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The
Skeletal System
Chemical composition of bone
Organic
• Osteoblasts – bone-forming cells
• Osteocytes – mature bone cells
• Osteoclasts – large cells that reabsorb or break down bone matrix
Inorganic
• Mineral salts
• Sixty-five percent of bone by mass
• Mainly calcium phosphates
• Responsible for bone hardness and its resistance to compression
Classification of Bones
• 206 bones in the adult skeleton
• composed of two basic kinds of osseous tissue that differ in their
texture:
– Compact bone
• looks smooth and homogeneous
– Spongy bone
• Composed of small trabeculae of bone and lots of open
space
• Bones are further classified on the basis of their relative gross
anatomy into four groups
– Long bones
• Femur
• Are much longer then they are wide
– Short bones
• Carpals and tarsals
• Are typically cube-shaped
– Flat bones
• Bones of the skull
• Many are curved
– Irregular bones
• vertebrae
• Bones that do not fall into one of the preceding categories.
• Two other subcategories
-Sesamoid bones
• Kneecap
• Are small bones formed in tendons
– Wormian bones
• Tiny bones between cranial bones
Five Major Functions
1. Support
-structural framework
2. Protection
-protects soft tissue/organs
3. Assistance in movement
-provides surface for muscles to contract against
4. Storage of Mineral Salts
-calcium and phosphate
5. Formation of blood cells
-blood cell production
Long Bone Anatomy
– Diaphysis = shaft
• Thick collar of compact bone
• Center = medullary cavity =
bone marrow
• Red bone marrow- produces blood
cells, is found in the cavities of
most bones.
• Yellow bone marrow-fat storage.
Long Bone Anatomy
• Epiphysis =
distal and
proximal end
– Compact bone
outside of
spongy bone
– Articular
Cartilage
covers the
joint surface
Long Bone Anatomy
• Metaphysis =
where diaphysis
and epiphysis meet
– Contains epiphyseal
plate (region of
bone growth)
Long Bone
• Articular Cartilage
– Covers joint surface
– Hyaline Cartilage
– Reduces friction and
absorbs shock
Long Bone Anatomy
• Periosteum
– Tough outer
covering
• (dense irregular
connective tissue)
surrounding bone.
Long Bone Anatomy
• Periosteum Contains:
• Lymph Vessels
• Blood Vessels
• Nerves
– Provides site for tendon
and ligament
attachment
– Allows for growth in
Diameter NOT length
– Assists in Fracture
repair
– Nourishment
Long Bone Anatomy
• Endosteum
• Lines the medullary
cavity
• Covers trabeculaemeshwork of spaces filled
with bone marrow.
Terms to identify bone landmarks or surface features:
• Process: A broad designation for any
prominence or prolongation
• Eminence: A raised area
• Spine: An abrupt or pointed projection
• Trochanter: A large, usually blunt process
• Tubercle: A smaller, rounded eminence
• Tuberosity: A large, often rough eminence
• Crest: A prominent ridge
Basic terms continued
• Head: A large, rounded, articular end of a
bone; often set off from the shaft by a neck
• Condyle: An oval articular prominence of a
bone
• Facet: A smooth, flat, or nearly flat
articulating surface
• Fossa: A deeper depression
• Sulcus: A groove
• Foramen: A hole
• Meatus: A canal or opening to a canal
The Axial Skeleton
• Divided into three parts:
– Skull
– Vertebral column
– Bony thorax
SKULL
• The skull is composed of two sets of bones:
– Cranium bones
• Encloses and protects the fragile brain
– Facial bones
• Present the eyes in an anterior position; and
• Form the base for the facial muscles
Skull cont.
• Most bones of the skull are joined by interlocking joints
termed sutures
– The mandible is attached to the rest of the skull by a
freely movable joint
– Other random bones– Hyoid bone-”U” shaped; not attached between lower
jaw & larynx
– Ossicles -”ear bones”- mallus (hammer);
incus (anvil); stapes(stirrup)
THE CRANIUM
PORTION OF THE SKULL
•
Frontal bone:
– Forms the forehead
•
Parietal bone:
– Forms the sides and the major top portion of the cranium, ( top of
your head)
•
Temporal bone:
– Located above you ears
•
Occipital bone:
– Located at the back of the cranium
– Houses the foramen magnum (spinal cord starts here)
•
Ethmoid bone:
– Located just inside the eye socket at the top portion of the nasal
bone.
