Skeletal System
Types of Animal Skeletons
• Endoskeleton
– Internal skeleton
Ex. Humans
• Exoskeleton
– External skeleton
Ex. Insects, Clams
• Hydrostatic
– Internal fluids receive and redistribute applied forces
Ex. Annelids
Bone Functions
•
•
•
•
Movement
Protection
Support
Mineral Storage
(Ca++, P)
• Energy Storage
(Yellow Marrow – Fat)
• Hematopoiesis - Produce Blood Cells
(Red Marrow)
Types of Bones
Name
Long
Short
-Sesamoid
Flat
Irregular
Characteristics
Longer than they
are wide
cube shaped
Sesame seed
shaped, formed in
tendon
flattened section
more than 1 shape
Examples
femur, humerus, other limb
bones except wrist,
ankles, and patella
carpals, tarsals
patella
cranium, ribs, scapula
vertebrae, mandible, hip
bones
Classification of Bones (cont.)
a = Long Bone
b = Short Bone
c = Flat Bone
d = Irregular Bone
e = Sesamoid Bone
Anatomy of a Long Bone
Epiphyseal Plate: hyaline cartilage that grows
during childhood to lengthen the bone
Epiphyseal Line: remnant of epiphyseal plate,
found only in adults
Epiphysis:
shorter section at end
Diaphysis:
long portion in middle
Epiphysis
Periosteum:
Compact Bone:
dense layer over medullary
cavity; supports weight
Bone covering, outer layer of
dense irregular c.t.; inner
layer of osteoblasts and
osteoclasts, supplied with
nerves and blood vessels
Spongy Bone:
lattice of trabecula filled with
red marrow; nourished directly
from circulating blood
Medullary Cavity:
Hollow center of diaphysis,
contains yellow marrow
Articular Cartliage:
Covers epiphysis at joints, reduces
friction, absorbs shock
Bone (Osseous) Tissue
Osteocytes – widely spaced, surrounded by intercellular substances
Osteoblasts:
add salts
Osteoid (organic):
Collagenous Fibers
Hydroxyapatite
Osteoclasts:
remove salts
(inorganic):
Mineral Salts
(calcium,
phosphorus)
- Provides strength
and hardness to bone
Osteon: structural unit of matrix and canals
•
•
•
•
•
Lamella (little plate): rings of
calcified matrix, intercellular
substance
Volkmann’s Canals:
horizontal canals; allow
blood vessels and nerves to
connect
Haversian Canals: vertical
canals; allow blood vessels
and nerves to connect
Canaliculi: tiny canals that
allow osteocytes to
exchange nutrients and
wastes
Lacunae: space for
osteocytes
Ossification (bone formation)
• begins around 6th or 7th week post
conception
• ends by age 25
2 types
Intramembranous Ossification
• Bone forms within fibrous membranes
(skull, clavicle)
– Osteoblasts cluster in fibrous membranes: Center of
Ossification
– Calcification: intercellular substances and collagen
are secreted into a network where calcium can be
deposited
– Trabecula Formation: complete when osteoblasts are
completely surrounded by calcified matrix
– Trabecula continue to fuse together = spongy bone
– Red marrow fills in space
Endochondral Ossification
(most bones)
• Cartilage is formed in embryonic stage
– Covered by perichondrium (membrane)
Primary Ossification:
Begins at periosteal collar (around
middle of diaphysis)
- Blood vessel penetrates
perichondrium
- Stimulates osteoblast
formation
- Bone replaces cartilage:
- Intercellular substances
calcify
- Nutrients are cut off by
hardened matrix
Secondary Ossification:
- Periosteum thickens bones,
especially at ends
- Blood vessel penetrates
ends, process repeats
EXCEPT
- 2 areas of cartilage will
remain:
- articulating cartilage
- epiphyseal plates (allow
lengthwise growth of bones)
Bone Remodeling
• Normal bone is always undergoing
remodeling
• Removes old bone tissue and replaces it
with new bone tissue
• Remodeling cycle continues throughout
life to maintain healthy bone
• About 20% of all bone tissue is replaced
annually
Bone Remodeling
• Sites of remodeling
– Where bone is experiencing growth
– Mechanical stress
– Microfractures
– Breaks
Bone Remodeling
Five Phases
1.
2.
3.
4.
5.
