Final answer:
Photoreceptors in the retina, including rods and cones, respond to light and exhibit spontaneous, graded release of inhibitory neurotransmitter through a process called a receptor potential, affecting the activity of bipolar and ganglion cells in the visual system.
Step-by-step explanation:
Cells that respond to light and show spontaneous, graded release of inhibitory neurotransmitter (NT) are known as photoreceptors in the retina. These photoreceptors include rods and cones, which continuously undergo tonic activity. They are slightly active even in the absence of light, maintaining a baseline firing rate. The release of NT in these cells occurs through a process called a receptor potential. In darkness, rods and cones inhibit bipolar cells. When exposed to light, they become hyperpolarized, lifting the inhibition off the bipolar cells, which in turn can stimulate the ganglion cells to send action potentials to the brain.
Bipolar cells and ganglion cells are part of the signal transmission pathway in the visual system. In this system, graded potentials play a crucial role in shaping the response to light stimuli. For example, the binding of neurotransmitter to ligand-gated ion channels can result in graded potentials, influencing the activity of neurons and the visual signal perceived. Additionally, variations in the neurotransmission process can be attributed to different types of receptors such as iGluRs (ionotropic glutamate receptors) and GABA(A) receptors, which modulate synaptic transmission and plasticity and are essential for functions like memory and learning.