Chapter 7 Part B

Chapter 7 – Part B

The Skeleton

7.2 The Vertebral Column

General Characteristics

· Extends from skull to pelvis

· Also called spine or spinal column

· Functions to transmit weight of trunk to lower limbs, surround and protect spinal cord, provide attachment points for ribs and muscles

· Flexible curved structure contains 26 irregular bones called vertebrae in five major regions

· Regions and curvatures

– Regions: ~28² long vertebral column broken into five major regions:

1. Cervical: consists of 7 vertebrae

2. Thoracic: 12 vertebrae

3. Lumbar: 5 vertebrae

– Remember meal times: 7 am, 12 noon, and 5 pm

4. Sacrum: one bone, formed from fusion of several bones, articulates with hip

5. Coccyx: also fused bones that form terminus of column

– Curvatures: four main curves in the column help to increase resilience and flexibility of spine

· Cervical and lumbar curvatures

– Concave posteriorly

· Thoracic and sacral curvatures

– Convex posteriorly

· Ligaments: along with trunk muscles, help support vertebral column

– Anterior and posterior longitudinal ligaments: continuous bands from neck to sacrum that run down front and back of spine

· Support and prevent hyperextension (backward) or hyperflexion (forward) bending

– Ligamentum flavum: connects adjacent vertebrae

– Short ligaments: connect each vertebra to those above and below

· Intervertebral discs

– Cushionlike pad sandwiched between vertebrae that act as shock absorbers

– Composed of two parts

· Nucleus pulposus

– Inner gelatinous nucleus

– Gives disc its elasticity and compressibility

· Anulus fibrosus

– Outer collar composed of collagen and fibrocartilage

– Limits expansion of nucleus pulposus when compressed

Clinical – Homeostatic Imbalance 7.2

· Abnormal spinal curvatures can be congenital or result from disease, poor posture, or unequal pull of muscles on spine

· Scoliosis: abnormal lateral rotation of spine, most often in thoracic region, which may lead to breathing difficulties

Clinical – Homeostatic Imbalance 7.2

· Kyphosis (hunchback): is abnormal dorsal thoracic curvature common in people with osteoporosis, tuberculosis of spine, rickets, or osteomalacia

· Lordosis (swayback): is accentuated lumbar curvature that can result from disease but is also seen in men with pot bellies and in pregnant women

General Structure of Vertebrae

· All have common structural pattern consisting of:

– Body (centrum), the anterior weight-bearing region

– Vertebral arch composed of:

· Two pedicles: short pillars form sides of arch

· Two laminae: fused, flattened plates form posterior arch

– Vertebral foramen: enclosure formed by body and vertebral arch coming together

– Vertebral canal: series of vertebral foramina

– Intervertebral foramina: lateral openings between vertebrae for passage of spinal nerves

· Vertebrae have seven processes:

– Spinous process: projects posteriorly

– Transverse processes (2): project laterally

– Superior articular processes (2): protrude superiorly

– Inferior articular processes (2): protrude inferiorly

Regional Vertebral Characteristics

· Cervical vertebrae

– C1 to C7: smallest, lightest vertebrae

– C3 to C7 share following features:

· Oval-shaped body

· Exception: C7 spinous processes are split (bifid)

· Large, triangular vertebral foramen

· Transverse foramen found in each transverse process for artery passageways

· C7 is vertebra prominens; large and can be felt through skin, so used as a landmark

Regional Vertebral Characteristics (cont.)

· Cervical vertebrae (cont.)

– C1 (atlas) and C2 (axis) have unique features

– Atlas (C1)

· No body or spinous process

· Consists of anterior and posterior arches, and two lateral masses

· Superior surfaces of lateral masses articulate with occipital condyles

– Occipital condyles “carry” skull

· Movement for nodding head “Yes”

– Axis (C2)

· Has body and processes like other vertebrae

· Major feature is knoblike dens that projects superiorly into anterior arch of atlas

– Dens is the “missing” body of atlas

· Dens is a pivot for rotation of atlas

· Movement allows side to side rotation for saying “No”

Regional Vertebral Characteristics (cont.)

· Thoracic vertebrae

– T1 to T12 increase in size and articulate with ribs

– Unique characteristics:

· Body is heart shaped with two small demifacets that articulate with ribs

– T10 to T12 have only single facet, not two

· Vertebral foramen is circular

· Long, sharp spinous process points inferiorly

· Transverse processes have transverse costal facets that articulate with ribs (except T11, T12)

· Location of articular facets allows rotation of this area of spine

· Lumbar vertebrae

– L1 to L5 “small of back”; receives most stress, so bodies are massive

– Other characteristics:

· Short, thick pedicles and laminae

· Flat, hatchet-shaped spinous processes point posteriorly

· Vertebral foramen is triangular

· Orientation of articular facets locks lumbar vertebrae together to prevent rotation

· Sacrum: triangular bone shapes posterior wall of pelvis; made from five fused vertebrae (S1–S5)

– Superior articular process articulates with L5

– Articulates inferiorly with coccyx and laterally with hip bones via its auricular surfaces, forming sacroiliac joints

– Sacral promontory: anterosuperior margin

– Transverse ridges mark lines of fusion

– Anterior sacral foramina: lie at lateral ends of ridges; act as openings for nerves and vessels

– Alae: winglike expansions

– Median sacral crest: roughened bumps on posterior midline and lateral sacral crest; roughened area seen laterally on posterior side

– Posterior sacral foramina: large openings for sacral spinal nerves

– Sacral canal: continuation of vertebral canal

– Sacral hiatus: large opening at end of canal

· Coccyx: tailbone formed from three to five fused vertebrae; articulates superiorly with sacrum

– Very little function

7.3 Thoracic Cage

· Composed of:

– Thoracic vertebrae posteriorly

– Sternum and costal cartilages anteriorly

– Ribs laterally

· Functions

– Protects vital organs of thoracic cavity

– Supports shoulder girdles and upper limbs

– Provides attachment sites for muscles of neck, back, chest, and shoulders

Regional Vertebral Characteristics (cont.)

Sternum

· Also called the breastbone; consists of three fused bones:

– Manubrium: superior portion that articulates with clavicular notches and ribs 1 and 2

– Body: midportion that articulates with costal cartilages of ribs 2 through 7

– Xiphoid process: inferior end that is site of muscle attachment

· Not ossified until ~age 40

· Sternum has three important anatomical landmarks:

– Jugular notch

· Central indentation in superior border of manubrium

– Sternal angle

· Horizontal ridge across front of sternum

– Xiphisternal joint

· Point where sternal body and xiphoid process fuse

Clinical – Homeostatic Imbalance 7.4

· Xiphoid process projects posteriorly in some people

· A blow to the chest (chest trauma) at the level of the xiphoid process can push process into underlying liver or heart

· Can cause massive hemorrhaging

Ribs

· 12 pairs form sides of thoracic cage

· All attach posteriorly to bodies and transverse processes of thoracic vertebrae

· True (vertebrosternal) ribs (pairs 1–7)

– Attach directly to sternum by individual costal cartilages

· False (vertebrochondral) ribs (pairs 8–10)

– Attach indirectly to sternum by joining costal cartilage of rib above

· Vertebral (floating) ribs (pairs 11–12)

– No attachment to sternum

· Main parts of rib:

– Shaft: flat bone that makes up most of rib

· Costal groove: houses nerves and vessels

– Head (posterior end)

· Articulates with facets (demifacets) on bodies of two adjacent vertebrae

– Neck: constricted portion beyond head

– Tubercle: knoblike structure lateral to neck

· Articulates posteriorly with transverse costal facet of same-numbered thoracic vertebra