Download 06. Skeletal System

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6.1 Functions of the Skeletal System
Support
Protection
Attachment sites for skeletal muscles
Blood cell production
Mineral storage
6.2 Bone Structure
There are four basic types of bone based on shape
Long bones e.g. thigh bone
Short bones e.g. wrist bone
Flat bones e.g. skull
Irregular bones e.g. spine bone
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Structure of a Long Bone
Epiphysis
Articular cartilage
Diaphysis
Epiphyseal plate (line)
Periosteum
Spongy bone
Compact bone
Medullary cavity
Endosteum
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Spongy (cancellous) bone
Interior of small bones, skull bones, and epiphyses
Consists of trabeculae and spaces filled with red bone marrow
Reduces bone weight without reducing strength
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Compact bone
Wall of diaphysis and surface of diaphysis
Tightly packed tissue with no spaces
Strong and gives supportive strength
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Microscopic Structure
Bone cells lie inside lacunae
Compact bone
Osteons
Osteonic canals
Lamellae
Foramen
Canaliculi
Spongy (cancellous) bone
Lack osteons
Receive nutrients by diffusion through canaliculi
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6.3 Bone Formation
Ossification is the process of bone formation during the 6th or 7th week of embryonic life
Two types of bone formation
1. Intramembranous ossification
2. Endochondral ossification
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For both types of bone formation
Primitive connective tissue cells become osteoblasts
Osteoblasts deposit bone matrix around them
Once trapped in matrix, osteoblasts become osteocytes
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1. Intramembranous Ossification
Forms most skull bones
Steps involved
Connective tissue membranes form at sites of future intramembranous bones
Some cells become osteoblasts and deposit spongy bone within the membrane starting in the center of bone
Osteoblasts from the covering membrane (periosteum) deposit a layer of compact bone over the spongy bone
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To produce the correct bone shape
Use osteoclasts to remove bone matrix
Use osteoblasts to reform new bone matrix
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2. Endochondral Ossification
Forms most bones of the body
Example: long bones
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Steps involved
Primary ossification center forms in center of cartilage
Periosteal osteoblasts form a collar of compact bone around primary ossification center
Cartilage in the primary center calcifies and chondrocytes die
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Blood vessels and nerves penetrate the center, bring osteoblasts with them
Osteoblasts form spongy bone at the primary ossification center
Secondary ossification center forms in the epiphyses
Osteoblasts form spongy bone at the primary ossification center
Secondary ossification center forms in the epiphyses
Osteoclasts remove the spongy bone and form the medullary cavity
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Bone continues to grow
At the end of the process, the epiphyseal plate separates the epiphyses from the diaphysis
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Continued growth in diameter due to formation of compact bone beneath the periosteum
Continued growth in length takes place at the epiphyseal disk
Cartilage grows on the epiphyseal side
Cartilage is converted into bone on the diaphysis side
Osteoblasts and osteoclasts continually reshape the bone as it grows
Bone growth in length continues until age 25
Epiphyseal plate is completely replaced by bone
Epiphyseal line is all that remains
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Homeostasis of Bone
Bone is continually remodeled due to activity of osteoclasts and osteoblasts
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Remodeling can be affected by
Physical activity
Dietary calcium intake
Age
6.4 Divisions of the Skeleton
Skeleton is divided into two divisions
Axial skeleton
Bones along the longitudinal axis of the body
Appendicular skeleton
Pectoral girdle and upper extremities
Appendicular skeleton
Pectoral girdle and upper extremities
Pelvic girdle and lower extremities
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6.5 Axial Skeleton
Skull
Divided into two segments
Cranium - 8 fused bones
Facial bones - 13 fused bones
Bones joined by sutures
Immovable joints
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Several bones possess paranasal sinuses
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Cranium
Frontal bone
Anterior part of cranium
Two frontal sinuses
Parietal bones
Sides and roof of cranium
sagittal suture, coronal suture
Occipital bones
Posterior portion and floor of cranium
