The Skeletal System

• Parts of the skeletal system– Bones (skeleton)– Joints– Cartilages– Ligaments ( connective

tissue that joins two bones)

• Divided into two divisions– Axial skeleton– Appendicular skeleton

Functions of Bones• Support of the body

– Framework to support and anchor delicate organs

– legs support the entire body when we stand

– Ribs support thoracic cavity’s wall

• Protection of soft organs– Skull protects brain– Ribcage protects lungs

and heart– Pelvis protects

reproductive organs

Functions of Bones• Movement due to attached

skeletal muscles– Muscles attach to the bones

by tendons– Helps in the movement of the

body

• Storage of minerals and fats– Stores calcium and phosphate

• Calcium stored is used in muscle contraction

– Stores fat in the bone marrow

• Blood cell formation– Bone marrow is the site for the

synthesis of• red blood cells• White blood cells

Bone Tissues Two basic types of bone tissue

Compact bone Homogeneous found in long bones

Spongy bone Small needle-like

pieces of bone Many open spaces found in short, irregular bones

Classification of Bones on the Basis of Shape

• The adult skeleton has 206 bones

• Based on the shape they are of 4 types– Long bones– Short bones– Flat bones– Irregular bones

• Long bones– Typically longer than wide– Have a shaft with heads at

both ends– Contain mostly compact

bone• Examples: Femur,

humerus

• Short bones– Generally cube-shaped– Contain mostly spongy

bone• Examples: Carpals,

tarsals

• Flat bones– Thin and flattened– Usually curved– Sandwich of spongy bone

between two layers of compact bone

• Examples: Skull, ribs, sternum

• Irregular bones– Irregular shape

• Example: Vertebrae and hip

Gross Anatomy of a Long Bone

• Diaphysis– Shaft that makes length of the bone– Composed of compact bone

• Periosteum– Outside covering of the diaphysis– Made up of Fibrous connective tissue

• Medullary cavity– Cavity of the shaft– Contains yellow marrow (mostly fat)

in adults– Contains red marrow (for blood cell

formation) in infants

• Sharpey’s fibers– Also known as perforating

fibers– Made of several Connective

tissue fibers– Help secure periosteum to

underlying bone

• Arteries– Supply bone cells with

nutrients– Also facilitates the repair of

bones on injury

• Epiphysis – Ends of the bone– Composed mostly of spongy bone

• Articular cartilage– Covers the external surface of the

epiphyses– Made of hyaline cartilage– Soft, slimy and smooth in texture– Decreases friction at joint

surfaces

• Epiphyseal line: – Bony line that separates the

epiphysis from diaphysis– Seen in adult– Remnant of epiphyseal plate– location for bone growth in length

during development • made of hyaline cartilage

Bone Markings• Surface features of bones• Appear as bumps, holes, projections• Sites of attachments for muscles,

tendons, and ligaments• Passages for nerves and blood

vessels• Categories of bone markings

– Projections and processes – grow out from the bone surface: tuberosity, tubercle, trochanter

– Depressions or cavities – indentations

• Foraman: an oval opening

Microscopic Anatomy of a compact Bone• Very organized structures made of

several units. Each unit is called• Osteon (Haversian System)

– A functional unit of bone consisting of

• 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

• Lamellae– Rings around the central canal– Sites of lacunae

• Lacunae– Cavities containing bone cells

(osteocytes)– Arranged in concentric rings

• Canaliculi – Tiny canals– Radiate from the central canal to

lacunae– Form a transport system connecting

all bone cells to a nutrient supply • Bone’s

– hardness is the result of calcium salts

– Flexibility and ability to resist tension is provided by collagen fibers

Bone formation, growth and remodeling• In embryos, the skeleton is primarily hyaline cartilage• During development, much of this cartilage is replaced by bone• Process of bone formation is called ossification• Cartilage remains in isolated areas such as

