Lab 8

Question 1

Muscle Fiber

Answer 1

Single muscle cell, comprised of many myofibrils, multiple nuclei, surrounded by a sarcolemma

Question 2

Myofibril

Answer 2

Long, rod-shaped organelles that fill sarcoplasm, contain the sarcomeres and the light/dark bands

Question 3

Sarcomere

Answer 3

The smallest contractile unit of muscle
Go from the middle of one I band (z disc) to the middle of the next I band.
So from Z disc to Z disc
Consists of actin, tropomyosin, troponin, myosin, titin

Question 4

Myofilament

Answer 4

Threadlike structures that make up myofibrils, composed primarily of actin and myosin

Question 5

Thick filament

Answer 5

Myosin, each thick filament is surrounded by 6 thin filaments

Question 6

Thin filament

Answer 6

Actin, each thin filament is surrounded by 3 thick filaments
Actin is what gets pulled in and shortens the sarcomere

Question 7

T Tubule

Answer 7

Located between the A and I band. Run deep into the muscle fiber between Terminal cisterns of the SR. Ca2+ storage

Question 8

Triad

Answer 8

Regions where SR terminal cisterns border a T tubule on each side.

Question 9

Endomysium

Answer 9

Surrounds each muscle fiber, subdividing the fascicles

Question 10

Perimysium

Answer 10

Connective tissue surrounding each muscle fascicle

Question 11

Epimysium

Answer 11

Dense connective tissue covering the entire muscle

Question 12

Tendon

Answer 12

All 3 sheaths converge to form cordlike attachment to bone or other muscles
Provide durability and conserve space, provide a route of entry/exit for nerves and blood vessels

Question 13

Aponeurosis

Answer 13

All 3 sheaths converge to a sheet like attachment to bones or other muscles.
Provide durability and conserve space, provide a route of entry/exit for nerves and blood vessels

Question 14

Tropomyosin

Answer 14

Blocks the myosin binding site on the actin, moved by Troponin

Question 15

Troponin

Answer 15

Reacts to calcium and moves tropomyosin off binding site to allow myosin to bind

Question 16

Break down of the Structure of skeletal muscle

Answer 16

I band: light band, Z disc in middle
A band: Dark band, contains the H zone and M line
3 connective tissue sheaths covering muscle at various layers

Question 17

Neuromuscular junction

Answer 17

Where the motor neuron axon connects with a muscle fiber, one motor neuron can innervate more than one muscle fiber. Motor neuron releases ACh
Entry of Na+ into muscle cell through ACh receptor channel initiates muscle action potential

Question 18

Excitation-contraction coupling

Answer 18

The conversion of electrical stimulus to movement.
The AP releasing ACh in motor neuron, ACh binds to receptors in end plate which causes depolarization, change in potential triggers contraction

Question 19

Electrical stimulus

Answer 19

Substitute for ACh, triggers a muscle twitch

Question 20

Muscle Twitch

Answer 20

The mechanical response to a single action potential
Composed of 3 phases: Latent, contraction, relaxation

Question 21

Latent period

Answer 21

Period of time that elapses between the generation of AP and the start of muscle contraction. Chemical changes occur in preparation for contraction. Length does not change with increase in stimulus.

Question 22

Contraction phase

Answer 22

Starts at end of latent period, ends when muscle tension peaks.

Question 23

Relaxation phase

Answer 23

Period of time from peak tension until the end of muscle contraction

Question 24

How do different intensities of electrical stim affect twitch

Answer 24

As you increase voltage the peak tension increases until you reach a max tension value, then increasing voltage will not increase tension anymore.

Question 25

End plate potential

Answer 25

The graded depolarization in the skeletal muscle fiber that is elicited in response to one action potential from the motor neuron

Question 26

What is released when there is an action potential in a motor neuron

Answer 26

Acetylcholine

Question 27

What is the motor unit

Answer 27

A neuron and all the muscle fibers it stimulates, stronger muscle contraction means more motor units are recruited

Question 28

Motor unit recruitment

Answer 28

Increasing the number of active motor units produces a steady increase in muscle force.

Question 29

Increasing tension affect on motor unit recruitment

Answer 29

A larger contraction implies more motor units are activated.
Weak contraction implies fewer motor units are activated but each motor unit develops its maximal tension regardless.

Question 30

Maximal voltage

Answer 30

When all the muscle fibers have been activated, maximal tension/contraction occurs

Question 31

Threshold Stimulus

Answer 31

Smallest stimulus required to induce action potential in a muscles sarcolemma

Question 32

Wave summation

Answer 32

When muscle fibers that are developing tension are stimulated again before the fibers have relaxed.

Question 33

Treppe

Answer 33

Progressive increase in force when a muscle is stimulated in succession, each successive twitch peaks slightly higher than the previous. The muscle must fully relax between the stimuli

Question 34

How does increasing stimulus frequency affect force generation

Answer 34

The faster the stimuli occur the larger the force, the stimuli are summed together to create a greater affect

Question 35

Unfused tetanus

Answer 35

When stimulus are applied frequently over a prolonger period the maximum possible muscle will reach a plateau

Question 36

Fused tetanus

Answer 36

Once plateau is reached, if stimuli are applied with an even greater frequency the twitches will fuse to where peaks and valleys are indistinguishable

Question 37

Maximal tetanic contraction

Answer 37

When the stimulus frequency reaches a value beyond which no further increases in force are generated by the muscle

Question 38

Causes of fatigue

Answer 38

Accumulations of lactic acid, ADP, Pi

Question 39

Fatigue

Answer 39

Decline of muscle’s ability to maintain a constant level of force after prolonged repetitive stimulation
OR
Failure of a muscle fiber to produce tension because of a previous contractile activity.

Question 40

Rest period affect on fatigue

Answer 40

Rest period will delay the onset of fatigue
Rest allows for Lactic acid, ADP, and Pi concentrations to decrease it will delay fatigue and allow for maintaining maximum force.

Question 41

Isometric contraction

Answer 41

Muscle stays at a fixed length, the load attempted to move is equal in weight to the force generated by the muscle.

Question 42

Isotonic contraction

Answer 42

Skeletal muscle length changes, so the load moves a measurable distance
If muscle is shortening it’s isotonic concentric contraction (muscle generates a force greater than the load)
Latent period gets longer as load increases

Question 43

Active force (know graph)

Answer 43

Generated when myosin thick filaments bind to actin thin filaments engaging the cross bridge cycle and ATP hydrolysis

Question 44

Passive force (Know graph)

Answer 44

Generated by the stretching of a muscle and results from the elastic recoil of the tissue, caused by titin which acts as molecular bungee cord

Question 45

Why is there a dip in the force graph

Answer 45

At 80 mm the active force has decreased but the passive force has not increased to a significant value

Question 46

Length tension relationship

Answer 46

Describes the amount of tension that is produced by a muscle as a feature of its length. The longer the muscle the larger the force. Peak tension is when sarcomeres are at their resting length because this provides optimum alignment between actin and myosin

Question 47

Load velocity relationship

Answer 47

The greater the load the smaller the shortening velocity (slower)
Lighter load also means longer contraction duration

Question 48

Can you label all the diagrams?

Answer 48

Prove it. Now.

Question 49

Latent period of isotonic contraction

Answer 49

cross bridges cycle and, when muscle tension exceeds the load, muscle shortening occurs.