TEST 2: Skeletal Muscle Flashcards
How many fiber types are within a single motor units?
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
Type I
ST: Slow Oxidative (SO)- Red
- 50% of fibers in average muscle
- Peak tension in 110 ms
Type II
FTa: Intermediate Fast Twitch a- Fast Oxidative Glycolytic (FOG)- Fast Fatigue Resistant
FTx: Fast Glycolytic (FG)- Fast Fatigueable
Characteristics of Fibers
- Myosine ATPase isozyme
- Sarcoplasmic Reticulum
- Power
- Alpha Motor Neuron Cell Body Size
- # of fibers per motor unit
- Aerobic vs. Anaerobic
Myosin ATPase isozyme
Staining.
Slow Twitch-Dark
Fast Twitch-Light
Sarcoplasmic Reticulum
More developed. More Calcium. Slow Twitch Poor
Power
- Fast Twitch fibers generate more force per x-secional area
- P = F x V
- FT power is 3-5x that of ST
Alpha Motor Neuron Cell Body Size
- Slow Twitch Fibers have a-motor neurons with small cell bodies
- Fast Twitch fibers have alpha motor neurons with large cell bodies
Aerobic vs. Anaerobic
Slow Twitch- good aerobically (oxidatively)
- more capillaries/ fiber, myoglobin, mitochondria, & triglycerides
- better endurance
Fast Twitch- better anareobically
-fatigue easily
Fiber Type Differentiation
- 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
Training and Fiber Type Shifts
- 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
Fiber Type Shifts in Elderly
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
Sarcopenia
loss of muscle mass and strength associated with agin
- 10% of loss 25-50 years
- 40% of loss 50-80 years
Low vs. High Force
Low Force- Motor Units with lowest numbers recruited first
High Force- Motor units with higher number are then added
___% recruitment with maximal voluntary effort
50-70
Principle of Orderly Recruitment
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
Size Principle and Force Requirements
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]
Agonists
muscles primarily responsible for a given movement (prime movers)
Antagonists
muscles that oppose agonists in a movement
Synergists
fixators. muscles that assist agonists in a movement
Isometric
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
Isotonic
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
Development of Muscle Force Depends on:
- Number of Motor Units
- Type of Motor Units
- Size of Muscle
- Rate Coding
- Muscle Length
- Joint Angle
Rate Coding
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
Twitch
response of a muscle fiber or a motor unit to a single electrical stimulus
Summation
series of two or more electrical stimuli in rapid sequence prior to complete relaxation from the first stimulus
Tetanus
highest tension developed by a muscle in response to stimulation of increasing frequency
Muscle Length
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
Joint Angle
- 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
Concentric F x V curves
- 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
Skeletal Muscle Tone
the “normal” amount of contraction that occurs within skeletal muscles to maintain normal body posture
