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.

SKELETON SYSTEM(CONTD.) 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.

AXIAL SKELETON It mainly serves a protective function. It is composed of 80 bones:

S. Name of the bone(s) Number no 1. Skull 22 (8- cranium+ 14- facial) 2. Ear 6 (2x Malleus, Anvil, Stapes) 3. Hyoid bone 1 4. Vertebrae 26 (7-cervix,12-thorax, 5-lumber, 1(or 5)- sacrum(n.m) , 1(or 5)- coccyx(n.m) 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 Name of the major regions Number o 1. Shoulder girdle 4 (2x clavicle , Scapula) 2. Upper extremities 64 (2x Humerus, ulna, radius 2x 8 carpal,5 metacarpal,14 phalanges,2 sesamoid bone) 3. Pelvic girdle 2 4. Lower extremities 64 (2x femur, tibia, patella, fibula, 2x 7 tarsals, 5 meta tarsal, 14 phalanges, 2 sesamoid bone) 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 Functional Classification 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?