Neurotransmitters are extremely important because they are the agents of chemical signaling between neurons. Neurotransmitters are too big to cross the blood brain barrier, so they are created within neuron axon terminals and stored in vesicles at these terminals. In these vesicles, they await the signal for their release into the synaptic cleft.
There are two kinds of neurotransmitters: excitatory and inhibitory. You can think of excitatory neurotransmitters like a caffeinated beverage: they can excite and increase the firing of action potentials. On the other hand, inhibitory neurotransmitters are like chamomile tea: they can calm down and reduce the firing of action potentials.
Neurotransmitters are either inhibitory or excitatory. Image: Daniela Gamba
Take glutamate, for instance. Glutamate is one of the most important neurotransmitters in the nervous system. Glutamate is excitatory, so when a neuron receives glutamate, an action potential is more likely to fire. Conversely, GABA is a significant inhibitory neurotransmitter. When it is received by the postsynaptic neuron, an action potential is less likely to occur.
We can compare the “lifespan” of neurotransmitter molecules to students going to elementary school! Let’s have a neuron cell represent a neighborhood and a molecule of neurotransmitter represent a student. The student wakes up in the morning and gets ready to go to school. A school bus picks up the student and takes them to school. This is quite similar to how a neurotransmitter is synthesized and packaged into a vesicle within a neuron. After the neurotransmitter is synthesized, the vesicle transports the neurotransmitter to the terminal bouton of the axon, paralleling the student’s bus ride from their neighborhood to school.
Gabby ( a GABA molecule) waking up and getting ready at the house
Gabby gets loaded onto the bus (a vesicle)
Gabby gets off the bus and rushes towards school (leaving neighborhood = leaving presynaptic neuron)
//GABA looks sort of like a caterpillar so that could be the inspiration for "Gabby"
//From Google, a GABA molecule
Overall, the release of neurotransmitter into the synaptic cleft is a highly regulated process because the neuron receiving neurotransmitters is very sensitive to the concentration of neurotransmitters. Thus, there are many ways that the concentration of neurotransmitters in the synaptic cleft is regulated. There are actions that the presynaptic neuron can do like recycling the neurotransmitters in the cleft that are not being used. This is called reuptake. In addition, there are some agents located in the cleft that have the sole job of destroying stray neurotransmitters.
Visual of molecules being recycled
//Could be cute to make it a play on the 3 Rs (reuptake as the "4th R")
Destroyed in Synaptic Cleft
A visual of getting destroyed in the cleft (some sort of predator/prey vibe potentially or something more light hearted and fun and less violent)
Communication in the brain depends on neurotransmitters. Action potentials are graded results of how many excitatory and inhibitory neurotransmitters bind to receptors on the postsynaptic neuron.