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Full summary of case 10 BBS1004 how do we move? show me your force
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Full summary with all the important concepts and mechanisms related to electromyography.
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Case 10: How do we move? Show your force1. How to determine angular acceleration patterns from joint patterns?
- Angular displacement:
θ denotes the change in angular position of the point in the time
interval between t1 and t2, θ = θ2 θ1 is called the angular
displacement of the point in the same time interval.
- Angular velocity
The time rate of change of angular position is called angular velocity,
and it is commonly denoted by ω. If the angular
position of an object is known as a function of time, its angular velocity
can be determined by taking the derivative of the angular position with respect to time:
ω =dθ/ dt
- Angular acceleration:
The angular velocity of an object varies during motion. The time rate of change of
angular velocity is called angular acceleration, denoted by α
α = dω/ dt
- In 2D, the motion is either in the clockwise or in the counterclockwise direction. Angular
displacement and velocity are positive in the direction of motion.
- Angular acceleration is positive when angular velocity is increasing, and is negative when
angular velocity is decreasing.
- Tangential acceleration:
Tangential acceleration measures how the tangential velocity
of a point at a certain radius varies with time.
- Radial acceleration:
The acceleration experienced by the body towards the center of the circle
is called the radial acceleration or centripetal acceleration.
1
, 2. What is the origin of a surface EMG-signal?
Excitation contraction:
1. A nerve action potential arriving at the neuromuscular junction releases acetylcholine and
triggers a muscle action potential.
2. The action potential spreads over the sarcolemma.
3. The action potential is carried deep into the muscle fiber along the transverse tubules.
4. The sarcoplasmic reticulum releases Ca+ which diffuses into the myofibrils.
5. The binding of Ca+ to troponin results in a conformational change in troponin and causes a
shift in the position of tropomyosin.
6. As a result , the actin binding sites are exposed and cross-bridges are formed between actin
and myosin filaments.
7. Due to the formation of the cross bridges a pull force between actin and myosin filaments is
generated.
8. The pull force causes the actin and myosin to slide past each other which causes the muscle
to contract.
9. The actin-myosin bond is broken with the splitting of ATP. The myosin head is free. For a new
attachment to actin.
10. The calcium concentration remains increased as long as the action potentials are triggered
on the muscle fiber. Cross bridges thereby formed continuously. The muscle remains
contracted.
11. If the sarcolemma is no longer excited, the Ca+ level decreases through active calcium uptake
by the sarcoplasmic reticulum. The calcium bound to troponin is removed and the
tropomyosin returns to its original position. Further cross-bridges are prevented and the
muscle relaxes.
2
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