– Bridge of the nose– Parts of ribs– Joints

Bone Growth• Epiphyseal plates allow for

growth of long bone during childhood– New cartilage is continuously

formed– Older cartilage becomes

ossified• Bone replaces cartilage

• In the adult bone grows in diameter

• It is appositional growth

Types of Bone Cells• Osteoblasts

– Bone-forming cells• Osteocytes

– Mature bone cells• Osteoclasts

– Bone-destroying cells– Break down bone matrix for

remodeling and release of calcium

• Bone Remodeling: Old bone is replaced with new bone

• Osteoclasts remove old bone and osteoblast forms new bone

• Regulated by nutrition, hormones

Rickets

• Lack of Calcium

• Lack of Vitamin D

• Soft bones

• Diagnosis: bowed feet

Bone Fractures

• A break in a bone: brittle bones, falls, injuries,

• Types of bone fractures– Closed (simple) fracture – break that does not

penetrate the skin• Immobilization: Cast

– Open (compound) fracture – broken bone penetrates through the skin

• Surgery to put the pieces back together by pins or wires

• It takes about 6-8 weeks to heal a simple fracture

Common Types of Fractures

Steps: Repair of Bone Fractures• Hematoma forms: Blood vessels are ruptured, Hematoma (blood-

filled swelling) forms, blood cells die due to lack of nutrients• Fibrocartilage Callus: Is mass of connective tissue that forms at a

fracture site and connects the broken ends of the bone• Bony Callus: Callus is replaced by a bony callus with the help of

osteoblasts and osteoclasts• Bony callus is remodeled to form a bone

Skeleton System

sku ll ve rte bra l co lu m n

th o rac ic ca ge h yo id

a x ia l ske le ton

p e c to ra l p e lv ic

g ird les

u pp er lo w e r

lim b s

a p p en d icu la r ske le ton

ske le ta l s ys tem

Skull: total 22 bones. Attached to one another by

sutures

Cranial bones

(Brain)

Facial bones

# 8 14

Function:

1. Protection

2. Attachment site for

Brain

Facial bones

Sensory organs such as eyes

Muscles of mastication and facial expression

Axial Skeleton

• Cranium: enclosing brain: made of 8 bones:

• 1 Frontal forms forehead and front of skull

• 2 temporal forms the sides and a part of the base of the skull

• Serves as Attachment site for • mandible and • cheek bone zygomatic

• 2 Parietals forms roof and sides of the cranium

• 1 sphenoid: butterfly shaped forming base of the cranium, floor of the eye orbits

• 1 ethmoid: present between the eyes forming a part of the orbit and nasal cavity

• I Occipital: forms back and part of the base of the skull

Facial Bones : composed of 14 bones:

• 1 Mandible: is lower jaw,

• only movable bone of the skull,

• and all others are immovable.

• 2 Maxillae: forms upper jaw by joining of two bones

• 2 Zygomatics: are cheek bones

Facial Bones

• 2 Nasal bones Lie side by side forming bridge of the nose

• 2 lacrimal bones are present inside of the eye in front of the orbital cavity

• 2 inferior nasal conchae form the sides of the nasal cavity.

Facial : composed of 14 bones:

• 1 vomer (shaped like blade of plow forms nasal septum

• 2 Palatine form the back part of the hard palateand floor of nasal cavity

Human Skull, Superior View

Paranasal Sinuses• Hollow portions of bones surrounding the nasal cavity• Include frontal sinus, ethmoid sinus, sphenoid sinus, maxillary sinus• Functions of paranasal sinuses

– Lighten the skull– Give resonance and amplification to voice

The Hyoid Bone• The only bone that does not

articulate with another bone

• It hangs in the middle of the neck above larynx

• Attached to the temporal bone with the help of ligaments

• Horse shoe shaped

• Serves as a moveable base for the tongue

• Attachment site for the muscles of neck

• Raise and lower the larynx when we swallow and speak

The Fetal Skull• The fetal skull is large compared to

the infants total body length • 1:4• Adult: 1: 8

• Fontanels – fibrous membranes connecting the cranial bones– Soft spots– Made of cartilage– Allow the brain

to grow– Convert to bone within 24

months after birth

• Vertebral Column:

• 26 bones in the adult

• 34 bones in the embryonic stage

• Vertebrae separated by intervertebral discs– Absorbs shocks and gives the spine

flexibility

• The spine has a normal curvature

• Each vertebrae is given a name according to its location

• Cervical 7,• Thoracic 12,• lumbar 5,• sacral 1(fused of 5)• coccygeal 1(fused from 4 or 5)

