kin 110: HUMAN ANATOMY PART 2

vertebral column/lectures 3 & 4

vertebral column

spine; extends from the cranium (skull) to the apex of the coccyx and forms the skeleton of the neck and back

is the main part of the axial skeleton

protects the spinal cord and spinal nerves, supports weight of the body superior to the level of the pelvis, provides a partly rigid and flexible axis for the body and a pivot for the head, plays important role in posture and locomotion

adult vertebral column

consists of 33 vertebrae arranged in 5 regions:

7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal

lumbosacral angle

located at the junction of the lumbar region of the vertebral column and sacrum

part of vertebral column where most motion occurs

significant motion occurs between ONLY the superior (up) 25 vertebrae

the 5 sacral vertebrae are FUSED in adults to form the SACRUM

the 4 coccygeal vertebrae are FUSED to form the COCCYX

structural differences in vertebrae

gradually become larger as the vertebral column descends to the sacrum, becomes progressively smaller towards the apex of coccyx

differences are related to the fact that the successive vertebrae bear increasing amounts of the body’s weight

why the presarcal vertebral column is flexible

bc it consists of vertebrae joined together by semirigid intervertebral (IV) discs

the 25 cervical, thoracic, lumber, and first sacral vertebrae also articulate at synovial zygapophysial joints which facilitate and control the vertebral column’s flexibility

height of presarcal vertebral column

the vertebral bodies contribute approx. three quarters of the height, and the fibrocartilage, of the IV discs contribute approx. one quarter

posterior aspect of the trunk

the torso, inferior (below) the neck and superior (above) the gluteal region

region of the body to which the head, neck, and limbs are attached

4 curvatures of adult vertebral column

cervical, thoracic, lumbar, and sacral

configuration of thoracic and sacral curvatures

they concave anteriorly (dome points forward)

configuration of the cervical and lumbar curvatures

they concave posteriorly (dome points backward)

primary curvatures

thoracic and sacral curvatures

develop during the fetal period, are reatained throughout life as a consequence of differences in height between the anterior and posterior parts of the vertebrae

secondary curvatures

cervical and lumbar curvatures

begin to appear in the cervical region during the fetal period but are not obvious until INFANCY

are maintained primarily by differences in thickness between the anterior and posterior parts of IV discs

how the cervical curvature becomes prominent

when an infant begins to hold their head erect/up on their own

how the lumbar curvature becomes apparent

apparent=clearly visible

when an infant begins to walk and assumes the upright posture

this curvature is generally more pronounced in females and ends at the lumbosacral angle (which is formed at the junction of the L5 vertebra with the sacrum)

sacral curvature in females

is reduced so that the coccyx protrudes (sticks out) less into the pelvic outlet (BIRTH CANAL)

why curvatures are important for vertebral column

they provide additional flexibility (SHOCK ABSORBING RESILIENCE) to the vertebral column, increasing the resilience already provided by the IV discs

typical vertebra

consists of a vertebral body, vertebral arch, and seven processes

vertebral body

anterior, more massive part of vertebra

gives strength to the vertebral column and supports body weight

the size, especially from T4 inferiorly, increases to bear the progressively greater body weight

covering of superior and inferior surfaces of vertebral bodies

covered with hyaline cartilage (remnants of the cartilaginous model from which bone develops), these remnants permit some diffusion of fluid between IV discs and capillaries in the vertebral body

EXCEPT AT THE PERIPHERY, NO HYALINE

epiphysial rim

at the periphery, there is a rim of smooth bone

vertebral arch

lies posterior (behind) to the vertebral body and is formed by the R/L pedicles and laminae

pedicles

short, stout processes that join the vertebral arch to the vertebral body

project posteriorly (behind) to meet the laminae

laminae

two broad, flat plates of bone that unite in the midline

where the pedicles project to

vertebral foramen

hole formed by the vertebral arch and the posterior (back) surface of the vertebral body form it

vertebral canal

contains the spinal cord, meninges (protective membranes), fat, spinal nerve roots, and vessels

vertebral notches

the indentations formed by the projection of the body and articular processes superior and inferior to the pedicles

