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the organs of the skeletal system
dynamic, living tissue
206 bones total

Flat, Long, Short, Irregular, Sesamoid, Sutural(Wormian)

Classification of Bone


thin and broad
sternum, scapula, cranium
provides protective shield
provides a large area for muscle attachment


Long and narrow
curved to distribute weight and resist bending and twisting
arms hands fingers and legs


small and boxy
square life; resists high pressure


complex shapes
vetebral, face, pelvis


small bones embedded in tendons and over joints
patella are the knee caps


small bones embedded between the flat bones of the skull

diaphysis, epiphysis, metaphysis

Parts of a Long Bone


long, center shaft
compact bone made of dense outer layer
marrow cavity is made of hollow central space
contains yellow bone marrow


expanded ends
spongy bone, a network of struts and plates called trabeculae
cortex made of thin outer layer of compact bone
contains red bone marrow


narrow region between diaphysis and epiphysis

Supportive framework

soft tissues and organs
one of the functions of one


function of bone that affects the brain (skull--> cranial cavity)
spinal cord (spinal column --> spinal cavity)
lungs and heart (rib cage --> thoracic cavity)
reproductive organs (pelvis --> pelvic cavity)


bones are levers pulled by muscles
function of bone

mineral storage

function of bone
calcium, phosphate (required for certain processes)

lipid storage

function of bone
adipocytes found in yellow bone marroe
store fat to protect from starvation

blood cell production

function of bone that occurs in red bone marrow


forms into circular layers called lamellae (bone cells, collagen fibers, and calcium phosphate)
remodels to patterns of activity


type of bone cell that is the stem cell.
differentiates into osteoblasts
maintains osteoblast population
located in periosteum and endosteum


the inner cellular layer


lining of marrow cavity


produces new bone matrix through osteogenesis
makes collagen fibers and ground substances
regulates the deposition of calcium salts in the matrix


removes and recycles bone matrix through process of osteolysis
secretes acids and enzymes that dissolve the matrix and releases the stored minerals in the blood stream
originates from stem cells that create macrophages
largest of the bone cells


mature bone cells
they are osteoblasts that have become encased in bone
breakdown and buildup the local matrix


concentric layers of matrix that is arranged in cylinders


functional unit of compact bone
a cylinder of lamellae
aligned parallel to surface of the bone
provides great compressive strength

central canal

center hole
contains blood vessels that supply the cells of the osteon

perforating canal

perpendicular canal that contains blood vessels that supply deeper osteons and marrow cavity


small chambers between lamellae that contains osteons


narrow passageway in the lamellaw that connects adjacent lacunae
allows osteocytes to form gap junctions
allows for passage of nutrients and hormones

spongy bone

located in epiphysis of long bone
is not organized in osteons


struts and plates of lamellae
forms an open network of light weight bone


2 layers of membrane covering the bone
composed of dense irregular conenctive tissue outer layer
the inside is made of epithelial

periosteum function

isolates and protects the bone
contains cells active in bone growth and repair
collagen fibers ancher other tissue to bone
blood vessels, tendons, sheaths, nerves, ligaments, capsules


membrane lining on compact and spongy bone
only one layer
lines marrow cavity and covers trabeculae
cells are active in bone growth and repair just like periosteum


bone formation


process of replacing tissue with bone


deposition of calcium salts
occurs 3 weeks after fertilization until age 25

endochondral ossification

hyaline cartilage
superficial bone formation
primary ossification center
marrow cavity formation
secondary ossification center
bone formation completes

hyaline cartilage

chondrocytes increase in size
matrix reduces to thin struts that calcify
chondrocytes die and disintegrate

superficial bone formation

blood vessels grow into perichondrium
osteoblasts form and produce thin layer of bone around shafts of the cartilage
perichondrium becomes periosteum

primary ossification center

blood vessels grow into center of cartilage
osteoblasts form and produce spongy bone
spongy bone spreads towards both epiphyses

marrow cavity formation

osteoclasts break down spongy bone to create marrow cavity
diaphysis becomes wider and longer

secondary ossification center

blood vessels grow into the epiphysis
osteoclasrs form and spongy bone is produced

bone formation completes

ossification completed
a thin layer of articular cartilage remains

intramembranous ossification

conversion of fibrous connective tissue to bone
occupy in the deep dermal layers
produces flat bones
any soft tissue can become bone if abnormally stretched


a homeostatic mechanism of bone
the recycling and renewing of bone matrix
the continuous breaking down and building up of bone
ongoing osteoclast and osteoblast activity
regulate blood calcium levels to ensure proper function of muscles and nerves
adapt bones to the mechanical stresses of muscles
repair and replace damaged or diseased bone


mechanical stress caused by
muscles pulling on bone
body weight

mechanical stress causes calcium mineral crystals to generate eletrical currents. electrical currents attract and stimulate osteoblast activity. lack of excercise promotes osteoclast activity.