• S shape give two types of curves– Primary: thoracic and sacral

region

– Present at the time of birth

– Secondary : • Cervical: when the baby begins

to raise neck• Lumbar: baby begins to walk

• Vertebral Column: Functions:

A. Supports weight of head and trunk,

B. protects spinal cord,

C. allows spinal nerves to exit spinal cord,

D. site of muscle attachment,

E. facilitates movement of head and neck

Each vertebra hasBody: gives strength,

Pedicles : 2 stalks arising from body.

Lamina: arise as projection from each pedicle

Spinous process: Lamina fuse to form spinous process

Transverse process: pedicels join with lamina giving raise to

transverse process-attaches to the muscles and

ligaments.

vertebral foramina: Canal through which spinal cord passes

Intervertebral discs: present between vertebra

made of firbocartilage-support and prevent rubbing of 2 vertebra.

Intervertebral Forman: Spinal nerves come out

Vertebra/feature

cervical thoracic lumbar sacral cocci

# 5 12 5 1( fused 5) 1( fused 3-5)

Unique feature

C1 altas: no body: only lateral process

Typical vertebra

Spinal process thick

Form dorsal portion of pelvis

Smallest vertebra

C2 axis: pivot. Connects vertebral column to skull

Large body

Largest body

Tail like projection

Oval foramina

Thoracic cage

• Forms a cage to protect major organs (heart, lungs)

• Consists of:

• Ribs: 12 pairs

• sternum (breast bone) anteriorly

• and• thoracic vertebra (12)

posteriorly.

Sternum: manubrium, body and xiphoid process

• Manubrium: The top portion

• Fuses with :• 1. clavicle (collarbone)

forming T shaped structure

• 2. Ribs ( first pair)laterally

Sternum

• Body: long and thin

• Attachment site: 2-7th pairs of ribs laterally.

• Xiphoid process:

• The tip of the sternum

• Ribs: Total 12 pairs:

• 1-7 pairs of ribs : true ribs attached to sternum directly by coastal cartilage

• 8-12 pairs of ribs are called false ribs not attached to sternum directly or not attached to the sternum at all

False Ribs: • 8-10 pair attach to

cartilage of 7th rib• 11 – 12 pair are

floating ribs.• Intercoastal spaces:

spaces between the ribs.

• Intercoastal spaces are filled with intercoastal muscles – help in breathing

Appendicular

Skeleton • Consists of 126 bones

• Consists of the upper and lower limbs

• And pectoral and pelvic girdle

Pectoral or Shoulder Girdle• These bones allow the upper

limb to have exceptionally free movement

• Pectoral girdle: clavicle and scapula

• clavicle: (collar bone):S shaped bone.

• Attaches to manubrium of sternum medially and to scapula laterally

• Scapula: triangular in shape• Acromium process: attaches to

clavicle• Coracoid process: holds the

arm out (laterally) from the body,

• increases arm’s mobility• Glenoid cavity: holds humerus

• Upper limb is composed of Humerus(arm)Head: fits into glenoid cavity of scapula

• Capitulum: articulates with radius• Trochlea: articulates with ulna

• Forearm • radius (towards thumb), Lateral bone• Head of radius articulates with capitulum of humerus • Ulna (towards little finger), Medial Bone• trochlear notch articulates with trochlea of humerus

• Hand:• carpal bones(wrist bones):8• metacarpals (palm bones):5• Phalanges (finger bones):14

Pelvic girdle: two coxa, sacrum fuse

• Coxa: known as hipbone

• Composed of three fused bones:

• Ileum ( gives shape to hip)

ischium ( helps in sitting)

pubis (joins in front)

• acetabulum, is formed by joining three pelvic girdle bones

• Attaches to head of the femur

Functions of pelvic girdle:

• attachment of lower limb• Provides base of

support for body weight• Protects abdominopelvic

organs• Protects developing fetus

(in female)

The lower limb is designed for

• A. stability,• B. weight-bearing

Lower limb is composed of • Femur (thighbone)

