The Axial Skeleton

By- Dr. Armaan SinghBy- Dr. Armaan Singh

I highly recommend Professor Wissman’s sites For bones:

http://homepage.smc.edu/wissmann_paul/bones/EBbonestutorial.html Check out all his links:

http://homepage.smc.edu/wissmann_paul/anatomy1/

Also check out:

Site for xrays & other diagnostic procedures:

http://www.radiologyinfo.org/en/sitemap/category.cfm?category=diag

http://homepage.smc.edu/wissmann_paul/bones/EBbonestutorial.html

This is an example of Prof Wissman’s bone site; this doesn’t show the roll-over answers

THE SKELETAL SYSTEMThe Axial Skeleton

The skeleton consists ofBones (206)CartilagesJoints – also called articulations, are the

junctions between skeletal elementsLigaments – connect bones

Divided into axial and appendicular

Axial skeleton - forms long axis of bodySkullVertebral columnThoracic cage

Appendicular skeleton – appendages and what they attach toUpper limbs (arms)Pectoral girdle (shoulder)Lower limbs (legs)Pelvic girdle

Axial skeletonSkullVertebral columnThoracic cage

Axial skeleton is shown in green

The Skull Cranial bones (or cranium)

Enclose the cranial cavity, which supports and protects the brain

Attachment sites for some head and neck muscles

Facial bones (anterior aspect of skull) Form framework of face Form cavities for sense organs of sight, taste and smell Provides openings for passage of air and food Hold the teeth Anchor the muscles of the face

Cranium Vault – “calvaria” = skullcap

Forms superior, lateral and posterior aspects of skull, and forehead

Base or floor: inferior part Prominent bony ridges divide

cranial base into 3 “fossae” (steps) – anterior, middle and posterior

Anterior cranial fossa

Middle cranial fossa

Posterior cranial fossa

(looking down on the floor of the skull)

Cranial bones

Frontal bone Parietal bones (paired) Occipital bone Temporal bones (paired) Sphenoid bone Ethmoid bone

Cranial bones

parietal parietalfrontal

temporal

parietal

occipital

_______sphenoid_____ethmoid

occipital

Temporal bones

this is the right temporal bone looking at it from the right side

Sphenoid

Ethmoid Small cranial bones…

Sutures

Immovable, interlocking joints of flat bones of skull

Irregular, saw-toothed appearance Largest 4 skull sutures: where bones articulate

with parietal bones Coronal Sagittal Squamous Lambdoid (FIND THEM)

Find: coronal, squamous and lamboid sutures

Find: sagittal and lambdoid sutures

Cranial “cavity” – houses brain Smaller cavities

Housing middle and inner earNasal cavityOrbitsSinuses

Openings (foramina, canals, fissures) for:Spinal cordBlood vesselsTwelve cranial nerves: I-XII

Remember, the skull is composed of:

1. Cranial bones (or cranium)[these were just reviewed]

and

2. Facial bones (anterior aspect of skull) Form framework of face Form cavities for sense organs of sight, taste

and smell Provides openings for passage of air and food Hold the teeth Anchor the muscles of the face

Facial bones

Mandible Vomer Maxillae (paired) Zygomatics (paired) Nasal (paired) Lacrimal (paired) Palatines (paired) Inferior nasal conchae (paired)

MandibleVomerMaxillae (paired)Zygomatics (paired)Nasal (paired)Lacrimal (paired)Palatines (paired)Inferior nasal conchae (paired)

Facial bones:

Mandible (lower jaw)

Maxilla (there are 2 which fuse, forming the upper jaw)

Nasal cavity

Of bone and cartilage Roof is ethmoid’s

cribriform plate Floor formed by palatine

processes of the 2 maxillae and horizontal plates of palatine bones These nasal-floor

structures form roof of the mouth, called the hard palate

nasal bone

ethmoid

vomer

inf nasal concha

(part of slide 18)

maxilla___________

Nasal cavity

To left, bones forming the left lateral wall of the nasal cavity (nasal septum removed)

