Unit 2: Muscle Fibers

Twitch time

Type 1:

- slow twitch

- long time to develop force and to relax

Type IIa & IIb:

- fast twitch

- rapidly develop force and relax

Power Development

Type I:

- limited in their ability to produce force rapidly

Type IIa & IIb:

- produce force very rapidly

Fatigue-resistance

Type I:

- generally efficient and resistant to fatigue

- have a high capacity for aerobic energy supply

Type IIa & IIb:

- insufficient and highly fatiguing

- low aerobic capacity

Oxidative (Type I)

- Reliance on oxidative phosphorylation

- Yields more ATP

- Fatigues slower than glycolysis

Glycolytic (Type II)

- Glycolysis for ATP

- Glycolytic fibers are said to be fatigable

Type I- red muscle

- Slow and less powerful contractions

- Smallest muscle cell

- Large amounts of myoglobin

Type IIa- red muscle

- Least numerous

- Intermediate size

Type IIb- white muscle

- Most prevalent

- Fast and most powerful contractions

- Largest in diameter

- Significantly less myoglobin

Wave summation

temporal summation of twitches

Incomplete tetanus

quivering contraction resulting from summed contractions but where the simulation occurs far enough apart that incomplete rest occurs

Tetanus

smooth, sustained contraction at maximal strength resulting from rapid successive action potential

What is motor unit recruitment?

The process of activating more motor units to increase the force of muscle contraction.

What is a threshold stimulus?

The stimulus where the first observable contraction occurs.

What is a maximal stimulus?

The strongest stimulus that recruits all motor units.

What is multiple-fiber summation?

The addition of motor neuron pools to increase muscle tension.

What does motor unit recruitment ensure?

Constant force over time during muscle contractions.

How are fibers in a motor unit arranged within a muscle?

They are dispersed throughout the muscle, not clustered.

What happens when a motor unit is stimulated?

It results in an evenly distributed contraction, known as a twitch.

What is muscle fatigue?

The inability to maintain muscle tension.

How is muscle fatigue countered?

By asynchronous recruitment of motor units.

Which type of muscles are recruited first during contraction?

Fatigue-resistant muscles are recruited first, followed by quickly fatiguing muscles.

Two primary types of contraction

isotonic and isometric

What does isotonic mean in terms of muscle tension?

Muscle tension (force generated) remains constant as muscle length changes.

What is concentric contraction?

Muscle is shortening with tension.

What is eccentric contraction?

Muscle is lengthening with tension.

Isometric

muscle doesnt change length, so tension develops at constant muscle length

What is hypertrophy?

Enlargement of muscle fiber cross-sectional area following training.

What proteins are synthesized during hypertrophy?

Contractile proteins actin and myosin, as well as other structural proteins.

What happens to the number of myofibrils during hypertrophy?

There is an increase in the number of myofibrils in the muscle fiber.

What is a benefit of hypertrophy?

It is beneficial for power and force production.

Which type of muscle fibers have greater potential for hypertrophy?

Type II fibers.

What is a consequence of hypertrophy on force generation?

It leads to increased force generation.

How does hypertrophy generally affect aerobic performance?

It is generally detrimental to aerobic performance.

What is a vascular consequence of hypertrophy?

There are fewer capillaries.

How does hypertrophy affect muscle fatigue?

Muscle fatigues more easily.

What determines the proportions of muscle fiber types?

Genetics

Can training lead to changes within muscle fiber subtypes?

Yes

What can high intensity resistance training and aerobic endurance training cause type IIb fibers to become?

More oxidative type IIa fibers

Are type I to type II transitions probable?

Less probable

Can you change your muscle type?

No, you can only improve the fitness of the muscles you have

What are the adaptations due to resistance and sprint training related to cytoplasmic density?

Leads to increased cytoplasmic density.

How does resistance and sprint training affect muscle hypertrophy?

Accommodates muscle hypertrophy and enhances muscle function.

What is one effect of resistance and sprint training on strength expression?

Enables greater expression of strength.

What adaptation occurs in calcium release due to resistance and sprint training?

Enhanced calcium release.

How does resistance and sprint training assist in speed and power production?

Assists in increasing speed and power production.

What happens to blood and muscle pH during exercise due to resistance and sprint training?

Decrease blood and muscle pH during exercise.

How does resistance and sprint training affect the accumulation of H+ in working muscle?

Better tolerate the accumulation of H+ in the working muscle.

What is one benefit of resistance and sprint training on muscular endurance?

Delay fatigue and produce greater muscular endurance.

What is one adaptation due to aerobic endurance training?

Increased aerobic capacity of the skeletal muscle

How does aerobic endurance training affect performance at the same absolute intensity?

Allows performance with less effort

What is one effect of aerobic endurance training on maximal aerobic power?