foramen magnum: a large opening through which the brain stem extends
occipital condyles: articulates with first vertebra (atlas) Fig 6.9
lambdoidal sutures: joined to the parietal bones
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Cranium
Temporal bones
Inferior to parietal bones on each side of the cranium
Squamosal sutures (parietal), lambdoidal sutures (occipital)
external auditory canal: leads inward to eardrum
mandibular fosssa
anterior to the auditory canal
a depression that receives the mandibular condyle
temporomandibular joint
processes
zygomatic process: projects anteriorly to join with zygomatic bone
mastoid process: a large, rounded projection inferior to the auditory canal. attachment site for some neck muscles
styloid process: medial to the mastoid process, spikelike
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Sphenoid bone
"Keystone" of the cranium
it articulates with all other cranial bones
sella turcica
a depression that contains the pituitary gland
Two sphenoidal sinuses below sella turcica
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Ethmoid bone
Anterior portion of cranium, including medial surface of eye orbit and roof of nasal cavity (ethmoid sinus)
perpendicular plate: form most of the nasal septum
Anterior portion of cranium, including medial surface of eye orbit and roof of nasal cavity (ethmoid sinus)
perpendicular plate: form most of the nasal septum
superior and middle nasal conchae
cribriform plate
the roof of the nasal cavity
crista galli (cock's comb): to which meninges are attached
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Facial Bones
Maxillae
Form upper jaw, anterior portion of hard palate, part of lateral walls of nasal cavity, floors of eye orbits
Each maxilla is formed separately, but they are joined at the midline during embryonic development → (cf. cleft lip)
palatine process → hard palate
alveolar process → teeth
alveoli: the sockets containing the teeth
Maxillary sinus: below orbits
Palatine bones
Form posterior portion of hard palate, lateral wall of nasal cavity
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zygomatic (=yoke)
Zygomatic bones
Cheek bones
Also form floor and lateral wall of each eye orbit
temporal process (zygomatic bone) + zygomatic process (temporal bone) = zygomatic arch
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Lacrimal bones
Medial surfaces of eye orbits
Nasal bones
Form bridge of nose
vomer (=plowshare, 보습)
Vomer
In midline of nasal cavity
Vomer
In midline of nasal cavity
Forms nasal septum with the ethmoid bone
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Inferior nasal conchae
Attached to lateral walls of nasal cavity
Mandible
Lower jawbone
Only movable skull bone
body: U-shaped
ramus:Y-shaped
coronoid process
mandibular condyle → mandibular fossa → temporomandibular joint
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Hyoid bone
F. hyoïde < L. hyoides < Gk. ὑοειδής huoeidēs
= "shaped like the letter υ" → Y,u (upsilon ← hu)
Found in anterior portion of neck, inferior to mandible
Does not articulate with any other bones
suspended from the styloid processes by ligaments
Used as attachment site for tongue muscles
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The infant skull
Newborn skull is incompletely developed
Possess fontanels
Non-ossified areas
Allow for flexibility during birth and growth afterwards
6 fontanels
Allow for flexibility during birth and growth afterwards
6 fontanels
anterior (1), mastoid (2), posterior (1), sphenoid (2)
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Vertebral Column
Extends from skull to pelvis
Flexible and sturdy longitudinal support for trunk
Formed by 24 movable vertebrae, a sacrum, and a coccyx
Possess intervertebral discs
Shock absorbers
Possess four distinct curvatures
cervical, thoracic, lumbar, pelvic
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Structure of a Vertebra
All vertebrae have common features
Body
Neural arch
Vertebral foramen
Spinous process
Transverse process
Superior and inferior articulating facets
Intervertebral foramina
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Cervical vertebrae
C1-C7, Support neck
Possess unique transverse foramen
a passageway blood vessels and nerves
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Atlas: cervical vertebra 1
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Atlas: cervical vertebra 1
Articulate occipital condyles of occipital bone
Supports head
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Axis: cervical vertebra 2
Possesses the odontoid process (dens)
Serves as a pivot point for axis
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Thoracic vertebrae
T1-T12
spinous processes are longer and slope downward
Ribs articulate on the transverse processes and bodies
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Lumbar vertebrae
L1-L5
Heavy, thick bodies to support greater stress and weight
Blunt spinous processes - attachment of back muscles
