Skeletal Muscle Flashcards
What are the 4 properties of skeletal muscle?
1: contractility
2: Irritable
3: Extensible
4: Elastic
How is skeletal muscle controlled?
Voluntarily- you can turn them on and off when you want. Except for some cases ( cramps, injury, muscle twitch)
What are the main contractile filaments of muscles?
Actin
Myosin
Why is it important to have the 4 properties of skeletal muscle?
If you were to lack any qualitative, muscle would not move as well, or allow basic human function????
How are cells/fibers arranged in skeletal muscle?
in long, multi-nucleated cells arranged in a series for max. force production
What is the overall hierarchy of muscle cells from smallest to largest
- myofilaments
- myofibirl
- muscle cell/fiber
- fasicle
- whole muscle
What are the three thin myofilaments
- actin
- troponin
- tropomyosin
what are thick filaments?
myosin (heaby and light chained)
how many thin filaments surround a thick filament?
six
what is the functional unit of the myofibril?
the sarcomere (contains thin and thick fil.)
what are the identifiable features within the sarcomere?
Z-disk M-line I-band H zone A band
Which part of the sarcomere anchors myosin to the middle
M-line
What is present in the I band?
only actin
What is only present in the H-zone?
Myosin filaments
What is the a-band?
the area that spans the length of myosin.
If a muscle were to contract, what would happen to the sarcomere?
-actin is mulled towards the M line –> the I band is decreased –> the z line shrinks which causes an over lap –> the H zone disappears because actin is pulled closer and closer to the middle
quiz question: which zones will decrease in sarcomere shortening?
- Hzone
- I band
What is muscle cell/fiber?
a bundle of myofibrils
What is the sarcolemma?
the cell membrane
Satellite cells?
on sarcolemma and migrate to sites of damage to rebuild muscle fibers to resist the next stressor (regulate growth and adaption)
why is satellite cell proliferation important in resistance training?
- they improve muscle fibers rebuilding for resistance to stress
What contains ATP-CrP, glycogen, fats, and mitochondria in a muscle cell?
sarcoplasm
What is the role of T-tubules?
they allow action potentials to depolarize muscles for contraction
What is the function of the Sarcoplasmic reticulum
longitudinal tubules that surround myofibrils for Calcium storage and release
What part of the SR is enlarged for calcium storage and release?
terminal cisternae
Are muscle cells multi-nucleated?
yes- they are control centers for muscle fiber
How does myostatin regulate muscle growth?
negatively regulates muscle growth b/c growth inhibitor
what protein is created within the muscle fiber and goes to receptor binding sites on muscles to regulate how large the muscle fibers get?
myostatin
How could a myostatin deficient human be a good thing?
they could be a super-athlete. their muscles could get really big, and they could be extremely strong
What linking protein prevents muscular dystrophy?
Dystrophin
Which protein links myofibrils to the sarcoplasmic reticulum and then to other fibers?
Dystrophin
What disease could a lack of dystrophin cause?
muscular dystrophy- excessive muscle damage as a result of certain types of activity
what is a fascicle?
a bundle of muscle fibers
what is a muscle fiber?
a bundle of fasciles
which connective tissue surrounds fascicles?
perimysium
list connective tissues deep to superficial
- endomysium
- perimysium
- epimysium
connective tissues come together to form ____
tendons
When stretching a tendon and snapping it back, this creates more force.. why?
stored elastic energy in tendons creates more force
How are muscle fibers arranged in parallel muscles?
fibers run along the same line of “pull”
what types of parallel muscles are there?
-flat
-fusiform
strap
radiate
How are pennated muscle fibers arranged?
Fibers fun obliquely or at an angle from the line of pull
what three types of pennated muscles?
bipennate
multipennate
-unipennate
what are the benefits of pennated muscles?
they can compact more muscle in to a space. this will allow for 1. greater force output and 2. increased cross-sectional area
Which features would not change size of length inside of a sarcomere in concentric muscle contraction?
- z line
- m line
- a band
how does each structure of a muscle contribute to muscle function and force development
??
What are the three main fiber types?
Tpye IIx
Type IIa
Type I
what differentiates the muscle types?
the amount of “stuff” inside… mitochondria, myoglobin.. ect.
Which fiber type has the most mitochondria, myoglobin and capillary density?
Type 1
why does type 1 have the most myoglobin?
it needs to take oxygen to the muscles (aerobic)
why does type 1 have the most mitochondria
with more myoglbin, more mitochondria is needed to process the myoglobin
Which fiber type is best for fatigue resistance?
type 1
which fiber has the fastest contractile speed, resulting in the greatest contractile strength?
type 2x
which fiber has fast myosin ATP-ase?
2x
what do the levels of mitochondria and creatine phosphate look like in 2x?
