Block 3 Flashcards
sclera
- tough, outer layer of the eye
- Gr. skleros, hard
cornea
- transparent, focusing apparatus of the eye
- performs 2/3 of the light bending
- is innervated by many nerve endings
lens
- performs the final 1/3 of light bending for proper focus
- shape controlled by the ciliary muscles
ciliary muscles
- control the shape of the lens
- by contracting they cause the lens to become more convex which sharpens the visual image on the retina
accommodation
The change in the shape of the lens is controlled by the ciliary muscles inside the eye. Changes in contraction of the ciliary muscles alter the focal distance of the eye, causing nearer or farther images to come into focus on the retina; this process is known as accommodation.
what controls how much light enters the eye by adjusting the size of the pupil?
-the smooth muscles of the iris
aqueous humor
-fills in the space in front of the lens and between the iris and the lens
vitreous humor
fills in the space between the lens and the retina
what muscles control eye position in the socket?
-extraocular skeletal muscles
retina
- is part of the CNS and derived from neural tube
- laminated and 250 microns thick
- 3 primary cell layers arranged inside out
the pigmented epithelium behind the retina
- absorbs light to prevent backscatter
- recycles retinal as part of the transduction process
- possesses tight junctions and forms a blood-retina barrier
name the principle cells of the retina
- photoreceptors: rods and cones
- local circuit neurons: bipolar, horizontal, and amacrine
- projection neurons: ganglion cells
fovea
- point of the retina with the highest visual acuity
- it lies in the center of the retina (aka the macula )
- there is a higher density of photoreceptors there
papilla
aka optic disk
- where axons of ganglion cells are bundled to form optic nerve
- since no photoreceptors are there, there is a blind spot
direct vertical pathway
-from photoreceptor to bipolar to ganglion cell
indirect lateral pathway
-involves horizontal spread of information through local circuit neurons, the horizontal and amacrine cells
what is the overall convergence ratio of rods and cones to ganglion cells
100 to 1
what photoreceptor dominates at the fovea?
cones
name the ways to increase visual acuity
- absence of intervening cells
- increased density of photoreceptors
- high concentration of cones
- low degree of convergence from photorecetors to ganglion cells
visual field
-part of the environment impinging upon the whole retina at any one time
binocular field
-subset of the visual field that impinges upon both eyes at the same time
monocular field
-parts of the visual field outside of the overlap of the binocular field
retinal field
- reversed image of the visual field that is projected onto the retina
- medial part: nasal field
- lateral: temporal field
receptive field
-part of the retina that when stimulated by light alters the electrical activity of a neuron