Activation
Resorption
Reversal
Formation
Quiescence
Bone Remodeling
•
Activation
1. Pre-osteoclasts are attracted to the
remodeling sites
2. Pre-osteoclasts fuse to form multinucleated
osteoclasts
•
Resporption
3. Osteoclasts dig out a cavity, called a
resorption pit, in spongy bone or burrow a
tunnel in compact bone
Bone Remodeling
4. Calcium can be released into the blood for
use in various body functions
5. Osteoclasts disappear
•
Reversal
6. Mesenchymal stem cells, pre-cursors to
osteoblasts, appear along the burrow or pit
where they…
7. …proliferate (increase in number) and
differentiate into preosteoblasts
Bone Remodeling
•
Formation
8. Pre-osteoblasts mature into osteoblasts at
the surface of the burrow or pit
9. Osteoblasts release osteoid at the site,
forming a new soft matrix
10. The new matrix is mineralized with calcium
and phosphorous
•
Quiescence
11. Site remains dormant until the next cycle
System Divisions
• Axial
–
–
–
–
Backbone
Skull
Ribs
Sternum
• Appendicular
– Everything Else
Axial Skeleton
Axial Skeleton
• Skull
– All bones immovable except
mandible
– Cranium
• Paranasal Sinuses
– Cavities within bones of skull
– Lined by mucous membranes
• Fontanels
– Fetal/Child
» Soft spots
» Incomplete Ossification
– Facial Bones
Fontanels of fetal skull
Axial Skeleton
• Hyoid Bone
– No articulation
Axial Skeleton
• Vertebral Column
– Protects spinal cord
– Shock absorbers
– Vertebrae separated
by intervertebral disks
• Fibrocartilage
Axial Skeleton
• 7 Cervical Vertebrae
– Atlas (C1) and Axis (C2)
• Allow rotation of the head
• 12 Thoracic Vertebrae
• 5 Lumbar Vertebrae
• Remember the common mealtimes to help
you remember the number of vertebrae
– Breakfast = 7, Lunch = 12, Dinner = 5
Axial Skeleton
• Sacrum
– Five fused vertebrae
• Coccyx
– Tailbone
• Bony Thorax
• Sternum
•Manubrium, Body,
Xiphoid process
•12 pairs of ribs
Axial Skeleton
• Ribs
– True ribs
• Attached to sternum
• 7 pair
– False ribs
• Attached to
costalcartilage of 7th rib
• 3 pair
– Floating ribs
• No anterior attachment
• 2 pair
Appendicular Skeleton
Appendicular Skeleton
• Pectoral (shoulder) girdle
– Scapula and clavicle (collar
bone)
• Upper limbs
– Humerus (arm)
– Radius and ulna (forearm)
• Carpals (wrist)
• Metacarpals (palm)
• Phalanges (fingers and thumb)
Appendicular Skeleton
• Pelvic (hip) Girdle
– Coxal (hip) bones
Female vs. Male
Female
Pubic arch = 90˚
Distance between iliac
crest wider
Male
Pubic arch = 60˚
Bones are heavier
Bone markings more
prominent
Appendicular Skeleton
•
Coxal Bones have 3
parts
1. Ilium (superior)
2. Ischium (posterior)
3. Pubis (anterior)
Appendicular Skeleton
• Lower Limbs
– Femur (thigh)
• Longest bone in body
– Tibia and Fibula (leg)
• Tibia = medial, Fibula = lateral
– Patella (knee cap)
– Tarsals
• Ankle
– Metatarsals
• Instep
– Phalanges
• toes
Joints
• Points of contact
between bones
• Functions
– Hold skeleton together
– Mobility
Joints (based on functional
differences)
(Articulations)
Synarthroses (axial)
Amphiarthroses (axial)
Diarthroses (appendicular)
Synarthroses
(Fibrous Joints)
• No Movement
Joining bones connected by
fibrous connective tissue
Example: sutures in skull, teeth
Amphiarthroses
(Cartilaginous joints)
• Slight Movement
Joining bones connected by cartilage
Example: vertebral joints
Diarthroses
(Synovial)
• Free Movement
Surrounded by synovial cavity:
- lined with synovial membrane
- lubricates bones/cartilage
- structured like a sleeve
- bursa often found between the bones
- ligaments secure bone together
- grow out of periosteum
Types of Diarthrotic Joints
Ball and Socket
Hinge
Head of one bone fits in concave socket of another bone
Allows widest range of motion
Head of one bone fits against concave socket of another
Allows only flexion and extension
Pivot
Small pin of one bone fits in arch of another
Allows rotation
Saddle
Gliding
Only found where thumb fits wrist
Allows movement in many directions
Flat surfaces of bones fit against each other
Allows little directional movement, only gliding
Condyloid/Ellipsoid
Oval projection fits into an elliptical socket
Allows most movement, no rotation