Related Experiment Video
Updated: Jul 14, 2026

Recording Light-evoked Postsynaptic Responses in Neurons in Dark-adapted, Mouse Retinal Slice Preparations Using Patch Clamp Techniques
Published on: February 11, 2015
Mechanisms of tonic, graded release: lessons from the vertebrate photoreceptor
1Department of Neurobiology and Anatomy and the Graduate School of Biomedical Sciences, University of Texas Medical School at Houston, 6431 Fannin Street, Houston, TX 77030, USA. ruth.heidelberger@uth.tmc.edu
Abstract:
The release of neurotransmitter via exocytosis is a highly conserved, fundamental feature of nervous system function. At conventional synapses, neurotransmitter release occurs as a brief burst of exocytosis triggered by an action potential. By contrast, at the first synapse of the vertebrate visual pathway, not only is the calcium-dependent release of neurotransmitter typically graded with respect to the presynaptic membrane potential, but release can be maintained throughout the duration of a sustained stimulus. The specializations that provide for graded and sustained release are not well-defined. However, recent advances in our understanding of basic synaptic vesicle dynamics and the calcium sensitivity of the release process at these and other central, glutamatergic neurons have shed some light on the photoreceptor's extraordinary abilities.
Related Concept Videos
Photoreceptors and Visual Pathways
G-Protein Gated Ion Channels
Sensory organs,...
Channel Rhodopsins
Rhodopsins belong to the family of cell surface proteins called G-protein coupled receptors,...
The Retina
Graded Potential
Graded potentials fall into two categories: depolarizing and hyperpolarizing. Depolarizing graded potentials typically occur when sodium (Na+) or calcium...
Relaxation of Skeletal Muscles
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.

