Neuromodulators are a subclass of neurotransmitters that are released from a presynaptic cell and will impact the transmission of signals between a diverse population of neurons. So a point of distinction between a neuromodulator and your standard neurotransmitter, we can view the image to the bottom here. On the left we've got your standard neurotransmitter.
It's releasing a signal from the presynaptic cell. and it is binding with a target receptor on a very close and adjacent single cell, as opposed to the image to the right where we've got neuromodulators, again, released from a presynaptic cell. But this time, we're impacting potentially tens of thousands of cells across a broad area of brain tissue. So... Just to give a bit of context to what's upcoming in terms of talking about the difference between neurotransmitters and neuromodulators, let's just do a quick review of the processes involved in synaptic transmission.
So up the top here we've got your sending neuron, the presynaptic cell, and each job is to basically house those neurotransmitters or neuromodulators. They're released as a result of an action. potential and they go into the junction which we call the synapse and then on the right we've got the target cell the postsynaptic one it's got a bunch of dendrites here and if we zoom in down the bottom here what we've got is a presynaptic axon terminal button the little sacks here house the neurotransmitters or neuromodulators they're released into the junction here pen right here and then they will bind with some target receptors on the postsynaptic dendrites.
So in terms of whether we classify these chemicals as neurotransmitters or neuromodulators, given there's some common ground between the two, they're both released from a presynaptic axon terminal, they're both binding with different types of receptors. Essentially the difference is all about the receptors and we have two major types. We have inotropic receptors which is what we have on the image here.
So how they work is if we look at this image here we've got some neurotransmitters released into the synapse that's this kind of blue area here and then they will bind with receptor sites. So we've got a couple here and when they do it will have a lock and key effect it will open up a ligand channel and then we have some ions which will just reside outside the cell and they'll basically permeate that cell membrane which is the skin and therefore as a result of basically the determination of whether they're positively or negatively charged that will alter the resting potential of that cell so if these ions are positively charged then when they permeate the cell because of the effects of that positive charge you'll increase their resting potential and therefore they will potentially hit an action potential threshold and they'll fire now if these ions are negatively charged then the opposite will happen their resting potential will decrease and therefore they're less likely to fire which is what we have with the case of GABA as opposed to excitatory ones like glutamide. So in the case of neuromodulators, again it's all about the receptors. They bind with metabotropic receptors and so what happens this time is we have our neurotransmitters, they will bind with the metabotropic receptors but this won't immediately open up the channel for those ions. It'll impact some of the proteins that are synthesized in terms of that post-synaptic cell.
And these proteins will impact the behavior of some of the channels. And so therefore, this will cause a more lasting, lingering effect in terms of the synthesis of these proteins that will open up these channels for these ions for a longer stretch. So if we look at the case of dopamine acting as a neuromodulator, In terms of its role in reward, addiction, etc. When it's acting as a neuromodulator, it will affect the postsynaptic cell activity.
and so this will have an impact on our behavior in terms of chasing a reward or trying to basically satisfy an urge that's been triggered from a cue that's activated the dopamine reward pathway so let's sum up here by clearly differentiating between a neurotransmitter and a neuromodulator a neurotransmitter will bind with an inotropic receptor and so therefore four we have if we think about a presynaptic cell it's releasing a neurotransmitter and it will bind with a receptor that is very close and just affect that one target cell the effect will be almost instantaneous within a thousandth of a second that cell will either fire or inhibited depending on what's going on with the ions that permeate that cell whether they're positively negatively charged now with a neuromodulator this time the modulator is binding with a metabotropic receptor. And so therefore, these cells are potentially far away. They cover a large area of brain tissue.
And rather than just targeting one cell, they can potentially impact up to 100000 neurons. And so therefore, consequently, because the effect is more indirect in terms of changing. some of the properties of the postsynaptic cell will get a more lasting lingering effect in terms of that behavior. So examples of neurotransmitters, again I'll repeat, include GABA, glutamate, they're the main two ones we learned in the VCE course, and in terms of examples of your neuromodulators, we're going to look at serotonin in depth in terms of its impact on mood, and dopamine in terms of the reward pathway.