Skeleton System

Function of the Skeleton System

- support by carrying the weight of the body
- protection of organs
- assist in movement along with the muscular system
- mineral homeostasis by controlling blood levels of calcium and phosphorus
- blood cell production (hemopoeisis)
- triglyceride storage

Long Bones

- bones that are longer than they are wide
- tibia

Short Bones

- bones that are equally long and wide
- wrist bones

Flat Bones

- bones that are thin, broad and commonly curved
- skull bones

Irregular Bones

- bones that do not fit into any other category
- vertebrae

Sesamoid Bones

- specialized bones found within tendons
- patella

Gross Anatomy of Bones

- nerves, blood vessels and cartilage

Osseous Tisse

- major structural and supportive connective tissue in the body
- the bone tissue

Marrow

- yellow is for fat storage
- red is the site of blood cell production

Compact Bone

- also called cortical bone
- solid and relatively dense external surface of all bones

Spongy Bone

- also called trabecular bone, main feature is trabeculae
- contains no osteons or central canal
- makes up most of smaller bones and epiphysis of long bones
- found where stress comes from many directions
- resembles a sponge and is the internal surface of bones

Epiphysis

- proximal portion of a bone

Metaphysis

- region of bone growth (upwards)

Diaphysis

- shaft or middle portion of a bone

Inner Layer of Periosteum

- consists of osteogenic cells

Outer Layer of Periosteum

- consists of dense, irregular connective tissue

Depressions

- where bone meets another bone
- can be facets, fovea, fossa or a groove (sulcus)

Openings

- allow blood vessels, nerves or something else to pass through
- can be a canal, fissure, foramen or fenestra

Projections

- attachment of muscles, tendons and ligaments
- can be a condyle, crest, head, tubercle, tuberosity, process, spine, trochanter or protuberance

Osteogenic Cells

- mitotically active stem cells that are found in periosteum
- differentiate into osteoblasts

Osteoblasts

- secrete the bone matrix and initiate calcification

Osteocytes

- mature bone cells that have developed from osteoblasts
- occupy lacunae and maintain the matrix

Osteoclasts

- giant, multinucleated cells related to macrophages
- breaks down the bone matrix
- regulates and forms new bone cells
- most important for disease repair

Bone Matrix

- 1/3 organic compounds of cells, collagen and ground substances
- 2/3 inorganic compound of hydroxyapatite

Nutrient Arteries

- one or more depending on the bone and supply most of the diaphysis
- can be periosteal, metaphyseal or epiphyseal

Bone Development

- called ossification
- either intramembranous or endochondral

Intramembranous Ossification

- when bone develops within a membrane
- starts off as mesenchyme cells into osteogenic cells and than osteoblasts
- osteoblasts secrete osteoid and are trapped within newly formed bone
- form trabeculae surrounded by periosteum in flat sheets

Endochondral Ossification

- bone develops from hyaline cartilage
- 6 stages

1st Stage of Endochondral Ossification

- fetal hyaline cartilage model develops and grows as chondrocytes divide

2nd Stage of Endochondral Ossification

- cartilage calcifies and bone collar forms

3rd Stage of Endochondral Ossification

- cavity forms within the cartilage model

4th Stage of Endochondral Ossification

- nutrient artery penetrates , delivering osteogenic cells and osteoclasts

5th Stage of Endochondral Ossification

- the primary ossification center forms

Last Stage of Endochondral Ossification

- bone replaces all cartilage except articular cartilage
- secondary ossification in epiphysis forms
- nutrient artery penetrates into the primary ossification centre

Epiphyseal Plate

- area of continued growth
- 5 zones

Zone of Resting Cartilage

- first area of the epiphyseal plate
- nothing occurs here

Zone of Proliferating Cartilage

- second area of the epiphyseal plate
- actively divides chondrocytes

Zone of Hypertonic Cartilage

- third area of the epiphyseal plate
- chondrocytes die

Zone of Calcified Cartilage

- fourth area of the epiphyseal plate
- where the matrix becomes calcified

Zone of Ossification

- last area of the epiphyseal plate
- osteoblasts lay down bone

Interstitial Growth

- growth at the epiphyseal plates responsible for bones increasing in length

Oppositional Growth

- osteoblasts lay down new bone under the periosteum to increase the diameter of bone

Skull

- protects the brain and sense organs
- sites of muscle attachment
- 8 cranial bones
- 14 facial bones

Parietal Bones

- has four sutures
- 2 bones

Occipital

- back of the head
- has the foramen magnum and occipital condyles

Temporal Bones

- in the tympanic and mastoid regions
- 2 bones

Frontal Bone

- forehead and upper part of the eye socket

Sphenoid Bone

- where the pituitary gland is and the optic nerve passes

Ethmoid Bone

- where the cribriform plate and nasal septum is

Soft Spots/Fontanelles

- at birth there are six spots to allow the baby to pass through the birth canal easier
- anterior fontanelle normally closes in 15 months