To right, nasal cavity with nasal septum in place, showing how the ethmoid bone, septal cartilage, and vomer make up the septum

OrbitCone-shaped bony cavities holding the eyes, muscles that move the eyes, some fat and tear-producing glands; you don’t need to know all these bones that form it, just realize how complex it is and recognize the optic canal (optic nerve passes out through it)

(right orbit shown)

Paranasal sinuses

Air-filled sacs in the bones “Paranasal” because they cluster around

and connect to the nasal cavity

Hyoid bone

Only bone which does not articulate with any other bone

Moveable base for the tongue

Points of attachment for neck muscles that raise and lower the larynx during swallowing

Remember that the Axial skeleton includes:

SkullVertebral columnThoracic cage

Axial skeleton is shown in green

The Vertebral Column

Fetus and infant: 33 separate bones, or vertebrae

Adult: 24 vertebrae Inferior 9 have fused forming

The sacrum (5) and The coccyx (4)

Vertebrae

Cervical – 7 Thoracic - 12 Lumbar - 5 Sacrum (5 fused) Coccyx (4 fused)

Spinal curvatures

Cervical and lumbar are concave posteriorly* (lordosis)

Thoracic and sacral are convex posteriorly* (kyphosis)

Abnormal (see lab book p120): Too much of either Scoliosis (more than 10 degrees

of lateral curvature)

*when viewed from the side

Abnormal curvatures

Non-bony parts Intervertebral

discs anulus fibrosis

and nucleus pulposus)

Anterior longitudinal ligament

Posterior longitudinal ligament

Ligamentum flavum

Anterior longitudinal ligament: wide, strong and attaches to vertebrae as well as discs (prevents hyperextension)Posterior longitudinal ligament: narrow and relatively weak, attaching only to discs

Note “intervertebral foramen” vs “vertebral foramen” on next slides

*

Structure of a typical vertebra

Cervical vertebrae (C1-C7)C1 (atlas)

C2 (axis)

Smallest Lightest Most flexible Triangular vertebral

foramen Transverse

processes have foramina (transverse foramen)

Spinous process bifid (forked) except for C7

Cervical Vertebrae

Heart shaped body

Additional small costal facets (costal=ribs)

Round or oval vertebral foramen

Form posterior part of rib cage

Thoracic Vertebrae T1-T12

Massive blocklike bodies

Short, thick hatchet-shaped spinous processes

Limited mobility

Lumbar Vertebrae L1-L5

The SacrumShapes posterior wall of pelvis

Composite bone of 5 fused vertebrae

Sacral foramina allow passage of vessels & nerves

Coccyx(the tailbone)

Remember that the Axial skeleton includes:

SkullVertebral columnThoracic cage

Axial skeleton is shown in green

The Thoracic Cage

Sternum Ribs

Manubrium

Body

Xiphoid process

True ribs 1-7

False ribs 8-12

Floating ribs 11,12

Vertebral and Sternal Articulations

Typical rib

Disorders of the axial skeleton

Scoliosis (over 10% curvature)

Kyphosis

Lordosis

Vertebral compression fractures

Spinal stenosis

Fontanels

Unossified remnants of membranes

Present at birth Anterior fontanel largest Called “soft spots” Ossify by 1 ½ - 2 years

Continue to ossify into adulthood; the sutures can become fused in old age

Some abnormalities (early fusion) of sutures: “craniosynostosis”Metopic Synostosis and trigonocephaly

A: Preop B: 2 years after

frontal orbital advancement

Pre-op CAT scan Diagram of surgery

2 years post-op

Sagittal synostosis and scaphocephalyThe most common suture to fuse is the middle or sagittal suture. Often the back or front of the skull will be worse but the overall shape is a long skull with a shortened distance from ear to ear.

From - http://www.ppsca.com/skull.htm