02THE SYNAPSEPC

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THE SYNAPSE

Where nerve

impulses convert toneurotransmitters

The Sanger Institute
http://www.sanger.ac.uk/Info/News-releases/2007/070305.shtml?;decor=printablehttp://www.sanger.ac.uk/Info/News-releases/2007/070305.shtml?;decor=printable


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The synapse is where the nerve impulsepasses from one cell to the next

The electrical signal (the action potential)stops and a chemical signal takes over tocross the gap between the cells

The chemical messenger is called a

neurotransmitter The neurotransmitter crosses the gap by

diffusion, which creates a small delay

!""# $aul %illiet &'WS
http://www.saburchill.com/IBbiology/bio_hp.htmlhttp://www.saburchill.com/IBbiology/bio_hp.html


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'esigner signals

The advantage of using neurotransmitter is

that the nerve impulse can be given some

more specificity eurotransmitters can also control the

operation of the nervous system by

inhibition orexcitation

any drugs that try to cure problems in the

nervous system operate at synapses



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eurotransmitters and

hormones

In many ways neurotransmitters are

hormonesworking over a very short

distance (about !"nm) Some of them work both at synapses and

in the circulatory system



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*+ ction potential arrives at

terminal button

embrane receptor

for neurotransmitter

-a!.

channel

/esicle storing

neurotransmitter



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'ept of %iology, Saint 0ouis 1niversity


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Ca2+ Ca2+Ca2+

Ca2+

2.'epolarisationopens -a!.channels

-a!.enters terminal

button

3.-a!.stimulates

vesicles to fuse

with membrane

4.2xocytosis of

neurotransmitter

It diffuses !"nm across

the synaptic cleft



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The passage across the

synapse

n action potential travels down an axon to thetermina buttonsor synaptic knobs at the end

The action potential depolarises the membrane ofa terminal button causing !otage"gate# $a2%channesto open

-a!.ions flood into the terminal button This stimulates hundreds of synaptic vesicles,

packed with neurotransmitter, to fuse with themembrane of the terminal button

%y exocytosis The -a!.ions are then pumped out again



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&.0ocalised

depolarisation as

ions leak in or out

of membrane+

'.eurotransmitter

receptor sites on the

postsynaptic membrane

are ion channels+They open when the

neurotransmitter binds



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The passage across the

synapse

The neurotransmitter #iffusesacross cleft topostsynaptic membrane

The neurotransmitter molecules bind withspecific receptor siteson postsynapticmembrane

The receptor sites are part of a igan#"gate# ionchanne

These channels let a.ions in or 3.ions outcausing ocaise# #epoarisationof themembrane



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(.eurotransmitterdestroyed by

en4ymes in the cleft+

Stops signal being

perpetuated+

).ction potential

generated which

travels down the

postsynaptic cell+



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new action potential

If the localised depolarisations build up to thenerve cell threshold, a full action potentiawill beproduced

This will travel away, down the postsynapticneurone

The action of the neurotransmitters stops5(i) as they dilute by #iffusionin the synaptic cleft(ii) by hy#roysisthrough the action of en*ymes

there +mportant,The signal must not be perpetuated

indefinitely



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The neuromuscular 6unction

is a synapse

The motor en# pateis the terminal button

of a motor neuronethat makes contact

with a musce ce The motor end plate releases the

neurotransmitter acetychoinethat

ultimately causes the muscle cell to

contract



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