Learn happily with Scientist Cindy at www.scientistcindy.com. nicotinic acetylcholine receptors, ligand-gated sodium ion channels, voltage-gated sodium ion channels, voltage-gated calcium channels. propagation, action potential, sarcolemma, sarcomere, sarcoplasmic reticulum, muscle fiber, excitation-contraction coupling, motor neuron, motor end plate, depolarization, influx, synaptic vesicles, presynaptic, receptors, troponin, myosin, actin, tropomysin, crossbridge cycle.
initiation of muscle contraction muscle
action begins with a signal coming from
the brain this electrochemical signal is
sent from the brain down the spinal cord
to the motor neuron existing at the
neuromuscular Junction the motor neuron
at the neuromuscular Junction will then
fire an action potential the action
potential is carried as positively
charged sodium ions down the axon of the
motor neuron when these positively
charged sodium ions reach the axon
terminal this triggers the opening of
voltage-gated calcium channels when
these channels open calcium floods into
the axon terminal the presence of
calcium in the axon terminal triggers
the release of synaptic vesicles from
their docking sites then the synaptic
vesicles fuse to the presynaptic
membrane and release neurotransmitter
into the synaptic cleft the type of
neurotransmitter used at the
neuromuscular Junction is acetylcholine
acetylcholine once released will
passively diffuse across a synaptic
cleft of the neuromuscular Junction
these molecules will then bind to
nicotinic acetylcholine receptors
located on the muscle fiber nicotinic
acetylcholine receptors are ligand gated
sodium ion channels when acetylcholine
binds to these receptors the ion
channels open and sodium floods into the
muscle fiber sodium is a positively
charged ion so the ado so the addition
of sodium in the muscle fiber causes a
localized depolarization if there is
enough depolarization nearby
voltage-gated sodium channels will then
open when voltage-gated sodium channels
are opened there is a further influx of
positively charged sodium ions entering
the muscle fiber
this further depolarizes the muscle
fiber triggering even more voltage-gated
sodium channels to open this chain
reaction is the action potential this
action potential is then propagated
across the sarcolemma and down the t
tubules when the action potential is
propagated voltage-gated calcium
channels located on the sarcoplasmic
reticulum will open when these channels
open the sarcoplasmic reticulum releases
calcium ions into the sarcoplasm when
calcium is in the sarcoplasm it is able
to bind to troponin when calcium binds
to troponin troponin will undergo a
conformational change which pulls
tropomyosin off of the myosin binding
site now that the myosin binding site is
available for binding the crossbridge
cycle to begin
