1.03 Skeletal System

Lecturer: Dr. Axel Elises

osteology

study of structure and function of bones and cartilages

arthrology

study of joints and ligaments

myology

study of muscles

skeletal system is consists of:

1. bones

2. cartilages

3. ligaments

4. joints

5. tendons

skeletal system

1. 20% of body weight

2. 206 bones

function

1. movement: provides point of attachments for muscle

2. support:

   • backbone is main support center for upper body

   • holds head up

   • protects spinal cord

3. protection:

   • skull: protects the brain

   • ribs: protects lungs and heart

4. makes blood (hematopoiesis): RBC, WBC, and platelets made from marrow

5. storage: store minerals (e.g. Ca, phosphorus)

functional parts

1. axial

   • 80 bones

   • cranium (22), ear ossicles (6), hyoid bone (1), vertebrae (24), ribs (24), sternum (1), sacrum (1), coccyx (1)

2. appendicular

   • 126 bones

   • pectoral/shoulder girdle (4), pelvic girdle (2), upper limbs (60), lower limbs (60)

bones

calcified connective tissue consisting of osteocytes in a matrix of ground substance and collagen fiber

organic matrix

1. 35%

2. providing tensile strength (mainly Type 1 collagen)

inorganic mineral component

1. 65%

2. provides compressive strength and rigidity

   • hydroxyapatite crystals, mainly calcium and phosphate

macroscopic composition of bones

1. cortical/compact bone

2. spongy/cancellous bone

3. medullary cavity

4. periosteum and endosteum

cortical/compact bone

1. dense outer layer

2. forms the diaphysis

spongy/cancellous bone

trabecular, honeycomb-like inner network

medullary cavity

1. bone marrow

2. majority found in the long bones

3. intraosseous (IO) cannulation: used when a patient requires immediate resuscitation and IV access cannot be established quickly

   • a needle is inserted though the bone cortex into the medullary cavity/trabecular bone

   • this provide direct access to the bone marrow vascular network, allowing rapid administration of fluid and medication into the blood stream

     • adult: humerus

     • pediatric: tibia

periosteum and endosteum

connective tissue membranes covering the outer & inner bone surfaces, respectively, except the articular surfaces

microscopic structures

1. organic matrix and inorganic minerals

2. haversian system (osteon): basic functional unit of the bone

number of bones

1. 270-300 during infancy

2. begins to ossify at 8 weeks of the embryonic period, complete at the age of 20 years old

3. mesenchymal in origin

frontal bone

1. number of segments at birth: 2

2. details of fusion: fuses completely into one by age of 8

occipital bone

1. number of segments at birth: 4

2. details of fusion: fuses as one by age of 6

   • squamous part, two lateral parts and a basilar part

sphenoid bone

1. number of segments at birth: 3

2. details of fusion: fuses into one during the first year of life

   • a central body with lesser wings and two separate greater wings

temporal bone

1. number of segments at birth: 8

2. details of fusion: fuses into two, during infancy and childhood

   • squamous, tympanic, petrous and mastoid parts

parietal bone

1. number of segments at birth: 2

2. details of fusion: remains as 2 separate bones in adulthood, but their margins securely interlock at the sagittal suture

ethmoid bone

1. number of segments at birth: 1

2. details of fusion: preformed in cartilage, it ossifies and unites into a single bone early in childhood

sacrum

1. number of segments at birth: 5

2. details of fusion: fuses as one that begins around late adolescence and is complete by ages 25 to 30

coccyx

1. number of segments at birth: 3-5

2. details of fusion: fuses as one that begins at age 20 & completes by age of 30

   • fusion of the coccyx to the sacrum occurs later in life or middle age

pelvic girdle

1. number of segments at birth: 6

2. details of fusion: fusion at the acetabulum socket begins by ages 15-17 & completely by age 20-25

   • consist of ilium, ischium, and pubis

bone classification (by shape)