Nasal Bones

- 2 bones that form the bridge of the nose

Zygomatic Bones

- 2 bones that form the cheekbones

Maxilla

- 2 bones
- upper jawbone that is connected to all other bones of the face

Mandible

- lower jaw
- only moveable skull bone

Vomer

- part of the nasal septum

Palatine

- 2 bones apart of the palate

Lacrimal Bones

- 2 smallest facial bones
- medial part of the orbit that the tear ducts pass through

Nasal Conchae

- 2 bones
- nasal cavity and surface lind by olfactory epithelium

Significance of the Palate

- high metabolic rates require rapid digestion
- palate enables chewing and breathing at the same time

Hyoid Apparatus

- doesn't articulate with any other bone and is maintained by ligaments
- supports the tongue and is involved in swallowing

Vertebral Column

- starts off as 33 bones and fuses into 26 bones
- provides a flexible rod that aids in movement and protects the spinal cord

Cervical Region

- neck area (C1-C7)

Thoracic Region

- attached to pairs of ribs (T1-T12)

Lumbar Region

- largest and strongest region (L1-L5)

Sacrum Region

- attached to the pelvis (S1-S5)

Coccyx

- last region of the vertebral column (Co1-Co4)

Curvature of the Vertebral Column

- starts with the thoracic vertebrae to better distribute body weight
- cervical region develops for crawlings
- lumbar and sacral region forms to hold up the head and start to walk

Kyphosis

- hunchback
- excessive anterior curvature in thoracic region

Lordosis

- excessive posterior curvature in lumbar region

Scoliosis

- vertebral column curves laterally

Cervical Atlas

- first cervical vertebrae that is specialized
- supports the head and allows it to move up and down
- lacks a body and spinous process

Cervical Axis

- second cervical vertebrae that is specialized
- has an odontoid process
- allows for side to side movement of the head

C3-C7 Vertebrae

- have a typical vertebral structure
- foramen transversarium

Thoracic Vertebrae

- larger and stronger than cervical vertebrae
- have a longer transverse process to articulate with the ribs

Lumbar Vertebrae

- largest and strongest vertebrae
- have short and thick processes

Sacrum

- formed by the fusion of five vertebrae
- attached to the pelvic girdle and hips

Coccyx

- formed by the fusion of four vertebrae
- tip

Intervertebral Discs

- sit between adjacent vertebrae
- cushion and absorb physical shock
- facilitates movement
- resists grinding between bones

Herniated Disc

- when intervertebral discs bulge laterally
- pain is caused by a nucleus pressing against a nerve

Sternum

- flat bone that articulates with the ribs
- 3 parts

Manubrium

- top portion of the sternum
- articulates with the pectoral girdle and first ribs

Body of the Sternum

- articulates with 2-7 ribs

Xiphoid Process

- bottom portion of the sternum
- attachment for some abdominal muscles

Ribs

- 12 pairs that articulate with 12 thoracic vertebrae
- 3 types

True Ribs

- ribs 1-7 that connect directly through the intercostal cartilage

False Ribs

- ribs 8-12 that attach indirectly or not at all to the
sternum

Floating Ribs

- ribs 11 and 12 that don't attach to the sternum

Pectoral Girdle

- attaches bones of upper limbs to the axial skeleton
- 2 bones that make up the shoulder

Clavicle

- articulates with the manubrium (sternal end) and scapula (acromial end)
- apart of the pectoral girdle
- provide an attachment site for muscles, acts as braces and transmits forces to the axial skeleton

Scapula

- not directly connected to the vertebral column
- apart of the pectoral girdle
- thin, triangular flat bones

Humerus

- only bone of the arm

Forearm

- radius and ulna forms the elbow, articulate with each other at both end
- olecranon prevents hyperextension
- thin at proximal end

Hand

- 8 carpals, marble-sized bones
- 5 metacarpals, palm of the hand
- 3 phalanges per finger except thumb, distal, middle and proximal

Pelvic Girdle

- differs from the pectoral girdle as it connects directly to the vertebral column
- 3 bones on each side that are fused together and come together at the acetabulum

Ilium

- superior region of the pelvis that connects to the sacrum

Pubis

- anterior region of the pelvis that joins at the pubis synphysis

Ischium

- posterior region of the pelvis
- "sit bones"

Differences between the Male and Female Pelvis

- bones are thicker and heavier in males
- female pelvic inlet is wider and the subpubic angle is wider

True Pelvis

- bony basin inferior to pelvic brim containing the pelvic organs
- part of the colon, rectum, bladder, uterus/ovaries

False Pelvis

- superior to pelvic brim bound by the ilia laterally and abdominal wall anteriorly
- intestines and muscle attachment sites