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5The Skeletal System
Yong Jeong, MD, PhD
Department of Bio and Brain Engineering
The Skeletal System
Parts of the skeletal system
Bones (skeleton)
Joints
Cartilages
Ligaments
Two subdivisions of the skeleton
Axial skeleton
Appendicular skeleton
2
Functions of Bones
Support the body
Protect soft organs
Allow movement due to attached skeletal muscles
Store minerals and fats
Blood cell formation
Bones of the Human Body
The adult skeleton has 206 bones
Two basic types of bone tissue
Compact bone
Homogeneous
Spongy bone
Small needle-like pieces of bone
Many open spaces
Figure 5.2b
3
Classification of Bones on the Basis of Shape
Figure 5.1
Classification of Bones
Long bones
Typically longer than they are wide
Have a shaft with heads at both ends
Contain mostly compact bone
Example:
Femur
Humerus
4
Classification of Bones
Figure 5.1a
Classification of Bones
Short bones
Generally cube-shape
Contain mostly spongy bone
Example:
Carpals
Tarsals
5
Classification of Bones
Figure 5.1b
Classification of Bones
Flat bones
Thin, flattened, and usually curved
Two thin layers of compact bone surround a layer of spongy bone
Example:
Skull
Ribs
Sternum
6
Classification of Bones
Figure 5.1c
Classification of Bones
Irregular bones
Irregular shape
Do not fit into other bone classification categories
Example:
Vertebrae
Hip bones
7
Classification of Bones
Figure 5.1d
Anatomy of a Long Bone
Diaphysis
Shaft
Composed of compact bone
Epiphysis
Ends of the bone
Composed mostly of spongy bone
8
Anatomy of a Long Bone
Figure 5.2a
Anatomy of a Long Bone
Periosteum
Outside covering of the diaphysis
Fibrous connective tissue membrane
Sharpey’s fibers
Secure periosteum to underlying bone
Arteries
Supply bone cells with nutrients
9
Anatomy of a Long Bone
Figure 5.2c
Anatomy of a Long Bone
Articular cartilage
Covers the external surface of the epiphyses
Made of hyaline cartilage
Decreases friction at joint surfaces
10
Anatomy of a Long Bone
Epiphyseal plate
Flat plate of hyaline cartilage seen in young, growing bone
Epiphyseal line
Remnant of the epiphyseal plate
Seen in adult bones
Anatomy of a Long Bone
Medullary cavity
Cavity inside of the shaft
Contains yellow marrow (mostly fat) in adults
Contains red marrow (for blood cell formation) in infants
11
Bone Markings
Surface features of bones
Sites of attachments for muscles, tendons, and ligaments
Passages for nerves and blood vessels
Categories of bone markings
Projections or processes—grow out from the bone surface
Depressions or cavities—indentations
Bone Markings
Table 5.1 (1 of 2)
12
Bone Markings
Table 5.1 (2 of 2)
Notch Indentation at the edge of the structure
Microscopic Anatomy of Bone
Osteon (Haversian system)
A unit of bone containing central canal and matrix rings
Central (Haversian) canal
Opening in the center of an osteon
Carries blood vessels and nerves
Perforating (Volkman’s) canal
Canal perpendicular to the central canal
Carries blood vessels and nerves
13
Microscopic Anatomy of Bone
Figure 5.3a
Microscopic Anatomy of Bone
Lacunae
Cavities containing bone cells (osteocytes)
Arranged in concentric rings
Lamellae
Rings around the central canal
Sites of lacunae
14
Microscopic Anatomy of Bone
Figure 5.3b–c
Microscopic Anatomy of Bone
Canaliculi
Tiny canals
Radiate from the central canal to lacunae
Form a transport system connecting all bone cells to a nutrient supply
15
Microscopic Anatomy of Bone
Figure 5.3b
Formation of the Human Skeleton
In embryos, the skeleton is primarily hyaline cartilage
During development, much of this cartilage is replaced by bone
Cartilage remains in isolated areas