1. long bones

2. short bones

3. flat bones

4. irregular bones

5. sesamoid bones

long bones

1. longer than wide

2. acts as levers to support weight and for movement

   • upper limbs: humerus, radius, ulna, metacarpals and phalanges

   • lower limbs: femur, tibia, fibular, metatarsals, and phalanges

   • clavicle

main parts of long bones

1. diaphysis

2. epiphysis

3. metaphysis

diaphysis

central tubular shaft or hard compact bone surrounding the medullary cavity

epiphysis

1. wider end portions, covered in articular cartilage

2. form joints and houses spongy bone

metaphysis

1. transitional zone

2. has growth plate (epiphyseal plate) in children

3. for bone lengthening

short bones

1. cuboidal, no shaft

2. for support, less for movement, and found only in the tarsus (ankle) and carpus (wrist)

   • carpals: pisiform, triquetral, lunate, scaphoid, hamate, capitate, trapezoid, trapezium

   • tarsals: calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform

flat bones

1. usually serve protective functions (e.g. flat bones of the cranium protect the brain)

2. flat & curved, protective functions, and have wide area muscle attachment

3. lack medullary cavity

   • cranial: frontal, parietal, occipital

   • thoracic cage: sternum and ribs

     • usually protective functions

     • thin and flattened

   • scapulae

   • pelvis components: ilium, ischium, and pubis

irregular bones

1. various shapes other than long, short, or flat

2. unique shape

   • example: vertebrae, sacrum & coccyx, hyoid bones, certain cranial & facial bones (sphenoid, ethmoid, temporal, mandible, and maxilla)

sesamoid bones

1. develop in tendons (e.g. patella, pisiform)

2. small, seed-shaped bones embedded inside tendons near joints

   • reduce friction

   • ease mechanical stress (stop tendons from wearing out)

   • change direction of muscle pull (acts like pulleys)

3. protect tendons from excessive wear and often change the angle of tendons as they pass to their attachments

4. patella (larges), pisiform (carpal), within flexor tendons (base of big toe, thumb and fingers)

bone surface markings

1. act as sites for muscles, tendon, and ligament attachment

2. form joints

3. allow the passage of blood vessels and nerves

depressions and openings

1. passageways or spaces

2. for passage of nerves, blood vessels, etc.

foramen

round or oval passage through a bone (e.g. obturator foramen)

fossa

shallow, basin-like depression (e.g. supraspinous & infraspinous fossa of scapula)

fissure

slit through bone (e.g. preorbital fissure)

groove/sulcus

long/narrow depression or furrow where nerve/blood vessel passes

meatus

tube-like passageway/canal

sinus

1. hollow, air-filled cavity within the bone

2. in scans:

   • radiopaque = filled with fluid; color white to gray

   • radiolucent = color black (ex. maxillary sinus)

notch

indentation at the edge of the bone

articulations

surfaces that form joints

head

1. large, rounded articular head

2. end of a bone (e.g. humeral head)

condyle

1. smooth, rounded knob which articulate with another bone

2. usually in pairs (e.g. medial & lateral condyles of tibia & femur)

capitulum

small, rounded articular head

facet

1. smooth, nearly flat surface

2. covered by cartilage

3. where another bone articulates (e.g. superior costal facet articulates with rib)

projections and elevations

muscle/ligament attachment

tuberosity

large, rounded elevation (e.g. tibial, ischial tuberosities)

tubercle

small, rough, raised eminence

trochanter

large, irregular, blunt elevation (only femur)

epicondyle

raised area on or above a condyle

crest

narrow, prominent ridge of bone

line

less prominent, narrow ridge (e.g. soleal line of tibia)

spine

sharp, slender, pointer projection

spinous process

long, spine-like projection

malleolus

rounded process

protuberance

bony projection

joints

consists of connection points between two or more bones

classifications of joints

1. synovial joints

2. fibrous joints

3. cartilaginous joints

synovial joints

1. freely movable

2. have joint cavities

3. most common type, found especially in limbs

4. joined by articular capsule (composed of outer fibrous layer lined with serous synovial membrane)

