7/28/2019 Paper 2 Synapse Chemical Reaction of Muscular Contraction
1/1
Elizabeth D. Neil
Due: Monday, June 18, 200
Synapse Chemical Reaction of Muscular Contraction
Start/End
Process
Action
Flow Direction
The nerve cellgets excited
Dendrites on thenerve cell in the
spinal cord receivemessages from
another nerve cell
The nerve cell sendsthe action potential
(electrical signal) downthe axon to the axon
terminal (bulb)
This opening growsuntil the vesicle
membrane collapsesand releases the
neurotransmittersinto the
Synaptic Gap(exocytosis)
The empty vesicleis broken down
and processed inthe cell body
Ionic channelson the
membrane openor close
dependent onthe mv reached
When it reaches theaxon bulb,
Depolarization causesvoltage-gated calcium
(Ca2+) channels areactivated and opened,and calcium rushes in
(influx)
Ca2+
causes thevesicles withneurotransmitters tofuse with presynaptic
membrane
The vesiclemembrane and the
pre-synapticmembrane connect
to form a smallopening
The vesicularmembrane pinches offfrom the pre-synapticplasma membrane to
form a new, emptyvesicle
Myosin headsbind to thepassive actin
filaments at themyosin binding
sites
Initially the muscle isin a resting state
where thin strands ofa protein (tropomyosin) are wrapped aroundthe actin filaments,
blocking the myosinbinding sites
Theintroduction of
calcium intothe muscle cell,ions then bind
to troponinmolecules
Troponin isattached to thetropomyosin
Calcium Ionbinding changes
the shape oftroponin and
movestropomyosin to
expose the myosinbinding sites on
the actin
Myosin binds tothe exposed
binding sites
The empty vesicleis recycled
Vesicles containingthe
neurotransmitter(acetylcholine)to
move to the pre-synaptic
membrane
Theneurotransmitterstravel to and bind
with the receptorson the muscle cell
(postsynaptic cellmembrane)
Depolarizationactivates voltage-
dependent calciumchannels in the T-tubule membrane
The actualmuscular
contraction beginsVia the sliding-
filamentmechanism
When re-energized by
ATP, themyosin head
detaches fromthe actin
filament, and isready to attachand bend again
Once the
head bends,the myosin
loses energy,and remainsattached to
the actin (thinfilament)
As soon as themyosin head onthe thick
filaments bindsto actin, the
head bends atits hinge
The resultingactions contractthe muscle fiber
The myosinheads all move in
the samedirection so
collectively theymove the actin
filament relativeto the myosin
filament
The action potentialtravels down a
network of inward-projecting T-tubulesthat reach deep into
the muscle fiber
Neurotransmitteris synthesized and
then stored invesicles within the
axon