laterallyby the articular processes. The sacral promontory is aprominent ridge at the upperanterior margin of the body. The body articulates withthe body of L-5 to form thelumbosacral articulation. On either side of the body is awing-like surface called the ala(wing) of the sacrum. (1) The dorsal surface of the sacrum is rough andconvex. In the middleline, the dorsal surface displays a ridge, the median sacralcrest, made up of three or
  • 5. four rudimentary spinous processes that are more or lessfused to form the crest. Thereare four posterior sacral foramina, which transmit severalsacral nerves. (2) The ventral or pelvic surface of the sacrum is smoothand concave. Theanterior sacral foramina transmit some of the sacralnerves. (3) The lateral surface or margin of the sacrum presentsin front an earshaped surface for articulation with the articular surfaceof the ilium. d. The Coccyx. The coccyx usually consists of three tofive rudimentarycoccygeal segments that fuse in adult life (figure 2-20D).From its base downward to itsapex, the coccyx diminishes in size. It curves downwardand forward from itsarticulation with the sacrum, often deviating from themedian plane of the bodyillustrated in figure 2-21.
  • 6. 3a. 1. The Cervical Vertebræ (Vertebræ Cervicales). 1cervical vertebræ (Fig. 84) are the smallest of thetrue vertebræ, and can be readily distinguishedfrom those of the thoracic or lumbar regions by thepresence of a foramen in each transverse process.The first, second, and seventh present exceptionalfeatures and must be separately described; thefollowing characteristics are common to theremaining four. The body is small, and broader from side to side thanfrom before backward. The anterior and posterior 2surfaces are flattened and of equal depth; the former isplaced on a lower level than the latter, and its inferiorborder is prolonged downward, so as to overlap theupper and forepart of the vertebra below. The uppersurface is concave transversely, and presents aprojecting lip on either side; the lower surface isconcave from before backward, convex from side toside, and presents laterally shallow concavities whichreceive the corresponding projecting lips of thesubjacent vertebra. The pedicles are directedlateralward and backward, and are attached to the body
  • 7. midway between its upper and lower borders, so thatthe superior vertebral notch is as deep as the inferior,but it is, at the same time, narrower. The laminæ arenarrow, and thinner above than below; the vertebralforamen is large, and of a triangular form.The spinous process is short and bifid, the twodivisions being often of unequal size.Thesuperior and inferior articular processes oneither side are fused to form an articular pillar, whichprojects lateralward from the junction of the pedicleand lamina. The articular facets are flat and of an ovalform: the superior look backward, upward, and slightlymedialward: the inferior forward, downward, andslightly lateralward. The transverse processes areeach pierced by the foramen transversarium, which,in the upper six vertebræ, gives passage to thevertebral artery and vein and a plexus of sympatheticnerves. Each process consists of an anterior and aposterior part. The anterior portion is the homologueof the rib in the thoracic region, and is therefore namedthe costal process or costal element: it arises from theside of the body, is directed lateralward in front of theforamen, and ends in a tubercle, the anteriortubercle. The posterior part, the true transverseprocess, springs from the vertebral arch behind theforamen, and is directed forward and lateralward; itends in a flattened vertical tubercle, theposteriortubercle. These two parts are joined, outside the
  • 8. foramen, by a bar of bone which exhibits a deep sulcuson its upper surface for the passage of thecorresponding spinal nerve. 15 FIG. 84– A cervical vertebra. (See enlarged image)FIG. 85– Side view of a typical cervical vertebra. (See enlarged image)First Cervical Vertebra.—The first cervicalvertebra (Fig. 86) is named the atlas because it 3supports the globe of the head. Its chief peculiarity isthat it has no body, and this is due to the fact that thebody of the atlas has fused with that of the nextvertebra. Its other peculiarities are that it has nospinous process, is ring-like, and consists of an anterior
  • 9. and a posterior arch and two lateral masses.The anterior arch forms about one-fifth of the ring:its anterior surface is convex, and presents at its centerthe anterior tubercle for the attachment of the Longuscolli muscles; posteriorly it is concave, and marked bya smooth, oval or circular facet (fovea dentis), forarticulation with the odontoid process (dens) of theaxis. The upper and lower borders respectively giveattachment to the anterior atlantooccipital membraneand the anterior atlantoaxial ligament; the formerconnects it with the occipital bone above, and the latterwith the axis below. The posterior arch forms abouttwo-fifths of the circumference of the ring: it endsbehind in the posterior tubercle, which is therudiment of a spinous process and gives origin to theRecti capitis posteriores minores. The diminutive sizeof this process prevents any interference with themovements between the atlas and the skull. Theposterior part of the arch presents above and behind arounded edge for the attachment of the posterioratlantoöccipital membrane, while immediately behindeach superior articular process is a groove (sulcusarteriæ vertebralis), sometimes converted into aforamen by a delicate bony spiculum which archesbackward from the posterior end of the superiorarticular process. This groove represents the superiorvertebral notch, and serves for the transmission of thevertebral artery, which, after ascending through the
  • 10. foramen in the transverse process, winds around thelateral mass in a direction backward and medialward; italso transmits the suboccipital (first spinal) nerve. Onthe under surface of the posterior arch, behind thearticular facets, are two shallow grooves, theinferiorvertebral notches. The lower border gives attachmentto the posterior atlantoaxial ligament, which connectsit with the axis. The lateral masses are the most bulkyand solid parts of the atlas, in order to support theweight of the head. Each carries two articular facets, asuperior and an inferior. The superior facets are oflarge size, oval, concave, and approach each other infront, but diverge behind: they are directed upward,medialward, and a little backward, each forming a cupfor the corresponding condyle of the occipital bone,and are admirably adapted to the nodding movementsof the head. Not infrequently they are partiallysubdivided by indentations which encroach upon theirmargins. The inferior articular facetsare circular inform, flattened or slightly convex and directeddownward and medialward, articulating with the axis,and permitting the rotatory movements of the head.Just below the medial margin of each superior facet isa small tubercle, for the attachment of the transverseatlantal ligament which stretches across the ring of theatlas and divides the vertebral foramen into twounequal parts—the anterior or smaller receiving theodontoid process of the axis, the posterior transmitting
