Physiology - Types of Skeletal Muscle Fibers and Whole Muscle Contraction

Muscle fibers are classified based on what 2 factors?

Maximal velocity of shortening (fast or slow), Major pathway of ATP production (oxidative or glycolytic)

Type I fibers are also known as what?

Slow fibers

Type II fibers are also known as what?

Fast fibers

These fibers have a high ATPase activity in the muscle and myosin is able to split ATP rapidly.

Fast fibers

These fibers have maximal rate of cross-bridge cycling, and thus maximal shortening velocities.

Fast fibers

These fibers have low ATPase activity

Slow fibers

These fibers have cross-bridge cycling that is 4X slower

Slow fibers

Which type of fiber has a higher force? Slow or fast?

They have the same force

These fibers have high concentration of mitochondria

Oxidative fibers

These fibers are dependent on oxygen supply

Oxidative fibers

These fibers are surrounded by many small vessels and contain large amounts of myoglobulin (oxygen binding protein).

Oxidative fibers

These fibers a dark red color.

Oxidative fibers

These fibers have few mitochondria but possess high levels of glycolytic enzymes and glycogen.

Glycolytic fibers

These fibers have relatively few blood vessels and low myoglobulin.

Glycolytic fibers

These fibers are white in color.

Glycolytic fibers

These fibers are generally larger in diameter.

Glycolytic fibers

Which has greater force? Oxidative or glycolytic fibers?

Glycolytic fibers

What are the 3 main types of skeletal muscle fibers?

Slow oxidative, Fast oxidative-glycolytic, fast glycolytic

These fibers have low myosin-ATPase activity and high oxidative capacity

Slow oxidative fibers

These fibers are very resistant to fatigue.

Slow oxidative fibers

Postural muscles are an example of what type of fibers?

Slow oxidative fibers

Type IIa fibers are also known as what?

Fast oxidative-glycolytic fibers

Type IIb fibers are also known as what?

Fast glycolytic fibers

These fibers have high myosin-ATPase activity with high oxidative and moderate glycolytic capacity.

Fast oxidative-glycolytic fibers

These fibers are moderately resistant to fatigue

Fast oxidative-glycolytic fibers

These fibers are located in the muscles used for swimming, short distance running, etc.

Fast oxidative-glycolytic fibers

These fibers have high myosin-ATPase activity and high glycolytic capacity.

Fast glycolytic fibers

These fibers fatigue quickly

Fast glycolytic fibers

These fibers are located in muscles that are good for sprinting

Fast glycolytic fibers

This system produces ATP the fastest, shortest endurance duration (8-10 sec)

Phosphagen system

This system has a moderate speed of ATP production, short endurance duration (1-1.6 minutes)

Glycogen-lactic acid system

This system is the slowest in terms of ATP production (requires end-products of 1st 2 systems), but has the greatest endurance value (unlimited*)

Aerobic system

Each motor unit contains how many types of fibers?

One

Each muscle contains how many types of fibers?

Multiple

What is the term for the mechanical response of a muscle fiber to a single action potential.

Twitch

What occurs during the latent period of twitch contractions?

excitation-contraction coupling

Muscle shortening begins when the muscle tension just _______________ the load on the fiber.

Exceeds

What is the term for the force exerted on an object by a contracting muscle

Muscle tension

What is the term for the force exerted on the muscle by an object

Load

Tension increases ____________.

Rapidly

Tension dissipates _____________.

Slowly

What is the term for the muscle develops tension but does not shorten or lengthen.

Isometric contraction

What is the term for the muscle changes length, yet load remains constant (constant tension).

Isotonic contraction

What is the term for the shortening of the muscle fibers due to tension > load?

Concentric

What is the term for the lengthening of muscle fibers due to load > tension?

Eccentric

Muscle tension control depends on what 2 factors?

Amount of tension, number of fibers

What is the term for the partial dissipation of elastic tension between subsequent stimuli

Unfused Tetanus

What is the term for no time for dissipation of elastic tension between rapidly recurring stimuli.

Fused tetanus

Action Potential frequency (AKA frequency-tension relation) has what 3 parts

Temproal summation, unfused tetanus, fused tetanus

In regards to muscle tension, there are 4 components. Name them

Action potential frequency, fiber length, fiber diameter, fatigue

What is the term for lots of actin-myosin overlap and plenty of room to slide?

Optimal length sarcomere

What is the term for actin filaments lack room to slide, so little tension can be developed?

Short sarcomere

What is the term for actin and myosin do not overlap much, so little tension can be developed?

Long sarcomere

Shortening velocity depends on what?

The load on the muscle, the types of motor units in the muscle, number of motor units recruited to work against the load

What is the term for the neural process of increasing the number of motor units active in a muscle at any given time?

Motor Unit Recruitment

Which diameter neurons are recruited first in motor unit recruitment?

Small

Small diameter neurons recruited first in motor unit recruitment innervate what type of muscle fibers

Type I fibers

Large diameter neurons innervate what type of muscle fibers?

Type IIa and IIb

Moderate strength exercises involve type I and IIa fibers that are ____________________________.

Resistant to fatigue

When a skeletal muscle fiber is continuously stimulated, the tension the fiber develops eventually decreases even though the stimulus continues. This is called what?

Muscle fatigue

Development of muscle fatigue and recovery from fatigue depends on 3 factors. What are they?

Type of skeletal muscle fiber, intensity and duration of stimulus, individual's fitness level

What is the term for fatigue that occurs rapidly when continuously stimulating, but also recover rapidly after a brief rest. Examples are high-intensity, short duration exercises like weight lifting?

High frequency fatigue

What is the term for fatigue that develops more slowly with low intensity, long duration exercise involving cyclical periods of contraction and relaxation. Requires much longer periods of rest. Example long distance running?

Low frequency fatigue

Does fatigue correlate with depleted ATP levels?

No

3 causes of fatigue

High-frequency exercise, low-frequency exercise, central command fatigue

What is the term for potassium builds up in the T-tubules during the repolarization of action potentials and cause persistent depolarization which eventually causes a failure to produce an action potential?

Conduction failure

What is the term for lactic acid changes the pH of the muscle, which can alter the conformation of proteins- including actin and myosin, and Ca pumps?

Lactic Acid buildup

What is the term for failure of cerebral cortex to send signals to motor neurons?

Central command fatigue