muscle contraction Flashcards
what is the function of myoepithelial cells
expel secretions from glandular acini
what are pericytes
smooth muscle like cells that surround blood cells
what are myofibroblasts
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
what is atrophy
decrease in the size of an organ
what are myocytes
muscle cells
what does the sarcolemma do
make t tubules that project downward to the centre of the muscle fibre
what is the functional unit of myocytes
sarcomere
what is the sarcoplasm
the cytoplasm of a myocyte
what does the sarcoplasmic reticulum do
stores calcium and runs parallel to t tubules
what is found within the sarcoplasm
myofibrils that consist of contractile proteins and regulatory proteins
what do contractile proteins consist of
thick myosin and thin actin filaments
what is thick myosin
hundreds of myosin proteins
what are actin filaments
small globular proteins made from g actin
what is found on each g actin that forms the actin filaments
an active site that the myosin heads bind to during contraction
what do g actin form
a filament that looks like a long helix structure
what is f actin
the long helix structure formed by the combination of g actin
which proteins are found on f actin
troponin and tropomyosin
what are troponin and tropomyosin
regulatory proteins found on f actin
what is tropomyosin
string like protein that wraps around g actin and covers the active sites so the myosin heads cant bind
what is troponin
a protein with three subunits - t subunit, i subunit and c subunit. each one binds to something different
what does the t subunit of troponin bind to
tropomyosin
what does the i subunit of the troponin bind to
f actin
what does the c subunit of troponin bind to
calcium ions
what is the m line
the centre of the sarcomere
what is the m line made up of
myomesin proteins
what are the borders of sarcomeres called
the z discs
what are the s discs made up of
alpha actin proteins
where do thick filaments attach on sarcomeres
m line
where do thin filaments attach on sarcomeres
z discs
how many thin filaments are there for each thick
two
what is the i band
the only thin filaments region
where are i bands found on each sarcoemere
there are two half i bands at either end
what is the a band of a sarcomere
the region with thick filament and thin filament
what happens to the lines of sarcomeres when the muscle contracts
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
what is the h zone
the region with only thick filament
what is maximal contraction
when there is almost complete overlap of thick and thin filament, and the h and i bands are almost completely gone
describe the process of muscle contraction
- 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.
what leads to the sliding of the thin filament over the thick filament
combined power strokw
what is the myosin head
an ATPase