IV foramina

what the superior and inferior vertebral notches of adjacent vertebrae combine to form

they give passage to spinal nerve roots and accompanying vessels, contain the spinal ganglia

seven processes that arise from vertebral arch of typical vertebra

one spinous process, two transverse processes, four articular processes (2 superior, 2 inferior)

spinous process

ONE median spinous process projecting posteriorly (and usually inferiorly) from the vertebral arch at the junction (meeting point) of the laminae

provides attachment for the deep back muscles, serving as levers in moving the vertebrae

transverse process

TWO, project posterolaterally (behind and to the side) from the junctions of the pedicles and laminae

provides attachment for the deep back muscles, serving as levers in moving the vertebrae

articular processes

FOUR (2 superior, 2 inferior), also arise from the junctions of the pedicles and laminae

each bear an articular surface (FACET)

are in apposition (placed in close contact) with the corresponding processes of vertebrae superior and inferior to them, forming the ZYGOPOPHYSIAL (FACET) JOINTS

interlocking of articular processes also assists in keeping adjacent vertebrae aligned, preventing one vertebra from slipping forward on the vertebra below

directionality of articular facets

facets found on articular process of vertebral arch, their direction determines the types of movements permitted and restricted between adjacent vertebrae of each region

characteristics of cervical vertebrae

body: small and wider from side to side than anterioposteriorly (front & back), top surface is concave between adjacent processes, bottom surface is convex

vertebral foramen: large and triangular

transverse processes: has none, only transverse foramen

articular processes: top facets directed superoposteriorly (above & behind), bottom facets directed infero-anteriorly (below & front)

spinous process: split into two parts

characteristics of atlas (C1) vertebrae

ring-like

NO SPINOUS PROCESS OR BODY bc its fused to C2

concave superior articular facets form ATLANTO-OCCIPITAL JOINTS with the occipital condyles

flat inferior facets meet with the C2 vertebra to form LATERAL ATLANTO-AXIAL JOINTS

articulates & supports condyle of the skull

characteristics of axis (C2) vertebrae

strongest cervical vertebra, articulates with C1

distinguishing feature is the DENS, which projects superiorly (above) from its body and provides a pivot around which the atlas turns and carries the cranium

articulates anteriorly with the anterior arch of the atlas and posteriorly with the transverse ligament of the atlas

characteristics of thoracic vertebrae

body: heart-shaped, bears one or two bilateral costal facets for articulation with the head of the rib

vertebral foramen: circular and smaller than those in cervical and lumbar regions

transverse process: long, strong, extends posterolaterally (behind & to side)

articular process: superior articular facets directed posterior & slightly laterally, inferior facets directed anteriorly & slightly medially (FACETS ARE FOR THE RIBS)

spinous process": long, sloped at an angle

characteristics of lumbar vertebrae

body: kidney shaped, larger and heavier

vertebral foramen: small triangle, larger than thoracic but smaller than cervical foramen

transverse processes: long and stubby, on posterior surface of the base of each process

articular processes: superior articular facet directed medially, inferior facets directed laterally

spinous process: short and sturdy, comes down as a plate as there is no spinal cord continuation at this level

joints found in vertebral column

joints of vertebral bodies, vertebral arches, craniovertebral, costovertebral, and sacro-iliac joints

joints of vertebral bodies

SYMPHYSES (secondary cartilaginous joints)

designed for weight bearing and strength

articulating surfaces of adjacent vertebrae are connected by IV discs and ligaments

IV discs of vertebral bodies

placed between bodies of adjacent vertebrae

provide strong attachments between the vertebral bodies and permit movement between adjacent vertebrae

have resilient deformability (serve as shock absorbers)

consist of: ANULUS FIBROSUS & NUCLEUS PULPOSES

anulus fibrosus

ring consisting of concentric lamellae of fibrocartilage, forms the circumference of the IV disc

they inset into the smooth, rounded epiphysial rims on the articular surfaces of the vertebral bodies

as nucleus pulposus dries, anulus takes on greater share of vertical load and its associated stresses & strains

nucleus pulposus

central core of IV disc, not in direct center but more posteriorly (behind) placed

