E-C Coupling

Question 1

how many neuromuscular junctions does a single muscle fibre have
which neurotransmitter causes excitation of muscle cells

Answer 1

1 - a fibre is one cell
ACh

Question 2

relationship of a whole muscle to a myofibril

Answer 2

a muscle is made of many muscle fibres packaged in connective tissue
a muscle fibre is made of many myofibrils

Question 3

what are myofibrils made of

Answer 3

dark A bands and light I bands

Question 4

what is a sarcomere

Answer 4

functional unit of myofibril

Question 5

what makes up the A band of a sarcomere

Answer 5

thick filaments and the regions of thin filaments that overlap them

Question 6

where are thick filaments found in a sarcomere

Answer 6

A band only

Question 7

what is the H zone of a sarcomere

Answer 7

region of the A band where thin filaments do not overlap with the thick filaments

Question 8

what is the M line of a sarcomere

Answer 8

the line down the middle of the H zone

Question 9

what is the I band of a sarcomere

Answer 9

the region between two sarcomeres made of only thin filaments

Question 10

what is the Z line of a sarcomere

Answer 10

a cylindrical disc of thin filaments that joins two sarcomeres

Question 11

what proteins make up a thin filament

Answer 11

actin, tropomyosin and troponin

Question 12

structure of F-actin

Answer 12

double stranded helix

Question 13

structure of tropomyosin

Answer 13

two thread like molecules double helix around actin covering myosin binding sites

Question 14

structure of troponin

Answer 14

heterotrimer
troponin T binds to tropomyosin
troponin C binds to Ca2+
troponin I binds actin and inhibits contraction

Question 15

structure of myosin

Answer 15

two identical golf-club shaped regions, an intertwined tail and globular heads
head contains actin binding site and an ATPase site
heads form cross-bridges

Question 16

where does the energy for muscle contraction come from

Answer 16

ATP hydrolysis

Question 17

what causes muscle contraction

Answer 17

an increase in Ca2+ triggers contraction by removing the inhibition of cross-bridge cycling

Question 18

what causes a muscle to relax

Answer 18

decrease in intracellular Ca2+

Question 19

explain the 5 stages of the cross-bridge cycle

Answer 19

ATP binding - causes dissociation of the actin myosin complex
ATP hydrolysis - causes myosin head to return to rest
Cross-bridge formation - myosin head binds to actin
Release of Pi from myosin - myosin head changes conformation resulting in filaments sliding
ADP release

Question 20

what effect does contraction have on the regions of a sarcomere

Answer 20

A band - same width
I band - shortens
H zone - shortens
Distance between Z lines - shortens

Question 21

explain rigor mortis

Answer 21

following death intracellular Ca2+ conc rises
cross bridges form binding myosin heads that were already charged before death
no ATP, so once bound cannot detach

Question 22

how do action potentials reach myofibrils on the interior of a fibre

Answer 22

T (transverse) tubules
invaginations of the membrane

Question 23

sarcoplasmic reticulum role

Answer 23

muscle equivalent of ER, acts as storage for intracellular free calcium ions

Question 24

what causes the latent period between AP onset and contraction onset

Answer 24

time is required for:
AP travelling through T tubules
calcium release from SR
cross bridge cycle initiation
generation of tension