TEST 2: Skeletal Muscle

Question 1

How many fiber types are within a single motor units?

Answer 1

All fibers within a motor unit receive the same stimulation patterns, so all fibers within a single motor unit are of a SINGLE FIBER TYPE

Question 2

Type I

Answer 2

ST: Slow Oxidative (SO)- Red

• 50% of fibers in average muscle
• Peak tension in 110 ms

Question 3

Type II

Answer 3

FTa: Intermediate Fast Twitch a- Fast Oxidative Glycolytic (FOG)- Fast Fatigue Resistant

FTx: Fast Glycolytic (FG)- Fast Fatigueable

Question 4

Characteristics of Fibers

Answer 4

1. Myosine ATPase isozyme
2. Sarcoplasmic Reticulum
3. Power
4. Alpha Motor Neuron Cell Body Size
5. # of fibers per motor unit
6. Aerobic vs. Anaerobic

Question 5

Myosin ATPase isozyme

Answer 5

Staining.
Slow Twitch-Dark
Fast Twitch-Light

Question 6

Sarcoplasmic Reticulum

Answer 6

More developed. More Calcium. Slow Twitch Poor

Question 7

Power

Answer 7

• Fast Twitch fibers generate more force per x-secional area
• P = F x V
• FT power is 3-5x that of ST

Question 8

Alpha Motor Neuron Cell Body Size

Answer 8

• Slow Twitch Fibers have a-motor neurons with small cell bodies
• Fast Twitch fibers have alpha motor neurons with large cell bodies

Question 9

Aerobic vs. Anaerobic

Answer 9

Slow Twitch- good aerobically (oxidatively)

• more capillaries/ fiber, myoglobin, mitochondria, & triglycerides
• better endurance

Fast Twitch- better anareobically
-fatigue easily

Question 10

Fiber Type Differentiation

Answer 10

• Geners determine which alpha motor neurons innervate which fibers, but after innervation is established, differentiation occurs according to firing patterns of alpha motor neurons
• Differentiation of fiber types seems to mostly have occurred by birth and changes little from childhood to middle age

Question 11

Training and Fiber Type Shifts

Answer 11

• recent research shoes that over years training, small shifts in fiber types can occur
• few % change over many years of training
• both endurance and resistance training have been showsn to reduce the %FTx fibers while increasing the %FTa fibers

Question 12

Fiber Type Shifts in Elderly

Answer 12

In elderly, fiber type distributions change. With age, muscles tend to lose FT motor units, resulting in greater % ST.

• Sarcopenia
• Coincides with losses of speed, power, and strength

Question 13

Sarcopenia

Answer 13

loss of muscle mass and strength associated with agin

• 10% of loss 25-50 years
• 40% of loss 50-80 years

Question 14

Low vs. High Force

Answer 14

Low Force- Motor Units with lowest numbers recruited first

High Force- Motor units with higher number are then added

Question 15

___% recruitment with maximal voluntary effort

Answer 15

50-70

Question 16

Principle of Orderly Recruitment

Answer 16

Motor Units generally activated on basis of a fixed order recruitment

• When little force needed, those motor units with the lowest numbers are recruited first
• When a lot of force is need, those motor units with higher numbers are then added

Question 17

Size Principle and Force Requirements

Answer 17

Size Principle: motor units are recruited in order of the size of their a-motor neuron’s cell body
-M.U.s with smaller cell bodies easier to recruit
-Order determined by force requirements
[ST–> FTa–> FTx]

Question 18

Agonists

Answer 18

muscles primarily responsible for a given movement (prime movers)

Question 19

Antagonists

Answer 19

muscles that oppose agonists in a movement

Question 20

Synergists

Answer 20

fixators. muscles that assist agonists in a movement

Question 21

Isometric

Answer 21

Static
Force generated, but length of muscle is unchanged
-No change in joint angle
-High forces produced but only at one joint angle at a time
-Holding something steady

Question 22

Isotonic

Answer 22

Dynamic

CONCENTRIC: force developed while muscle is shortening
ECCENTRIC: force generated while muscle is lengthening
-Stretches sarcomere: high injury potential
-Movements against gravity or antagonistic muscles in deceleration
-Largest forces produced, but takes progressively less cross bridge cycling, which means it takes less energy for you to perform

Question 23

Development of Muscle Force Depends on:

Answer 23

• Number of Motor Units
• Type of Motor Units
• Size of Muscle
• Rate Coding
• Muscle Length
• Joint Angle

Question 24

Rate Coding

Answer 24

process by which the tension generated by a given motor unit can vary from twitch to tetanus by increasing the frequency of stimulation of that motor unit

• Twitch
• Summation
• Tetanus

Question 25

Twitch

Answer 25

response of a muscle fiber or a motor unit to a single electrical stimulus

Question 26

Summation

Answer 26

series of two or more electrical stimuli in rapid sequence prior to complete relaxation from the first stimulus

Question 27

Tetanus

Answer 27

highest tension developed by a muscle in response to stimulation of increasing frequency

Question 28

Muscle Length

Answer 28

Maximal force is created when muscle is ~20% > normal resting length

If muscle longer or shorter, force production decreases

When muscle is stretched, potential energy is stored in muscle

During subsequent muscle activity, stored energy is released, increased force created
-stretch-shortening cycle

~20% > normal resting length maximizes elasticity while maintaining sufficient actin-myosin overlap for force production

Question 29

Joint Angle

Answer 29

• Sticking Points
• Traditional weight lifting, such as with free weights or regular machine weights, has a disadvantage in that only the weakest points in the range of motion are ever maximally worked, or the strongest points of the ROM and never maximally worked
• Varaible Resistance

Question 30

Concentric F x V curves

Answer 30

• heavy strength training improves strength at low velocities
• low load, high velocity training improves strength at higher velocities
• both required to move entire strength curve

Question 31

Skeletal Muscle Tone

Answer 31

the “normal” amount of contraction that occurs within skeletal muscles to maintain normal body posture