Skeletal System-Axial System

Chapter 7Part B

Axial Skeleton

Axial system:

1) Skull 22 bones2) Bones associated with skull:

Hyoid 1 boneAuditory ossicles 6 bones

3) Vertebral column:Vertebrae 24 bonesSacrum 1 boneCoccyx 1 bone

4) Thorax:Sternum 1 boneRibs 24 bones

80 bones

Skull – Associated Bones

Auditory ossicles

Auditory ossicles:Six smallest bones…3 in each ear.Malleus, Incus and StapesFunction: amplify sound stimulus.

Greaterhorn

Lesser horn

Body

An anterior view of the hyoid bone

Hyoid:Single, U-shaped bone.Located between mandible and larynx.Often fractures during strangulation.Does not articulate with any other

bone…floats.Body: horizontal part.Greater and lesser horns/cornua:

projections for muscle attachment.Function: supports tongue and attach

some of the neck and tongue muscles.

Axial Skeleton

Axial system:

Skull 22 bonesHyoid 1 boneAuditory ossicles 6 bonesVertebral column 26 bonesThorax:

Sternum 1 boneRibs 24 bones

80 bones

Vertebral Column

Strong, flexible column.Encloses the spinal cord.Supports head at the superior end.

Composed of:Vertebrae - series of irregular bones –

….provide the strength.

Intervertebraldisc

Vertebra

Vertebral Column

Intervertebral discs:Cartilage discs inserted between the vertebrae.Provide the flexibility.Become compressed with years of pressure reduce flexibility and shorten height!

Herniated disc: sudden pressure in the lumbar region intervertebral discs may tear and push out posteriorly pressure on the spinal nerves severe pain.Complete rest or surgery.

Intervertebraldisc

Vertebra

Vertebral Column – Normal Curves

Four major curves:Cervical curve – neck curve.Thoracic curve – upper back curve.Lumbar curve – lower back curve.Sacral curve – hip curve.

Function: help absorb shock and provide flexibility and balance.

New bone- a single curve with C shape-fromthoracic and sacral curves-Primary curves (appear late in fetal development). Present at birth.- Also called Accommodation curves-because they accommodate visceral organs.

Thoracic curve- accommodates thoracic organsSacral curve-accommodates abdominopelvic organs

Vertebral Column – Normal Curves

Secondary curves-cervical and lumbar curves- Appear several months after birth- Also called Compensation curves-permits upright

posture/helps shift the trunk weight over the legs as the child begins to stand.

All four curves are fully developed by age 10!

Vertebral Column – Abnormal Curves

Normal Curves

Sacral curve

Lumbar curve

Thoracic curve

Cervical curve

Vertebral Column – Abnormal Curves-Scoliosis

- Abnormal lateral curvature of the spine in one or more of the movable vertebrae.

- Most common distortion of the spinal curvature.

Scoliosis

Vertebral Column – Abnormal Curves-Kyphosis

Kyphosis- Kyphos-humpbacked or bent

- The normal thoracic curvature becomes exaggeratedposteriorly, producing a "round-back" appearance.

Vertebral Column – Abnormal Curves-Lordosis

- “Swayback“ appearance- Both the abdomen and the buttocks protrude

abnormally- Caused by an anterior exaggeration of the lumbar

curvature- Occur during pregnancy or the result from abnormal

obesity or weakness in the muscles of the abdominal wall

Lordosis

Lumbarvertebrae

Vertebral Column – Typical Vertebra

Parts of a typical vertebra:Body/Centrum: thick disc located on the anterior side…where intervertebral disc is placed to

align the vertebrae.

Pedicles: extend from the centrum become lamina fuse to become spinous process.

Spinous process: a projection that points out on the posterior side.

Vertebral foramen: a hole formed by fusion of pedicles/lamina forms vertebral canalhouses spinal cord.

Transverse process: projections on the lateral sides.

Body/Centrum

Pedicle

Articularprocess/facet

Transverseprocess

Spinousprocess

Lamina

Vertebralforamen

Vertebral canal

Arrow passing through vertebral foramen

Intervertebral foramen

Superior articular processes- articulates with inferiorarticular process of the vertebra just above.

Inferior articular processes- articulates with superior articular process of the vertebra just below.

Intervertebral foramen: openings in between vertebraefor spinal nerves to exit.

Superior viewAnterior

Posterior

Vertebral Column – Typical Vertebra

* Slide 19

Vertebral Column – Typical Vertebra

Spina bifida: A congenital defect where pedicles fail to unite vertebral foramen is open on the posterior side meninges protrude out spinal cord is not protected.Partial or complete paralysis, loss of urinary control, absence of reflexes.Can be detected prenatally….sonography, amniocentesis, testing mother’s blood.

Body/Centrum

Pedicle

Articularprocess/facet

Transverseprocess

Spinousprocess

Lamina

Vertebralforamen

Vertebral Column – Cervical Vertebrae

7 cervical vertebrae….C1 C7.Smallest vertebrae.Extend from occipital bone of skull to

thorax.

Typical cervical vertebra:- Small centrum.- Large vertebral foramen- Very short transverse processes.Bifid spinous process.Transverse foramen: next to transverse

process protect blood vessels going to or coming back from the brain.

Vertebral body

Vertebralforamen

Transverseprocess

Bifid spinousprocess

Superior articular

facet

Transverseforamen

)

)

Vertebral Column – Cervical VertebraeC1: atlas.