- low mitochondria
- high creatine phosphate (to produce ATP quickly)
Why are more myosin heavy chained filaments beneficial for type 2x muscle fibers?
-they have a stronger structure and can withstand more force.
what binds actin and myosin?
ATP
Which fiber type has the most glycogen and CrP i the sarcoplasm?
Type 2a
Make a table comparing the fiber types (tab 3 in word doc)
- amounts of myoglobin, mitochondria, and blood capillaries
- amount of CrP
- How fast myosin ATPase is formed
- Contraction velocity
- resistance to fatigue
- contraction force
- what activities good for
what distribution of fiber types are in your own body?
-more type 2a in legs for volleyball
What type of fiber distribution would you give a super hero athlete?
i would give a super athletes lot of type 2a distribution, but also type 2 in places where a lot of force would be needed. in the legs, so it could jump really high.
what type of motor neurons determine fiber distribution
alpha motor neurons
What type of fiber are postural muscles?
type 1 because they always need to be on and fatigue resistant
what provides feedback on muscle length and rate of change in length to the CNS?
muscle spindles
what is an intrafusal muscle fiber innervated by gamma motor neurons?
muscle spindle
do gamma motor neurons send info to or from the CNS ?
from CNS to muscle spindle
What sends info in to the CNS away from muscle spindles?
type Ia aferent neurons (stimulated by lengthening of intrafusal fibers)
what do gamma motor neurons regulate?
sensitivity of the muscle spindle by stimulating the intrafusal fibers to contract by shortening the spindle. (stretch reflex)
What feedback type stimulates muscle spindles?
change in length
rate in change of length
-small change can initiate “stretch reflex”
What is the response of muscle spindles to feedback?
reciprocal inhibition- CNS stimulates alpha motor neurons for the agonist muscle fiber contraction and inhibits alpha motor neuron for the antagonist muscle
what is also known as a stretch reflex?
myostatic reflex-
what stimulates myostatic stretch reflex?
lengthening of whole muscle
explain how muscle spindles work by using the stretch reflex
lengthening of muscle fiber spindles stimulates Ia afferent neruons to send signal to CNS–>CNS processes–>sends message through gamma motor neurons back to extrafusal muscle –> agonist contracts –> antagonist relaxes
give an example of reciprocal inhibition
- quad contracting, hamstring relaxing
- patellar tendon hit at doctor- quick contraction of quad, hamstring relax
- ballistic stretching
how is ballistic and static stretching beneficial to improve human performance?
ballistic stretching- triggers feedback to CNS, but if you hold it, the CNS can recognize that it is a safe movement and calm spindle fibers to relax muscles. this can allow you to tune muscle spindles to make them more receptive to stretch (more flexible) by a myotatic reflex that desensitizes muscle spindles
static- reduces force output
Where are golgi tendon organs located?
at the muscle/tendon junction
what feedback do GTOs provide to the CNS?
- tension or force output in muscles
- rate of change in tension
what response do GTOs to changes in tension and rate of tension?
agonist muscle relaxation
-antagonist muscle contraction (reciprocal exhitation)
explain differences in reciprocal inhibition and reciprocal excitation…
excitation- antagonist muscle contracts, agonist relaxes
inhibition- agonist contracts, antagonist relaxes
what is autogenic inhibition?
when deformation of 10-20 motor units from tension within GTO stimulates 1b afferent neurons to send info to CNS –> alpha motor neurons signal agonist to relax and excites antagonist (reciprocal excitation)
give an example of autogenic inhibition
walking- calf flexes, tibialis anterior relaxes
how can response from GTOs improve human performance
- stretching GTOs can add to voluntary muscle recruitment
what is voluntary muscle recruitment?
about 80% of motor units recruited is from voluntary, but 10% is from stretch reflex. –> improves from 80 to 90%.
can improve performance,, vertical jump
what is definitely of motor unit
all muscle fibers that innervate
at what level do GTOs work
at low levels of whole muscle force- only 10-20 motor units
** all motor units that are on, are on at full force
what are the two processes for skeletal muscle contraction?
exhitation-contraction coupling
2. sliding fillament theory
Explain the excitaion- contraction coupling process
- action potential is fired from nervous stimulus –> alpha motor neuron
- acetylcholine is released by exocytosis from synaptic vesicles
- nicotinic recptors bind Ach and gates open up for sodium and potassium open up
- AcH action potential is generated, and depolarizes across sarcolemma and down T-tubules
- activates DHP receptors and through triadic feet to get to Sarcoplasmic reticulum
- Ryanodine receptors signal Ca2+ release from terminal cistern in SR into the muscle sarcoplasm.
explain what happens to Calcium after it has been released to the sarcomere
Sliding Filament Theory:
Ca++ binds to troponin. tropomyosin is pushed off active binding sites on actin –> actin and myosin can come together
Explain the sliding filament theory..
