7/28/2019 Paper 2 Synapse Chemical Reaction of Muscular Contraction

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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