Lecture 5: Skeletal Muscle Flashcards
skeletal muscle converts ___energy to __ energy
electrical; mechanical
the process of converting electrical energy to mechanical energy is called __
excitation-contraction coupling
an individual muscle cell is called a
muscle fiber
t/f the movement of skeletal muscle is under conscious control
true
skeletal muscle is striated and multinucleate (t/f)
true
myofibrils are the ___ elements
contractile
t/f myofibrils run the entire length of of a muscle
true
myofibrils contain a regular repeated pattern of ___
protein filaments
protein filaments interact with each other in an ___ pattern
interdigitating
what are the 3 zones/bands in a myofibril?
I band, H zone, A band
what happens to thick and thin filaments during muscle contraction?
they slide against us
t/f filaments change shape when they slide over each other
false
how does the A band change during muscle contraction?
doesn’t change
how does the I band change during muscle contraction?
gets shorter
how does the H band change during muscle contraction?
gets shorter until it almost disappears
thick protein filaments are made of ___
myosin
a myosin filament consists of 2 ___ chains and 2 ___ chains
heavy; light
what are the 2 binding sites on a myosin head?
atp and actin binding sites
myosin heads have ___ activity
atpase
what is the energy source for filament movement?
atp hydrolysis at myosin head
thin protein filaments are made of __ , ___ and __
actin, tropomyosin, and troponin
actin is made of ___ that are strung together to make __
g actin. f actin
troponin are ___ proteins
globular
tropomyosin are __ proteins
filamentous
explain the steps of the powerstroke
- myosin head hydrolyses ATP and becomes energized and cocked
- the myosin binds to the actin, forming a crossbridge
- the myosin cross bridge pivots, puling the thin filament past the thick filament toward the centre of the sarcomere
- atp binds to myosin head and head detaches from actin
calcium is the __ for muscle contraction
trigger
explain the role of calcium in muscle contraction
ca binds to troponin, which causes tropomyosin to move and reveal the actin binding sites so myosin can bind
the sarcoplasmic reticulum has a high concentration of __
calcium ions
the T-tubule network is an extension of the ___
cell membrane
what allows an action potential to penetrate into a muscle fibre?
t-tubule
the t-tubule comes in close contact with ___
sarcoplasmic reticulum
the t-tubule network is filled with ___
extracellular fluid
what is the purpose of the T tubule network?
allow action potential into muscle fibre to stimulate the release of ca from the sarcoplasmic reticulum
t/f dihydropyridine receptors are functional ca channels
false
t/f ryanodine receptors are functional ca channels
true
what is the function of the dihydropyridine receptors?
detect action potentials and activate ryanidine receptors
t/f calcium atpase is constantly pumping calcium in by using atp
true
what happens when ryanidine receptors are activated?
they allow ca to be released from the sarcoplasm reticulum
list the 9 steps in EC coupling
- ach release from nerve
- ach induced endplate potential leading to muscle ap
- acetylcholinesterase destroys ach
- ap causes ca to be released from sr
- ca binds to troponin
- cross bridge cycling ; contraction
- ca reuptake by SR
- tropomyosin prevents cross bridge formation
- relaxation
after an action potential there is a brief ___ period before actual contraction that is caused by ___
latent; sliding filaments taking up slack
what causes a muscle twitch?
single action potential
t/f a twitch is the smallest single unit muscle contraction
true
the number of cross bridges formed is proportional to the amount of ___ generated
tension
___ is when max tension is reached and all cross bridges are formed
fused tetanus
unfunded tetanus occurs when:
multiple action potentials sequentially (wave summation)
why is there less muscle tension when a muscle is overstretched?
less overlap of thick and thin to make cross bridges required for tension
why is there less muscle tension when a muscle is under stretched?
too much overlap, causing thin filaments to overlap with each other instead and preventing cross bridge formation
