UNIT-1: SKELETAL SYSTEM

AND PROPERTIES

CONTENTS OF THE

LESSON

1. Skeletal System

2. Articulations

3. Biomechanical Properties

SKELETAL SYSTEM

“A framework” that includes;

• bones,

• Joints, and

• Connective tissues.

SKELETAL SYSTEM : BONES

Has 206 bones.

The human skeleton has two major divisions:

• the axial skeleton

• the appendicular skeleton.

The axial skeleton includes the bones of the center or axis of the body.

The appendicular skeleton consists of the bones of the upper and lower extremities.

SKELETON SYSTEM(CONTD.)

AXIAL SKELETON

It mainly serves a protective function.

It is composed of 80 bones:

S.

no

Name of the bone(s) Number

1. Skull

(8- cranium+ 14- facial)

22

2. Ear

(2x Malleus, Anvil, Stapes)

6

3. Hyoid bone 1

4. Vertebrae

(7-cervix,12-thorax, 5-lumber, 1(or 5)-

sacrum(n.m) , 1(or 5)- coccyx(n.m)

26

5. Ribs 24

6. Sternum 1

AXIAL SKELETON

APPENDICULAR

SKELETON

It serves in the function of movement .

It is composed of 126 bones:

S.n

o

Name of the major regions Number

1. Shoulder girdle

(2x clavicle , Scapula)

4

2. Upper extremities

(2x Humerus, ulna, radius

2x 8 carpal,5 metacarpal,14 phalanges,2

sesamoid bone)

64

3. Pelvic girdle 2

4. Lower extremities

(2x femur, tibia, patella, fibula,

2x 7 tarsals, 5 meta tarsal, 14 phalanges,

2 sesamoid bone)

64

APPENDICULAR

SKELETON

TYPES OF BONES

Based on the geometry there are five types of bones:

Long bones

Short bones

Flat bones

Irregular bones

Sesamoid bones

Irregular bones

FUNCTIONS OF BONES

IN SKELETAL SYSTEM

• Structural support of the body

• Provide levers for body movements

• Protection of underlying structures

• Blood cell formation(hematopoiesis)

• Storage reservoir for calcium and phosphorus.

• Provide site for muscular attachment.

BONE AS A LEVER

In anatomical levers:

Bone = bars or lever

Muscle insertion= effort

joints= axis

Segments or

COM of the = Resistence

segments

BIOMECHANICAL

PROPERTY OF BONE:

WOLFF’S LAW

“Calcium is laid down in response to stress.”

• The more the physical stress placed on the bone, the more

bony matrix and calcium is deposited. (provided proper

nutrition)

• “Use it or Lose it”

• Based on Piezoelectric effect:

“ pressure placed on a tissue generates electric charge

in it”

Osteoclasts cannot use these tissues.

SKELETAL SYSTEM:JOINTS

“Articulations”

• connection between two or more bones that links the

bones in the skeletal system into a functional whole.

Classification of joints

Structural Classification

Functional Classification

STRUCTURAL

CLASSIFICATION

Based on type of connective tissue joining the bones.

STRUCTURAL CLASSIFICATION-

FIBROUS JOINTS

Also known as “ Synarthrodial joints.”

Bones are connected by dense fibrous connective tissues.

It’s examples;

Sutures(found in skull)

Synostosis

Syndesmosis

Gomphosis

STRUCTURAL

CLASSIFICATION-

CARTILAGINOUS JOINTS

Also known as “Amphiarthrodial joints”

Bones are connected via either hyaline cartilage or fibrocartilage.

It’s examples:

Synchondrosis

Symphysis

STRUCTURAL

CLASSIFICATION-

SYNOVIAL JOINTS

Also known as diarthrosis.

Joins bones via a fibrous joint capsule.

This capsule envelopes the bones and has a outer fibrous layer and an

inner synovial membrane.

This capsule is filled with synovial fluid secreted from synovial

membrane.

TYPES OF SYNOVIAL

JOINTS

FUNCTIONAL

CLASSIFICATION

These classify joints on the basis of movement permitted by them.

It’s types are:

• Immovable Joints

• Semi movable Joints

• Mobile Joints

FUNCTIONAL CLASSIFICATION-

IMMOVABLE AND SEMI MOVABLE

Immovable Joints

• Allows almost no movement b/w bones.

• All synarthrodials joints except syndesmosis.

Semi mobile joints

• All the amphiarthrodial joints + syndesmosis.

Ex. Synchondrosis, symphysis, syndesmosis.

FUNCTIONAL

CLASSIFICATION-

MOBILE JOINTS

FUNCTIONAL

CLASSIFICATION-

MOBILE JOINTS

BIOMECHANICAL PROPERTIES OF

JOINTS AND CONNECTIVE TISSUES.

• Stretch

• Weight Bearing

• Stiffness and Mechanical strength

• Viscoelasticity

• Creep and Stress Relaxation

STIFFNESS

“How elastic a tissue is”

• The ratio of stress to strain in the elastic region of the

curve.

• approximated by the ratio of load to deformation. (no

change in dimension)

STIFFNESS

Load-deformation curve for a human’s tendon

MECHANICAL

STRENGTH

“how much force a material absorb before failure”

VISCOELASTICITY

“the strain response of material to a stress depends on the

rate of loading”

“faster rate of loading leads to higher stiffness than slower

rate.”

CREEP AND STRESS

RELAXATION

Creep:

• “gradual elongation of material over time when placed

under constant tensile stress”

Stress Relaxation:

• “decline in stress overtime when the material is

elongated/deformed to a set length.”

• Useful for flexibility of muscles but NOT for ligaments.

REFERENCES

McCaw,Steve.(2014)Biomechanics for Dummies. Hoboken,

New Jersey:John Wiley & Sons, Inc.

Knudson,Duane.(2007)Fundamentals of Biomechanics.New

York,USA:Springer Science.

https://www.teachpe.com/anatomy/skeleton_axial.php

https://www.verywellhealth.com/wolffs-law-in-physical-

therapy-2696151

DOUBTS?