rod spherule


rod spherule 

The onion-shaped synaptic terminal of a rod photoreceptor located in the outer molecular (plexiform) layer of the retina. There is a deep pit (invagination) in the base of the terminal, which contains the dendrites of bipolar and horizontal cells, often two of each. The neurotransmitter is glutamate, which is stored in vesicles contained in the terminal, and when the photoreceptors are stimulated by light the release of glutamate is decreased. See rod cell; hyperpolarization; neuro-transmitter.