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The Axial Skeleton (Anatomy exam 4)
Terms in this set (49)
the axial skeleton is made up of the vertebral column (primary skeleton) along with the cranium, sternum and the ribs. All of these components have a protective function as well as a support function.
Structure of vertebral column
-the vertebral column is composed of a series of individual bones (vertebrae) articulated in a series of curves bound together by deformable discs. There are 33 bones in all.
Function of vertebral column
The vertebral column:
-provides a rigid but flexible axis for movement
-provides a firm base for suspending structures (i.e. ribs) that allow body to maintain cavities with relative constant shape and size
-Creates a link between the upper and lower extremities
-Provides protection for the spinal cord
-Serves as a strong and flexible support for the trunk
-Primary functions are posture, support of body weight, locomotion, and protection of the spinal cord and nerves.
Movements in vertebral column
Flexion/extension; side-bending; rotation --> 3 degrees of freedom.
Divisions of vertebral column
The vertebral column is divided into five distinct regions:
-Each region is unique in structure: different curves and body articulations
-Each region meets different functional demands: structure will dictate function.
-Of the 33 bones only 24 actually move/allow movement.
-5 regions: cervical, thoracic, lumbar, sacrum, coccyx.
-The cervical region is the axial skeleton of the neck
-It supports and moves the head
-Composed of 7 cervical vertebrae in humans (C1-C7)
-Distinctive feature = foramina transversarium. The vertebral arteries pass through these openings in the transverse processes.
-The transverse diameter of the vertebrae is greater than the anterior/posterior diameter and height.
-C1 has no spinous process or body; referred to as the atlas; ring shaped and supports the skull
-C2 is called the axis because C1 rotates on it; distinguishing feature is the dens which projects superiorly...held in place by the transverse ligament of the atlas
-No spinous process or body
-Ring shaped and supports the skull
-Articulates with the occipital bone
-Distinguishing feature = dens which projects superiorly. Held in place by the transverse ligament of the atlas. The dens articulates with the atlas in a flexible pivot joint
-Called the axis because C1 rotates on it
-12 thoracic vertebrae in humans (T1-T12)
-Suspends the ribs
-Less flexible and more stable than cervical region because of rib articulations
-Supports the thoracic (respiratory) cavity
-Distinct characteristics are the costal facets for articulation with the ribs
The thoracic cage: Rule of Threes
-Relates to the spinous processes in relation to transverse processes:
--T1-T3: spinous processes project posteriorly in the same plane as the transverse processes
--T4-T6: spinous processes are directed slightly downward; located midway between the transverse process of its own vertebra and that of the vertebra below.
--T7-T9: Tips of spinous processes are in the same plane as the transverse processes of the vertebra below
--T10: same as T7-T9
--T11: same as T4-T6
--T12: same as T1-T3
-Region of the spine that is posterior to the abdominal cavity
-Allows mobility between the thorax and the pelvis
-5 lumbar vertebrae in humans (L1-L5)
-Large bodies, no costal facets
-Provides support for the upper axial skeleton and extremities during static and dynamic situations
-Distinctive feature is mammillary process (on the superior articular process)
-Region of the spine that unites vertebral column with the pelvic girdle to which it is strongly bound.
-Primary function is to support body weight and transmit upper extremity forces to the lower extremities
-5 fused sacral vertebrae in humans (S1-S5)
-Vertebral column exhibits 4 curves (two types) in humans: kyphotic curves and lordotic curves
-Curves provide additional stability
-When you are born, you are in fetal curvature--this is the primary curvature (kyphotic). Other curvatures, called secondary curvatures, start appearing when you start bearing weight.
-Curves located in the thoracic and sacral region
-Determined by the shape of the vertebrae
-Kyphotic curves are convex posteriorly
-An increase in the thoracic kyphosis often develops in the elderly, esp. women and is referred to as Dowager's hump.
-This type of curvature is more stable/rigid and less mobile than lordotic curves.
-Curves located in the cervical and lumbar regions
-Found in regions of greatest mobility
-Curvature is convex anteriorly
-Obesity can increase the lordosis and cause back pain 2nd to the change in the center of gravity
-This type of curvature is more mobile than kyphotic curves
Osteology of vertebrae
-Each vertebra is made of the following components:
1) vertebral body
2) vertebral arch
3) seven processes
-Body becomes progressively larger as we move down the spine (from C1-L5) in order to accommodate progressively increasing loads
-The arch encloses the vertebral foramen
-Resembles a short long bone
-7 processes: The spinous process is a median posterior projection arising at the junction of the two laminae; a transverse process extends laterally from each side of the vertebral arch; the paired superior and inferior articular processes protrude superiorly and inferiorly, respectively, from the pedicle-lamina junctions.
