PSYC10003 Lecture Notes - Lecture 7: Ganglion Cell Layer, Vitreous Body, Electromagnetic Spectrum
14 Jun 2018
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MBB1 – Lecture 7
The human visual system
Electromagnetic spectrum
• Our eyes detect the presence and pattern of light reflected off objects in the world
• We are sensitive to a very narrow range of wavelengths– visible spectrum
o Not qualitatively different from the rest of the spectrum
• Colour of light is determined by hue (wavelength of electromagnetic radiation),
brightness (intensity) and saturation (purity)
Human eye
• Light enters eye through the transparent outer layer – cornea
• Immediately behind cornea is lens, which is made of a number of transparent layers
• Shape of lens can be altered to help focus the image onto the back of the eye which
is lined by a light sensitive structure called the retina
o Light sensitive rods and cones in retina send axons out of eye from a common
point – optic disk
▪ There are no photoreceptors at the optic disk → blind spot
▪ Axons bundled together at optic disk are collectively the optic nerve
• Eyeball itself is filled with a clear gelatinous fluid called the vitreous humour
Cells of the retina
• Each layer contains specialized neurons, their axons & dendrites, & photoreceptors
• Photosensitive cells are located at the back, so light must pass through the other
layers first – there are two types of these cells
o Rods and cones – contain photopigments that break down when exposed to
light, triggering a series of stages that leads to the neural impulses that are
eventually conveyed to the brain by the optic nerve
• Less cones than rods, but rods are the most important for seeing fine detail, and are
most active in daylight
o Cones are concentrated in a region of the retina called the fovea, which is
responsible for the central few degrees of our visual field
o Different types of cones sensitive to different wavelengths, so are
responsible for our ability to see colour
• Rods do’t disriiate etee aelegths or fie details, ut are uh ore
sensitive to light, and so are used in dim environments
• Retina is divided into 3 distinct layers
o Photoreceptor layer, bipolar cell layer, ganglion cell layer
• Rods and cones form synapses with
bipolar cells, which in turn form
synapses with ganglion cells
o Ganglion cells send their axons
through the optic nerve (2nd
cranial nerve) to the brain
• 2 other cell types in middle layer of
retina – horizontal and amacrine cells –
combine messages from several
photoreceptors
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