Physiology of Vision - Photoreceptors and Signal Transduction

This set of vocabulary flashcards covers the retinal layers, types of photoreceptors, the chemical components and states of photopigments, and the process of receptor potentials and neurotransmitter release in vision.

Pigment portion (Retina)

The non-visual portion of the retina consisting of cuboidal cells.

Neural portion (Retina)

The visual portion of the retina containing three layers: photoreceptors, bipolar cells, and ganglia cells.

Rods

Photoreceptors used for low intensity light and night vision.

Cones

Photoreceptors used for high intensity light, day vision, and colors.

Photopigments

Substances located in the outer portion of photoreceptors that change light into electrical potentials.

Rhodopsin

The photopigment found specifically in rods, allowing for vision in low intensity light.

Opsin

A glycoprotein component of photopigments; four different types allow for variations in color.

Retinal

A derivative of Vit. A that serves as the light-absorbing portion of photopigments.

Cis-retinal

The bent form of retinal that is attached to opsin while in darkness.

Trans-retinal

The straightened form of retinal produced after cis-retinal absorbs light.

Isomerization

The activation process where cis-retinal absorbs light and "straightens" into trans-retinal.

Bleaching

The process where trans-retinal separates from opsin, leaving the opsin "colorless."

Isomerase

The enzyme that converts trans-retinal back to cis-retinal in darkness.

Cyclic-GMP

The molecule responsible for holding the $Na^+$ gates open in photoreceptors during darkness.

Glutamate

The neurotransmitter released in darkness that hyperpolarizes bipolar cells.

Transducin

The enzyme that activates phosphodiesterase (PDE) when light is present.

Phosphodiesterase (PDE)

The enzyme that breaks down cyclic-GMP, leading to the closing of $Na^+$ gates in photoreceptors.