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Sacrum
Five fused sacral bones
Fused spinal processes → tubercles
sacral foramina, sacral canal, sacral hiatus
Forms posterior wall of pelvic girdle
Coccyx
Tailbone
Three to five fused rudimentary vertebrae
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Three to five fused rudimentary vertebrae
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Thoracic Cage
Composed of
Thoracic vertebrae
Ribs
Costal cartilages
Sternum
Functions
Protection of internal organs
Support of upper body
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Ribs
Attached to thoracic vertebrae
True ribs (#1-7)
Attached to sternum directly by costal cartilages
False ribs (#8-10)
Attach to costal cartilage of superior ribs
Floating ribs (#11-12)
Do not attach anteriorly, no costal cartilages
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Sternum
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Sternum
Flat, elongated bone in the anterior midline of thoracic cage
Composed of three fused bones
Manubrium
Body
Xiphoid process
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6.6 Appendicular Skeleton
Consists of
Pectoral girdle and upper extremity
Pelvic girdle and lower extremity
Composed of 126 individual bones
c.f. 80 axial bones → Total 206 bones
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Pectoral Girdle
Composed of
Two clavicles
Two scapula
Clavicle
Articulates with sternum and scapula
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Scapula
Located on each side of vertebral column
Does not articulate with the axial skeleton
Held in place by muscles to allow free shoulder movement
Scapular spine
acromion process
Scapular spine
acromion process
glenoid cavity
coracoid process
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Humerus
Articulates with scapula at the shoulder and ulna and radius at the elbow
Head fits into glenoid cavity of the scapula
greater tubercle: lateral
intertubercular groove
lesser tubercle: medial
neck: anatomical vs. surgical (fracture)
deltoid tuberosity
deltoid muscle
condyles
trochlea: medial → ulna
capitulum: lateral → radius
lateral, medial epicondyles
fossa
coronoid f.: anterior, coronoid process of ulna
olecranon f.: posterior, olecranon process of ulna
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Ulna
Medial bone in forearm
Bone does not move with hand rotation
olecranon process
fits into olecranon fossa (of humerus)
trochlear notch
articulates with trochlea (of humerus)
coronoid process
fits into coronoid fossa (of humerus)
head: distal, articulates with medial surface of radius
fits into coronoid fossa (of humerus)
head: distal, articulates with medial surface of radius
styloid process: ligaments of the wrist
Radius
Lateral bone in the forearm
Bone that rotates when the hand is rotated
head: proximal, articulates with capitulum
radial tuberosity: biceps muscle
styloid process: ligaments of the wrist
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Carpals
Wrist bones
Metacarpals
Bones of the palm of the hand
Phalanges
Bones of the fingers
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Pelvic Girdle
Consists of
Two coxal bones
Sacrum
Forms a rigid, bony pelvis
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Coxal Bones
Attachment site for the legs
Formed by three fused bones
Ilium
iliac crest
greater sciatic notch
iliac crest
greater sciatic notch
sacroiliac joint
Ischium
Pubis
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Coxal Bones
Attachment site for the legs
Formed by three fused bones
Ilium
iliac crest
greater sciatic notch
sacroiliac joint
Ischium
ischial tuberosity
ischial spine: determines the diameter of the pelvic opening during childbirth
Pubis
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Coxal Bones
Attachment site for the legs
Formed by three fused bones
Ilium
iliac crest
greater sciatic notch
sacroiliac joint
Ischium
ischial tuberosity
ischial spine
Pubis
obturator foramen
symphysis pubis
obturator foramen
symphysis pubis
Three bones join at acetabulum
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The pelvic girdles of males and females have several structural differences
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Lower Extremity
Femur
Thigh bone
Largest and strongest bone in the body
head ( → acetabulum)
greater (lesser) trochanter
lateral (medial) condyle → tibia
Patella
Kneecap, anterior to the knee joint
It is a sesamoid bone, which refers to a bone that is embedded in the tendon
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Tibia
Shinbone
Lager, medial bone in lower leg
Bears body weight
lateral (medial) condyle: femur
tibial tuberosity: patellar ligament
medial malleolus: medial prominence of the ankle
Fibula
Slender, lateral bone in lower leg
lateral malleolus: lateral prominence of the ankle
Slender, lateral bone in lower leg
lateral malleolus: lateral prominence of the ankle
