Lec 15 Flashcards
Light pathway
1- cornea
2- aqueous humor
3- pupil
4- lens
5- vitreous fluid
6- retina (fovea)
Optic nerve
Primary neurons axon
Optic disk
Anatomical blind spot
No photoreceptor
Light is focused by
Light is bend by
Cornea (2/3)
Lens (1/3) changeable shape
Photoreceptors
Specialized cell in retina that transduce light energy to electrical signal
Eye lens is
Convex
Converging light rays on focal point
Focal point=fovea on retina
Light must be focused on ——— for clear vision
Retina
How?
Lens change its shape by accommodation
Accommodation is due to
Due to Contraction and relaxation of ciliary muscles
Ciliary muscle
Ring of smooth muscle surrounding the lens
Ciliary muscle is connected to lens by
Ligaments
When ciliary muscle is relaxed,
Lens is flattened—more distant objects can be seen
When ciliary muscle is contracted m,
Lens is rounded—closer objects can be seen
Presbyopia
Loss of accommodation due to loss of lens elasticity
Macula
Super-focused region
In the middle is fovea
Fovea
Free of neurons and blood vessels
Cells in order from vitreous space
1- retina ganglion cell—neurons
2- amacrine cell
3- bipolar neurons—intermediary
4- horizontal cell
5- cone/rods—photoreceptors
6- retina pigment epithelium—melanin absorbs excess light
Rods and cons
Sensory cell/photoreceptors
Light energy—>Electrical energy
Produce Graded potential(release neurotransmitters)
Rod is dim light
Con is bright light
Bipolar-amacrine-horizontal cells
-Connect sensory cells to neurons
-Converge signal from several receptors
Ganglion cells
-Transmitting cells (output to CNS)
-Carry information via optic nerve to brain
-produce AP
Periphery of retina vs center of retina
Periphery:
— many bipolar cells are synapses with one ganglion cell (bigger receptive field)
Center of fovea:
— one ganglion cell is synapsing with one bipolar cell (very small receptive field)
Old disks at tip of cons/rods are
Phagocytized by pigment epithelial cells
Outer segment of photoreceptors
Light transduction takes place using visual disks
Inner segment photoreceptors
Location of major receptors and metabolic operations
Synaptic terminal
Synapses with bipolar cells
Disks are activated by ———
Light
Disks have ——— which are ——— that are activated by ———
1- opsin in rhodopsin
2- GPCR
3- light
Rhodopsin
=Opsin + Retinal
Photopigment that is signal transducer
Cones are responsible for
Sharp vision
Color vison
3 different types of cones
-Each has different photopigment
-Respond to specific color (red/blue/green)
Retinal
11-cis retinal
Visual pigment
Derivative of vitamin A
When opsin and retinal are tightly bound, rhodopsin is
Inactive
11-cis retinal
Inactive—kinked—required
Change to active by light
All-trans retinal is active
G protein in rods
Gtransducin
Phototransduction in Rods in darkeness
1-Retinal(11-cis) and opsin is bound
2-Rhodopsin is inactive
3-PDE is inactive
4-cGMP level inside the cell are high
5-CNG channels are open (Ca will move in)
6-Rod cells are depolarized
7-Voltage-gated Ca channel are open
8-Ca into cell
9-Neurotransmitter=glutamate is released
Phototransduction in Rods in light
0-Retinal photoisomerizes
0-11-cis to trans
0-cause conformational change in rhodopsin
1-Rhodopsin is activated(opsin released)
2-Activate Gtransducin
3-Active phosphodiesterase (PDE)
4-PDE break down cGMP
5-Decrease in [cGMP] will close CNG channels
6-Cell hyperpolarize (k link channel)
7-V-gated Ca channels close
8-Decrease NT(glutamate) release
9-Excite adjacent bipolar cell by removing inhibition
10-bipolar cell excite
11-receptor potential
12-bipolar cells release glutamate
13- now excitatory on ganglion cell
14- AP in ganglion cell
From optic nerve to brain
1- optic nerve
2- optic chiasm
cross happens
3- optic tract
4- lateral body
5- thalamus
6- visual cortex on occipital lobe
Glutamate is inhibory/excitatory??
Inhibitory