Bridge of the nose
Parts of ribs
Joints
16
Bone Growth (Ossification)
Epiphyseal plates allow for lengthwise growth of long bones during childhood
New cartilage is continuously formed
Older cartilage becomes ossified
Cartilage is broken down
Enclosed cartilage is digested away, opening up a medullary cavity
Bone replaces cartilage through the action of osteoblasts
Long Bone Formation and Growth
Figure 5.4a, step 3
Bone startingto replacecartilage
Epiphysealplatecartilage
Articularcartilage
Spongybone
In a childIn a fetusIn an embryo
New boneforming
Growthin bonewidth
Growthin bonelength
Epiphysealplate cartilage
New boneforming
Bloodvessels
Hyalinecartilage
New center ofbone growth
Medullarycavity
Bone collar
Hyalinecartilagemodel
(a)
17
Bone Growth (Ossification)
Bones are remodeled and lengthened until growth stops
Bones are remodeled in response to two factors
Blood calcium levels
Pull of gravity and muscles on the skeleton
Bones grow in width (called appositional growth)
Long Bone Formation and Growth
Figure 5.4b
18
Types of Bone Cells
Osteocytes—mature bone cells
Osteoblasts—bone-forming cells
Osteoclasts—bone-destroying cells
Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone
Bone remodeling is performed by both osteoblasts and osteoclasts
Bone Fractures
Fracture—break in a bone
Types of bone fractures
Closed (simple) fracture—break that does not penetrate the skin
Open (compound) fracture—broken bone penetrates through the skin
Bone fractures are treated by reduction and immobilization
19
Common Types of Fractures
Table 5.2
Repair of Bone Fractures
Hematoma (blood-filled swelling) is formed
Break is splinted by fibrocartilage to form a callus
Fibrocartilage callus is replaced by a bony callus
Bony callus is remodeled to form a permanent patch
20
Stages in the Healing of a Bone Fracture
Figure 5.5, step 4
Hematoma
Externalcallus
Bonycallus ofspongybone
Healedfracture
Newbloodvessels
Internalcallus(fibroustissue andcartilage)
Spongybonetrabecula
Hematomaformation
Fibrocartilagecallus formation
Bony callusformation
Bone remodeling
The Axial Skeleton
Forms the longitudinal axis of the body
Divided into three parts
Skull
Vertebral column
Bony thorax
21
The Axial Skeleton
Figure 5.6a
The Axial Skeleton
Figure 5.6b
22
The Skull
Two sets of bones
Cranium
Facial bones
Bones are joined by sutures
Only the mandible is attached by a freely movable joint
Human Skull, Lateral View
Figure 5.7
23
Human Skull, Superior View
Figure 5.8
Human Skull, Inferior View
Figure 5.9
24
Human Skull, Anterior View
Figure 5.11
Paranasal Sinuses
Hollow portions of bones surrounding the nasal cavity
Functions of paranasal sinuses
Lighten the skull
Give resonance and amplification to voice
25
Paranasal Sinuses
Figure 5.10a
Paranasal Sinuses
Figure 5.10b
26
The Hyoid Bone
The only bone that does not articulate with another bone
Serves as a moveable base for the tongue
Aids in swallowing and speech
The Hyoid Bone
Figure 5.12
27
The Fetal Skull
The fetal skull is large compared to the infant’s total body length
Fontanels—fibrous membranes connecting the cranial bones
Allow the brain to grow
Convert to bone within 24 months after birth
The Fetal Skull
Figure 5.13a
28
The Fetal Skull
Figure 5.13b
The Vertebral Column
Each vertebrae is given a name according to its location
There are 24 single vertebral bones separated by intervertebral discs
Seven cervical vertebrae are in the neck
Twelve thoracic vertebrae are in the chest region
Five lumbar vertebrae are associated with the lower back
29
The Vertebral Column
Nine vertebrae fuse to form two composite bones
Sacrum
Coccyx
The Vertebral Column
