The visual system: eye and retina Flashcards
How much of the neocortex is involved in analysing the visual world?
1/3
What colour do short wavelengths in visible light appear?
Blue
What is the wavelength?
Distance between peaks and throughs
What is the frequency?
Number of waves per second
What is the amplitude?
The difference between a wave peak and a trough
What are optics?
Light interacting with the environment
Why does refraction occur?
The speed of light differs between mediums
Function of the pupil
Lets light inside the eye
Function of the iris
Contains muscles which control the amount of light entering the eye
Function of the cornea
Glassy transparent covering of the pupil and iris
-Refracts light and focuses towards the back of the eye
- Nerve endings which adapt over time
Function of the sclera
Forms the tough, protective wall of the eyeball to give it shape
Function of the extraocular muscles
Move the eyeball
Controlled by oculomotor nerve (cranial nerve 3)
Function of the optic nerve
Carries axons from the retina to the brain
- Cranial nerve 3
What type of animal has horizontal pupils?
Prey animals
- For wider vision
What is the optic disk?
Origin of blood vessels and the optic nerve
- Cannot sense light
What is the macula?
Region of the retina for central vision
- Devoid of large blood vessels to improve vision quality
What is the fovea?
Thinnest section of the retina
- Area of highest visual acuity
How does stretching of the lens occur?
Lens is suspended by zonal fibres (suspensory ligaments), attached to ciliary muscle, enabling stretching
What is the degree of refraction determined by?
Difference in refractive indices between the two media
The angle at which light hits the interface between the two media
Describe refraction by the cornea
Cornea is mainly water
- Light travels more slowly through water than air due to higher density so refraction occurs
What is the focal distance?
Distance from refractive surface to convergence of parallel light rays
What happens to the lens when objects are <7m away?
The lens fattens to provide additional refraction
What is emmetropia?
Eye is in a normal state and can focus on the back of the retina
What is hypertropia?
Eyeball is too short so near objects are focussed behind the retina due to lack of refraction
How is hypertropia fixed?
With convex glasses
What is myopia?
Eyeball is too long so near objects are focused before the retina
How is myopia fixed?
Concave glasses
What cells does light pass through before it reaches photoreceptors?
Ganglion and bipolar cells
What are plexiform layers?
Regions where synaptic connections occur
Function of a ganglion cell in the retina
Output from the retina
- Produce action potentials
Function of an amacrine cell
Modulates information transfer between ganglion and bipolar cells
Function of bipolar cells in the retina
Connect photoreceptors to ganglion cells
Function of horizontal cells
Modulate information transfer between photoreceptors and bipolar cells
Function of a photoreceptor in the retina
Sensory transducers
- Both rods and cones
Describe the structure of a photoreceptor
Membranous disks that contain light-sensitive photopigments that absorb light
Function of a rod
High sensitivity
- Enable vision in low light
Function of a cone
High resolution
-Colour
- Daylight photopic
Structure of a rod
Greater number of disks than a cone
Higher photopigment conc
100x more light sensitive than cones
Structure of a cone
Fewer disks than rods
Describe convergence, sensitivity and resolution in the central retina
Low convergence
Low sensitivity
High resolution
Describe convergence, resolution and sensitivity in the peripheral retina
High convergence
High sensitivity
Low resolution
What changes the polarity of bipolar cells ?
Glutamate release at the synapse
