E-C coupling and skeletal muscle contraction

Question 1

what is the primary function of muscle?

Answer 1

to generate force or movement in response to a physiological stimulus

Question 2

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

Answer 2

mechanical

Question 3

what are the three types of muscle

Answer 3

cardiac, smooth and skeletal

Question 4

what is the trigger for all 3 types of muscle

Answer 4

an increase in calcium ions

Question 5

how does skeletal muscle contract

Answer 5

in response to neuromuscular synaptic transmission

Question 6

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

Answer 6

single NMJ

Question 7

are ACh receptors selective or non-selective cation channels

Answer 7

non-selective

Question 8

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

Answer 8

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

Question 9

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

Answer 9

an action potential is generated

Question 10

what happens when there is a generation of an action potential

Answer 10

there is a sequence of events leading to contraction

Question 11

what inactivated ACh rapidly

Answer 11

ACh-esterase

Question 12

name properties of muscle fibers

Answer 12

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

Question 13

what makes up a muscle

Answer 13

muscle fiber

Question 14

what makes up muscle fibers

Answer 14

myofibrils

Question 15

what makes up myofibrils

Answer 15

thick and thin myofilaments

Question 16

what makes up the A band

Answer 16

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

Question 17

what makes up the I band

Answer 17

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

Question 18

what is the z line

Answer 18

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

Question 19

what is the m line

Answer 19

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

Question 20

what is the H zone

Answer 20

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.

Question 21

what are the levels of organization in a skeletal muscle

Answer 21

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)

Question 22

how large is a single muscle fiber

Answer 22

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

Question 23

what are myofibrils

Answer 23

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

Question 24

what makes up thick and thin filaments

Answer 24

in thick there is myosin
in there there is actin

Question 25

what makes up a thin filament

Answer 25

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

Question 26

Heterotrimers what do troponin T, C and I bind to

Answer 26

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

Question 27

what does each heterotrimer of troponin interact with

Answer 27

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

Question 28

what is the structure of myosin forming the thick filaments

Answer 28

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

Question 29

what is on the globular head of the myosin filaments

Answer 29

the actin-binding site and myosin ATPase site

Question 30

each myosin II molecule is a double trimer composed of what

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

explain the muscle contraction cycle

Answer 33

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

Question 34

where does the energy come from for the muscle contraction

Answer 34

hydrolysis of ATP

Question 35

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

Answer 35

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

Question 36

what happens to the calcium ions upon stimulation

Answer 36

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

Question 37

what happens when there is a decrease in calcium ions

Answer 37

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

Question 38

how do calcium ions modulate contraction

Answer 38

via regulatory proteins rather than interacting directly with the contractile proteins

Question 39

what happens in the absence of Ca2+

Answer 39

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

Question 40

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

Answer 40

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