Muscle System

Question 1

Muscle’s have different shapes. A muscle’s shape will affect its ability to produce force.

Match the 7 muscle shapes to its corresponding muscle.

Fusiform

Parallel

Convergent

Unipennate

Bipennate

Multipennate

Circular

Answer 1

Fusiform - biceps brachii

Parallel - rectus abdominis

Convergent - pectoralis major

Unipennate - palmar interosseous

Bipennate - rectus femoris

Multipennate - deltoid

Circular - orbicularis occuli

Question 2

Match the correct answer.

1. Type 1 Muscle fibers
2. Type 2A Muscle fibers
3. Type 2b muscle fibers

Answer 2

a) Low fatigability, fast mechanical speed, moderate twitch tension, medium motor unit size, MU type fast fatigue resistant, fast oxidative glycolytic
b) Fast glycolytic fiber type, fast fatigable MU type, large MU size, high twitch tension, fast mechanical speed, high fatigabiilty
c) low fatigability, slow mechanical speed, low twitch tension, small MU size, slow MU type, Slow oxidative fiber type.

Question 3

Define muscle force, using the force-velocity graph

Which type of muscle contraction generates the most force?

Answer 3

Muscle force: is the ability of the muscle to generate movement (push or pull)

Concentric contraction: as the velocity increases the force decreases. If muscle force is greater than the load, the muscle will contract in a shorten position. To generate more tension, you should slow down the speed of contraction.

Eccentric contraction: As the velocity of lengthening. increases, the tension increases up to a point.

Isometric contraction: force is equal to load, V=0

Question 4

What is passive tension? (Length-tension relationship-isometric)

Answer 4

When the muscles is passively lengthened the tension will increase as the muscle reaches its outer range.

Question 5

Name and describe the different sheaths in the skeletal muscle?

What is their role?

Answer 5

Epimysium

Perimysium

Endomysium

Are connective sheaths that surround the various divisions of the muscle ..are all linked together and are importat in the transmission of passive forces through a muscle, such as when a muscle is stretched.

Question 6

What gives the striated appearance of muscle fibers?

Answer 6

saromeres lined up along the fiber length

Question 7

How do the thick and thin filaments generate muscle contraction?

Answer 7

Myosin is the motor protein that when allowed to bind to actin, it pulls the actin toward the center. The actin molecule, is a twisted bundle of bubbles and at either end is attached to a Z-plate. When myosin tugs on actin, it causes the thin filament to move, pulling the ends of the sarcomere closer together.

A muscle contraction consists of a series of repeated events. First, calcium triggers a change in the shape of troponin and reveals the myosin-binding sites of actin beneath tropomyosin. Then, the myosin heads bind to actin and cause the actin filaments to slide. Finally, ATP breaks the actin-myosin bond and allows another myosin ‘oar stroke’ to occur. Repetition of these events causes a muscle to contract.

Question 8

length tension relationship of a contractile unit

Answer 8

Describe that our muscle have an optimal length to produce maximal force.

The strength of muscle contraction is influenced by the initial length of muscle fiber.

muscle that is in an lengthened position: few myosin actin crossbridges could form as the overlap is small

Shortened position: too much overlap and the myosin filaments cannot move any further down the thin filaments as the Z disc is in the way.

Valid for isometric contraction only when no movement occurs.

.

(in other words, when a muscle is in a lengthened position there are very few crossbridges between the myosin and actin, as the overlap is small, and muslce is unable to generate much tension. Similarly if the muscle is in a shortened psoition, there is too much overlap, and the myosin filaments cannot move any further down the thin filanents as the Z dis is in the way which liits tension)

Question 9

What is a tetanic contraction?

Differenced between tetanic and a twich summation?

Answer 9

is a prolonged contraction of a muscle (with no relaxation) and only stops when the stimulus stops or the muscle fatigues.

A twitch summation occurs when the muscle is stimulated before it has a chance to completely relax. A temporal contraction is the addition of a second twitch resulting in greater tension.

