Nerve Junctions Flashcards
What is a neurotransmitter?
chemical that diffuses across cleft of synapse to transmit signal to post synaptic neurone
What is a synapse?
junction between 2 or more neurones
What are cholinergic synapses?
ones which use acetylcholine as their transmitter substance
What is the synaptic knob?
swelling at end of pre synaptic neurone
Approximately how wide is the synaptic cleft?
20nm wide
What does the presynaptic action potential cause?
the release of neurotransmitter which diffuses across gap to generate new action potential in post synaptic neurone
What specialised features does the synaptic knob contain?
many mitochondria (active process using ATP occurs), lots of SER, vesicles of acetylcholine, voltage gated calcium ion channels in membrane
How is the post synaptic membrane specialised?
contains specialised Na+ channels that can respond to neurotransmitters, channels are 5 polypeptide mols, 2 mols are receptor with complementary shape to acetylcholine, when it binds the channels open
What happens in the synaptic knob before the neurotransmitter can be released?
action potential arrives, voltage gates calcium ion channels open, Ca2+ diffuse in, cause synaptic vesicles to move and fuse with presynaptic membrane
How is acetylcholine released? What does it do once released?
By exocytosis, mols diffuse across cleft, bind to receptor sites in post synaptic neurone, Na+ channels open
What happens when the sodium ion channels open on the post synaptic membrane?
Na+ diffuse across membrane into post synaptic neurone, generator potential or excitatory postsynaptic potential (EPSP) created, if sufficient generator potentials combine then threshold potential reached = new action potential
What is acetylcholinesterase?
enzyme in synaptic cleft, hydrolyses acetylcholine to ethanoic acid and choline
What does the breakdown of acetylcholine do?
stops the transmission of signals so synapse does not continue to produce action potentials in the post synaptic neurone
What happens to the ethanoic acid and choline?
recycled, re enter synaptic knob by diffusion and recombined into acetylcholine using ATP, stored in vesicles for future use
