Unit 10: skeletal muscle

Question 1

how much % of body mass is attributed to skeletal muscle?

Answer 1

40

Question 2

skeletal muscle stores (4):

Answer 2

1. ions
2. fluids
3. proteins
4. glycogen

Question 3

relate the following terms: skeletal muscle, glycogen, energy

Answer 3

skeletal muscles do a lot of work and constantly need energy; since skeletal muscle stores glycogen in the muscles itself, it can break down glycogen to glucose to be used as energy

Question 4

besides skeletal muscle, where else can glycogen be stored in the body?

Answer 4

the liver

Question 5

ligaments attach _____ together

Answer 5

bones

Question 6

(the majority of) tendons attach _____ & _____ together

Answer 6

muscle and bones

some muscles are attached TOGETHER by tendons

Question 7

name the structures that comprise a skeletal muscle from the smallest unit to the largest unit

Answer 7

1. sarcomere
2. myofibril
3. muscle fiber (cell)
4. fasiculous (multiple = fasiculi)
5. muscle

Question 8

what makes up a “motor unit”

Answer 8

1 or more skeletal muscle cells controlled by ONE motor neuron

Question 9

differentiate the function of small motor units vs large motor units

Answer 9

small motor units:
* fine motor control
* easy to excite
* gets activated FIRST

large motor units:
* recruited when a lot of work needs to be done
* harder to excite
* gets activated after small motor units have been activated

Question 10

• slow contractions; sustained contraction
• a lot of myoglobin
• a lot of mitochondria
• red (as a result of Fe from myoglobin)

think geese flying to the south

Answer 10

type 1 skeletal muscle

Question 11

• “fast twitch” - fast acting but not sustainable
• little myoglobin
• fewer mitochondria
• white

Answer 11

type 2 skeletal muscle

think chickens flying up a tree

Question 12

give examples of type 1 and type 2 muscles

Answer 12

type 2 skeletal muscle:
* ocular muscle

type 1 skeletal muscle:
* soleus muscle

middle: gastrocnemius; not necessarily clear-cut divisions

Question 13

name 6 structures that make up a skeletal muscle fiber

Answer 13

• sarcolemna (cell wall)
• sarcoplasm
• SR
• T-tubules
• mitochondria
• actin/myosin filaments

Question 14

what is a sarcomere?

Answer 14

the smallest functional unit of the skeletal muscle

comprised of actin (thin filament) & myosin (thick filament)

Question 15

name the structures that make up a sarcomere

Answer 15

• Titin: large protein that anchors myosin to z-disk
• A band: actin + myosin segment
• Z discs: two ends of each sarcomere
• H zone/band: myosin only segment
• I band: actin only segment
• M line: middle of H band

TAZ-HIM “taze him”

Question 16

list out the mechanics for the “sliding filament mechanism”

Answer 16

• I bands shrink
• H bands dissapear
• Z discs move closer together
• muscle decreases its overall length (shortens)
• A band doesn’t change width during contraction; myosin fibers have a fixed length

Question 17

what is the benefit of skeletal muscles being multi-nucleated?

Answer 17

the skeletal muscle cell is very long and contains many compartments for ions, glycogen, fluids, and proteins, – and it does not have a special transport system like neurons do in terms of getting proteins from where they’re made to where they need to go; therefore, having more nuclei located along the long tracts of the skeletal muscle will allow increased production of necessary proteins to reach their target destinations quicker and easier

Question 18

about how many myosin molecules make up a myosin filament?

Answer 18

~200

Question 19

describe the structure of the skeletal muscle myosin filament

Answer 19

consists of:
* (2) heavy chains (tail)
* (4) light chains
+ (2) regulatory light chains (involved with determining activity level of myosin heads
+ (2) essential light chains that primarily have ATPase activity
* (2) myosin heads
+ have high affinity active sites for actin

Question 20

describe the actin/thin filaments

Answer 20

consists of:
* (2) strands
+ f-actin (contains active binding sites)
+ tropomyosin (shields active sites on f-actin
* troponin complex
+ trop. I, trop. T, trop. C

Question 21

delineate the steps of the troponin complex revealing active sites

Answer 21

1. trop I is anchored to the f-actin strand
2. trop T is anchored to the tropomyosin strand
3. trop C is the Ca2+ binding site and contains (4) sites for calcium to bind to
4. **once 4 calcium is bound **to trop C, troponin T and I “twist” their respective strands’ conformation
5. tropomyosin then reveals the active sites on f-actin which are ready for binding

