AMPA receptors in the mammalian brain mediate fast neurotransmission and are typically found in the postsynaptic densities (PSDs). Across synapses a great variability of PSDs sizes and number of AMPA receptors has been described . In the mammalian inner ear, glutamatergic synapses are formed between inner hair cells (IHCs) and spiral ganglion neurons (SGNs). All aspects of sound information are encoded and transmitted to the brain through this synapse. A key aspect of the presynapse (IHCs) is the presence of a ‘synaptic body’ or ‘ribbon’ that concentrates large amounts of synaptic vesicles, ensuring high rates of exocytotic events. Postsynaptic terminals of SGNs are characterized by large PSDs, 5 to 10 times bigger than those found in the brain. The role that these large PSDs play in synaptic function is unknown. We speculate that normal neurotransmission activates only a portion of the PSDs area, resulting in non-saturation of the AMPA receptors. To investigate this, we recorded SGNs terminals by patch-clamp technique and used competitive antagonists (CAs) on physiological events and compared them with glutamate photolysis (GP). GP stimulates the entire post-synapse and can be modulated to produce different glutamate transients, making it possible to saturate the receptors. The block by CAs was used to calculate the relative glutamate concentration of physiological events of a wide variety of amplitudes and assess whether they are close to saturation by comparison with GP.