Transcript PO121 - University of Alabama at Birmingham

VS131 Visual Neuroscience
Retinal Recipient
Nuclei
Which responds faster to a change
in light, ON or OFF bipolar cells?
20%
20%
20%
20%
20%
1.
2.
3.
4.
5.
ON Bipolar Cells
OFF Bipolar Cells
ON and OFF bipolars are the same speed
This is a wrong answer
This is also a wrong answer
The major targets of the retinal ganglion cells:
RETINA  LGN  CORTEX (“vision’)
 Superior Colliculus (saccades)
 Suprachiasmatic Nucleus (circadian)
 Pretectum (pupilary light reflex)
 Accessory Optic System (‘steadicam’)
Only about 10% of retinal ganglion cells do not terminate in the
Lateral Geniculate Nucleus (LGN).
‘BLINDSIGHT’: preservation of very limited ability to
perform visually guided tasks after destruction of the
retina to LGN to cortex pathway, in the apparent
absence of conscious perception.
Bottom line: take out the LGN-cortical system and you
are for all practical purposes completely blind. Some
reflexes and other limited abilities remain, however –
but this does not mean that the LGN and cortex can
compensate if one of the ‘lesser’ systems is
damaged!!!
Relevant sections of Oyster that you should read:
Superior Colliculus: pg.150, 204-205
Suprachiasmatic Nucleus: pg.205-207
Accessory Optic System: pg.205
Pretectum (& Edinger-Westphal): pg.204-205, 224,
233-235, 433-434.
Accessory Optic System: stabilize the eyes using information
from the visual system (as opposed to from the vestibular
system).
-> Eye stabilization is critical for vision
-> RGC axons go to three small nuclei in the brain stem: dorsal,
lateral, and medial terminal nuclei.
-> Only a few thousand axons.
-> These nuclei have cells that respond to large areas of
motion, they are selective for both direction and velocity.
-> Medial, Lateral, and Dorsal Terminal Nuclei (MTN, LTN, DTN)
-> Definition of retinal slip.
Suprachiasmatic Nucleus (SCN): A small cluster of
cells in the hypothalamus above (duh) the optic
chiasm.
-> Has cells fire in direct proportion to the total amount
of light (presumably not center-surround!).
-> In animals lesioning this area causes disturbances
of diurnal rhythms.
-> Visual inputs entrain the natural rhythm in the SCN.
-> Only other known clock in the human body is in the
retina itself, but that one only seems to be involved
with specifically retinal adaptation and maintenance.
The SCN does jet lag etc.
Pretectum: Part of the Midbrain.
-> Nucleus of the optic tract: eye movement control
and stabilization.
-> Pretectal Olivary Nuclei: pupillary light reflexes.
Superior Colliculus: also part of the midbrain.
-> Has a variety of functions, including generating
saccadic eye movements and visual orienting reflexes.
-> Relatively bigger and more important in other
species, such as reptiles (“Gamera”) where it has
turned into the optic tectum, a homologous structure to
our superior colliculus.
Superior colliculus (SC) has
seven layers.
-> Three sensory maps:
visual map
body map
sound map
-> Also a motor map
-> Maps are aligned.
Superficial layers: direct
input from retina and also
cortex
Deeper layers: somatic and
auditory inputs, also motor
outputs.
-> If you stimulate the SC in a particular place in the map,
you will generate a rapid saccadic eye movement to that
place in space represented by that location on the map.
-> SC also gets inputs from the frontal eye fields in
cortex, direct volitional as well as reflex control of
saccades.
-> SC projects to regions of brainstem that are
involved in oculomotor control, and to other regions
as well.
-> Also involved in reflex control of head and neck
movement.
-> Eye movements are incredibly fast and precise.
It takes a lot of ‘machinery’ to give you that
capability. The SC is just one (very important!!)
part of this system.