  • 11. the medulla spinalis and its membranes. This part ofthe vertebral canal is of considerable size, muchgreater than is required for the accommodation of themedulla spinalis, and hence lateral displacement of theatlas may occur without compression of this structure.Thetransverse processes are large; they projectlateralward and downward from the lateral masses, andserve for the attachment of muscles which assist inrotating the head. They are long, and their anterior andposterior tubercles are fused into one mass; theforamen transversarium is directed from below,upward and backward.FIG. 86– First cervical vertebra, or atlas. (See enlarged image)
  • 12. FIG. 87– Second cervical vertebra, or epistropheus, from above. (See enlarged image)
  • 13. Second Cervical Vertebra.—The second cervicalvertebra (Fig. 87 and 88) is named 4theepistropheus or axis because it forms the pivotupon which the first vertebra, carrying the head,rotates. The most distinctive characteristic of this boneis the strong odontoid process which risesperpendicularly from the upper surface of the body.The body is deeper in front than behind, and prolongeddownward anteriorly so as to overlap the upper andfore part of the third vertebra. It presents in front amedian longitudinal ridge, separating two lateraldepressions for the attachment of the Longus collimuscles. Its under surface is concave from beforebackward and covex from side to side.The dens or odontoid process exhibits a slightconstriction or neck, where it joins the body. On itsanterior surface is an oval or nearly circular facet forarticulation with that on the anterior arch of the atlas.On the back of the neck, and frequently extending onto its lateral surfaces, is a shallow groove for thetransverse atlantal ligament which retains the processin position. The apex is pointed, and gives attachmentto the apical odontoid ligament; below the apex theprocess is somewhat enlarged, and presents on eitherside a rough impression for the attachment of the alarligament; these ligaments connect the process to theoccipital bone. The internal structure of the odontoidprocess is more compact than that of the body.
  • 14. The pedicles are broad and strong, especially in front,where they coalesce with the sides of the body and theroot of the odontoid process. They are covered aboveby the superior articular surfaces. The laminæ arethick and strong, and the vertebral foramen large, butsmaller than that of the atlas. The transverseprocesses are very small, and each ends in a singletubercle; each is perforated by the foramentransversarium, which is directed obliquely upwardand lateralward. The superior articular surfaces areround, slightly convex, directed upward andlateralward, and are supported on the body, pedicles,and transverse processes. Theinferior articularsurfaces have the same direction as those of the othercervical vertebræ. Thesuperior vertebral notches arevery shallow, and lie behind the articular processes;theinferior lie in front of the articular processes, as inthe other cervical vertebræ. The spinous process islarge, very strong, deeply channelled on its undersurface, and presents a bifid, tuberculated extremity. FIG. 88– Second cervical vertebra, epistropheus, or
  • 15. axis, from the side. (See enlarged image) FIG. 89– Seventh cervical vertebra. (See enlarged image)The Seventh Cervical Vertebra (Fig. 89).—The mostdistinctive characteristic of this vertebra is the 5existence of a long and prominent spinous process,
  • 16. hence the name vertebra prominens. This process isthick, nearly horizontal in direction, not bifurcated, butterminating in a tubercle to which the lower end of theligamentum nuchæ is attached. The transverseprocesses are of considerable size, their posterior rootsare large and prominent, while the anterior are smalland faintly marked; the upper surface of each hasusually a shallow sulcus for the eighth spinal nerve,and its extremity seldom presents more than a trace ofbifurcation. The foramen transversarium may be aslarge as that in the other cervical vertebræ, but isgenerally smaller on one or both sides; occasionally itis double, sometimes it is absent. On the left side itoccasionally gives passage to the vertebral artery;more frequently the vertebral vein traverses it on bothsides; but the usual arrangement is for both artery andvein to pass in front of the transverse process, and notthrough the foramen. Sometimes the anterior root ofthe transverse process attains a large size and exists asa separate bone, which is known as a cervical rib. Note 15. The costal element of a cervical vertebra not only includes the portion which springs from the side of the body, but the anterior and posterior tubercles and the bar of bone which connects them (Fig. 67). [back]20 . AT Y P I C AL V E RTE BR AEAtypical ve rteb rae (f igure 2 -20 ) a r e t h o s e ve rteb rae w h o s e st r u ct u r e is h i g h l y
  • 17. modified by f u n c t i o n a n d position. They consist of t h e first cervical ve rt e b ra(C-1) oratlas, t h e s e c o n d cervical ve rte bra (C-2 ) or axis , Special cervical vertebrae (C1, C2, and C7) C1 or atlas: The Atlas is the topmost vertebra, and – along with C2 – forms the joint connecting the skulland spine. Its chief peculiarity is that it has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra. C2 or axis: It forms the pivot upon which C1 rotates. The most distinctive characteristic of this bone is the strong odontoid process (dens) that rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra. C7 or vertebra prominens: The most distinctive characteristic of this vertebra is the existence of a long and prominent spinous process, hence the name vertebra prominens. In some subjects, the seventh cervical vertebra is associated with an abnormal pair of ribs, known as cervical ribs. These ribs are usually small, but may occasionally compress blood vessels (such as the subclavian artery) or nerves in thebrachial plexus, causing ischemic muscle pain, numbness, tingling, and weakness in the upper limb. t h e sacrum, a n d t h e coccyx

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