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human physiology and pharmacology > E-C coupling and skeletal muscle contraction > Flashcards

E-C coupling and skeletal muscle contraction Flashcards

1
Q

what is the primary function of muscle?

A

to generate force or movement in response to a physiological stimulus

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2
Q

all muscles transduce a chemical or electrical signal into a (blank) response

A

mechanical

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3
Q

what are the three types of muscle

A

cardiac, smooth and skeletal

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4
Q

what is the trigger for all 3 types of muscle

A

an increase in calcium ions

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5
Q

how does skeletal muscle contract

A

in response to neuromuscular synaptic transmission

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6
Q

a skeletal muscle cell has a (blank) where ACh receptors are concentrated

A

single NMJ

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7
Q

are ACh receptors selective or non-selective cation channels

A

non-selective

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8
Q

when the ACh cation channels open in response to ACh binding what is the result

A

depolarization of EM known as an end plate potential (epp)

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9
Q

what happens if the EPP exceeds the threshold for activating the V-gated sodium ion channels

A

an action potential is generated

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10
Q

what happens when there is a generation of an action potential

A

there is a sequence of events leading to contraction

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11
Q

what inactivated ACh rapidly

A

ACh-esterase

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12
Q

name properties of muscle fibers

A

excitability
contractability
extensibility
elasticity
they are elongated and cylindrical
muscle fibres have multiple nuclei and have many mitochondria

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13
Q

what makes up a muscle

A

muscle fiber

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14
Q

what makes up muscle fibers

A

myofibrils

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15
Q

what makes up myofibrils

A

thick and thin myofilaments

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16
Q

what makes up the A band

A

thick and thin filaments with the protein myosin. (appears dark)

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17
Q

what makes up the I band

A

there are only thin filaments in the I band and this appears lighter

18
Q

what is the z line

A

it is a boundary for each sarcomere and it is disk-shaped, there is also actin found here

19
Q

what is the m line

A

the m line is in the center of the A band and contains a protein called myomesin.

20
Q

what is the H zone

A

the h zone is in the middle of the A band, and the m line runs down the middle of it. in the h zone thick and thin filaments do not overlap and it only contains thick filaments.

21
Q

what are the levels of organization in a skeletal muscle

A

whole skeletal muscle (an organ)
muscle fiber (single cell)
myofibril (a specialised intracellular structure)
thick and thin filaments (cytoskeletal elements)
myosin and actin (protein molecules)

22
Q

how large is a single muscle fiber

A

10-100 micrometers and up to approx. 75cm in length

23
Q

what are myofibrils

A

specialized contractile elements that extend the entire length of the muscle fiber
muscle fibers can contain 100s-1000s of myofibrils

24
Q

what makes up thick and thin filaments

A

in thick there is myosin
in there there is actin

25
Q

what makes up a thin filament

A

there are the actin molecules with the binding site for attachment with myosin.
these molecules form an actin helix of 2 chains.
tropomyosin acts as a ribbon and covers the myosin-binding site stopping troponin from binding and the troponin binds to tropomyosin

26
Q

Heterotrimers
what do troponin T, C and I bind to

A

T binds to tropomyosin
C binds to calcium ions
I binds to actin and inhibits contraction

27
Q

what does each heterotrimer of troponin interact with

A

a single molecule of tropomyosin which in turn interacts directly with 7 actin monomers

28
Q

what is the structure of myosin forming the thick filaments

A

2 identical subunits- tails intertwined with the globular head sticking out. the tail is 100nm long

29
Q

what is on the globular head of the myosin filaments

A

the actin-binding site and myosin ATPase site

30
Q

each myosin II molecule is a double trimer composed of what

A

2x intertwined heavy chains
2x regulatory light chains
2x alkali (or essential) light chains

31
Q

the two heavy chains have 3 regions a tail, a hinge, and a head region. go into detail about all of these

A

the tail portions are alpha helices that intertwine
at the hinge region the molecules opens to form 2 globular heads
The head regions (aka S1 fragments) are the cross-bridges between the thick and thin filaments of the sarcomere

32
Q

the head portions of each myosin form a complex with 2 light chains, 1 alkali and 1 regulatory

A

the alkali light chain stabilizes the myosin head region

the regulatory light chain regulates the ATPase activity of myosin. The activity of this chain is regulated via phosphorylation by kinases

33
Q

explain the muscle contraction cycle

A

myosin-II heads bind to actin,
these cross bridges become distorted
myosin heads detach from actin

34
Q

where does the energy come from for the muscle contraction

A

hydrolysis of ATP

35
Q

in all 3 muscle types, what does the increase of free calcium ions trigger

A

contraction by removing the inhibition (tropomyosin) of cross bridges cycling

36
Q

what happens to the calcium ions upon stimulation

A

rises from resting levels of less than 10-7M to greater than 10-5M

37
Q

what happens when there is a decrease in calcium ions

A

the decrease is the signal to cease cross-bridge cycling and relax

38
Q

how do calcium ions modulate contraction

A

via regulatory proteins rather than interacting directly with the contractile proteins

39
Q

what happens in the absence of Ca2+

A

the regulatory proteins act together to inhibit actin-myosin interactions, thus inhibiting the contractil process

40
Q

what happens when Ca2+ binds to one or more of the regulatory proteins

A

a conformational change takes place in regulatory complex that releases the inhibition of the contraction

human physiology and pharmacology (16 decks)

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