Neuroscience - Synaptic Transmission & Neurotransmitters

The initial step of chemical synaptic transmission where an action potential depolarizes the presynaptic axon terminal membrane, opening voltage-gated calcium channels.

Depolarization opens voltage-gated ${\text{Ca}}^{2+}$ channels, driving intracellular ${\text{Ca}}^{2+}$ elevation down its electrochemical gradient to trigger vesicle exocytosis.

Synaptotagmin acts as the primary ${\text{Ca}}^{2+}$ sensor. Upon binding ${\text{Ca}}^{2+}$, it triggers the SNARE complex (v-SNARE Synaptobrevin; t-SNAREs Syntaxin and SNAP-25) to catalyze membrane fusion and exocytosis.

Transmembrane ion channels that open directly upon binding a specific neurotransmitter, producing rapid, short-duration postsynaptic responses (e.g., Nicotinic ACh, AMPA, NMDA, ${\text{GABA}}_A$).

Seven-transmembrane domain receptors that activate intracellular G-proteins and second messenger cascades upon ligand binding, producing slower, longer-lasting postsynaptic effects.

The primary excitatory neurotransmitter in the central nervous system (CNS). Synthesized from glutamine by glutaminase and removed from the synaptic cleft primarily by astrocyte EAAT transporters.

An ionotropic glutamate receptor permeable to ${\text{Na}}^{+}$ and ${\text{K}}^{+}$ (and sometimes ${\text{Ca}}^{2+}$). Responsible for the fast component of the excitatory postsynaptic potential (EPSP).

An ionotropic glutamate receptor permeable to ${\text{Ca}}^{2+}$, ${\text{Na}}^{+}$, and ${\text{K}}^{+}$. Blocked by ${\text{Mg}}^{2+}$ at resting membrane potentials; requires both glutamate binding and membrane depolarization to unblock ${\text{Mg}}^{2+}$, acting as a coincidence detector.