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Tarsals
ankle bones
talus: the prominent tarsal bone
calcaneus: heel bone
Metatarsals
Bones of the instep
Phalanges
Toe bones
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6.7 Articulations
An articulation is a joint or junction between two bones
Joints allow for varying degrees of movement
Three categories of joints
Immovable
Slightly movable
Freely movable
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Immovable Joints (synarthrosis)
Bones are tightly joined and separated by thin fibrous connective tissue
No movement at the joint
Example: sutures
Slightly Movable Joints (amphiarthrosis)
Bones separated by layer of cartilage or fibrous connective tissue
Limited flexibility
Bones separated by layer of cartilage or fibrous connective tissue
Limited flexibility
Example: joints between vertebrae
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Freely Movable Joints (diarthrosis)
Joints are freely movable
Structurally more complex
Several types of freely movable joints
joint (articular) capsule
: formed of ligament
cf. ligament vs. tendon
synovial membrane
synovial fluid
articular cartilage
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Gliding Joints
Involve sliding of bones across each other
Example: carpal and tarsal bones
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Condyloid Joints
Allow movement from side to side and back and forth
Example: between carpals and bones of forearm
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Hinge Joints
Allow movement in one direction only
Example: knee and elbow joints
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Saddle Joints
Ends of each bone are saddle shaped
Movement is side to side and back and forth
Example: joint between trapezium and metacarpal of thumb
Example: joint between trapezium and metacarpal of thumb
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Pivot Joints
Allow rotational movement
Example: atlas on the axis
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Ball-and-Socket Joints
A rounded head of one bone fits into a concavity on another bone
Movement may be rotational or in any plane
Example: hip and shoulder joint
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Movements at Freely Movable Joints
Movement is caused by contraction of muscles that span the joint
Movement depends upon joint type and location of muscle(s) involved
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6.8 Disorders of the Skeletal System
Common disorders can be characterized as
Disorders of bones
Disorders of joints
Orthopedics
Branch of medicine that specializes in treating skeletal disease and abnormalities
Disorders of Bones
Fractures: broken bones
Complete: The break is completely through the bone.
Compound: A broken bone pierces the skin.
Complete: The break is completely through the bone.
Compound: A broken bone pierces the skin.
Simple: A bone does not pierce the skin.
Comminuted: The bone is broken into several pieces.
Segmental: Only one piece is broken out of the bone.
Spiral: The fracture line spirals around the bone.
Oblique: The break angles across the bone.
Transverse: The break is at right angles to the long axis of the bone.
Incomplete: The bone is not broken completely through.
Green stick: The break is only on one side of the bone, and the bone is bowed.
Fissured: The break is a lengthwise split in the bone.
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Osteomyelitis
Inflammation of bone and bone marrow due to bacterial infection
Osteoporosis
Weakening of bone due to loss of calcium salts
Common in older people, especially postmenopausal women
Caused by inactivity and decrease in hormone production
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Rickets
Childhood disease
Due to deficiency of calcium salts in bones
Dietary deficiency in calcium or Vitamin D
Children have a bowlegged appearance
Disorders of Joints
Arthritis
Characterized by inflammation, swelling, and pain
Rheumatoid arthritis
Most painful and crippling type
Most painful and crippling type
Result is ossification of joint, making it immovable
Auto-immune disorder
Osteoarthritis
Most common type
Loss of articular cartilage makes movement restricted and painful
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Bursitis
Inflammation of bursa
Dislocation
Displacement of bones forming the joint
Herniated disk
Intervertebral disc protrudes out beyond vertebrae
Caused by excessive pressure
May apply pressure to nerves
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Spinal curvatures
Kyphosis (hunchback)
Excessive thoracic curvature
Lordosis (swayback)
Excessive lumbar curvature
Scoliosis
Abnormal lateral curvature
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Sprain
Tearing or stretching of ligaments and tendons without dislocation
Kyphosis
Lordosis
Scoliosis
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Scoliosis