• Head: fits into acetabulum of the pelvic girdle

• condyles: articulate with

• A. Patella: knee cap• B. Tibia

Lower Limb

Leg: • Tibia (shin bone is longer) : articulates with

femur, oriented medially• Fibula (thin and short) articulates with tibia

Foot: • Tarsals (ankle): 7• Calcaneus is the largest tarsal or heal bone

Metatarsals (sole of the foot): 5Phalanges (toes): 14

Gender Differences of the Pelvis

male female

Heavy, thick and acetabulum closer

Light, thin with acetabulum being small and farther apart

Pelvic cavity has smaller diameter

Pelvic cavity has larger diameter

Sacrum is narrow Sacrum is wide and bent sharply

Male coccyx is less mobile

Female coccyx is relatively more movable

Arches of the Foot

• Bones of the foot are arranged to form three strong arches– Two longitudinal– One transverse

• Joints: where two or more bones come together or Articulations of bones

• Functions of joints

– Hold bones together

– Allow for mobility

• Classification of Bones– Structurally: cartilageous,

fibrous and synovial

– Functionally: synarthrosis, amphiarthrosis, diathrosis

Joints

Classification of joints

f ib ro u s jo in tssyn a rth ro ses

ca rtilag in o usa m p h ia rth ro ses

b a ll a n d socke t co n dylo id

g lid ing h inge

p ivo t jo in t sa dd le jo in t

syn o v ia ld ia th ro ses

jo in ts

• Fibrous joints

• Bones are joined by fibrous tissues

• Immovable joints • Located in the skull between

cranial and facial bones

• except mandible which forms a movable joint.

• The sutures are jagged rather than straight.

• e.g. Sagittal suture joins the two parietal bones.

• Coronal suture joins the frontal bone with the parietal bone.

Cartilageous joints• Immovable or slightly

moveable

• allows limited motion in response to compression , twisting or stress.

• e.g. between ribs and sternum is united by

hyaline cartilage,

• fibrous cartilage in intervertebral discs

Freely moveable

Allow considerable movement between bones

Most joints that unite bones of appendicular skeleton are synovial joints

Articulaing bones are covered by articular cartilage, provides smooth surface for articulation

Joint surfaces are enclosed by joint capsule, lined by synovial membrane which encloses joint cavity

Which contains synovial fluid

In some synovial joints, such as shoulder, knee, synovial membrane extends as a pocket or sac called Bursae, which provides cushion between structures

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

Types of Synovial Joints Based on Shape

Name e.g. function

Pivot joint Atlas/axis

Radius and ulna

rotation

Saddle Thumb

( between carpels and metacarpels)

Flexion/extension

Abduction/adduction, circumduction

Gliding metacarpels and metatarsals Flexion/extension

Abduction/adduction, circumduction

Ball and socket joint

coxa and femur

Scapula and humerus

Flexion/extension

Abduction/adduction, rotation, circumduction

Hinge joint ulna and humerus

Femur and tibia

Flexion/extension

Condyloid joint Metacarpals and phalanges Movement in different planes

Functional Classification of Joints

• Synarthroses – immovable joints

• Amphiarthroses – slightly moveable joints

• Diarthroses – freely moveable joints

Inflammatory Conditions Associated with Joints

• Bursitis – inflammation of a bursa usually caused by a friction

• Tendonitis – inflammation of tendon sheaths

Clinical Forms of Arthritis

• Arthritis – inflammatory or degenerative diseases of joints– Over 100 different types– The most widespread

crippling disease in the United States

– Osteoarthritis• Most common chronic

arthritis• Probably related to normal

aging processes

Clinical Forms of Arthritis– Rheumatoid arthritis

• An autoimmune disease – the immune system attacks the joints

• Symptoms begin with bilateral inflammation of certain joints

• Often leads to deformities

– Gouty Arthritis• Inflammation of joints is

caused by a deposition of urate crystals from the blood

• Can usually be controlled with diet

Diseases of bones

• Osteoporosis:• Bones become porous• Seen in women more

commonly• Strikes after menopause• Leading cause of bone

fractures in older women