Figure 5.14
30
The Vertebral Column
The spine has a normal curvature
Primary curvatures are the spinal curvatures of the thoracic and sacral regions
Present from birth
Secondary curvatures are the spinal curvatures of the cervical and lumbar regions
Develop after birth
The Vertebral Column
Figure 5.16
31
A Typical Vertebrae, Superior View
Figure 5.17
Regional Characteristics of Vertebrae
Figure 5.18a
32
Regional Characteristics of Vertebrae
Figure 5.18b
Regional Characteristics of Vertebrae
Figure 5.18c
33
Regional Characteristics of Vertebrae
Figure 5.18d
Sacrum and Coccyx
Sacrum
Formed by the fusion of five vertebrae
Coccyx
Formed from the fusion of three to five vertebrae
“Tailbone,” or remnant of a tail that other vertebrates have
34
Sacrum and Coccyx
Figure 5.19
The Bony Thorax
Forms a cage to protect major organs
Consists of three parts
Sternum
Ribs
True ribs (pairs 1–7)
False ribs (pairs 8–12)
Floating ribs (pairs 11–12)
Thoracic vertebrae
35
The Bony Thorax
Figure 5.20a
The Appendicular Skeleton
Composed of 126 bones
Limbs (appendages)
Pectoral girdle
Pelvic girdle
36
The Appendicular Skeleton
Figure 5.6a
The Appendicular Skeleton
Figure 5.6b
37
The Pectoral (Shoulder) Girdle
Composed of two bones
Clavicle—collarbone
Scapula—shoulder blade
These bones allow the upper limb to have exceptionally free movement
Bones of the Shoulder Girdle
Figure 5.21a
38
Bones of the Shoulder Girdle
Figure 5.21b
Bones of the Shoulder Girdle
Figure 5.21c–d
39
Bones of the Upper Limbs
Humerus
Forms the arm
Single bone
Bones of the Upper Limbs
Figure 5.22a–b
40
Bones of the Upper Limbs
The forearm has two bones
Ulna
Medial bone in anatomical position
Radius
Lateral bone in anatomical position
Bones of the Upper Limbs
Figure 5.22c
41
Bones of the Upper Limbs
The hand
Carpals—wrist
Metacarpals—palm
Phalanges—fingers
Bones of the Upper Limbs
Figure 5.23
42
Bones of the Pelvic Girdle
Formed by two coxal (ossa coxae) bones
Composed of three pairs of fused bones
Ilium
Ischium
Pubis
Bones of the Pelvic Girdle
The total weight of the upper body rests on the pelvis
It protects several organs
Reproductive organs
Urinary bladder
Part of the large intestine
43
The Pelvis
Figure 5.24a
The Pelvis: Right Coxal Bone
Figure 5.24b
44
Gender Differences of the Pelvis
The female inlet is larger and more circular
The female pelvis as a whole is shallower, and the bones are lighter and thinner
The female ilia flare more laterally
The female sacrum is shorter and less curved
The female ischial spines are shorter and farther apart; thus the outlet is larger
The female pubic arch is more rounded because the angle of the pubic arch is greater
Gender Differences of the Pelvis
Figure 5.24c
45
Bones of the Lower Limbs
The thigh has one bone
Femur
The heaviest, strongest bone in the body
Bones of the Lower Limbs
Figure 5.25a–b
46
Bones of the Lower Limbs
The lower leg has two bones
Tibia
Shinbone
Larger and medially oriented
Fibula
Thin and sticklike
Bones of the Lower Limbs
Figure 5.25c
47
Bones of the Lower Limbs
The foot
Tarsals
Two largest tarsals
Calcaneus (heelbone)
Talus
Metatarsals—sole
Phalanges—toes
Bones of the Lower Limb
Figure 5.26
48
Arches of the Foot
Bones of the foot are arranged to form three strong arches
Two longitudinal
One transverse
Arches of the Foot
Figure 5.27
49
Joints
Articulations of bones
Functions of joints
Hold bones together
Allow for mobility
Ways joints are classified
Functionally
Structurally
Functional Classification of Joints
Synarthroses
Immovable joints
Amphiarthroses
Slightly moveable joints
Diarthroses
Freely moveable joints
50
Structural Classification of Joints