85% water at birth, dehydrate with age (this is what “shrinks” you when the nucleus loses/gains water), this makes the IV discs lose their turgor and become stiff and more resistant to deformation

nuclei becomes broader when compressed and thinner when tensed or stretched

avascularity of nucleus pulposes

is avascular, meaning it receives its nourishment by diffusion from blood vessels at the periphery of the anulus fibrosus & vertebral body

IV discs & C1 and C2 vertebrae

NO IV DISCS BETWEEN C1 AND C2 VERTEBRAE

IV disc thickness

thickest in cervical and lumbar regions, thinnest in superior (top) thoracic region

thickness is RELATED TO RANGE OF MOVEMENT

uncovertebral “joints”

not really joint, but LANDMARK of CERVICAL VERTEBRAE

they are joint-like structures at the lateral and posterolateral (behind & to side) margins of IV discs

anterior longitudinal ligament

description: strong, broad fibrous band that covers and connects the anterolateral (front & to side) aspects of the vertebral bodies and IV discs

location: extends from the pelvic surface of the sacrum to anterior tubercle (small rounded projection) of C1 (atlas) vertebra and the occipital bone anterior (in front) of the foramen magnum

function: maintains the stability of the IV joints and limits the extension of the vertebral column

posterior longitudinal ligament

description: narrow, weaker compared to anterior L.L

location: runs within the vertebral canal along the posterior aspect of the vertebral bodies, is mainly attached to IV discs

function: helps prevent hyperflexion of the vertebral column and posterior herniation of IV discs

joints of the vertebral arches

zyagpophysial joints (facet joints)

facet joint= paired joint on back of the spine that connects two adjacent vertebrae

zygapophysial joints

synovial plane joints between the superior and inferior articular processes of adjacent vertebrae

each joint is surrounded by a thin, loose joint capsule

function: permit the gliding movements between articular processes (the shape and disposition/arrangement of the articular surfaces determine the type of movement possible)

ligamenta flava

description: broad, pale, yellow, elastic fibrous tissue

location: posterior part of the vertebral column’s ligaments, running thru the arches of adjacent lamina

function: resist separation of the vertebral laminae by arresting abrupt flexion of the vertebral column and thereby preventing injury to the IV discs, help preserve posture and assist with straightening the column after flexing

interspinous ligaments

the weak, almost membranous ligaments that unite adjacent spinous processes

supraspinous ligaments

the strong fibrous ligament that unites adjacent spinous processes

the supraspinous ligament merges superiorly (above) with the nuchal ligament

nuchal ligament

description: strong median ligament of the neck composed of thickened fibro- elastic tissue

location: extends from the external occipital protuberance and posterior border of the foramen magnum to the spinous process of cervical vertebrae

function: bc of the shortness of the C3-C5 spinous processes, the nuchal ligament substitutes for bone in providing muscular attachments

craniovertebral joints

types: the atlanto-occipital joints (between atlas/C1 vertebra) and occipital bone of the cranium, and the atlanto-axial joints (between the C1 and C2 vertebra)

description: craniovertebral articulations are SYNOVIAL JOINTS that have NO IV DISCS

their design allows a wider range of movement than in the rest of vertebral column

atlanto-occipital joints

location: between the lateral masses of C1 (atlas) and occipital condyles

function: permit nodding of the head (neck flexion and extension), also permits sideways tilting of the head

description: are synovial joints of the CONDYLOID TYPE, have thin, loose joint capsules

anterior & posterior atlanto-occipital membranes

location: extends from the anterior and posterior arches of C1, to the anterior and posterior margins of the foramen magnum

function: also connects C1 and cranium, help prevent excessive movement of the atlanto-occipital joint