The Visual System Extends from the Eye to the Brain Flashcards
Retina
The receptive surface inside the eye that contains photoreceptors and other neurons.
Transduction
The conversion of one form of energy to another, as converting light into neuronal activity.
Cornea
The transparent outer layer of the eye, whose curvature is fixed. The cornea bends light rays and is primarily responsible for forming the image on the retina.
Figure 7.1
Structures of the Human Eye
Refraction
The bending of light rays by a change in the density of a medium, such as the cornea and the lens of the eyes.
Lens
A structure in the eye that helps focus an image on the retina.
Ciliary Muscle
One of the muscles that control the shape of the lens inside the eye, focusing an image on the retina.
Accomodation
The process by which the ciliary muscles adjust the lens to focus a sharp image on the retina.
Myopia
Nearsightedness; the inability to focus the retinal image of objects that are far away.
Figure 7.2
Focusing Images on the Retina
Extraocular Muscle
One of the muscles attached to the eyeball that control its position and movements.
Photoreceptor
A neural cell in the retina that responds to light.
Rod
A photoreceptor cell in the retina that is most active at low levels of light.
Cone
Any of several classes of photoreceptor cells in the retina that are responsible for color vision.
Figure 7.3
A.
Anatomy of the Retina
Figure 7.3
B.
Anatomy of the Retina
Bipolar Cell
An interneuron in the retina that recieves information from rods and cones and passes the information to retinal ganglion cells.
Ganglion Cell
Any of a class of cells in the retina whose axons form the optic nerve.
Optic Nerve
Cranial nerve II; the collection of ganglion cell axons that extend from the retina to the brain.
Horizontal Cell
A specialized retinal cell that contacts both receptor cells and bipolar cells.
Amacrine Cell
A specialized retinal cell that contacts both bipolar cells and ganglion cells, and is especially significant in inhibitory interactions within the retina.
Scotopic System
A system in the retina that operates at low levels of light and involes rods.
Convergence
The phenomenon of neural connections in which many cells send signals to a single cell.
Phototopic System
A system in the retina that operates at high levels of light, shows sensitivity to color, and involves the cones.
Table 7.1
Properties of the Photopic and Scotopic Visual Systems
Rhodospin
The photpigment in rods that responds to light.
Figure 7.4
Hyperpolarization of Photoreceptors
Figure 7.5
The Wide Range of Sensitivity to Light Intensity
Pupil
The opening, formed by the iris that allows light to enter the eye.
Iris
The circular structure of the eye that provides an opening to form the pupil.
Figure 7.6
The Iris Controls the Size of the Pupil Opening
Range Refraction
The means by which sensory systems cover a wide range of intensity values, as each sensory receptor cell specializes in just one part of the overall range of intensities.
Photoreceptor Adaptation
The tendency of rods and cones to adjust their light sensitivity to match ambient levels of illumination.
Visual Acuity
Sharpness of vision.
Figure 7.7
A.
Densities of Retinal Receptors and Visual Acuity
Fovea
The central portion of the retina, which is packed with the highest density of photoreceptors and is the center of our gaze.
Figure 7.7
B.
Densities of Retinal Receptors and Visual Acuity
Figure 7.8
An Unobstructed View
Optic Disc
The region of the retina that is devoid of receptor cells because ganglion cell axons and blood vessels exit the eyeball there.
Blind Spot
The portion of the visual field from which light falls on the optic disc. Because there are no receptors in this region, light striking the blind spot cannot be seen.
Figure 7.9
Experiencing the Blind Spot
Occiptal Cortex
Also called visual cortex. The cortex of the occipital lobe of the brain.
Figure 7.10
Visual Pathways in the Human Brain
Optic Chiasm
The point at which the two optic nerves meet.
Optic Tract
The axons of retinal ganglion cells after they have passed the optic chiasm; most of these axons terminate in the lateral geniculate nucleus.
Lateral Geniculate Nucleus (LGN)
The part of the thalamus that recieves information from the optic tract and sends it to visual areas in the occipital cortex.
Optic Radiation
Axons from the lateral geniculate nucleus that terminate in the primary visual areas of the occipital cortex.
Primary Visual Cortex (V1) or Striate Cortex
Also called area 17. The region of the occipital cortex where most visual information first arrives.
Binocular
“Two eyed” inputs, used for depth perception.
Extrastriate Cortex
Visual cortex outside of the primary visual (striate) cortex.
Visual Field
The whole area that you can see without moving your head or eyes.
Topographic Projection
A mapping that preserves the point-to-point correspondence between neighboring parts space. For example, the retina extends a topographic projection onto the cortex.
Figure 7.11
Location of the Primary Visual Cortex
Scotoma
A region of blindness within the visual fields, caused by injury to the visual pathway or brain.
Blindsight
The paradoxical phenomenon whereby, within a scotoma, a person cannot consciously percieve visual cues but may still be able to make some visual discrimination.
