Final answer:
The neurotransmitter used by most of the brain's excitatory ionotropic synapses is glutamate, which is pivotal for neural communication, learning, and memory.
Step-by-step explanation:
Most of the brain's excitatory ionotropic synapses use the neurotransmitter glutamate.
Glutamate is a ubiquitous anionic amino acid in all cell types and in the brain, it plays a pivotal role in signaling. It is considered the main excitatory neurotransmitter in the central nervous system (CNS), used by approximately half of the neurons. Glutamate is involved in key functions related to cognitive processes and is essential for neural communication, memory formation, and learning.
After being released into the synaptic cleft, glutamate binds to specific ionotropic receptors on the postsynaptic membrane, such as AMPA and NMDA receptors, enhancing excitatory transmission. These receptors are crucial for the depolarization of the postsynaptic neuron which is necessary for the transmission of electrical signals in the brain.