Special Senses: Vision Flashcards
Describe the phenomenon of Refraction.
Which structures in the eye will bend light?
This is how the eye will focus the image!
*** Light being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density
- CORNEA is the first place where the refraction can occur (account for about 2/3 of light bending); FIXED bending
- LENS is going to bend the rest of the light (depends on how round the lens is); uses the Ciliary Muscle and Suspensory Ligaments
- Far Vision –> Flat Lens (don’t need to bend light as much)
- Near Vision –> Round Lens (need to bend the light!)
Describe how you can change the shape of the lens in the eye.
Become more ROUND (globular) –> CONTRACT the ciliary muscle to RELAX the suspensory ligaments; This is for NEAR vision because there are many light rays that are converging and you need to focus them on the Retina
Become more FLAT (decrease the curvature of the lens) –> RELAX the ciliary muscle to CONTRACT the suspensory ligaments; This is for FAR vision
What happens to the lens with aging?
Becomes STIFFER and it cannot assume that natural curvature when the Ciliary Muscle is CONTRACTED
*** Lens adds about 20 diopters in young kids
*** Lens adds about 10 diopters with young adults
*** Lens might only add 1 diopter when you’re 50
Presbyopia –> “Old Eyes”, lens cannot accomodate due to age
What are some additional changes that are required for Near Vision to work?
- Contraction of the Ciliary Muscle
- Convergence of the eyes to the point of focus
- Constriction of the Pupil (allows us to focus better by getting rid of diverging light rays)
Where are the cones and rods located?
Cones –> Macula
Rods –> Around the Cones
What are the five different cell types in the retina?
- Photoreceptors
- Bipolar Cells
- Ganglion Cells
- Horizontal Cells (not involved in the process of going to the brain)
- Amacrine Cells (not involved in the process of going to the brain)
Describe the components of the Vertical Pathway.
Composed of:
- Photoreceptor
- Bipolar Cell
- Ganglion Cell (axons of these cells become the optic nerve, this is where the action potentials are going to occur!)
Describe the Vertical Pathway for Cones (Photorecetpor).
Photoreceptors have a constant release of Glutamate
- Dark: Release of Glutamate is HIGH
- Light: Release of Glutamate is LOW because the light hyperpolarizes the rods and cones
Step 1: PHOTORECEPTOR struck by a photon of light
Step 2: Decreases Glutamate release onto a BIPOLAR cell
What are the different types of Bipolar Cells?
- On-center Bipolar Cells: Activation of a photoreceptor in the center of the bipolar cell’s receptive field causes DEPOLARIZATION of the bipolar cell; Activation of a photoreceptor in the surrounding region causes HYPERPOLARIZATION of the bipolar cell
- Off-center Bipolar Cells: Activation of a photoreceptor in the surrounding region causes DEPOLARIZATION of the bipolar cell; Activation of a photoreceptor in the center of the bipolar cell’s receptive field causes HYPERPOLARIZATION of the bipolar cell
Describe the state of the “On-center Bipolar Cells” in the Dark versus the Light within the Vertical Pathway.
*** Photoreceptor synapses on an ON-center Bipolar Cell
- Metabotropic Receptor is activated
- Glutamate release causes a DECREASE in cation reflux
- Dark: On-Center Bipolar cell is HYPERPOLARIZED because release of Glutamate!
- Light: Glutamate release is going to DECREASE and the Cation Influx is going to INCREASE to cause DEPOLARIZATION of the Bipolar Cell
Describe the state of the “Off-center Bipolar Cells” in the Dark versus the Light within the Vertical Pathway.
AMPA Receptor is activated
- Glutamate release causes an INCREASE in cation influx
- Dark: Off-Center cell is DEPOLARIZED because there is plenty of Glutamate around
- Light: AMPA receptor is not activated (due to a decrease in Glutamate) and the Off-Center Bipolar Cell is going to be HYPERPOLARIZED
Describe the state of the Ganglion Cell in the Dark versus the Light within the Vertical Pathway.
*** Bipolar Cells are going to Synapse with the GANGLION CELLS
- Light and Dark: Depends on “On-“ or “Off-Center Bipolar Cells”
- Bipolar cell is going to release Glutamate to excite the Ganglion Cell
- Ganglion Cell Axons become the fibers on the OPTIC NERVE!
*** Action Potentials occur here
Describe the components of the Vertical Pathway for Rods (Photorecetpor).
*** SEVERAL RODS are going to synapse on the SAME On-Center Bipolar Cell!
Bipolar Cell then synapses on an A11 Amacrine Cell
A11 Amacrine Cell synapses on a Cone ON-Center Bipolar Cell
Cone ON-Center Bipolar Cell then synapses on a Ganglion Cell
Rods –> ROD ON-Center Bipolar Cells –> A11 Amacrine Cell –> CONE ON-Center Bipolar Cell –> Ganglion Cell
*** Need many rods to converge on a bipolar cell to increase our chances of seeing what we need to see!
Describe the role of ON- and OFF-Center cells.
Describe the role of Amacrine and Horiztonal Cells.
Two types of cells help us increase the ability to detect edges and so they sharpen our vision!
ON-center: Tells us where something IS
OFF-center: Tells us where something ENDS
Amacrine and Horizontal Cells add to that by prividing INHIBITORY signals that modify the activity of neighboring photoreceptors, bipolar cells or ganglion cells.
How is the image that is seen in the retina and then reconstructed in the Brain?
RIGHT TEMPORAL and LEFT NASAL retina is activated by light coming from the LEFT Visual Field
****** NASAL Part of Retina is going to CROSS @ the Optic Chiasm and join the Temporal Parts of the Retina!
Differentiate between the Dorsal and Ventral Pathways in the Primary Visual Cortex.
Dorsal Pathway: Leaves the Occipital Cortex and relays visual information to the motor cortices and enables us to complete motor acts based on visual input! Sends infomortion to the Primary Motor Cortex
Ventral Pathway: Relays information to areas of the brain involved in higher processing of sensory inputs. Allows us to NAME/RECOGNIZE an object! Specialized area for recognizing faces! Similar or related objects are all coded for in localized regions of the TEMPORAL lobe! Autism children will not be able to RECOGNIZE the face as something special!