Looks like a ring.Skull rests on it.No centrum and no spinous process.Large round vertebral column foramen with anterior and posterior arch.Superior articular facet – articulates with occipital condyles nodding movement…yes!Inferior articular facet – articulates with superior articular facet of C2.

C2: axis.Rests on C1. C1 sits on top of C2.Dens/odontoid process - a finger-like peg in place of the centrum fits inside vertebral foramen of C1 allows rotation movement of the head…no!

C3-C6: typical cervical vertebrae.

C7: vertebra prominens.Spinous process has a rounded tip…for attachment of ligaments…support head.

Vertebral Column – Thoracic Vertebrae12 thoracic vertebrae….T1 T12.(increase in size from superior to inferior)T2-T8-typical vertebraeT1, T9, T10, T11 and T12-atypical vertebrae

Characteristic features- Vertebral body is heart shaped.- Presence of demi-facets (superior & inferior costal

facets) on the sides of each vertebral body – these articulate with the heads of the ribs (except T1, T9, T10, T11 and T12-single costal facet-atypical vertebrae).

- Presence of costal facets on the transverse processes –these articulate with the tubercles of the ribs. They are present on T1-T10 only.- The spinous processes are long, pointed, and bent inferiorly.

Vertebral Column – Thoracic Vertebrae

Thoracic vertebrae

Rib

Articulation of thoracic vertebrae with ribs

Vertebral Column – Lumbar Vertebrae

5 lumbar vertebrae….L1 L5.- Largest and the strongest vertebrae ….weight

bearing.- Huge centrum, oval shaped (no costal facet)- Slender transverse process (no costal facets)- Spinous process is thick, broad, flattened and

projects out posteriorly.

Vertebral Column – Sacrum

- A triangular bone formed by fusion of 5 sacral vertebrae….S1 S5.- Fusion takes place around age 16-25 years.

- Sacral apex- Narrow inferior portion of sacrum

- Sacral base- Broad superior surface.- Sacral ala- Wings extending on either side at the base of the sacrum

(extensive area for muscle attachment).

- Sacral promontory- Prominent bulge at the anterior tip of base.

- Transverse lines/ridges: represent fusion of the sacral vertebrae.

Anterior view

Vertebral Column – Sacrum

Sacral canal: continuation of vertebral canal…contains spinal nerves.

Sacral hiatus: inferior end of the sacral canal.

Sacral cornua: two small processes projecting inferiorly on either side of the sacral hiatus

Median sacral crest-Ridge formed by fused spinous process.

Lateral sacral crest- Ridge formed by fused transverse process. Auricular surface- Flattened area lateral and anterior to lateral crest-articulates with ilium (hip bone).

Sacral tuberosity- Roughened area between lateral sacral crest and auricular surface (site of ligament attachment that stabilizes sacroiliac joint).

Sacral foramina- 4 pairs-on either side of median sacral crest.

Auricular surface

Vertebral Column – Coccyx

- Small triangular shaped bone/s formed by fusion of Co1 Co4 (Happens around age 20-30).

Coccygeal cornua-Prominent laminae of first coccygeal vertebrae-curve to meet sacral cornua.

- At the very bottom portion of the spine- represents a vestigial tail (hence the common term "tailbone")

Axial Skeleton

Axial system:

Skull 22 bonesHyoid 1 boneAuditory ossicles 6 bonesVertebral column 26 bonesThorax:

Sternum 1 boneRibs 24 bones

80 bones

Thorax

Refers to chest or thoracic cage.Composed of:

Sternum….the breast bone…on anterior side.Thoracic vertebrae…on the posterior side.Ribs…connect sternum and vertebrae.

Rib cage-formed by ribs and sternum

Anterior view Posterior view

Thorax - Sternum

Sternum: the breastbone.Flat, narrow bone present on the anterior side of the thorax.

Made of 3 parts:Manubrium: Widest and most superior portion of sternum-articulates with medial end of clavicle (sternoclavicular joint)

and 1st pair of ribs.

Jugular notch/Suprasternal notch-shallow indentation on superior surface of manubrium (large, visible dip in between the neck and the collar bone).

Body: articulates directly with 2nd – 7th rib; indirectly with 8th – 10th ribs.

Xiphoid: remains cartilaginous till age 40, attaches diaphragm and abdominal muscles, often fractures during improper CPR internal bleeding.

Jugular notch/Suprasternal notch

Thorax - Ribs

Ribs: 12 pairs of flat bones.Intercostal spaces: spaces between the ribs…contain respiratory muscles.Anteriorly – sternal end of some ribs attach to the sternum.Posteriorly – vertebral end connect to two facets on thoracic vertebrae.

Head of the rib to the facet on the centrum of thoracic vertebrae.Tubercle of the rib to the facet on the transverse process of thoracic vertebrae.

11, 12

(sternal end)

(vertebral end)

Thorax - Ribs

Classification of the ribs:Pairs 1 7: true ribs or vertebrosternal ribs…connect to thoracic vertebrae and directly to

sternum through costal cartilage.

Pairs 8 12: false ribs…articulate indirectly or do not attach to sternum at all.Pairs 8 10 – vertebrochondral ribs…attach to thoracic vertebrae and indirectly to

sternum-costal cartilages of ribs 8-10 fuse together and merge with rib 7 before they reach sternum.

Pairs 11, 12 – floating/vertebral ribs…only attached to thoracic vertebrae…no connection to sternum (sternal end is free!)

11, 12