Download Skeletal System -Axial System

Skeletal System
-Axial System
Chapter 7
Part B
Axial Skeleton
Axial system:
1) Skull
22 bones
2) Bones associated with skull:
Hyoid
1 bone
Auditory ossicles 6 bones
3) Vertebral column:
Vertebrae
24 bones
Sacrum
1 bone
Coccyx
1 bone
4) Thorax:
Sternum
1 bone
Ribs
24 bones
80 bones
Skull – Associated Bones
Auditory ossicles:
Six smallest bones…3 in each ear.
Malleus, Incus and Stapes
Function: amplify sound stimulus.
Auditory ossicles
Greater
horn
Body
Lesser
horn
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
Hyoid
Auditory ossicles
Vertebral column
Thorax:
Sternum
Ribs
22 bones
1 bone
6 bones
26 bones
1 bone
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.
Intervertebral
disc
Vertebra
Vertebral Column
Intervertebral
disc
Vertebra
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.
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.
Vertebral Column – Normal Curves
New bone- a single curve with C shape-from
thoracic 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 organs
Sacral curve-accommodates abdominopelvic organs
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
Cervical curve
Thoracic curve
Lumbar curve
Sacral curve
Normal Curves
Vertebral Column – Abnormal Curves-Scoliosis
Scoliosis
- Abnormal lateral curvature of the spine in one or
more of the movable vertebrae.
- Most common distortion of the spinal curvature.
Vertebral Column – Abnormal Curves-Kyphosis
Kyphosis
- Kyphos-humpbacked or bent
- The normal thoracic curvature becomes exaggerated
posteriorly, producing a "round-back" appearance.
Vertebral Column – Abnormal Curves-Lordosis
Lordosis
Lumbar
vertebrae
- “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
Vertebral Column – Typical Vertebra
Spinous
process
Transverse
process
Vertebral
foramen
Intervertebral
Lamina
foramen
Articular
process/
facet
Pedicle
Body/
Centrum
Arrow passing through
vertebral foramen
Vertebral canal
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 canal 
houses spinal cord.
Transverse process: projections on the lateral sides.
Vertebral Column – Typical Vertebra
Posterior
Superior articular processes- articulates with inferior
articular process of the vertebra just above.
Anterior
Superior view
Inferior articular processes- articulates with superior
articular process of the vertebra just below.
Intervertebral foramen: openings in between vertebrae
for spinal nerves to exit.
* Slide 19
Vertebral Column – Typical Vertebra
Spinous
process
Transverse
process
Vertebral
foramen
Lamina
Articular
process/
facet
Pedicle
Body/
Centrum
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.
Vertebral Column – Cervical Vertebrae
7 cervical vertebrae….C1  C7.
Smallest vertebrae.
Extend from occipital bone of skull to
thorax.
Typical cervical vertebra:
Bifid spinous
process
Vertebral
foramen
Vertebral body
Transverse
process
Transverse
foramen
Superior
articular
facet
- 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 Column – Cervical Vertebrae
C1: 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 Vertebrae
12 thoracic vertebrae….T1  T12.
(increase in size from superior to inferior)
T2-T8-typical vertebrae
T1, 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
Articulation of thoracic vertebrae with ribs
Thoracic vertebrae
Rib
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
Anterior view
- 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.
Vertebral Column – Sacrum
Auricular surface
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.
Vertebral Column – Coccyx
- At the very bottom portion of the spine- represents a vestigial tail (hence the common term
"tailbone")
- 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.
Axial Skeleton
Axial system:
Skull
Hyoid
Auditory ossicles
Vertebral column
Thorax:
Sternum
Ribs
22 bones
1 bone
6 bones
26 bones
1 bone
24 bones
80 bones
Thorax
Anterior view
Posterior view
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
Thorax - Sternum
Sternum: the breastbone.
Flat, narrow bone present on the anterior side of the thorax.
Jugular notch/
Suprasternal notch
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.
Thorax - Ribs
11, 12
(vertebral end)
(sternal end)
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.
Thorax - Ribs
11, 12
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!)