-Increase in size from C1 to L5 to accommodate progressively increasing loads
-Made up of: trabeculae, ring apophyses, vertebral endplates.
-Trabeculae = thick core in body surrounded by thin shell of cortical bone, supports & distributes weight
-Ring apophyses (epiphysis/growth plates) = over superior and inferior portions of cortical bone, ring of smooth bone that surrounds trabecular bone, represent secondary areas of ossification.
-vertebral endplates = superior and inferior surfaces of trabecular bone, covered with hyaline cartilage
-Thick core of trabecular bone in the vertebral body surrounded by a thin shell of cortical bone
-Function is to support and distribute the weight
-Has canals for basivertebral veins
-Nutrient foramen on the anterior surface of the body and a larger foramen on the posterior for the basivertebral veins
Ring apophysis (epiphysis)
-Located over the superior and inferior portions of the cortical bone
-A ring of smooth bone that surrounds the trabecular bone (ring at the top of the body)
-Represent secondary areas of ossification
-Superior and inferior surfaces of trabecular bone
-Covered with hyaline cartilage
-Forms the vertebral foramen together with the vertebral body
-Formed by the body, lamina, and the pedicles
-Protects neural tissue
-Composed of less trabecular bone and more cortical bone than the vertebral body: enables the vertebral arch to better withstand torsional forces.
-Spinal cord travels through the foramen.
-Ventral (anterior) part of vertebral arch
-Function is primarily protection
-Vertebral notches are indentations in the pedicle (the pedicles have notches on their superior and inferior borders, providing lateral openings btw adjacent vertebrae called intervertebral foramina)
-Superior and inferior concavities of pedicles form intervertebral foramen when adjacent vertebrae articulate (transmit spinal nerves from spinal cord)
-short, bony pillars projecting posteriorly from the vertebral body
-Extend dorsally (posteriorly) from the pedicles and fuse in the midline to form spinal process.
-Function is primarily protection
-Flattened plates that fuse in the median plane, and complete the vertebral arch posteriorly.
-Projects dorsally (posteriorly) from junction between the two laminae (median posterior projection arising at the junction of the two laminae)
-Functions as lever for the back extensors; primarily for movement
-the circular opening made by the posterior body of the vertebrae, the pedicles, the lamina, and the spinous process is the vertebral canal.
-The vertebral canal houses the spinal cord and associated meningeal coverings.
-The inferior vertebral notch of the superior vertebrae in a pair matches with the superior vertebral notch of the inferior member in a pair to form an intervertebral foramina
-The intervertebral foramen transmit spinal nerves from the spinal cord
-Paired articular processes
-Superior and inferior
-Extend from junctions of pedicles and laminae
-Each process has an articular facet for either the superior or the inferior
-The inferior articular processes of each vertebra form movable joints with the superior articular processes of the vertebra immediately below.
-Sometimes referred to as the facet joint
-Helps to resist anterior movement of a superior vertebra on an inferior.
-pars interarticularis between the superior and inferior facet
Superior articular process
-Located on the superior part of the vertebrae
-Articulates with the inferior articular process of the vertebrae above
inferior articular process
-Located on the inferior part of the vertebrae
-Articulates with the superior articular process of the vertebrae below
-Together with the superior process forms the zygapophyseal joints
-Region between the superior and inferior articular processes
-If defective results in a spondylolysis (defect of the pars)
-When anterior displacement occurs it is called spondylolisthesis
-Fracture of the articular facet, usually due to a congenital defect or fracture in the pars
-Results in anterior displacement of vertebra
-spondylolysis only refers to the separation of the pars interarticularis (a small bony arch in the back of the spine between the facet joints), whereas spondylolisthesis refers to anterior slippage of one vertebra over another (in the front of the spine).
-Project laterally from the junction between the pedicles and laminae
-Serves as levers for muscles
---Increases leverage on the vertebral column
-Formed by fusion of five sacral vertebrae
-Concave ventrally and convex dorsally
-Concavity serves to increase the pelvic cavity
-Strength and stability of the pelvis.
