Skeletal Bio Mechanics Slide Show

Biomechanics I

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Axial vs. Appendicular  Axial

skeleton refers to the body of

the animal  Appendicular

refers to the limbs

Biomechanics I

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Biomechanics I

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Introduction Axial skeleton

Appendicular







Forms the long axis of the body 80 bones in three major regions  skull  vertebral column  bony thorax • •



Bones of upper & lower extremities and girdles 126 bones in three major regions

Ribs Sternum



• Shoulder girdle • Pelvic girdle

 

Biomechanics I

Girdles

upper extremity lower extremity 4

Classification of Bones

Biomechanics I

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Types of bones  short

bones: approximately cubical; include the carpals and tarsals

 flat

bones: protect organs & provide surfaces for muscle attachments; include the scapulae, sternum, ribs, patellae, some bones of the skull Biomechanics I

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Types of bones  irregular

bones: have different shapes to serve different functions; include vertebrae, sacrum, coccyx, maxilla

 long

bones: form the framework of the appendicular skeleton; include humerus, radius, ulna, femur, tibia, fibula Biomechanics I

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Joints 

Classify by function 

Synarthroses • Joints with little or no movement



Amphiarthroses • Slightly moveable joints



Diarthroses / Synovial joint • Freely moveable joints Biomechanics I

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Biomechanics I

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Joint Architecture  diarthroses

or synovial: (freely movable) characterized by:  articular cartilage - a protective layer of dense white connective tissue covering the articulating bone surfaces  articular capsule - a double-layered membrane that surrounds the joint Biomechanics I

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Joint Architecture  diarthroses

or synovial: (freely movable) characterized by:  synovial fluid - a clear, slightly yellow liquid that provides lubrication inside the articular capsule  associated bursae - small capsules filled with synovial fluid that cushion the structures they separate Biomechanics I

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Functions of articular cartilage  distributing

loads over joint surfaces



improving the fit of articulations



limiting slip between articulating bones



protecting the joint periphery

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lubricating the joint

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absorbing shock at the joint Biomechanics I

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Types of Synovial Joints Plane joints 

Articular surfaces are flat and allow short slipping or gliding movements

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Intercarpal and intertarsal joints Biomechanics I

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Types of Synovial Joints Hinge joints 



Movement resembles a door hinge Elbow joint – ulna and humerus; Interphalangeal joints Biomechanics I

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Types of Synovial Joints Pivot joints 





Rounded end of one bone protrudes into a ring formed by another bone or by ligaments of that bone. Proximal radioulnar joint Atlas-axial joint Biomechanics I

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Types of Synovial Joints Condyloid joints 

 

Oval articular surface of one bone fits into a complementary depression on another. Radiocarpal joints Metacarpophalang eal joints Biomechanics I

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Types of Synovial Joints Saddle joints 



Each articular surface has convex and concave areas Each articular surface is saddleshaped. Carpometacarpal joints of the thumbs Biomechanics I

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Types of Synovial Joints Ball-and-Socket joints 





Spherical or semispherical head of one bone articulates with the cuplike socket of another. Allow for much freedom of motion. Shoulder and hip joints Biomechanics I

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Joint Stability  ability

of a joint to resist abnormal displacement of the articulating bones

 factors 



increase joint stability

a closely reciprocating match of the articulating bone surfaces a strong array of ligaments and muscle tendons crossing the joint Biomechanics I

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Factors increase joint stability  articulating  



bone surfaces

wide contact area - high stability different among joints and individuals change in joint angle - change in contact area - change in stability Biomechanics I

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Factors increase joint stability  Connective 





tissues crossing the joint

weak and lax connective tissues low stability strengthening of tissues - increase in stability muscle activity and fatigue decrease in stability Biomechanics I

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Joint Flexibility a

description of the relative ranges of motion allowed at a joint in different directions

 range

of motion (ROM) - the angle through which a joint moves from anatomical position to the extreme limit of segment motion in a particular direction Biomechanics I

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Factors influence joint flexibility  Shapes

of articulating bone surfaces  Intervening muscle or fatty tissue  Laxity  Extensibility of collagenous tissue and muscles  Fluid contents in cartilagenous disc  Temperature of collageneous tissues  Stretching program Biomechanics I

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Types of muscle

Biomechanics I

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Skeletal muscle  Characteristics 

of skeletal muscle;

Extensibility - ability to be stretched or to increase in length • Viscoelasticity - having the ability to stretch or shorten over time Biomechanics I

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Skeletal muscle  Characteristics

of skeletal muscle;  Contractility - ability to contract (develop tension) 



Excitability (Irritability) - ability to respond to a stimulus Elasticity - ability to recoil to normal length following a stretch Biomechanics I

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Elastic components  Parallel

elastic component (PEC)  passive elastic property of muscle derived from muscle membranes (epimysium, perimysium, endomysium, sarcolemma)  Series elastic component (SEC)  passive elastic property of muscle derived from the tendons (primarily responsible for elasticity) Biomechanics I

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Elastic components  Contractile

component (CC)  actual part of muscle that contracts (actin and myosin)

Biomechanics I

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Motor unit  single

motor neuron and all fibers it

innervates  considered

the functional unit of the

neuromuscular system

Biomechanics I

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Biomechanics I

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Basic fiber arrangement  parallel

fiber arrangement: fibers are roughly parallel to the longitudinal axis of the muscle

 Convergence:

fan-shaped

 pennate

fiber arrangement: short fibers attach to one or more tendons within the muscle Biomechanics I

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Arrangements of Muscle Fibers

Biomechanics I

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Types of muscle contraction  isometric

contraction: muscle length does not change

 concentric

decreases

 eccentric

increases

contraction: muscle length

contraction: muscle length

Biomechanics I

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Skeletal Muscle Function  agonist:

acts to cause a movement

 antagonist:

movement

acts to slow or stop a

 stabilizer:

acts to stabilize a body part against some other force

 neutralizer:

acts to eliminate an unwanted action produced by an agonist Biomechanics I

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Muscle’s length-tension relationship  Tension

present in a stretched muscle is

the sum of the active tension provided by the muscle fibers and the passive tension provided by the tendons and membranes

Biomechanics I

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Tension

Total Tension Active Tension

Passive Tension

50 100 150 Length (% of resting length)

Biomechanics I

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Muscle’s force-velocity relationship

Biomechanics I

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