Question 10

• *What is the tropomyosin-Troponin Complex?**
• *How does Troponin Complex get activated?**

Answer 10

Prevents the muscles from continued contraction

Tropomyosin is a rope like proten that wraps around actin, preventing myosin from grabbing it. Tropomyosin is like the guard in a muscle cell. It blocks myosin, until the muscle should contract. How does the muscle know when to contract?

Troponin - is a protein that can move the tropomyosin off the myosin binding site on the actin. Essestially, troponin gives tropomyosin a tap on the shoulder to move when it receives the signal from calcium.

Muscle cells receives electrical messages in the forms of action potential. When the AP arrives at the muscle cell, it triggers a release of calcium ions. the released calcium then bind to the troponin complex and activates it. Trypomyosin gets the boot, then the muscle can contract.

Question 11

Provide an example of a fusiform shaped muscle

Answer 11

Biceps brachii

Fusiform muscles are spindle like, it’s wider in the middle and narrow at either ends.

Question 12

What are the two principles of muscle gradation force?

Answer 12

Size principle: the order of motor unit recruitment

Summation or frequency (the amount of stimulation that the motor unit received affects whether the muscle fibers just twitches or produces a full force of muscle contraction

Question 13

What is Summation (Frequency of recruitment)?

Answer 13

Summation (Frequency of recruitment) is another mechanism by which the nervous system gradate muscle force.

Essentially, low frequencies of stimulation will generate a single twitch of the motor unit…to a few twitches. As the frequency increases, the sum of muscle twitches will increase the force (typically above 80 hertz).

Question 14

Give 2 reasons why it is important to measure muscle strength.

Answer 14

1. to determine if there is any deviation from the normal
2. to assess wehther the condition is getting wrose or better or remain the same.
3. to give a baSe meaSurement to the muscle condition.
4. to assess whether any treatment you implement is having a positive or neg. effect.

Question 15

Describes the components of the sarcomere.

Z line, I band, A band, H zone, M line.

Answer 15

Z line: determines the zones of one sarcomere

I band: the area where the thin and thick filaments do not overlap

A band: formed by the dark thick filaments, with areas overlapping with the thin filaments

H zone: the area of the A band where the thick and thin filaments do not overlap.

The M line is the center of the sarcomere, which is between the H zone and the A band.

The A band is the area formed by myosin and actin.

Question 16

Describe passive tension

Answer 16

• Passive tension is the resistance that the muscle tissue has to being passively stretched

While the passively stretched muscle approaches the outer range, the tension in the muscle increases without the muscle being active.

The tension increases as the muscle is taken from mid-range to outer range, possibly to stop the sarcomere from being overstretched.

Question 17

The area where thin and thick filaments overlap is called the:

Answer 17

A- band

Question 18

How is muscle forced controlled?

Answer 18

• increasing in the number of motor units activated (size principle)
• increasing in the frequency of stimulation (summation)
  (eg. , low frequencies of summation = single twitch

the sum of the frequency will result in increased muscle contraction - tetanus summation

Question 19

a muscle fiber is a made up of lots of _______lying parallel to each other

Answer 19

myofibrils

Question 20

Define muscle work involves?

Answer 20

The amount of work a muscle could produced is equal = force x distance

Question 21

What is the force-velocity relationship of skeletal muscle?

Answer 21

Could be defined as the speed in which the muscle changes length and produces force.

Force of contraction = load –> no change velocity, no change in muscle length - and a isometric contraction occurs.

Concentric contraction = “and increase in the speed of contraction will lead to a decrease of the force that is generated by the muscle” . – the greater the speed, the less force is required to overcome the load. This happens because - the rate of crossbridge cycle also increases, leaving less crossbridge possible at a certain time.

Eccentric contraction = “ as velocity increases so does the force, up until a certain point

Question 22

How does the arrangement of the sarcomere influence muscle force production compacity?

Answer 22

The greater the number or sarcomeres in parallel (rather than in a straight line) the greater the force generation compacity of the muscle because this arrangement allows the force to be transmitted directly.

Question 23

What is a fascicle?

Answer 23

A fascicle is a bundle of muscle fibers and is held together by perimysium. A group of fascicle form a muscle and is held together by epimysium.

