lecture 15- visual system sensory III Flashcards
Optic disk (blind spot)
area where optic nerve and blood vessels leave the eye
lens
bends light to focus it on the retina
Zonules
attach lens to ciliary muscle
pupil
changes amount of light entering the eye
retina
layer that contains photoreceptors
sclera
is connective tissue
how does light enter the eye
the cornea and lens focus light rays onto the retina
specialized cells in the retina (photoreceptors) transduce light energy into an electrical signal
a network of neurons collect electrical signals to be transmitted along the optic nerve to the brain
how is light refracted when it enters the eye?
refracted twice
2/3 cornea (large difference in refractive index)
1/3 by lens (large curvature)
accomodation
the lens can change its shape to focus onto the retina
(due to contraction and relaxation of the ciliary muscle
ciliary muscle
a right of smooth muscle surrounding the lens
presbyopia
loss of accommodation due to loss of elasticity
what happens when ciliary muscle is relaxed
the lens is flattened
–> more distant objects are focused on the retina
when ciliary muscle contracts
the lens is rounded
–> closer objects are focused on the retina
concave lens
scatters light rays (diverges)
convex lens
light rays diverge
Light from center of field of view is focused on the
fovea
area of most acute vision and center of visual field
fovea and macula
does the fovea have neurons or blood vessels?
no
Rods and cones
sensory cells (photoreceptors)
- transduce light energy into electrical signal
- only produce graded potentials
Bipolar cells, amacrine cells, horizontal cells
- connect sensory cells to transmitting cells, process and integrate information, converge signals from several photoreceptors
Ganglion cells
transmitting cells (output to CNS)
- carry information via the optic nerve to the brain
- produce action potentials
info from —- rods and cones converges on —– ganglion cells
100 million rods and cones
1 million ganglion cells
the size of the receptive field depends on…
the location on the retina
compare ganglion cell receptive fields in the periphery vs in the fovea
ganglion cells in the periphery have large receptive fields
ganglion cells in the fovea have very small receptive fields