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Flashcards in taleta Deck (19)
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1
Q

Describe the principle of antagonism.

A

two or more muscles acting in opposite directions

task: stop and control movements

2
Q

What is necessary to enable movement?

A

all muscles have to have a lever arm with respect to the joint they are acting on

3
Q

What is the force relation between agonist and antagonist?

A

example upper arm: Ft = 0.4*Fb

4
Q

Why are joint forces higher than the original mass?

A
  • lever arms

- principle of antagonism

5
Q

Difference between normal and shear stresses?

A

normal: perpendicular direction of the plane
shear: acting in x-dir. on y-plane

6
Q

Bone growth characteristic?

A

in direction of the normal stresses

-> prevention of shear stress

7
Q

What is a stress state?

A

consists of normal and shear stresses. it depends on the outer forces and the cutting plane (like rotation)

8
Q

How does the bone try to prevent shear/tensile stresses?

A

by growing according to the direction of the principle stresses

9
Q

Describe the principle stress state.

A

only normal stresses are acting, shear is zero.

stress state and direction is different in each point

10
Q

What do the material laws describe?

A

how materials deform und forces:

  • relation between force and displacement (stress+strain)
  • relation between kinetic and kinematic behavior
11
Q

Origin of plastic bone behavior?

A

results from breakdown (fracture) of microscopical structures. bone plasticity may heal, may lead to permanent deformations

12
Q

What behavoir do ligaments, cartilage, ligaments and natural materials have?

A

liga: hypoelastic
tendons: hypoelastic
carti: visco-elastic
natural: displacement-dependant

the quicker a tendon/ligament is pulled, the stiffer it gets.
-> velocity dependant material behavior

13
Q

Which material properties describe elastic behavior?

A
  • youngs modulus
  • poissons ratio
  • shear modulus
14
Q

What joint principles exist?

A
  • fibrous (synarthrodial)
  • cartilargiuous (amphiarthrodial)
  • synovial (diarthrodial)
15
Q

biomechanical tasks of joints?

A
  • damping (spongious bone & cartilage)
  • movement (incongruency, capsule, ligaments)
  • peak stress/force reduction (large proximal, thin cortical bone)
16
Q

Describe the features of joints.

A
  • incongruency (surfaces do not fit together)
  • > allows for other movements
  • larger proximal bone parts compared to distal
  • spongious in proximal part, no in distal
  • cartilage in the bearing surface
  • ligaments for the stabilization and movement restriction
  • capsule
17
Q

Name the types of joints.

A
  • ball and socket (3dof): hip, shoulder
  • egg (2dof): wrist
  • hinge (1dof): elbow
  • pivot (1dof): radio-ulnar
  • saddle (2dof): thumb
  • rotational (5dof): knee
18
Q

Describe the movement patterns.

A
  • swing: flex/exten, adduc/abduc
  • spin: rotation
  • diagonal: circumflexion
19
Q

Why are muscle movements mostly diagonal?

A
  • several muscles involved (agonist, antagonist)

- > increased velocity, force, stability, control