Topic 5 Exam 2

Question 1

Draw and describe the force-length curve for passive changes in muscle length.

DRAW EXAM

Answer 1

• Force Zero at resting length
• Lengthens and force increases
• Stretched beyond range

Question 2

Draw and describe the force-length curve for active changes in muscle length.

DRAW EXAM

Where is the max force generated? TEST

Answer 2

Force Decreases, but length continues to increase

Question 3

Draw and describe the force-velocity curve.

DRAW EXAM

Answer 3

Resisting the breaking of cross bridges which increases Force and Velocity in the eccentric action (lengthening)

Question 4

What is a motor unit?

What determines the size of the motor unit?

Answer 4

• 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

Question 5

What are the three general types of motor units? (FF, FFR, S)

Answer 5

1. Fast twitch, fatigable (Large diameter) - Produce a lot of force then die out
2. Fast twitch, fatigue resistant (Medium diameter)
3. Slow twitch, fatigue resistant (Small diameter)

Question 6

Why does fiber diameter matter? What does it tell us?

Answer 6

Faster - Check

Question 7

How might fiber diameter differ among Motor Unit types and indicate functional role?

Answer 7

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

Question 8

Twitch Contractions

Answer 8

Happens once

Question 9

Tetanic Contraction

Answer 9

Continuous Firing

Question 10

Describe the ‘size principle’ – what is it and how does it work? [include Ohm’s law]

Answer 10

• 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

Question 11

Size Principle for Inward Current

Answer 11

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

Question 12

Ohms Law

Answer 12

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

Question 13

What are the two mechanisms of force change?

Answer 13

To increase muscle force the CNS

1. recruits new motor units

and/or

2. increases the frequency of firing of already
   recruited/active motor units

Question 14

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

Answer 14

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

Question 15

What is motor unit synchronization?

Answer 15

• 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

Question 16

What is a synergy?

Answer 16

Pattern of movement/muscle contractions

A neural signal sent out to a muscle, joint, effectors that we can observe and measure?

Electrical activity that we can read from the muscle - understand how movements are created

a neural organization of signals sent to elements (muscles, joints, effectors, etc.) of a multi-element system that assures stable performance of a task

Question 17

Describe in detail how a movement could be performed using a motor synergy.

Answer 17

Example:

Arm swings then a pattern of movement (this and that is contracted) and then the ball is released to perform the movement

Walking - groups of muscle that contract in a specific pattern