E-C Coupling Flashcards
how many neuromuscular junctions does a single muscle fibre have
which neurotransmitter causes excitation of muscle cells
1 - a fibre is one cell
ACh
relationship of a whole muscle to a myofibril
a muscle is made of many muscle fibres packaged in connective tissue
a muscle fibre is made of many myofibrils
what are myofibrils made of
dark A bands and light I bands
what is a sarcomere
functional unit of myofibril
what makes up the A band of a sarcomere
thick filaments and the regions of thin filaments that overlap them
where are thick filaments found in a sarcomere
A band only
what is the H zone of a sarcomere
region of the A band where thin filaments do not overlap with the thick filaments
what is the M line of a sarcomere
the line down the middle of the H zone
what is the I band of a sarcomere
the region between two sarcomeres made of only thin filaments
what is the Z line of a sarcomere
a cylindrical disc of thin filaments that joins two sarcomeres
what proteins make up a thin filament
actin, tropomyosin and troponin
structure of F-actin
double stranded helix
structure of tropomyosin
two thread like molecules double helix around actin covering myosin binding sites
structure of troponin
heterotrimer
troponin T binds to tropomyosin
troponin C binds to Ca2+
troponin I binds actin and inhibits contraction
structure of myosin
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
where does the energy for muscle contraction come from
ATP hydrolysis
what causes muscle contraction
an increase in Ca2+ triggers contraction by removing the inhibition of cross-bridge cycling
what causes a muscle to relax
decrease in intracellular Ca2+
explain the 5 stages of the cross-bridge cycle
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
what effect does contraction have on the regions of a sarcomere
A band - same width
I band - shortens
H zone - shortens
Distance between Z lines - shortens
explain rigor mortis
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
how do action potentials reach myofibrils on the interior of a fibre
T (transverse) tubules
invaginations of the membrane
sarcoplasmic reticulum role
muscle equivalent of ER, acts as storage for intracellular free calcium ions
what causes the latent period between AP onset and contraction onset
time is required for:
AP travelling through T tubules
calcium release from SR
cross bridge cycle initiation
generation of tension