Question 22

list out the steps for cross-bridge cycling

Answer 22

1. myosin head is “ready” to go (ADP + Pi)
2. calcium influx into skeletal muscle > binds to troponin C
3. conformation change of actin filament and tropomyosin unshields active sites on f-actin
4. actin binds with myosin heads on active site; Pi gets released, leaving ADP only on myosin head
5. actin filament gets “pulled” and sarcomere shortens > contraction occurs
6. myosin head releases ADP
7. myosin head stuck onto actin filament
8. ATP releases myosin head from actin molecule and then metabolized to ADP + Pi
9. myosin head back in “cocked state”

Question 23

name what happens when all of the myosin heads are “stuck” on the actin filaments and NO ATP is available

Answer 23

rigor mortis - stiff skeletal muscles

Question 24

how much force is produced if the actin and myosin filaments do not line up with each other (AKA the length of the sarcomere is extremely long)

Answer 24

no force is produced
very minimal tension developed
the muscle is overstretched

ex) LV gets overstretched over time, less force produced

Question 25

if there is no room for the sarcomere to shorten, AKA the actin and myosin filaments are already overlapping, how much force is produced?

Answer 25

no force is produced (100% tension) there is no room to shorten the sarcomere this muscle is **understretched**

Question 26

developed muscles are (over/under) stretched?

Answer 26

**understretched**

Question 27

repaired muscle is typically (over/under) stretched?

Answer 27

**overstretched**

Question 28

relate the length/tension relationship to cardiac sarcomeres

Answer 28

at rest, the sarcomeres of the heart are typically **understretched** in a healthy patient if the ventricles of the wall are stretched out a little more after filling with blood, there is typically better cardiac performance frank starling's law: more volume in the heart will stretch the ventricles and will increase stroke volume

Question 29

what is active tension?

Answer 29

the amount of force measured when the muscle contracts

Question 30

what is passive tension?

Answer 30

the amount of force applied to the muscle to create tension/stretch

Question 31

what is total tension?

Answer 31

the measured force of stretch applied to the muscle plus how much force the muscle is generating during contraction total = passive + active tension

Question 32

relate the muscle stretch length to amount of tension

Answer 32

as the length of the muscle increases with passive stretch, the amount of tension increases however, the tension will decrease once the muscle is passed its optimal amount of stretch (the optimal amount of stretch is where there is optimal overlap of the actin and myosin filaments)

Question 33

differentiate isotonic contraction vs isometric contraction

Answer 33

in isoMETRIC contraction, a great amount of tension might be generated but there will be no force exerted (you're trying to curl a very heavy weight but cannot curl it - a lot of tension but no lengthening/shortening of the muscle) in isotonic contraction, the muscle will shorten/lengthen with normal contraction/relaxation (lifting a manageable weight at the gym)

Question 34

what is the relationship of the "velocity of contraction" vs the "load opposing contraction"?

Answer 34

as weight of the load increasing, the slower the speed of muscular contraction as the weight of the load decreases, the faster the speed of muscular contraction the relationship is *inversely* related | you can curl a 3lb weight much faster than a 50 lb weight

Question 35

relate the load/contraction velocity relationship to cardiac physiology

Answer 35

**this is a more important concept in cardiac muscle** -- if your BP is higher (resistance is greater), the slower the heart can eject blood

Question 36

what is quantal summation? how does voltage play into this? | AKA quantal regulation

Answer 36

recruiting larger motor neurons to produce more force usually managed by **voltage** * strong voltage = larger motor neurons recruited * weak voltage = smaller motor neurons recruited

Question 37

what is temporal summation? how does tetany play into this?

Answer 37

temporal summation relates the rate of stimulation (measured in Hz) vs the strength of muscle contraction 1. a **supramaximal** voltage stimulates a muscle nerve at the same voltage per second 2. as the rate of stimulation increases, the strength of muscle contraction stacks as the neuron will continue to depolarize despite the muscle "resetting" from its previous contraction 3. temporal summation can become additive in regards to stacked contractions and Ca2+ accumulation 4. after a certain point, the amount of Ca2+ released by SR will become faster than the rate at which Ca2+ is being placed BACK into the SR > this can lead to **tetany** 4. since the Ca2+ getting placed back into the SR is slower than it is getting effluxed from the SR, there will be less "resetting" of the contraction > the amount of force the muscle can generate will **plateau** once tetany starts to manifest

Question 38

this happens when skeletal muscle has not been used for a significant amount of time

Answer 38

atrophy | AKA denervation/disuse

Question 39

this happens when you exercise your skeletal muscles regularly

Answer 39

hypertrophy expansion of myofibril size occurs; the **vascular bed also increases in these muscles**

Question 40

this happens when your skeletal muscle gets exercised excessively

Answer 40

hyperplasia skeletal muscle cell generation increases, but slowly