Vertebral Column - The Axial Skeleton PDF

Vertebral Column The Axial Skeleton The Axial Skeleton - longitudinal axis Supports and protects organs in body cavities Attaches to muscles of: – head, neck, and trunk – respirat...

Vertebral Column The Axial Skeleton The Axial Skeleton - longitudinal axis Supports and protects organs in body cavities Attaches to muscles of: – head, neck, and trunk – respiration – appendicular skeleton  Bones of the Axial Skeleton The skull: The thoracic cage: – 8 cranial bones – 24 ribs – 14 facial bones – the sternum Bones associated with the skull: – 6 auditory ossicles – the hyoid bone The vertebral column: – 24 vertebrae – the sacrum – the coccyx  The Vertebral Column Formed from 26 bones in the adult Transmits weight of trunk to the lower limbs Surrounds and protects the spinal cord Serves as attachment sites for muscles of the neck and back Held in place by ligaments – Anterior and posterior longitudinal ligaments – Ligamentum flavum Regions of the vertebral column  Regions and Normal Curvatures Vertebral column is about 70 cm (28 inches) Vertebral column is divided into five major regions – Cervical vertebrae 7 vertebrae of the neck region – Thoracic vertebrae 12 vertebrae of the thoracic region – Lumbar vertebrae 5 vertebrae of the lower back – Sacrum Inferior to lumbar vertebrae Articulates with coxal bones – Coccyx Most inferior region of the vertebral column Regions and Normal Curvatures Four distinct curvatures give vertebral column an S-shape – Cervical and lumbar curvature Are concave posteriorly – Thoracic and sacral curvatures Are convex posteriorly Curvatures increase the resilience of the spine The Vertebral Column Segments & Curvatures: Cervical- lordosis Thoracic- kyphosis Lumbar- lordosis Sacral- kyphosis Ligaments and Intervertebral Discs  Intervertebral Discs Cushion-like pads between vertebrae Act as shock absorbers Compose about 25% of height of vertebral column Composed of – Nucleus pulposus and annulus fibrosis Nucleus pulposus – The gelatinous inner sphere of intervertebral disc – Enables spine to absorb compressive stresses Annulus fibrosis – An outer collar of ligaments and fibrocartilage – Contains the nucleus pulposus – Functions to bind vertebrae together, resist tension on the spine, and absorb compressive forces  Herniated Disc May be caused by trauma to the spine Aging is also a contributing factor – Nucleus pulposes loses cushioning properties – Anulus fibrosis weakens  General Structure of Vertebrae 3 Functions of Vertebrae 1. Protection 2. Rigidity/Balance 3. Anchor Muscles Vertebrae  Regions Vertebral Characteristics Specific regions of the spine perform specific functions Types of movement that occur between vertebrae – Flexion and extension – Lateral flexion – Rotation in the long axis  Regional variations of vertebrae Cervical vertebrae Vertebrae Body: small Vertebral foramen: larger and triangular Spinous processes: short and bifid in C3 to C5, long in C6,and longer in C7 Transverse processes: short and bifid, transverse foramen Articular processes: horizontal  Cervical Vertebrae Seven cervical vertebrae (C1 – C7) – smallest and lightest vertebrae C3 – C7 are typical cervical vertebrae – Body is wider laterally – Spinous processes are short and bifid (except C7) – Vertebral foramen are large and triangular – Transverse processes contain transverse foramina – Superior articular facets face superoposteriorly cervical vertebrae cervical vertebrae  The Atlas C1 is termed the atlas because it supports the globe of the head. it has no spinous process, is ring- like, and consists of an anterior and a posterior arch and two lateral masses. anterior arch: its anterior surface is convex, and presents at its center the anterior tubercle for the attachment of the Longus colli muscles; posteriorly it is concave, and marked by a smooth, oval or circular facet (fovea dentis), for articulation with the odontoid process (dens) of the axis. upper and lower borders respectively give attachment to the anterior atlantooccipital membrane and the anterior atlantoaxial ligament;  The Atlas posterior arch: ends behind in the posterior tubercle, which is the rudiment of a spinous process; The posterior part of the arch presents above and behind a rounded edge for the attachment of the posterior atlantoöccipital membrane; immediately behind each superior articular process is a groove (sulcus arteriæ vertebralis); On the under surface of the posterior arch, behind the articular facets, are two shallow grooves, the inferior vertebral notches. The lower border gives attachment to the posterior atlantoaxial ligament, which connects it with the axis. The Atlas  The Atlas lateral masses: Each carries two articular facets, a superior and an inferior. superior facets: are large size, oval, concave, and approach each other in front, but diverge behind; each forming a cup for the corresponding condyle of the occipital bone. inferior articular facets: circular in form, flattened or slightly convex , articulating with the axis, and permitting the rotatory movements of the head. Just below the medial margin of each superior facet is a small tubercle, for the attachment of the transverse atlantal ligament which stretches across the ring of the atlas and divides the vertebral foramen into two unequal parts—the anterior or smaller receiving the odontoid process of the axis;  The Atlas transverse processes are large; they serve for the attachment of muscles which assist in rotating the head. are long, and their anterior and posterior tubercles are fused into one mass; the foramen transversum is directed from below, upward and backward.  