Fibrous joints
Generally immovable
Cartilaginous joints
Immovable or slightly moveable
Synovial joints
Freely moveable
Summary of Joint Classes
[Insert Table 5.3 here]
Table 5.3
51
Fibrous Joints
Bones united by fibrous tissue
Example:
Sutures
Syndesmoses
Allows more movement than sutures
Example: Distal end of tibia and fibula
Fibrous Joints
Figure 5.28a–b
52
Cartilaginous Joints
Bones connected by cartilage
Example:
Pubic symphysis
Intervertebral joints
Cartilaginous Joints
Figure 5.28c–e
53
Synovial Joints
Articulating bones are separated by a joint cavity
Synovial fluid is found in the joint cavity
Synovial Joints
Figure 5.28f–h
54
Features of Synovial Joints
Articular cartilage (hyaline cartilage) covers the ends of bones
A fibrous articular capsule encloses joint surfaces
A joint cavity is filled with synovial fluid
Ligaments reinforce the joint
Structures Associated with the Synovial Joint
Bursae—flattened fibrous sacs
Lined with synovial membranes
Filled with synovial fluid
Not actually part of the joint
Tendon sheath
Elongated bursa that wraps around a tendon
55
The Synovial Joint
Figure 5.29
Types of Synovial Joints
Figure 5.30a–c
56
Types of Synovial Joints
Figure 5.30d–f
Inflammatory Conditions Associated with Joints
Bursitis—inflammation of a bursa usually caused by a blow or friction
Tendonitis—inflammation of tendon sheaths
Arthritis—inflammatory or degenerative diseases of joints
Over 100 different types
The most widespread crippling disease in the United States
57
Clinical Forms of Arthritis
Osteoarthritis
Most common chronic arthritis
Probably related to normal aging processes
Rheumatoid arthritis
An autoimmune disease—the immune system attacks the joints
Symptoms begin with bilateral inflammation of certain joints
Often leads to deformities
Clinical Forms of Arthritis
Gouty arthritis
Inflammation of joints is caused by a deposition of uric acid crystals from the blood
Can usually be controlled with diet
58
Developmental Aspects of the Skeletal System
At birth, the skull bones are incomplete
Bones are joined by fibrous membranes called fontanels
Fontanels are completely replaced with bone within two years after birth
Ossification Centers in a 12-week-old Fetus
Figure 5.32
59
Skeletal Changes Throughout Life
Fetus
Long bones are formed of hyaline cartilage
Flat bones begin as fibrous membranes
Flat and long bone models are converted to bone
Birth
Fontanels remain until around age 2
Skeletal Changes Throughout Life
Adolescence
Epiphyseal plates become ossified and long bone growth ends
Size of cranium in relationship to body
2 years old—skull is larger in proportion to the body compared to that of an adult
8 or 9 years old—skull is near adult size and proportion
Between ages 6 and 11, the face grows out from the skull
60
Skeletal Changes Throughout Life
Figure 5.33a
Skeletal Changes Throughout Life
Figure 5.33b
61
Skeletal Changes Throughout Life
Curvatures of the spine
Primary curvatures are present at birth and are convex posteriorly
Secondary curvatures are associated with a child’s later development and are convex anteriorly
Abnormal spinal curvatures (scoliosis and lordosis) are often congenital
Skeletal Changes Throughout Life
Figure 5.16
62
Skeletal Changes Throughout Life
Osteoporosis
Bone-thinning disease afflicting
50% of women over age 65
20% of men over age 70
Disease makes bones fragile and bones can easily fracture
Vertebral collapse results in kyphosis (also known as dowager’s hump)
Estrogen aids in health and normal density of a female skeleton
Skeletal Changes Throughout Life
Figure 5.34
63
Skeletal Changes Throughout Life
Figure 5.35