sarcolemma
cytosol of a muscle cell
sacroplasm
cytoplasm of a muscle cell
sarcomere
gives striation to the muscle cell
made up of thick and thin filaments
fundamental to muscle contraction
motor unit
= 1 motor neuron + all the muscle fibers the neuron innervates
those with fewer muscle fibers are better for precise movement
characteristics of muscle fibers
excitability
contractibility
extendability
elasticity
parts of a sarcomere
A-band I-band H-zone M-line Z-line
A-band
myosin filaments
I-band
actin filaments and Z-line
H-zone
area of myosin that DOESN’T overlap
M-line
middle of myosin filament
Z-line
anchored actin filament
what changes in the sarcomere when a muscle contracts?
z-lines move closer together
I-band shortens
H-zone disappears
what are thin filaments mostly made of?
actin filaments
what are thick filaments mostly made of?
myosin
anatomy of myosin
head: binds actin
neck and tail: have variable lengths
which myosin type is present in muscles?
myosin II
myosin II
aka muscle myosin
has very long tail region that gives the structure of thick filaments
myosin I
acts as an anchor between the cell membrane and the cytoskeleton
myosin V
transports various cargo molecules
one of the main transport molecules
proteins involved in regulating access to myosin binding sites
troponin
tropomyosin
tropomyosin
binds and obscures myosin binding sites
troponin
respond to calcium ions
troponin subunits
TnC: binds to calcium ions
TnI: interacts with actin and obscures the binding site
TnT: interacts with tropomyosin
proteins responsible for changes in intracellular calcium ion concentration
ATPase SERCA sodium/calcium reversible exchanger L-type calcium channel RyR
ATPase
actively transports calcium ions outside the cell
SERCA
actively transports calcium ions from the sarcoplasm into the sarcoplasmic reticulum (SR)
sodium/calcium reversible exchanger
moves sodium and calcium either inside or outside the cell
L-type calcium channel
first responder to voltage changes across the sarcolemma
RyR
calcium channel that allows calcium to rapidly exit the SR
is where most of the intracellular calcium comes from
factors that determine the force of muscle action
the length of the muscle fiber before stimulation
the number of recruited motor units
the frequency of neuronal stimulation
summation
stimuli of increasing frequency that result in combining individual twitches
which type of muscle is NOT striated?
smooth (visceral) muscle
fast twitch muscle
reaches depolarization faster because of the number and the properties of the present sodium and calcium channels
slow twitch muscle
has slower depolarization and a longer contraction cycle
cardiac muscle
contraction is similar to slow twitch muscles, but differs in repolarization
what stimulates contraction of cardiac muscle?
pacemaker cells
what forms connections between the cytoplasms of two cardiac muscle cells?
desmosomes
gap junctions
which type of muscle has NO organized sarcomeres?
smooth (visceral muscle)