The Axis forms the pivot upon which the first vertebra, carrying the head; distinctive characteristic of this bone is the strong odontoid process which rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly;  The Axis The dens or odontoid process: on its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch of the atlas. On the back of the neck, and frequently extending on to its lateral surfaces, is a shallow groove for the transverse atlantal ligament which retains the process in position. The apex is pointed, and gives attachment to the apical odontoid ligament; below the apex the process presents on either side a rough impression for the attachment of the alar ligament;  The Axis pedicles are broad and strong, especially in front; laminæ are thick and strong, and the vertebral foramen large, but smaller than that of the atlas. The transverse processes are very small, and each ends in a single tubercle; each is perforated by the foramen transversarium, which is directed obliquely upward and lateralward. superior articular surfaces are round, slightly convex, directed upward and lateralward, and are supported on the body, pedicles, and transverse processes. inferior articular surfaces have the same direction as those of the other cervical vertebræ. superior vertebral notches are very shallow, and lie behind the articular processes; the inferior lie in front of the articular processes, as in the other cervical vertebræ. spinous process is large, very strong, deeply channelled on its under surface, and presents a bifid, tuberculated extremity. Cervical vertebrae C1 (Atlas): note articular facets (2) for occipital condyles,vertebral foramen, and vertebral arch (4)  1. Odontoid Process (Dens) 2. Superior Articular Surface 3. Transverse foramen 4. Spinous process 5. Transverse process 6. Vertebral (spinal) foramen 7. Body C2 (Axis): note the dens (1), vertebral foramen (6), & vertebral arch (4). Dens is ‘post’ around which atlas rotates (to turn your head). anterior view (fig 2) posterior view (fig 3) Atlas & axis together: Note dens (c) & articular facets (d) of atlas.  Seventh Cervical Vertebra: most distinctive characteristic of this vertebra is the existence of a long and prominent spinous process, hence the name vertebra prominens; process is thick, nearly horizontal in direction, not bifurcated, but terminating in a tubercle to which the lower end of the ligamentum nuchæ is attached. transverse processes are of considerable size, their posterior roots are large and prominent, while the anterior are small and faintly marked; the upper surface of each has usually a shallow sulcus for the eighth spinal nerve, and its extremity seldom presents more than a trace of bifurcation. foramen transversarium may be as large as that in the other cervical vertebræ, but is generally smaller on one or both sides;  thoracic vertebrae Thoracic Vertebrae (T1 – T12) All articulate with ribs Have heart-shaped bodies from the superior view Each side of the body of T1 – T10 bears demifacts for articulation with ribs – T has a full facet for the first rib 1 – T – T only have a single facet 10 12 Vertebrae Body ： heart-shape, superior and inferior costal fovea Vertebral foramen ： smaller, rounder Spinous processes ： long, point obliquely downward Transverse processes ： transverse costal fovea Articular processes: coronal Spinous processes are long and point inferiorly Vertebral foramen are circular Transverse processes articulate with tubercles of ribs Superior articular facets point posteriorly Inferior articular processes point anteriorly – Allows rotation and prevents flexion and extension  Thoracic vertebrae Vertebrae Body ： heart-shape, superior and inferior costal fovea Vertebral foramen ： smaller, rounder Spinous processes ： long, point obliquely downward Transverse processes ： transverse costal fovea Articular processes: coronal  First Thoracic Vertebra has, on either side of the body, an entire articular facet for the head of the first rib, and a demi-facet for the upper half of the head of the second rib. superior articular surfaces are directed upward and backward; the spinous process is thick, long, and almost horizontal. transverse processes are long, and the upper vertebral notches are deeper than those of the other