Synapses are sites of neuron-to-neuron connections. They are spaces between a presynaptic (giving information) neuron and a postsynaptic (receiving information) neuron. The synaptic connections between neurons and skeletal muscle cells are generally called neuromuscular junctions, and the connections between neurons and smooth muscle cells or glands are known as neuroeffector junctions. Neurotransmitters are brain chemicals that communicate information via electrical impulses throughout our brain and body. They relay signals between neurons (nerve cells), transmitting signals across a chemical synapse from one neuron to another "target" neuron. This process is called neurotransmission.
Source: https://www.semanticscholar.org/paper/Neurotransmitter-Receptors-in-the-Postsynaptic-Stephenson-Hawkins/6148a8948a3145d1cfe6de61a3d161235bffe9bd
Action potential travels down the axon (check out the post about the structure of a neuron). When depolarized, the signal arriving releases pre-made neurotransmitters into the synaptic cleft (space that separates 2 neurons). It happens in the following way. Neurotransmitters are packed into vesicles that fuse into the membrane. Those vesicles then become part of the membrane and the molecules of neurotransmitters are released into the synaptic cleft. They diffuse across the cleft and bind to specific molecules called receptors on the postsynaptic terminal. Ionotropic receptors (e.g., ligand-gated ion channels) open as soon as the right neurotransmitter is binded, while metabotropic receptors (G protein-coupled receptors) cause a complex chain of actions.
Neurotransmittors have been shown to have a range of different effects on human behaviour, such as mood, sleep, sexual arousal or mental illness. In Antonova’s study, male participants were asked to take part in a double-blind study, meaning that the participant and the researcher were not aware of which group they were a part of. The participants were randomly allocated to either the scopolamine group or the placebo saline solution group. The participants were then placed into an fMRI in order to read their brain activity. They were told to play a few rounds of a virtual reality game with a joystick in order to become familiar with the controls. The game consisted of the participants being dropped in the middle of an arena and told to find a special landmark. Each round of the game started them at a different location within the arena. After a few rounds, the researchers recorded their brain activity in the next few rounds.
The participants were asked to come back after 3 to 4 weeks where they repeated the procedure. The researchers found that when participants were injected with scopolamine, they demonstrated a significant reduction in the activation of the hippocampus compared to when they received a placebo. This shows that the scopolamine actually blocked the receptors on the neuron for acetylcholine and prevented neurotransmission from taking place, thus impairing the participants’ ability to create spatial memories. It appears that acetylcholine could play a key role in the encoding of spatial memories in humans, as well as in rats.
