Topic 5 Exam 2 Flashcards
Draw and describe the force-length curve for passive changes in muscle length.
DRAW EXAM
- Force Zero at resting length
- Lengthens and force increases
- Stretched beyond range
Draw and describe the force-length curve for active changes in muscle length.
DRAW EXAM
Where is the max force generated? TEST
Force Decreases, but length continues to increase
Draw and describe the force-velocity curve.
DRAW EXAM
Resisting the breaking of cross bridges which increases Force and Velocity in the eccentric action (lengthening)
What is a motor unit?
What determines the size of the motor unit?
- a motoneuron and the muscle
fibers it innervates
Number of muscle fibers it innervates determines the size of the motor unit
- Alpha-motoneurons in the spinal cord send
their axons through the ventral roots.
- axons branch in a target muscle
- each axon innervates several muscle fibers
What are the three general types of motor units? (FF, FFR, S)
- Fast twitch, fatigable (Large diameter) - Produce a lot of force then die out
- Fast twitch, fatigue resistant (Medium diameter)
- Slow twitch, fatigue resistant (Small diameter)
Why does fiber diameter matter? What does it tell us?
Faster - Check
How might fiber diameter differ among Motor Unit types and indicate functional role?
M1 - produce a lot of force then turn off (Doesn’t stay active long)
Functional Role: Fast Forceful
M2 - Medium force, but is active for a longer period of time.
Functional Role: Quick Burst of force that can last longer
M3- Lowest amount of force, but stays active the longest.
Functional Role: Postural muscles
Twitch Contractions
Happens once
Tetanic Contraction
Continuous Firing
Describe the ‘size principle’ – what is it and how does it work? [include Ohm’s law]
- How motor units are being recruited
- Motor units are recruited in a precise order
according to their force output in order to
meet task demands - Small motor units recruit first at low muscle forces
- Increase in muscle force leads to
recruitment of larger motor units
Size Principle for Inward Current
IMPORTANT (Small motor units Will drive to threshold faster than large motor units because it has less resistance) (Alpha motor neurons fire)
Same inward current (I) from interneuron
- Smaller MN
- Smaller surface area
- Higher Resistance
- Results in large EPSP that reaches threshold and generates an action potential
Ohms Law
E (Resting Membrane Potential) = I (Inward Potential) R
Higher R for same I = greater change in resting
membrane potential (E)
Smaller one will have a bigger change in E
What are the two mechanisms of force change?
To increase muscle force the CNS
- recruits new motor units
and/or
- increases the frequency of firing of already
recruited/active motor units
Describe motor unit (MU) rotation –
What is it?
What does it do?
What is the result of it?
Why is it important for posture and balance CHECK QUESTION
Inverse relationship of active motor units and mean of firing
Allows constant muscle force. A change in the number of recruited motor units correlates
(negatively) with their mean frequency of firing
The result of motor unit rotation = constant force level
Muscle force needs to stay constant so posture stays steady and upright
Why is it important for posture and balance CHECK QUESTION
Allows smooth movements
What is motor unit synchronization?
- Two firing at the same time then you will Maximize force being produced
-Maintained over a period of time
Occurs at
- High levels of force
- During fatigue
- Due to neurological disorder
