ELM14: Sensory systems, vision Flashcards
What are the two features of light?
Wavelength
Amplitude
What is meant by the wavelength of light?
The colour
What is meant by the amplitude of light?
Intensity
What is the role of the lens?
To focus the light onto the retina
Changes shape
What is the role of the cornea?
Refracts light into the eye
Bulk
What are the aqueous and vitreous humour?
Fluid filled areas
Help eye maintain shape
What occurs when you look at something far away?
Lens gets flatter
What happens when you look at something close?
Lens gets fatter
What is myopia?
Short sighted
Focal point is too far forwards
Concave lens used
What is hyperopia?
Far sighted
Focal point is too far back
Convex lens is used
What are some features of the retina?
Several layers of specialised neurons
Has rods and cones
What is the retinal pigment epithelium?
Inside of sclera
Recycles retinaldehyde and helps rods and cones with oxidative stress
Where are rods and cones?
In the fovea which has max visual acuity
What are rods more useful for?
Night and peripheral vision
1000x more sensitive than cones
What are cones useful for?
Distinguishing colour
How are rods and cones different in terms of structure?
Similar apart from outer segments
What is the structure of the outer segments in rods and cones?
Multi-layered segments
Lots of membranous discs
What do the membranous discs in the outer segments of rods and cones contain?
Opsins
What are opsins?
Proteins that form a photopigment when bound to retinaldehyde
Humans have 5 types
Why do rods have a larger outer segment?
So they can contain more opsins and be more sensitive to light
What is retinal?
Vitamin A derivative
Absorbs light and changes conformation
Pigment is bleached until retinal is reset In discs
What is the role of rhodopsin?
Binds to retinal in discs and forms a photopigment
What happens when photoreceptors are in the dark?
Sodium channels open
Photoreceptors are depolarised
What happens when photoreceptors are in the light?
Sodium channels close
Hyperpolarisation
What is the overall process of retinal becoming activated?
- Absorbs light and changes conformation
2.Sodium channels close - Hyperpolarisation
What is the process of phototransduction?
- Retinal absorbs light and becomes all trans retinal
- Conformational change in rhodopsin
- Transducin has change of GDP to GTP
- Activates phosphodiesterase
- Reduces cyclic GMP
- Closure of sodium channels
What are trichromats?
Humans
3 types of cones
What are monochromats?
Whales and seals
1 type of cone
What are dichromats?
Mice cats and horses
2 types of cone
What type of opsins does the X chromosome have?
Red and green
What kind of opsin does chromosome 7 have?
Blue
What are the 3 other types of retinal cells?
Bipolar
Horizontal
Amacrine
What are bipolar cells?
Relay cell between photoreceptor and retinal ganglion cell
What are horizontal cells?
Light intensity adaptation
Spatial processing
Colour processing
What are amacrine cells?
Directional motion
Modulate light adaptation
Modulate circadian rhythm
Sensitivity of night vision
What are retinal ganglion cells?
Further process colour motion and shapes
Only output cells and fire APs
Detect light with melanopsin
What is melanopsin?
Doesn’t help image formation
Affects circadian rhythms pupil size and body temperature