regulate bone growth and remodeling

human growth hormone

hormone that is secreted by pituitary and functions in growth thoughout lifetime


secreted by ovaries and testes; horomone that controls growth and puberty and beyond


secreted by kidneys
hormone that promotes intestinal calcium absorption

parathyroid hormone

secreted by parathyroid gland
increases blood calcium levels by increasing osteoclast activity


secreted by thyroid gland
decreases blood calcium levels by decreasing osteoclast activity


reduces hgh and sex hormones
begins at age 30
slow osteoblast activity
osteoclast activity remains constant


inadequate ossification
affects epiphysis, vertebrae, and mandible


a condition of severe bone loss
affects females more than men because of estrogen

and close

types of fractureopen

closed fracture

simple: internal; no projection of bone through skin

open fracture

compound; bone projects through skin
possible blood loss and infection

healing process

fracture hematoma formation
callus formation
spongy bone formation

fracture hematoma formation

blood clot
many blood vessels broken; causes extensive bleeding
lack of blood leads to much bone death

healing process

callus formation; internal and external

internal callus

forms in the marrow cavity from hematoma

external callus

cartilage forms around bone from the hematoma

spongy bone formation

calluses are replaced with spongy bone (ossification)
dead/damaged bone is removed and replaced
the break is secured with a large mass of bone


osteoclasts and osteoblasts reform the bone to normal

Axial skeleton

80 bones, supports and protects, muscle attachment for: movement of head/neck/trunk, respiration, stabilize and position the appendicular skeleton

Cranial Bones

8 bones

Facial bones

14 bones of the skull which protect and support the eyes, ears, nose and mouth

Thoracic cage

consists of thoracic vertebrae, the ribs and the sternum; protects the heart, lungs, thymus and other structures within the cavity; serves as an attachment site for muscles involved in respiration, positioning vertebral column, movements of the pectoral girdle and upper limb


the bony structure units of the spinal column (26)


lower posterior region of the head/skull

occipital condyles

projections of the occipital bone that articulate with lateral masses of the first cervical vertebra

foramen magnum

large opening in occipital bone that allows spinal cord to attach to brain

occipital protuberance

a bump that extends out from the occipital bone


the two bones forming the sidewalls and roof of the cranium, lat. superior skull


superior anterior skull, forms roof of orbits

lacrimal fossa

fossa of the frontal bone that contains the lacrimal gland, located just inside the lateral portion of the supraorbital ridge.


inferior lateral skull (temples)

external acoustic canal

ear hole

mastoid process

part of the temporal bone that attaches to some of the muscles of the neck

zygomatic process

part of the temporal bone that forms part of the posterior cheekbone

styloid process

sharp (needle-like) projection from the bottom of the temporal bone


suture that separates occipital from parietal


Suture across top front, between frontal and parietal


suture b/t parietal bones


suture that separates parietal and temporal


butterfly-shaped bone at the base of the skull, articulates with the 7 other cranial bones, most central cranial bone, post. walls of orbits and ant. floor of cranium

sella turcica

bony process on sup. center of sphenoid bone

hypophyseal fossa

"seat of the saddle" part of the sella turcica, holds the Pituitary gland

lesser wings

sphenoid; bat-shaped portions of the spheniod anterior to the sella turcica

greater wings

portions of the sphenoid seen exteriorly anterior to the temporal and forming a part of the eye orbits

optic canals

openings in the bases of the lesser wings through which the optic nerves enter the orbits to serve the eyes


anterior to sphenoid, forms medial wall of orbits, roof of nasal cavity + part of nasal septum

cribriform plate

part of the ethmoid bone that forms the roof of the nasal cavity found in the anterior floor of the cranium

olfactory foramina

openings for olfactory nerves

perpendicular plate

forms the superior part of the nasal septum

superior nasal conchae

scroll shaped projections on the lateral walls of the nasal cavity; they increase vascular & mucus membrane surface area in the nasal cavities, which aids in the snese of smell, and warm, moisten and filter incoming air