- ca++ binds to troponin and kicks off tropomyosin off binding sites on actin
- myosin heads bind to actin at 45’ angle
- atp binds to myosin heads –> myosin dissociates from actin
- ATPase hydrolyzes ATP to ADP and Pi –> cocks myosin heads
5.myosin and actin bind weakly at 90’
6.Pi is released from myosin head and initiates power stroke - myosin head rotates back to 45’ position, actin goes closer to m line
- ADP is released after power stroke , mosin is still bound to actin
HAPPENS LOTS OF TIMES
why do people get rigor mortis at death?
because cells are still producing calcium and active sites are being exposed (rigor state)
what results from the movement of myosin head and repeated coupling and uncoupling with actin
muscle shortening and lenthening under tension
what is the role of ATP is skeletal muscle contraction
binds actin and myosin
what are the types of muscle contraction
- isotonic
- isometric
- isokinetic
what are two types of isotonic contractions
- concentric
2. eccentric
what is isotonic contraction
force while shortening (concentric) or lengthening (eccentric) while actin and myosin are still forming cross bridges
what is isometric contraction
contraction with no movement. muscle produces static force
- only develops strength to a certain point
- develops strength and control (in therapy setting)
Isokinetic contraction
muscle produces max force at a fixed velocity
force vs. velocity
contraction speeds up –> force decreases
force vs. power
as force increases, power continues to increase. power=f*d/time
only drops off due to time elapsed.
give an example of isotonic contraction
bicept curls- concentric use biceps to pull up. eccentric to go back down
what is the most powerful type of contraction
eccentric (addition of stored elastic energy) > isometric (static cross bridges) > concentric (actin and myosin overlap)
what are 3 ways to increase neuromuscular recruitment
- increase number of motor units
- recruit higher size
- increase rate coding
what type of coding produces max force output
continued stimulation/tetanus
what is stretch shortening cycle
eccentric followed by concentric action
what is CAP
concurrent-activation potentiation:
-voluntary contractions or H-reflex may cause an overflow to excite target motor neurons
what is PAP
post-activation potentiation:
30 sec to a few minutes after high intensity contraction– activated motor units are more excitable and easily recruited for greater force production
how does maximal force output happen in ideal sarcomere length
max number of actin-myosin cross bridges
how are fiber types determined?
by the type of motor neuron that innervates it
type 2–type 2
which type are motor units are easier to recruit
Type 1. recruited first
what myofilament keeps the myosin filament aligned correctly within the sarcomere?
titin
what myofilament links myofibrils to the SR
Dystophin
what myofilament determines strength of fiber
collagen
what myofilament negatively regulates muscle growth
myostatin
what is the role of the sarcoplasmic reticulum in skeletal muscle contraction
it releases calcium to the myofibrils
which myofilaments give rise to skeletal muscle contractility
actin and myosin
what properties in type i skeletal muscle fibers support high fatigue resistance?
lots of mitochondria
lost of blood capillaries
lost of myoglobin
what are the roles of ATP in skeletal muscle contraction
binds to myosin heads causing myosin to dissociate from actin
how does concurrent activation potentiation work to increase muscle force output?
- H reflex may induce motor overflow to excite target motor neurons
- remote voluntary contraction in other muscles can induce motor overflow to excite target motor neurons
when a muscle produces max force at a fixed velocity it is known as ____
isokinetic contraction
what explains why the concentric contractions elcite less force than isometric contractions
actin-myosin cross-bridging is minimized during concentric contractions
what explains why eccentric contractions elicited more force than isometric contractions
-stored elastic energy in eccentric contractions contribute force production
what happens to moment velocity as weight increases?
velocity decrease
How can you best maximize power output while lifting?
increase weight and speed up.
-power=force*velocity
what strategies are suggested in a mixed model approach to power development?
- use a variety of training loads with the intent to lift them as explosively as possible
- use a variety of training exercises to target various portions of the force-velocity curve
which test in lab had the highest peak power output?
vertical jump
which muscle fiber type correlates with the wingate test?
type IIA
how could force-contraction relationship be useful in a resistance training scenario?
- using eccentric movements would allow for the most effect way to get max force output
how could force-contraction relationship be useful in a sport performance scenario
if you don’t want a lot of force, use concentric or isometric exercises. (PAP)?
how does continued muscle stimulation effect sport performance?
continued stimulation increases rate of coding, which is a factor that increases neuromuscular recruitment.
What is the definition of lactate threshold?
When lactate export from muscles equals the lactate export outside of muscles
what are the three stimulation types that may be used to increase rate of coding in neuromuscular recruitment?
- single stimulation (muscle twitch)
- repeated/rapid stimulation (summation)
- continued stimulation (tetanus)
which enzymes regulate the glycolytic system?
- myosin ATPase
- creatine kinase
- myokinase