5. potential space, articular cavity, filled with synovial fluid secrete by synovial membrane

6. articulating surface of bone is lined with articular cartilage

7. categorized into six major types based on articulating surface shapes and movement capabilities

fibrous joints

1. united by dense fibrous tissue rich in collagen

2. limited movement

3. lacks joint cavity

4. with three main types based on structure and movement

cartilaginous joints

1. united by hyaline cartilage or fibrocartilage

2. slight moveable or temporary

3. lacks joint cavity

4. with two structure types

synovial joint types

1. plane/gliding joints

2. hinge joints

3. saddle joint

4. condyloid joint

5. ball and socket joint

6. pivot joint

plane/gliding joints

flat surfaces slide past each other (e.g. acromioclavicular joint, wrist joint)

hinge joints

1. moves back and forth in one direction like a door

2. uniaxial

3. flexion & extension only (e.g. knee joint, elbow joint)

saddle joint

1. shaped like a riding saddle for back-and-forth and side-to-side play

2. abduction, adduction, flexion, extension

3. some circumduction

4. biaxial (e.g. carpometacarpal (CMC) joint of thumb)

condyloid joint

1. oval surfaces move in 2 planes

2. flexion, extension, abduction, and adduction

3. less/restricted circumduction compared to saddle

ball and socket joint

1. allow turning and rotating in many ways

2. flexion, extension, abduction, adduction, medial rotation, lateral rotation, and full circumduction

3. multiaxial (e.g. shoulder joint, hip joint)

pivot joint

1. rotation around a central axis (single point)

2. uniaxial

   • example: atlanto-axial joint in which atlas (C1) rotates around finger-like dense (odontoid process) of the axis (C2) during head rotation

fibrous joint types

1. sutures

2. gomphoses

3. syndesmoses

sutures

1. narrow fibrous joints

2. bones are close together, either interlocking along a wavy line or overlapping

3. found only between the flat bones of the skull

4. immovable (synarthrosis) for brain protection

5. can ossify into solid bone over time (synostosis)

example: coronal and sagittal joints of the skull

gomphoses

1. dentoalveolar syndesmosis

2. specialized peg-and-socket joints

3. anchor the roots of teeth into mandible and maxilla

4. bound tightly by periodontal ligament

5. immovable (synarthrosis), but with micromovement detected by nerves for proprioception (detect pressure of biting/chewing)

example: articulation between dental roots and bony alveolar sockets in maxilla and mandible

syndesmoses

1. parallel bones united by an interosseous membrane or broad ligaments

2. fibrous joints units the bones with a sheet of fibrous tissue, either a ligament or fibrous membrane

3. slightly moveable (amphiarthrosis) or tightly restricted

4. the blood vessel going here will not be trapped because it is protected by two bones

example: interosseous membrane between radius & ulna, tibia & fibula

cartilaginous joint types

1. synchondrosis

2. symphysis

synchondrosis

1. primary cartilaginous joint

2. joined by hyaline cartilage

3. mostly immovable (synarthrosis), slight bending during early life

4. can be temporary or permanent

examples:

• epiphyseal plates: growing hyaline cartilage in long bones of children (temporary synchondrosis)

• 1st sternocostal joint: between 1st rib and manubrium of sternum (permanent synchondrosis)

symphysis

1. secondary cartilaginous joint

2. joined by a broad, flat disc of fibrocartilage

3. strongly, slight movable (amphiarthrosis) to provide strength and shock absorption

example:

• pubic symphysis: between R and L pubic bones of pelvis

• intervertebral disc: adjacent vertebral bodies

cartilages

1. macroscopic structures

2. a tough, flexible connective tissue that cushions joints, reduces friction between bones, and gives shape to structures like the ears and nose

perichondrium

1. dense connective tissue that surrounds most of the cartilages consists of:

   • outer layer (fibroblast, collagen)

   • inner layer (chondroblast)

2. absent in articular and fibrocartilage

3. found in hyaline cartilage (nose and ribs) and all elastic cartilage (outer ear)