middle nasal conchae

scroll-like projection on each lateral wall of nasal cavity


largest facial bones, form upper jaw/ supports upper teeth, forms inferior orbits + hard palate

infraorbital foramen

sensory nerve to face

palatine process

forms the anterior portion of the hard palate (roof) of the mouth also forms parts of the nasal cavity and eye orbits


posterior hard palate


forms the inferior portion of the nasal septum, articulates w/ perpendicular palate

zygomatic bone

cheek bone, lateral walls of orbits

temporal process

Articulates with zygomatic process of the temporal bone to form the zygomatic arch


form the bridge of the nose, attachment site for cartilage of nose


smallest facial bones, form medial walls of orbits

lacrimal sulcus

A groove along the anterior lateral surface of the lacrimal bone


lower jaw bone

mandible body

Main part of the jaw bone, horizontal part, holds lower teeth

mandible ramus

verticle part of jaw.

condylar process

the posterior upward projection of the ramus that fits into the temporomandibular joint, which is the hinge of the mandible

coronoid process

the anterior, non-articulating process of the ramus of the mandible which serves as the insertion for the temporalis muscle.

paranasal sinuses

air cavities within the cranial bones that open into the nasal cavities, lighten skull bones, acts as resonating chambers for voice, produce mucus, wash debris into nasal cavity, prevent debris from entering nasal tract

Maxillary, Frontal, Sphenoid, Ethmoidal

4 types of paranasal sinuses

Vertebral Column

26 bones, support head, limbs and trunk, support upper organs, transfers body weight to lower limbs, protects spinal cord


'neck', 7 vertebrae, C1-C7, supports skull, most flexible region, smallest lightest vertebrae,large vertebral foramen, all have 2 transverse foramen, to support artery


superior back, 12 vertebrae, T1-T12, supports thoracic cage, very little flexibility, larger, thicker bodies, smaller vertebral foramen, inferiorly angled spinous processes, each vertebrae articulates w/ a pair of ribs


inferior back, 5 vertebrae, L1-L5, supports abdominal regions, more flexible than thoracic spine, large oval bodies, small triangular vertebral foramen,very large, short spinous processes


base of spine, 5 fused vertebrae, S1-S5, transfers upper body weight to lower limbs


tail bone, 3-5 fused vertebrae, Co1-Co3-5)

Primary Curves

c curve of spine, during infancy

secondary curves

cervical and lumbar curves after several months, allows for upright posture and even distribution of weight

lordotic curve

spine arches anteriorly, forms cervical and lumbar curves

kyphotic curve

spine arches posteriorly, forms thoracic and sacral spinal curves


part of vertebrae that is the main structure and most anterior part

vertebral arch

posterior part of vertebrae

vertebral foramen

surrounds the spinal cord, formed by body and vertebral arch

spinous process

posterior projection of vert. arch, site of muscle attachment

transverse process

lat. projection of vert. arch,site of muscle attachment

articular facets

articulations b/t vertebrae


no body or spinous process, extra large vertebral foramen (for brain stem), articulates w/ skull at the occipital condyles, forming the atlantoccipital joint , allows for 'yes'


contains dens process- vertical projection of the body, provides pivot for rotation of atlas, articulates w. atlas forming atlanaxial joint, allows for 'no'

ligamentum nuchae

long post. ligament, attaches all spinous process to externa occipital protuberance, provides large area for muscle attachment

intervertebral foramen

openings b/t adjoining vertebrae, allow spinal nerves to exit spinal cavity

intervertebral disc

fibrocartilage pads located b/t discs, cushion vertebrae +absorb shock

annulus fibrosis

outer layer of fribrocartilage of disc

nucleus pulposis

gelatinous inner core of disc

herniated disc

protrusion of a degenerated or fragmented intervertebral disk so that the nucleus pulposus protrudes, causing compression on the nerve root


triang. wedge, 5 vertebrae fused by 25-30 years old, attaches axial skeleton to appendicular skeleton


sup. edge of sacrum


inferior edge of sacrum

median sacral crest

ridge of the fused spinous processes of the sacral vertebrae

sacral canal

continuation of vertebral canal

sacral foramina

Allow the passage of sacral spinal nerves.

articular surface

lateral edge, articulates with pelvis, forms sacroilac joint

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