SUBCORTICAL MECHANISMS
The Eye
© The eye focuses an image onto the retina.
© High concentration of receptors on the fovea- higher
resolution image.
© Most refraction done by the cornea.
© Lens fine- tunes the focal length.
© Superficial layers moved aside at the foveola to allow
better image.
© Acuity is determined by the separation of the
photoreceptors.
© The closer these receptors are packed together, smaller
receptive fields, lots of receptors. That means you get
a better-quality image.
The Retina
© Has five layers.
© Cell bodies clearly visible.
© Photoreceptors at the “back”.
© Golgi staining reveals shape and diversity of neurones.
© Photoreceptors are rods and cones.
Morphology of Receptors
© Both have outer and inner segments.
© Outer connected to inner through a cilium.
© Inner segment contains metabolic machinery.
© Rods have low resolution (dark).
© Cones have high resolution (light).
o Light to electrical signal phototransduction.
o Cones allow for colour discrimination. Endowed by differences in the
photoreceptor pigment.
o Vision during the light photopic vision.
o Cones have different pigment- different molecular structure.
o Rods are more sensitive, but they don’t recover as quickly as cones.
o With cones, the onset is slower, but the recovery is quicker.
Photoreceptors
- They have “dark current”.
- Light causes hyperpolarization. Downwards, negative.
- Neurotransmitter release increases with depolarization.
The Eye
© The eye focuses an image onto the retina.
© High concentration of receptors on the fovea- higher
resolution image.
© Most refraction done by the cornea.
© Lens fine- tunes the focal length.
© Superficial layers moved aside at the foveola to allow
better image.
© Acuity is determined by the separation of the
photoreceptors.
© The closer these receptors are packed together, smaller
receptive fields, lots of receptors. That means you get
a better-quality image.
The Retina
© Has five layers.
© Cell bodies clearly visible.
© Photoreceptors at the “back”.
© Golgi staining reveals shape and diversity of neurones.
© Photoreceptors are rods and cones.
Morphology of Receptors
© Both have outer and inner segments.
© Outer connected to inner through a cilium.
© Inner segment contains metabolic machinery.
© Rods have low resolution (dark).
© Cones have high resolution (light).
o Light to electrical signal phototransduction.
o Cones allow for colour discrimination. Endowed by differences in the
photoreceptor pigment.
o Vision during the light photopic vision.
o Cones have different pigment- different molecular structure.
o Rods are more sensitive, but they don’t recover as quickly as cones.
o With cones, the onset is slower, but the recovery is quicker.
Photoreceptors
- They have “dark current”.
- Light causes hyperpolarization. Downwards, negative.
- Neurotransmitter release increases with depolarization.