Increases maximal aerobic power

What is an example of improvement from aerobic endurance training?

Run the same distance faster with the same perceived effort

What happens to type I muscle fibers due to aerobic endurance training?

Increase in size

How does the increase in size of type I muscle fibers compare to type II fibers?

Not as great as seen in type II fibers

What structural changes occur in capillaries and mitochondria due to aerobic endurance training?

Increases in the size and number of capillaries and mitochondria

How does aerobic endurance training enhance a cell's ability regarding oxygen?

Enhances the ability of the cell to receive oxygen

What improvement occurs in a muscle's ability to utilize oxygen due to aerobic endurance training?

Improves the muscle's ability to utilize oxygen to produce ATP via oxidation and resist fatigue

What do sedentary leisure activities lead to?

Skeletal muscle mass and tone loss

What happens to skeletal muscle that is not regularly stimulated?

It atrophies

What are the effects of inactivity on muscle size, tone, and power?

There is a reduction in muscle size, tone, and power

Are the effects of inactivity initially reversible?

Yes, they are initially reversible

Can dying muscle fibers be replaced?

No, dying muscle fibers cannot be replaced

What is the origin of a muscle?

The muscle's proximal attachment, usually the more stationary attachment.

How are muscles typically attached at their origin?

Muscles are usually attached via 'fleshy' attachments.

What is the role of the epimysium at the origin?

The epimysium is attached to the periosteum, distributing force.

What is the insertion of a muscle?

The muscle's distal attachment, usually the more mobile attachment.

How are muscles typically attached at their insertion?

Muscles are usually attached via 'fibrous' attachments, such as tendons.

What is the function of tendons at the insertion?

Tendons focus force as they insert into the bone.

What is an agonist in muscle movement?

A muscle or muscle group directly involved in creating a movement.

What is an antagonist in muscle movement?

The opposing muscle or muscle group to the agonist.

What role does the antagonist muscle play during movement?

It stabilizes a joint during movement and slows down the limb at the end of fast movement.

What is reciprocal inhibition?

CNS signals contraction in the agonist and relaxation in the antagonist.

What is the role of synergist muscles?

They stabilize the body during movement but are not directly responsible for bringing about a movement.

What are pennate muscles?

Muscle fibers attach obliquely to tendon.

What does a high angle of pennation indicate?

There is very little muscle force being transmitted to the tendon.

Why do pennate muscles produce greater force?

Due to greater density of crossbridges/volume of muscle.

What are non-pennate muscles?

Muscle fibers are parallel to the line between the origin and insertion.

Why do non-pennate muscles produce higher velocities?

Due to a greater number of sarcomeres in a row.

How many skeletal muscles does the human body have?

More than 500

What do muscle names often provide clues about?

Their location, position, structure, size, shape, origin and insertion, or action

What is an example of a muscle name that indicates orientation of muscle fibers?

Rectus

What are examples of muscle names that indicate size?

Brevis, longus, major, minor, vastus

What is an example of a muscle name that indicates shape?

Deltoid

What are examples of muscle names that indicate action?

Abductor, adductor, depressor, extensor, flexor, levator, opponens

What shape does the deltoid muscle resemble?

Triangle

What does the term 'brevis' indicate about a muscle?

It is short

What does the term 'longus' indicate about a muscle?

It is long

What is the shape and nucleus count of smooth muscle cells?

Spindle-shaped and uninucleate

How do smooth muscle cells differ from skeletal muscle in terms of sarcomeres?

Smooth muscle cells have no sarcomeres

What are dense bodies in smooth muscle cells?

Structures that contain the same protein as Z lines, held in place by intermediate filaments

Why do smooth muscle cells create more cross-bridges than skeletal muscles?

Due to the greater ratio of myosin to actin

What shape do myosin and actin filaments create in smooth muscle?

A diamond-shaped lattice

How do the number of thick and thin filaments in smooth muscle compare to skeletal muscle?

Smooth muscle has fewer thick and thin filaments

How do thick myosin filaments in smooth muscle differ from those in skeletal muscle?

Thick myosin filaments in smooth muscle are longer than in skeletal muscle

What is a key difference in thin actin filaments between smooth muscle and skeletal muscle?

Thin actin filaments in smooth muscle lack troponin

What role do intermediate filaments play in smooth muscle cells?

They are part of the cytoskeleton and are non-contractile

How are smooth muscle cells connected to each other?

By mechanical junctions and sometimes electrically coupled gap junctions.

What is the function of the sarcoplasmic reticulum in smooth muscle?

It sequesters Ca2+.

What is the relationship between smooth muscle cells and the cell membrane?

Smooth muscle cells have close proximity to the cell membrane, specifically invaginations called calveolae.

Do smooth muscle cells have T-tubules?

No, smooth muscle cells do not have T-tubules.