-Inferior 1/2 is NWB and why it is tapered...Wolff's law
-Vertebrae which has some characteristic features of both adjacent spinal segments
-Typically occurs where morphology of vertebrae markedly changes from one level to the next (i.e. cervicothoracic, thoracolumbar, lumbosacral)
-Orientation of the facets changes to promote different movements
Intervertebral discs: general characteristics
-major compression-bearing structures of the spine
-interposed between adjacent vertebrae
-present from C2-C3 to L5-S1. Not present between C1 and C2, or after S2.
-Together with the vertebral bodies form anterior elements of vertebral column, giving it support.
-Deeper anteriorly in lumbar and cervical regions contributing to the anterior convexities
-Nutrition via diffusion from trabecular portions of the vertebral bodies
Intervertebral discs: components
1) Nucleus pulposis
2) Annulus fibrosis
-Fills 20% to 50% of the total disc area depending on the region. Least in cervical discs and most in lumbar discs.
-Fine fibrous strands within proteoglycan gel
-Gel properties provide for viscoelasticity (elastic and viscous properties--viscous = thick consistency btw solid and liquid) and water imbibement (to take in water)
-Gel begins to be replaced by fibrocartilage by end of first decade until eventually gel is not distinguished from annulus fibrosis. This compromises disc's capacity for water imbibement and viscoelasticity.
-Concentric lamellar bands of fibrocartilage and collagenous fibers
-Attaches to the apophyseal ring of the vertebral body via Sharpey's fibers
-Insert into the epiphyseal rim
-The intervertebral disc forms a bond between two adjacent vertebral bodies
-Fibers of annulus attach at cartilaginous endplates and peripheral osseous portions of the vertebral bodies via Sharpey's fibers
-Joint between adjacent vertebrae, via intervertebral discs.
Ligaments of intervertebral joints
-Anterior longitudinal ligament
-Posterior longitudinal ligament
Ligaments of the vertebral arch
Anterior longitudinal ligament
-Ligament of intervertebral joints
-Runs from occiput to body of S1 on the anterior aspect of the vertebral column
-Firmly attached to the margins of the vertebral bodies and discs and less firmly to the midparts of the bodies.
-thickest portion opposite the discs
-Prominent and thickest in the thoracic region
-In cervical region, presents as a thin narrow strip
-Broad and thin in the lumbar region
-Helps to prevent hyperextension of the vertebral column
-Maintains the structure of the joints and helps restrict extension
Posterior Longitudinal ligament
-Runs from the body of axis (C2) to S1 along the posterior aspect of the vertebral bodies.
-Lies within the vertebral canal, anteriorly to the spinal cord, and expands cranially to form the tectorial membrane
-Forms a protective barrier between the spinal cord, vertebrae, and discs.
-Attaches to discs and margins of vertebral bodies
-Broadest superiorly where it continues as the tectorial membrane
-Does not attach to discs in the cervical region
-Narrow in lumbar region
-Implications for posterolateral disc herniations
-Helps to prevent hyperflexion of the spine and posterior displacement of the disc.
Zygapophyseal (Facet) Joints
-Synovial joints formed between the superior and inferior articular processes of adjacent vertebrae.
-Enclosed by a fibrous joint capsule (loose articular capsule)
-Different characteristics in cervical, thoracic, and lumbar spine
-this joint is very strong and fairly loose. It is relatively more taut in the lumbar and thoracic spine
-Permits gliding motions between the vertebrae
-During extension, facet joint closes (both facets close)
-During flexion, facet joint opens (both facets open)
-During side-bending and rotation: facet joint closes down on same side as rotation, opens on other side.
-Connects laminae of adjacent vertebrae from C1-sacrum
-Thickest in the lumbar spine; thin in the cervical region
-Extends ventrally from facet joint capsules
-Composed of yellow elastic tissue (elastin)
-Springlike properties that permits control of flexion of the spine as it assists in restoring the force required for extension--elasticity of ligamenum flavum assits the vertebral column in resuming upright posture after flexion (ability to recoil back assists in coming back into extension)
-Loses elasticity with age
-Helps to maintain normal spinal curvature
-Extends from C7 to sacrum
-Connects the tips of spinous processes
-Relatively thick in lumbar spine
-Extends between adjacent spinous processes
-Attaches along the length of the spinous process
-Thin compared to the supraspinous ligament
-Thickest in the lumbar spine
-Definitive interspinous ligament is lacking in cervical spine
-Runs from C7 to Occiput
-Merges with the supraspinous ligaments
-From the external occipital protuberance and the foramen magnum to the spinous processes of cervical vertebra
-Actually a continuation of supraspinous and interspinous
-stabilizes head and neck
-Extend between adjacent transverse processes
-Relatively thin in the lumbar spine
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