Lecture 5: Skeletal Muscle Contraction Flashcards
connective tissue surrounding an entire muscle
epimysium
made up of several fascicles
Muscle
connective tissue surround individual fascicles
perimysium
a bundle of myofibers
fascicle
a delicate connective tissue surrounding each myofiber
endomysium
membrane of a myofiber
sarcolemma or plasmalemma
myofiber is also know as a _____
muscle cell
muscle cells are _____ in reference to an important organelle
multinucleated
individual multinucleated muscle cell
myofiber
a chain of sarcomeres within a myofiber
myofibril
actin and myosin filaments that make up a sarcomere
myofilament
T-tubules are inside what type of cells
muscle cells
_____ spans from the sarcolemma to ____ of the sarcoplasmic reticulum and forms _____ with it
T-tubules reach down close to cisternae and form triads
1 triad = 1 tubule & 2 cisternae on either side
How many triads are present in each sarcomere?
2
name the 4 major landmarks in sarcomeres
Z-lines — on each side of sarcomere
I-bands
A-bands
H-bands
which bands of the sarcomere change width in contraction and which do not?
H-band, I-band = change width
A-band = does not change
I-bands are composed of?
actin
A-bands are composed of?
actin and myosin
H-bands are composed of?
myosin
Z-lines are made up of?
actin filaments
what does the M line refer to in a sarcomere?
the middle line when the sarcomere is in a contracted state
H band is part of the ___ -band that is not overlapped in a relaxed state
a-band
which band disappears in a contracted state and why?
H-band
because actin and myosin now overlap, the H-band is the region of no overlap in the myosin/A-band
going from one side of a sarcomere to the other name the lines/bands in order
Z-line to I-band to A-band –>H-band (center of A)–>continuation of A-band to I-band to Z-line
sarcomeres are aligned to produce a banding pattern which is a major characteristic of what type of muscle?
striated muscle
in a muscle contraction, does myosin or actin require ATP to release?
myosin requires ATP to release actin
when does a contraction stop?
when ATP-dependent calcium pumps sequester calcium ions back into sarcoplasmic reticulum
what is the first step in muscle contraction?
arrival of an action potential to terminal end of nerve fiber/alpha motor unit
what receptor on the SR, undergoes conformational change in order for calcium ions to be released?
ryanodine receptors
increasing Ca concentration in the cytosol will …..?
activate the sliding filament mechanism
sarcoplasmic reticulum calcium ATPase
SERCA
uses ATP to pump Ca back into the SR
SERCA
does SERCA utilize active or passive transport of Ca into the SR?
active transport
the Ca concentration is higher inside the SR, so it must move Ca up it’s concentration gradient
maintains optimum Ca concentration gradient to facilitate the return of Ca into the SR
calsequestrin
helps out so that SERCA doesn’t have to work so hard to get Ca back inside SR
describe DHP receptors
located on t-tubules — voltage sensitive
allow small amounts of Ca into cytosol
cause conformational change to ryanodine receptors
describe ryanodine receptors
Ca release channels
located on cisternae of SR
open due to conformational change caused by DHP
allowing Ca into cytosol from SR
load on a muscle in the relaxed state, no contraction has occurred
pre-load
preload generates ____?
passive tension
load the muscle works against
afterload
force generated by muscle is greater than the afterload
isotonic contraction
force generated by muscle is less than the afterload
isometric contraction
active tension is produced by…?
produced by cross-bridge cycling
this refers to the contracting and re-tracting of the sliding filaments continuously
cross-bridge cycling
cross-bridge cycling will continue until…..?
Ca is recaptured or ATP depleted
sarcomere at _____ micrometers
tension = 0
3.5
no actin overlap
sarcomere at ____ micrometers
tension = maximum
all actin cross-bridges overlapped
2.2
sarcomere at _____ micrometers
actin filaments touch
1.65
tension = maximum
sarcomere at _____ micrometers
actin filaments overlap
<1.65
tension = dropping to zero
sarcomere length at rest
2.0 micrometers
where is ATP required through one cycle of contraction/relaxation?
ATP is required for myosin to release actin
SERCA requires ATP to sequester Ca
concentration of ATP allows 1-2 second contraction
ATP is muscle fiber
phosphocreatine
releases energy fast by transferring P bond from phosphocreatine to store ADP
concentration of ATP allows 5-8 second contraction
phosphocreatine ATP release
concentration of ATP allows 60 second contraction
glycolysis ATP release
concentration of ATP allows >1 min contractions
aerobic metabolism
> 95% of all energy needed for long term contraction is derived from this pathway
aerobic metabolism
an increase in tension but no mvt of muscle fibers
isometric contraction
increase in tension results in changing of muscle fiber lengths
isotonic contraction
other names for fast twitch fibers
white fibers
light fibers
characteristics of white fibers
contract rapidly fatigue quickly anaerobic respiration few mitochondria little myoglobin
other names for slow twitch fibers
red fibers
dark fibers
characteristics of red fibers
contract slowly fatigue slowly aerobic respiration many mitochondria high myoglobin conc. = gives it red color
how can fibers and fibrils be changed after birth?
# of fibers cannot be increased # of fibrils can be increased
lost muscle tissue is replaced by….?
scar tissue = fibrous CT
a neuron plus all the myofibers it innervates
motor unit
relate the all or none principle to motor units
all fibers within a motor until will contract
but
not all motor units will fire
additional contractions that occur before Ca ions have been recaptured
summation
if frequency of _____ is fast enough, no ______ time will exist between ______ . result?
frequency
no relaxation time between contractions
result:
tetany - muscle remains maximally contracted
fulcrum in center
in and out forces move in opposite directions
1st class lever teeter totter
another name for out force
resistance
out force in center
in and out force on same side of fulcrum
2nd class levers
another name for in force
effort
in force in center
in and out force on same side of fulcrum
in and out force move in same directions
3rd class levers designed to move things more rapidly