thoracic vertebræ. Ninth Thoracic Vertebra may have no demi-facets below. In some subjects however, it has two demi-facets on either side; when this occurs the tenth has only demi-facets at the upper part. Tenth Thoracic Vertebra has an entire articular facet on either side, which is placed partly on the lateral surface of the pedicle. Eleventh Thoracic Vertebra the body approaches in its form and size to that of the lumbar vertebræ. The articular facets for the heads of the ribs are of large size, and placed chiefly on the pedicles, which are thicker and stronger in this and the next vertebra than in any other part of the thoracic region. The spinous process is short, and nearly horizontal in direction. The transverse processes are very short, tuberculated at their extremities, and have no articular facets; Twelfth Thoracic Vertebra has the same general characteristics as the eleventh, but may be distinguished from it by its inferior articular surfaces being convex and directed lateralward, like those of the lumbar vertebræ; and by each transverse process being subdivided into three elevations, the superior, inferior, and lateral tubercles: the superior and inferior correspond to the mammillary and accessory processes of the lumbar vertebræ. Thoracic vertebra Thoracic vertebra  Lumbar Vertebrae (L1 – L5) Bodies are thick and robust Transverse processes are thin and tapered Spinous processes are thick, blunt, and point posteriorly Vertebral foramina are triangular Superior and inferior articular facets directly medially Allows flexion and extension – rotation prevented lumbar vertebrae Lumbar Vertebrae Lumbar Vertebrae Figure 7.17c  Lumbar vertebrae Vertebrae Body ： larger, kidney-shape Vertebral foramen: larger and triangular Spinous processes: projects horizontally Transverse processes: long Articular processes: sagittal Lumbar vertebra Herniated disc impinging on a spinal nerve Comparing Vertebrae Table 7–2  Sacrum (S1 – S5) Shapes the posterior wall of pelvis Formed from 5 fused vertebrae Superior surface articulates with L5 Inferiorly articulates with coccyx Sacral promontory – Where the first sacral vertebrae bulges into pelvic cavity Center of gravity is 1 cm posterior to sacral promontory  Sacrum Anterior surface: promontory, anterior sacral foramina (four pairs) Posterior surface: median sacral crest, posterior sacral foramina (four pairs), sacral hiatus, sacral cornu Lateral part: auricular surface, sacral tuberosity Sacral foramina – Ventral foramina Passage for ventral rami of sacral spinal nerves – Dorsal foramina Passage for dorsal rami of sacral spinal nerves Sacrum  Coccyx Is the “tailbone” Formed from 3 – 5 fused vertebrae Offers only slight support to pelvic organs  The Sacrum and Coccyx Characteristics - sacrum: – is curved, more in males than in females – protects reproductive, urinary, and digestive organs – attaches-the axial skeleton to pelvic – The adult sacrum: girdle of appendicular consists of 5 fused sacral skeleton vertebrae – broad muscles that fuses between puberty move the thigh and ages 25–30 leaving transverse lines – Sacral canal: replaces the vertebral canal – Sacral cornua: horn-shaped formed by laminae of the 5th sacral vertebra which do not meet at midline – Sacral hiatus: opening at the inferior end of the sacral canal formed by ridges of sacral cornua covered by connective tissues  – Median sacral crest: fused spinous processes – Lateral sacral crest: attach to muscles of lower back and hip – Auricular surface: articulates with pelvic girdle (sacroiliac joint) – Sacral tuberosity: attaches ligaments of the sacroiliac joint  4 Regions of the Sacrum – Base - the broad superior surface – Ala - wings at either side of the base to attach muscles – Sacral promontory - at the center of the base – Apex - the narrow inferior portion articulates with the coccyx  Characteristics - coccyx: – attaches ligaments and a constricting muscle of the anus – mature coccyx-consists of 3 to 5 fused coccygeal vertebrae – first 2 coccygeal vertebrae-have transverse processes and have unfused vertebral arches – coccygeal cornua - formed by laminae of 1st coccygeal vertebra  Cornua Sacral hiatus palpation Transsacral (epidural) anasthesia Segments of spinal cord & spinal nerves: Cervical (C1 – C8) Thoracic (T1- T12) Lumbar (L1- L5) Sacral (S1- S5) 1. Vertebral artery 2. Vertebral veins 3. Posterior longitudinal ligament 4. 3rd cervical spinal ganglion 5. Ventral (anterior) median fissure with anterior spinal artery 6. Subdural space 7. Denticulate ligament 8. Dorsal rootlets of 3rd cervical nerve 9. Arachnoid trabeculae 10. Arachnoid mater 11. Dura mater 12. Epidural fat  Cauda equina 9. Femoral nerve 10. 5th lumbar spinal nerve ganglion 11. Obturator nerve 12. 