Neuronal Synapses Signal Propagation: The Movement of Signals Between Neurons: There can be a lot of different pre and postsynaptic neurons at a synapse Complexin: a protein that acts as a brake to stop vesicles from fusing to the membrane of the presynaptic neuron and releasing their contents into the synaptic cleft Synaptotagmin: binds and releases complexin in the presence of calcium (which then allows for vesicle fusion across the membrane) Glutamate: the major excitatory neurotransmitter GABA: the major inhibitory neurotransmitter Synapse Structure: Chemical Synapse: has a gap between the pre and postsynaptic cells (releases chemicals) Electrical Synapse: the pre and postsynaptic cells are physically connected that have special channels known as gap junctions Neurotransmitter Release: Voltage gated Ca2+ channels open when an AP arrives, allowing for Ca2+ to flow into the cell ([Ca2+] is higher outside of the cell) Introduction of calcium causes the vesicles to fuse and allow neurotransmitter to be released into the synaptic cleft b. Types of Neurotransmitters: 3 main categories: Amino Acids: Glutamate (most common excitatory), GABA (most common inhibitory), and glycine (second?? most common inhibitory) Peptides: polymers/chains of specific amino acids (important in our perception of pain) Opioids: Monoamines: where there is a single amino group connected to an aromatic group by a 2 carbon chain (important for attention, cognition, and emotion) Includes serotonin, histamine, dopamine, epinephrine, and norepinephrine (last three are catecholamines) Catecholamines: have a catechol group on the benzene ring (2 hydroxyl groups) - Types of Neurotransmitter Receptors: Ionotropic Receptor: ligand gated ion channels that can cause either excitatory or inhibitory graded potentials Metabotropic Receptor: activate secondary messengers within the neuron (many different types such as G-protein coupled receptors, etc.) Effects may be slower, but their effects will likely be longer lasting or more widespread 1. a. 2. a. 3. a. Neurotransmitter Removal: Neurotransmitter can be removed through diffusion (if there is lower frequency of APs), enzymes (breakdown the neurotransmitter into its component parts), and special pumps (actively pump back in neurotransmitter back into the presynaptic cell - reuptake pumps) → also astrocytes can also pump neurotransmitter back in if need be (CNS) Neuroplasticity: Neuroplasticity: how the nervous system changes based on experience Potentiation: strength of information flowing through a particular section of the nervous system can increase Depression: strength of information flowing through a particular section of the nervous system can decrease