muscle contraction

Question 1

what is the function of myoepithelial cells

Answer 1

expel secretions from glandular acini

Question 2

what are pericytes

Answer 2

smooth muscle like cells that surround blood cells

Question 3

what are myofibroblasts

Answer 3

cells with a contractile role in addition to secreting collagen. important following tissue damage during the process of healing and repair, leading to the formation of a scar

Question 4

what is atrophy

Answer 4

decrease in the size of an organ

Question 5

what are myocytes

Answer 5

muscle cells

Question 6

what does the sarcolemma do

Answer 6

make t tubules that project downward to the centre of the muscle fibre

Question 7

what is the functional unit of myocytes

Answer 7

sarcomere

Question 8

what is the sarcoplasm

Answer 8

the cytoplasm of a myocyte

Question 9

what does the sarcoplasmic reticulum do

Answer 9

stores calcium and runs parallel to t tubules

Question 10

what is found within the sarcoplasm

Answer 10

myofibrils that consist of contractile proteins and regulatory proteins

Question 11

what do contractile proteins consist of

Answer 11

thick myosin and thin actin filaments

Question 12

what is thick myosin

Answer 12

hundreds of myosin proteins

Question 13

what are actin filaments

Answer 13

small globular proteins made from g actin

Question 14

what is found on each g actin that forms the actin filaments

Answer 14

an active site that the myosin heads bind to during contraction

Question 15

what do g actin form

Answer 15

a filament that looks like a long helix structure

Question 16

what is f actin

Answer 16

the long helix structure formed by the combination of g actin

Question 17

which proteins are found on f actin

Answer 17

troponin and tropomyosin

Question 18

what are troponin and tropomyosin

Answer 18

regulatory proteins found on f actin

Question 19

what is tropomyosin

Answer 19

string like protein that wraps around g actin and covers the active sites so the myosin heads cant bind

Question 20

what is troponin

Answer 20

a protein with three subunits - t subunit, i subunit and c subunit. each one binds to something different

Question 21

what does the t subunit of troponin bind to

Answer 21

tropomyosin

Question 22

what does the i subunit of the troponin bind to

Answer 22

f actin

Question 23

what does the c subunit of troponin bind to

Answer 23

calcium ions

Question 24

what is the m line

Answer 24

the centre of the sarcomere

Question 25

what is the m line made up of

Answer 25

myomesin proteins

Question 26

what are the borders of sarcomeres called

Answer 26

the z discs

Question 27

what are the s discs made up of

Answer 27

alpha actin proteins

Question 28

where do thick filaments attach on sarcomeres

Answer 28

m line

Question 29

where do thin filaments attach on sarcomeres

Answer 29

z discs

Question 30

how many thin filaments are there for each thick

Answer 30

two

Question 31

what is the i band

Answer 31

the only thin filaments region

Question 32

where are i bands found on each sarcoemere

Answer 32

there are two half i bands at either end

Question 33

what is the a band of a sarcomere

Answer 33

the region with thick filament and thin filament

Question 34

what happens to the lines of sarcomeres when the muscle contracts

Answer 34

the thick filaments pull the thin filaments up and below it toward the m line. z discs are pulled toward m line. whole sarcomere is shorter a band does not change as it is the length of the thick filament h and i band shortens

Question 35

what is the h zone

Answer 35

the region with only thick filament

Question 36

what is maximal contraction

Answer 36

when there is almost complete overlap of thick and thin filament, and the h and i bands are almost completely gone

Question 37

describe the process of muscle contraction

Answer 37

- action potential travels along the sarcolemma and reaches the t tubule - DHP receptors stimulated - these receptors are connected to the ryanodine receptor on the SR - when DHP is stimulated and changes shape, it causes the ryanodine receptor to open - this allows calcium to flow into the sarcoplasm from the SR - these float to the thin filament and bind to C subunit of troponin - this subunit changes shape - this moves tropomyosin out of the way, allowing myosin head to bind to the g actin proteins on f actin - before myosin can bind to actin, it must power up. - the myosin head is an ATPase and releases energy to cock the head backward - it then binds to an active site - this is cross bridge formation, which is the trigger to release stored energy in the myosin head - when this happens the myosin head launches toward the m line - actin is pulled along with it - this is the power stroke - once the action potential ends the calcium ions are pumped back into the R and the subunit is no longer bound to the calcium, so the tropomyosin covers the actin once more.

Question 38

what leads to the sliding of the thin filament over the thick filament

Answer 38

combined power strokw

Question 39

what is the myosin head

Answer 39

an ATPase