1st sacral dorsal foramen 13. Coccygeal nerve 14.Gluteus maximus muscle 15. Termination of filum terminale Lumbar puncture = spinal tap Herniated disc impinging on the spinal cord  The Thoracic Cage The skeleton of the chest-supports the thoracic cavity Consists of: – thoracic vertebrae – ribs – sternum (breastbone) Rib Cage - formed of ribs and sternum  Bony Thorax Forms the framework of the chest Components of the bony thorax – Thoracic vertebrae – posteriorly – Ribs – laterally – Sternum and costal cartilage – anteriorly Protects thoracic organs Supports shoulder girdle and upper limbs Provides attachment sites for muscles The Bony Thorax Parts of the sternum: Manubrium Body Xiphoid  The Sternum The sternum - a flat bone in the midline of the thoracic wall 3 parts: – 1- manubrium: superior portion of sternum broad, triangular shape articulates with collarbones (clavicles) & cartilages of 1st rib pair has a jugular notch between clavicular articulations – 2- sternal body: tongue-shaped attaches to the manubrium & costal cartilages of ribs 2–7  – 3 - xiphoid process: smallest part of the sternum attaches to the sternal body & diaphragm and rectus abdominis muscles – Xiphoid process: last part of sternum to fuse can easily be broken away Development – Sternum consists of 4 unfused bones completes fusion about age 25  Sternum Anatomical landmarks – Jugular notch Central indentation at superior border of the manubrium – Sternal angle A horizontal ridge where the manubrium joins the body Formed from three sections – Manubrium – superior section Articulates with medial end of clavicles – Body – bulk of sternum Sides are notched at articulations for costal cartilage of ribs 2–7 – Xiphoid process – inferior end of sternum Ossifies around age 40  Sternum Manubrium sterni : jugular notch, clavicular notch Body of sternum, Xiphoid process ★ Sternal angle : the junction of manubrium and body, which connects 2nd costal cartilage laterally, and lies opposite lower border of T4 posteriorly  ★ Sternal angle which connects 2nd costal cartilage laterally lies opposite lower border of T4 posteriorly The Bony Thorax  Characteristics of “typical” rib Posterior end: costal head, costal neck, costal tubercle Shaft: costal angle, costal groove Anterior end  Functions The Ribs – are flexible – are mobile – can absorb shock Rib movements (breathing): – affect width and depth of thoracic cage – changing its volume Ribs (costae)-12 pairs of long, curved, flat bones extending from the thoracic vertebrae  Ribs 1–7 (true ribs) – vertebrosternal ribs – connected to the sternum by costal cartilages Ribs 8–12 (false ribs): – do not attach directly to the sternum – Vertebrochondral ribs (ribs 8–10): fuse together merge with cartilage before reaching the sternum – Floating or vertebral ribs (ribs 11–12): connect only to the vertebrae have no connection with the sternum  Structures of the Ribs – The head (capitulum): at the vertebral end of the rib has superior and inferior articular facets – The neck: the short area between the head and the tubercle – The tubercular body – The tubercle (tuberculum): (shaft): a small dorsal elevation attaches muscles of the has an auricular facet that contacts the pectoral girdle and trunk facet of its thoracic vertebra (at T1–T10 attaches to the only) intercostal muscles which move the ribs Ribs Figure 7.20a Ribs Rib Cage Articulations of ribs  Atypical rib First rib: is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward; head is small, rounded, and possesses only a single articular facet, for articulation with the body of the first thoracic vertebra; upper surface: tubercle for scalenus anterior, sulcus for subclavian artery and vein; is no angle; under surface is smooth, and destitute of a costal groove;  Atypical rib Second Rib: is much longer than the first, but has a very similar curvature; angle is slight, and situated close to the tubercle; Body: external surface is convex, and looks upward and a little outward; near the middle of it is a rough eminence for the origin of Serratus anterior; behind and above this is attached the Scalenus posterior; internal surface, smooth, and concave, is directed downward and a little inward: on its posterior part there is a short costal groove.  Atypical rib 11th and 12th ribs lack costal necks, tubercles and angles; have each a single articular facet on the head; Avoiding the neurovascular bundle in a thoracentesis procedure (chest tube) Articulations of Ribs and Vertebrae Functions – Protects organs of the thoracic cavity-heart, lungs, and thymus – Attaches muscles: for respiration of the vertebral column of the pectoral girdle of the upper limbs  The Axial Skeleton Throughout Life Membrane bones begin to ossify in second month of development Bone tissue grows outward from ossification centers Fontanels – Unossified remnants of membranes  Disorders of the Axial Skeleton Abnormal spinal curvatures – Scoliosis – an abnormal lateral curvature – Kyphosis – an exaggerated thoracic curvature – Lordosis – an accentuated lumbar curvature – “swayback” Stenosis of the lumbar spine – A narrowing of the vertebral canal  Scoliosis Spina bifida Pathologies Kyphosis