The Eye

Flashcards covering key vocabulary and concepts about the eye and visual processing.

Pupil

The opening in the center of the iris that allows light to enter the eye.

Visual Acuity

The ability of the eye to distinguish two nearby points.

Accommodation

The process by which the eye changes its focus from distant to near objects, accomplished by the lens.

Photoreceptors

Specialized cells in the retina (rods and cones) that detect light and convert it into electrical signals.

Rods

Photoreceptors that are sensitive to low light levels and do not detect color.

Cones

Photoreceptors that function in bright light and are responsible for color vision.

Neural Retina

The part of the retina containing photoreceptors and synaptic connections for processing visual information.

Ganglion Cells

Cells in the retina that receive input from bipolar cells and send information to the brain via the optic nerve.

Center-Surround Antagonism

A mechanism in which stimulation of the center of the receptive field activates ganglion cells while stimulation of the surround inhibits them.

Color Opponency

Theory where the perception of color arises from the antagonistic responses to pairs of colors (e.g., red-green, blue-yellow).

Peripheral retina

Location for rods

Central retina

Location for cones

Rod membrane potential in darkness

-30mV • Na+ channels are open, causing influx of ions • “Dark current” • Voltage-gated Ca channels open • Neurotransmitters released

Rod membrane potential in light

• -60mV (hyperpolarize) • Rhodopsin activated by light • Na+ channels close, no ion flow • Voltage-gated Ca channels close • Neurotransmitter release stops

Dark adaptation

• “getting used to the dark” • Reaching peak rod sensitivity • Caused by • Pupil dilation • Regeneration of rhodopsin

Light adaptation

• “getting used to bright light” • Caused by • Reversing dark adaptation • Ca2+ stops entering the cell, stops G-protein signaling pathway (this pathway requires Ca2+)

Cone membrane potential in darkness

• -40mV • Na+ channels are open, causing influx of ions • “Dark current” • Voltage-gated Ca channels open • Neurotransmitters released

Cone membrane potential in light

• -60mV (hyperpolarize) • Conopsin activated by light • Na+ channels close, no ion flow • Voltage-gated Ca channels close • Neurotransmitter release stops

Receptive field

the area of the retina (or other sensory organ) that, when stimulated, changes neuronal membrane potential

P cells (detail)

• 90% of cells • Small receptive fields • Slower action potential propagation • Sustained discharge of APs • Respond less to low-contrast stimuli • Color opponency

M cells (motion)

• 5% of cells • Large receptive fields • Faster action potential propagation • Transient burst of APs • Respond more to low-contrast stimuli • Lack color opponency