Bones
Definition
Composed of bones, muscles, and connective tissues which include the following: 
Ligaments
dense fibrous tissues that connect the articular extremities of bones and help stabilize the articulations of bones at joints
Tendons
dense fibrous connective tissues that connect muscles to bones and transmit forces exerted by muscles to the attached bones
Fascia
covers and sepearates body structures
Cartilage
Translucent elastic tissue that can be found on some articular bony structures and in some organs such as the nose and the ear
Bones
the rigid skeletal structure that plays a major supportive and structural roles
  • 206 bones in the human body
Main functions
  • Support and protect main body parts
  • Maintain posture
  • Produce body movement 
  • Generate heat
  • Maintain body temperature
Joints
Types of joints
Synovial
no tissue exists between highly lubricated joint surfaces
Fibrous
those connecting the bones of the skull through fibrous tissues
Cartilaginous
those bridging vertebral bones and inter-vertebral discs
No-Mobility
do not support movement
Hinge
permits motion in only one place (ex elbow)
Pivot
allows two degrees freedom (ex wrist)
Ball and Socket
Allows three degrees of freedom
Bone Fracture
Caused by three important load factors:
1. Amount
2. Repetition
3. Frequency of loading
Muscles
Musculo-Skeletal System
Muscles
  • 400 muscles in the human body
  • composed of bundles of muscle fibers, connective tissue, and nerves
  • Muscles with larger cross sections can exert larger forces
Myofibrils
Long cylindrical cells consisting largely of contractile elements
Motor Unit
Basic functional unit of the muscle; group of muscle fibers regulated by the branches of the same motor nerve
Muscle Structure
Description
Muscle Strength
Amount and direction of force or torque
  • Static Strength - Maximal voluntary isometric muscle exertion level measured when a group of static exertions is performed
  • Dynamic Muscle Strength - measured when moving
  • Biomechanical Models - mathematical models of mechanical properties of the human body
Muscle Contractions
Description
Concentric (isotonic) Contraction
muscle shortens while contracting and producing a constant internal muscle force (arm flexor muscles when object is lifted 
Isometric Contraction
muscle length remains unchanged during contraction
Eccentric Contraction
when person picks up heavy object and is unable to hold it in desired position because muscles lengthen while contracting
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