Question 24

What are myofibrils?

Answer 24

they are elognated contractile threads found in striated muscle cells.

• Myofibrils are composed of thin and thick myofilaments arranged in a precise fashion that enables them to slide in relations to each other.

Question 25

Describe Strap and fusiform muscles. Provide an example of each.

Answer 25

• Strap have a tendon at either end and relatively long muscle fibres that run between the tendons. The muscle fibres are arranged in parallel to or are very similar to the angle of pull of the tendon.

Eg., of Strap muscles: Sartorious

• Fusiform muscles are wider and cylindrically shaped in the center and taper off at the ends. This overall shape of fusiform muscles is often referred to as a spindle

Eg., of Fusiform muscles: biceps brachii

Question 26

What is aerobic capacity (endurance) dependent on?

Answer 26

The muscle’s ability to resist fatigue

Question 27

Explain Unipennate vs bipennate vs multipennate muscle fibers

Give an example of each

Answer 27

Unipennate and bipennate muscles have a central tendon into which short muscle fibres are inserted. The fibre direction is different to the angle of pull of the tendon. Unipennate muscle fibres are on the same side of the tendon, eg. palmar interossei, wherease bipennate muscles has fibers on both sides of the tendon, rectus femoris. And deltoid muscles are multipennate

Triangle muscles display mixed characteristics.

Question 28

What molecule is needed to break the contraction of muscles. So it could relax

Answer 28

ATP is required to disrupt the myosin-actin interaction and prepare the system for another ‘oar stroke.’ Repetition of these oar-like myosin strokes constitutes a muscle contraction. Note that the bond between actin and myosin is so strong that it requires an input of energy via ATP to break the bond. This explains why muscles stiffen shortly after death. Without a steady supply of ATP to break the actin-myosin bond, muscles stay contracted in a process known as rigor mortis.

Question 29

What is muscle endurance? What is it dependent on?

Define Fatigue. What are the sources of fatigue?

Answer 29

The muscle’s ability to resist fatigue and is dependent on muscle’s aerobic compacity, their ability to use oxygen to produce energy.

In other words, muscle endurance is defined as the abilty of a muscle to maintain isometric contraction or continued dynamic contractions.

Fatigue:

The inability of the muscle to sustain a force (contraction).

Sources:

1) diminish response to stimuli
2) depletion of energy.
3) build up of metablic waste

Question 30

What affects muscle strength?

Answer 30

Length tension relationship of a contractile unit (isometric) - generate greater force in contraction/tension

Force-velocity relationship (concentric) - the greater the velocity of contraction, the smaller the tension in the muscle.

Question 31

Discuss the sliding filament theory

Answer 31

” The sliding filament theory explains how the actin and myosin protein fibrils slide over one another and form a series of crossbridges that rotate and pull the sarcomeres closer together, thus shortening the muscle and producing force.”

Question 32

What is a sarcolemma?

Answer 32

Is the cell membrane of a striated muscle fiber.

Question 33

Explain the role of calcium ions on muscle contraction.

Answer 33

• Calcium ions binding to the troponin change its shape, which in turn pulls the tropomyosin out of the way of the binding site, allowing the myosin head to attach to the actin. Once attached to the actin, the myosin neck flexes, pulling the thin filament along. This flexing has the effect of sliding the thick and thin filaments over each other.

Question 34

Define muscle power

Muscle Power is the rate at which work is being done.

= Force (of contraction) x velocity (of contraction)

Answer 34

Define muscle power

Muscle Power is the rate at which work is being done.

= Force (of contraction) x velocity (of contraction)

Velocity is the distance of contraction

Power = net joint moment x joint angular velocity.

(Aerobic vs anaerobic power depending whether type 1 or 2 fibers are recruited)

Question 35

Which physiological process has to occur for muscle strength to increase?

