Unit 10: skeletal muscle Flashcards
how much % of body mass is attributed to skeletal muscle?
40
skeletal muscle stores (4):
- ions
- fluids
- proteins
- glycogen
relate the following terms: skeletal muscle, glycogen, energy
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
besides skeletal muscle, where else can glycogen be stored in the body?
the liver
ligaments attach _____ together
bones
(the majority of) tendons attach _____ & _____ together
muscle and bones
some muscles are attached TOGETHER by tendons
name the structures that comprise a skeletal muscle from the smallest unit to the largest unit
- sarcomere
- myofibril
- muscle fiber (cell)
- fasiculous (multiple = fasiculi)
- muscle
what makes up a “motor unit”
1 or more skeletal muscle cells controlled by ONE motor neuron
differentiate the function of small motor units vs large motor units
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
- 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
type 1 skeletal muscle
- “fast twitch” - fast acting but not sustainable
- little myoglobin
- fewer mitochondria
- white
type 2 skeletal muscle
think chickens flying up a tree
give examples of type 1 and type 2 muscles
type 2 skeletal muscle:
* ocular muscle
type 1 skeletal muscle:
* soleus muscle
middle: gastrocnemius; not necessarily clear-cut divisions
name 6 structures that make up a skeletal muscle fiber
- sarcolemna (cell wall)
- sarcoplasm
- SR
- T-tubules
- mitochondria
- actin/myosin filaments
what is a sarcomere?
the smallest functional unit of the skeletal muscle
comprised of actin (thin filament) & myosin (thick filament)
name the structures that make up a sarcomere
- 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”
list out the mechanics for the “sliding filament mechanism”
- 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
what is the benefit of skeletal muscles being multi-nucleated?
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
about how many myosin molecules make up a myosin filament?
~200
describe the structure of the skeletal muscle myosin filament
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
describe the actin/thin filaments
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
delineate the steps of the troponin complex revealing active sites
- trop I is anchored to the f-actin strand
- trop T is anchored to the tropomyosin strand
- trop C is the Ca2+ binding site and contains (4) sites for calcium to bind to
- **once 4 calcium is bound **to trop C, troponin T and I “twist” their respective strands’ conformation
- tropomyosin then reveals the active sites on f-actin which are ready for binding
list out the steps for cross-bridge cycling
- myosin head is “ready” to go (ADP + Pi)
- calcium influx into skeletal muscle > binds to troponin C
- conformation change of actin filament and tropomyosin unshields active sites on f-actin
- actin binds with myosin heads on active site; Pi gets released, leaving ADP only on myosin head
- actin filament gets “pulled” and sarcomere shortens > contraction occurs
- myosin head releases ADP
- myosin head stuck onto actin filament
- ATP releases myosin head from actin molecule and then metabolized to ADP + Pi
- myosin head back in “cocked state”
name what happens when all of the myosin heads are “stuck” on the actin filaments and NO ATP is available
rigor mortis - stiff skeletal muscles
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)
no force is produced
very minimal tension developed
the muscle is overstretched
ex) LV gets overstretched over time, less force produced
if there is no room for the sarcomere to shorten, AKA the actin and myosin filaments are already overlapping, how much force is produced?
no force is produced (100% tension)
there is no room to shorten the sarcomere
this muscle is understretched
developed muscles are (over/under) stretched?
understretched
repaired muscle is typically (over/under) stretched?
overstretched
relate the length/tension relationship to cardiac sarcomeres
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
what is active tension?
the amount of force measured when the muscle contracts
what is passive tension?
the amount of force applied to the muscle to create tension/stretch
what is total tension?
the measured force of stretch applied to the muscle plus how much force the muscle is generating during contraction
total = passive + active tension
relate the muscle stretch length to amount of tension
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)
differentiate isotonic contraction vs isometric contraction
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)
what is the relationship of the “velocity of contraction” vs the “load opposing contraction”?
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
relate the load/contraction velocity relationship to cardiac physiology
this is a more important concept in cardiac muscle – if your BP is higher (resistance is greater), the slower the heart can eject blood
what is quantal summation? how does voltage play into this?
AKA quantal regulation
recruiting larger motor neurons to produce more force
usually managed by voltage
* strong voltage = larger motor neurons recruited
* weak voltage = smaller motor neurons recruited
what is temporal summation? how does tetany play into this?
temporal summation relates the rate of stimulation (measured in Hz) vs the strength of muscle contraction
- a supramaximal voltage stimulates a muscle nerve at the same voltage per second
- 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
- temporal summation can become additive in regards to stacked contractions and Ca2+ accumulation
- 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
- 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
this happens when skeletal muscle has not been used for a significant amount of time
atrophy
AKA denervation/disuse
this happens when you exercise your skeletal muscles regularly
hypertrophy
expansion of myofibril size occurs; the vascular bed also increases in these muscles
this happens when your skeletal muscle gets exercised excessively
hyperplasia
skeletal muscle cell generation increases, but slowly