Facial Bones- thirteen bones fused together, and a movable
mandible.
• Superficial facial bones – provides areas for the
attachment of muscles
• Deeper facial bones – separates oral and nasal
cavities & help to form the nasal septum
•The vomer is not paired-divides the nasal cavity
•Nasal bones-small bones that form the bridge of
the nose
•Lateral to the nasals are the maxillary bones.
•Below the eye orbits are the zygomatic bones
(cheek bones).
•Lateral to the bridge of the nose are the small
lacrimal bones
•Lower jaw is the mandible
Vertebral Column
• Consists of 24 single bones called vertebrae.
- two fused bones- the sacrum and coccyx
- connected extending from the skull to the
pelvis
• Forms the body’s major axial support
• Surrounds and protects the spinal cordallowing the spinal nerves to extend
Number of Vertebrae
• The 24 single vertebrae are
groups as follows:
– Cervical Vertebrae
• 7 bones
• Forms a concave shape
• Commonly termed “NECK”
– Thoracic Vertebrae
• 12 bones
• Forms a convex shape
• Connected to the ribs
– Lumbar Vertebrae
• 5 bones
• Forms a concave shape
• Supports the lower back
LETS NOT FORGET THE SACRUM
AND COCCYX
• Sacrum
– 5 FUSED bones
– Forms a convex shape
• Coccyx
– FUSED bones
– Termed the tailbone.
– It is attached to the
sacrum by ligaments
Cervical Vertebrae
• Seven bones
• Referred to as C1-C7
• The first two cervical
vertebrae termed
– Atlas (C1)
• Lacks a body
• Allows you to nod “YES”
– Axis (C2)
• Acts as a pivot for the
rotation of the atlas and skull
• Allows you to rotate your
head to indicate “NO”
Cervical C3-C7
• Distinguished from the thoracic and lumbar vertebrae by
several features:
– They are the smallest;
– Lightest; and
– Triangular
– They have foramina (holes) to allow blood vessels to go
through.
Thoracic Vertebrae
•
•
•
•
12 bones
Referred to as T1-T12
Have larger body
Spinous process are long
with a sharp downward
hook
Lumbar Vertebrae
• Five bones
• Termed L1-L5
• Have massive block like bodies and
short thick hatchet-shaped spinous
processes
Intervertebral Disk
• Vertebrae are separated by pads termed “fibrocartilage’
• They cushion the vertebrae and absorb shocks
• Aging causes the water content of the discs to decrease
and become thinner and less compressible.
• Herniated disc- common back injury.
Vertebral Column
Abnormalities:
Thoracic Cage
• AKA- “RIBCAGE” or “BONY THORAX”
• Forms a protective cone-shaped enclosure around the organs
of the thoracic cavity
– Heart; lungs; and major arteries/veins
•
Composed of the following:
– The sternum
– Ribs
– Thoracic vertebrae
Sternum
•
•
AKA-“BREASTBONE”-flat
Is a fusion of three bones:
– Manubrium
• Top
• Looks like a knot of a tie
• Connects to the clavicle (collarbone)
– Body
• Middle
• Forms the bulk of the sternum
– Xiphoid process
• Pointed tip
• Can easily break with a strike or during CPR
and can penetrate the heart or liver
•
Is attached to the first seven pairs of ribs
• The sternum has three
important bony landmarks
– Jugular notch
• Located on the manubrium
– Sternal angle
• Is where the manubrium and
body join
• It starts at the second rib
• (DO NOT WRITE)so doctors
use this to count ribs before
placing needles into the
body or to listen to heart
valve
Rib Cage
Individual Rib
•
•
•
•
•
12 pairs of ribs
All the ribs connect to the thoracic
vertebrae
TRUE RIBS
• First 7 ribs
• Attached directly to the sternum
FALSE RIBS
– Next 5 ribs
– Attach indirectly to the sternum or
lack a sternal attachment via cartilage)
• Ribs 8-10 connect via cartilage to
sternum
FLOATING RIBS
– Last two pair of ribs
– no sternal attachment