Answer 35

• Increase in actin and myosin (muscle stimulated is relayed to CNS which in turns stimulates the ribosomes to replicdate more A & M). As a result myofibrils increases in length and width.
• The number of myoctye increases
• The size and the number of sarcomeres increases
• Increase in density of mitochondria within muscle tissue (increaSe in glycogen, cP, ATP substrate)
• Increase concentration and activity of glycolytic enzYmes, myokinase and creatube phosphokinase (the enzymes needed for growth)

4 weeks process

Question 36

Stages of Summation

Answer 36

Stages of Summation

A few fibers twitching (5 Hz)

Temporal Summation (20 Hz)

Unfused Tetanus (80 Hz)

Fused Tetanus (100 Hz)

Question 37

What is a sarcomere?

Answer 37

A sarcomere is the smallest functional unit of contraction, which is formed by protein filaments arranged in a precise way to produce muscle contraction.

The arrangement of alternating bundles of thick and thin filaments stacked in a long line produces the the straited appearance of muscle tissue and allows the column to change lentgth

Question 38

What are the main differences between strength and endurance training?

Answer 38

Cardiovascular endurance is measured by its VO2 max which is function of intensity. Intensity is prescribed through heart rate. Local muscle endurance is measured by the length of time the muscle can function before fatigue occurs or the muscle ability to recover after a workout.

High repetitions against low resistance is necessary for increased endurance.

Strength gains requires high loads and low reps

Question 39

What physiological factor could affect the range of movement the muscle could work through and speed of contraction?

Answer 39

The number of sarcomeres in series. The more sarcomeres in series is able to shorten through a greater range and at a greater velocity compared with the muscle with less. The more you trained, the more sarcomeres you’ll add to your muscle fiber, the greater your strength would be because of the ability of your muscle to produce force.

Question 40

Muscle Force?

Versus muscle strength?

Answer 40

muscle force: ability of muscle to move the body part, or object, to push or to pull

Muscle strength: is the forced produced by a muscle that can be measured

Question 41

What is the difference between the different types of pennate muscles – bipennate, unipennate or multipennate muscle shape?

Provide some examples of each type.

Answer 41

Unipennate: all the fascicles are on the same side of the tendon, include certain muscles in the hand eg_, palmar interosseous._

Bipennate: the fascicles are on both sides of the central tendon, the pennate muscle is called bipennate. Example: Rectus Femoris

Multipennate: muscles have multiple rows of diagonal fibres, with a central tendon which branches into two or more tendons. An example is the Deltoid muscle which has three sections, anterior, posterior and middle.

Question 42

What is a muscle twitch?

Type 1 fibers has a low twitch tension, is that true?

Answer 42

It is a very low level muscle contraction resulting from a low frequency stimulation

Type 1 fibers: low,

Type 2: moderate

Type 3: high

Question 43

What is the size principle?

Answer 43

Explains that the motor units within a muscle are recruited in a set order according to the force needed for the task

1) Recruitment of smallest motor units; Type I fibers (slow oxidative, slow to fatigue, low force, slow force production rate, has low twitch tension ) are recruited first.
2) Recruitment of medium size MU; Type IIA are recruited to increase the amount of force. Type 2a fibers are glycolytic. They can withstand fatigue, produces moderate amount of twitch tension, fast.
3) Recruitment of the bigger MU are last. Type IIB fibers are fast glycolytic, can generate a lot of force/power, due to ability to twitch fast, but they fatigue very quickly. recruited

Question 44

Define the length tension relationship of a muscle

Answer 44

Explains that the muscle is strongest is when it is holding a contraction somewhere in the mid-range of motion rather than when it is fully shortened or fully lengthened.

Question 45

How does the length tension relationship explains force production?

Answer 45

Production of force by a muscle is proportional to the number of crossbridges that occur between the actin and myosin. Therefore, if a muscle is in a lengthened or shortened position the number of cross-bridges that can occur are reduced and therefore the force generated is smaller (active tension)

Question 46

Define muscle power

Answer 46

is the rate at which work is being down and is calculated by the equation for power

Muscle Power = force of contraction x velocity of contraction

Question 47

Muscle twitch versus contraction

Answer 47

In summary, a muscle twitch is a single contractionresulting from a threshold stimulus, where a threshold stimulus is the smallest stimulus strength that actually results in a contraction. … Our postural musclesproduce tetanic contractions, thus maintaining posture for long periods of time.