Midterm 2 Flashcards
What is the function of the iris?
Adjust pupil size
What is the cornea?
Specialized transparent tissue
What is the aqueous humor?
Liquid that supplies nutrients to cornea and lens
What is the ciliary body?
Muscle that adjusts refractive power of the lens; ciliary processes produces fluids
What is the function of the retina?
Contains neurons that transducer sensory signals and transmit electrical signals to central targets in the brain
What is the function of the optic disk?
Area where blood vessels enter the eye and retinal axons leave the eye
What are 5 classes of neurons in the retina?
- Photoreceptors
- Bipolar cells
- Horizontal cells
- Amacrine cells
- Ganglion cells
What is phototransduction?
Process by which absorption of light by photopigment
What is the process for phototransduction?
- Photon of light is absorbed by chromophore retinal, coupled ti GPCR-opsins
- Absorption of light causes changes in retinal configuration (cis to trans)
- Changes in retinal configuration activates transducin
- Transducin activates PDE, which hydrolyzes cGMP reducing cGMP level
- cGMP channels are closed
- Hyperpolarization
What are the roles of retinal pigment epithelium?
- Phagocytose oldest disks are the tip of the outer segment
2, Regerneration of photopigment after exposure to light
What is the retinoid cycle in photoreceptors?
- Light absorption by cis-retinal
- Photoisomerization of retinal
- Trans-retinal dissociates from opsin and is converted to trans-retinol
- Trans-retinol is transported into pigment epithelium and converted to cis-retinal
- cis retinal is transported back into the outer segment where it recombines with opsins
What are the specialized vision aspects of rods and cones?
- Rods have high sensitivity to light, low resolution (night vision)
- Cones have low sensitivity to light, high resolution (day vision)
- Cones are responsible for color vision
What is the range of luminance for rods and cones?
Rods = scotopic and mesotopic Cones = mesotopic and photopic
How do rods improve detection of light and signal?
Convergence improves detection of light, but reduces a spatial resolution.
Amplification contributes to detection of signal
Where is cone receptor density the highest?
Highest at the center of macula (in the fovea)
How many photopigments does the human retina have?
4
Where are the genes for cone pigments located?
Localized on X chromosome (Red and green) and on chromosome 7 (blue)
What is protanopia?
Loss of long-wavelength sensitive cones = difficult to discriminate between green and red
What is deuteranopia?
Loss of medium-wavelength sensitive cones = difficult to discriminate between red and green
What is the difference between on-center and off-center ganglion cells?
- “on” responds to onset of small bright light and offset of and annulus light
- “off” responds to offset of bright light and onset of annulus light
What determines the difference between on- and off-center cells?
- “on” responds to decreased glutamate by becoming depolarized
- “off” responds by becoming hyperpolarized
What do horizontal cells to in terms of surround response?
modulatory inputs generate the surround response
What are characteristics of M, P and K ganglion cells
- M: larger receptive fields than P, M axons have faster conduction velocity than P cells, respond transiently to visual stimuli, do not transmit info about color because contain same classes of cones in center and in surrounds
- P: cells respond in sustained fashion, convey color info because receptive field centers and surrounds contain difference classes of cones
- K: might contribute to color vision as they receive info from S cones
What is binocular visual field?
Consists of two symmetrical visual hemifields
What is contralateral visual field?
Represented by axon of ganglion cells that originate in both eyes
What does the LGN do?
Receives input from both eyes, responses are similar to retinal ganglion cell responses
What are the different layers of LGN?
- Magnocellular (large neurons)
- Parvocellular (small neurons)
- konicellular (small neurons)
What is optic radiation?
Portion of internal capsule that comprises the axons of lateral geniculate neurons that carry visual info to striate cortex
What is the architecture of primary visual (striate) cortex?
- LGN neurons primarily synapse on layer 4 of striate cortex
- laminar organization of visual cortex serves to segregate populations of neurons that are having distinct patterns of connections
What are ocular dominance columns?
Stripes of neurons in the visual cortex that respond to input from one eye or the other
What are the characteristics of neurons along the radial axis?
- Have receptive fields centered on the same region of visual space
- Exhibit similar orientation preferences
- orientation preference that progressively shift
Where do retinal ganglion cells project to?
- Pretectum
- Hypothalamus
- Superior colliculus
- Thalamus (LGN)
