CHP 7 The Axial Skeleton (axis of the body)

How many bones are in the human body

206

How many bones are in the axial skeleton

80

How many bones are in the appendicular skeleton

126

Axial skeleton

Skull (22 bones), Hyoid (1 bone), Vertebral Column (24 vertebrae + Sacrum + Coccyx)

Skull

Cranium (8 bones), Facial (14 bones), * auditory ossicles (3 bones on each side)

Bone classification

Long, Short, Flat, Irregular, Sesamoid, Sutral

Red Marrow locations

Epiphyses of long bones, flat bones, and Irregular bones

Markings: 2 main types

Depression/openings, and Processes( projections, outgrowths)

8 Cranial bones

(1) Frontal bone, (2) parietal bones, (2) Temporal bones, (1) Occipital/Sphenoid/Ethmoid

14 Facial bones

(2) Nasal bones, (2) Maxillae, (2) Zygomatic, (2) Lacrimal, (2) Palatine, (2) Inferior nasal conchae, (1) Yomer bone, (1) Mandible

Frontal Bone

Forehead, superior roots of orbits, anterior cranial floor. “Frontal Square” forms forehead. “Supraorbital Margin” = the brow

Parietal Bones (L,R)

Most of the roots & sides of the cranium

Temporal Bones (L,R)

Inferior lateral sides (and floor) of cranium. Contains “Mastoid Process” & “Syloid Process” attachments for muscle.

Occipital Bone

Posterior & base of cranium. Contains “foramen magnum” for spinal cord & brain stem.

Sphenoid

“Keystone of cranium” all other cranial bones articulates with it. Contains “Sella turrica” to protect pituitary. Also carotid & jugular foramen (for major vessels).

Ethmoid

Honeycomb shape (grape to walnut size). Between sphenoid & nasal bones. Houses "olfactory foramina” to accomodate olfactory nerve receptors. Air Spaces (Sinuses) + Superior, midle nasal canche.

Facial bones

14

(2) Nasal bones (Fused)

Bridge of nose

(2) Lacrimal bones

Smallest facial bones. Medial side of orbits. House lacrimal sacs/ducts

(2) Paletine bones (Fused)

Posterior hard plate

(2) Inferior Nasal conchae

Not part of the ethmoid. In the nasal cavity

(1) Yomer

Thin, triangular. Inferior portion of nasal septum

(2) Maxillae bones (Fused)

Upper jaw, face below orbits. Articulates with every facial bone except mandible. Contains “Infraorbital foramen”

(2) Zygomatic bones(L,R)

Cheek bones

(1) Mandible bone

Lower Jaw. Largest, strongest facial bones. *Only moveable facial bone. Contains “Mental foramen”

Sutures

Immovable joints found between cranial plates (bones).

4 major sutures

Coronal, Sagittal, Lambdoid, Squamos (2-L,R)

Paranasal sinuses

Air chambers in the skull. Lined with mucus membranes.

-small or absent at birth

-develops when teeth erupts & during puberty

Paranasal Sinuses Functions

Allows for bone growth without increasing weight of the skull.

Sound Resonance

Fontanels (fontanelle)

Dense CT in unfused cranial plates at birth (“soft spots”). Bones eventually fuse and sutures are found. Allows for accommodation through birthing canal and growth after birth(Crainal & Brain).

4 Major Fontanels

1) Anterior Fontanel, 2) Posterior Fontanel, 3) Anterolateral Fontanel (L,R), 4) Posterolateral Fontanel (L,R)

1) Anterior Fontanel

Largest. Between 2 parietals and frontal bone. Diamond shaped. Closes at 18-24 months.

2) Posterior Fontanel

Between posterior parietals & occipital bone. Closes 2 months after birth

3) Anterolateral Fontanel (L,R)

Between frontal, parietal & sphenoid (on both sides). Closes at 3 months

4) Posterolateral Fontanel (L,R)

Between parietals, occipital, temporals (on both sides). Closes between 2 months to 12 months.

Hyoid bone

Horse shoe shaped. Located in neck above the larynx. Only bone that doesnt articulate with any other bones.

-Helps anchor tounge muscles (helps speech)

Vertebral column

The spine (24 vertebrae+sacrum+coccyx)

Vertebral locations

7 cervical at the top, 12 thoracic in the middle, 5 lumbar under that, sacrum & cocckyx at the bottom

Herniated disc

When annulus ruptures & nucleus pulposus protrudes from disc. Most common in lumbar area

Spina Bifida

A congenital defect of vertebral column. L5 and/or S1 vertebral lamina dont fuse normally at midline.

Spina Bifida Occulta

Less severe form of Spina Bifida

Spina Bifida Cystica

Very severe form of Spina Bifida. CNS membranes protrude through spine (vertebral column) and produce a sac with spinal membranes and nerve roots. This may interfere with natural control of urinary bladder & bowel control.

Sacrum

5 fused vertebrae. Fully fused at 16-18 years

Coccyx

4 fused vertebrae. Fully fuse at 20-30 years

Thoracic Cage(Ribs)

12 pairs of ribs. Articulate with 12 thoracic vertebrae. Anterior connects to sternum is via costal cartilage pairs 1-7 are “true ribs”, pairs 8-10 are “false ribs”, and pairs 11/12 are “floating ribs”