Vision Flashcards
Where is the ganglion for vision located?
Primary Neuron (Ganglion Cell), lies wihtin the retina
Visual Pathways: Superior Colliculus (Pretectal Nucleus)
- Reaction to visual stimuli without creating a perception of vision
- To Facial Motor Nucleus – Blink to threat response
- To Visceral Oculomotor Nucleus – Pupillary response (Shine in one eye and dilation in both)
Visual Pathways: Lateral Geniculate Nucleus
Posterior portion of the thalamus
- Perception of vision
- To Primary Visual Cortex via the Geniculocalcarine Tract (near occipital lobe)
Important principles of the Geniculocalcarine Tract
- Lens Optics
– Image information projects onto the retina is upside down and backwards
– Orientation doe snot change as the image information passes through the neural pathways - Visual Field is divided into left and right halves in both eyes
– Information from each visual field is kept seperate as it is sent to the visual cortex
Optic Pathway (Visual Perception)
- Optic Nerves pass through the skull through the optic canal of the sphenoid bone
- Two nerves merge as the optic chiasm
– Partial decussation of information from the two visual fields of each eye seperate (½ stays, ½ crosses over) - Neural Pathways leaving chiasm become known as optic tracts (each convey a single visual field)
- Optic tracts pass into thalamus and synapse within the Lateral Geniculate Nucleus
– Axons leave nucleus as optic radiations (4) - Optic radiations convey information to the visual cortex in the occipital lobe
What could this be caused by?
Damage to the Right Optic Nerve: Right Eye Blindness
What could this be caused by?
- Damage to the Right Optic Tract: Left Homonymous Hemianopsia (lose one visual field)
OR - Damage to the Right Optic Radiation: Left Homonymous Hemianopsia (All radiations taken out on one side)
What could this be caused by?
- Damage to the Optic Chiasm: Bitemporal Hemianopsia
- Outer portions of the visual fields taken out giving you tunnel vision
What could this be caused by?
- Damage to the Meyer’s Loop of the Right Optic Radiation: Left Homonymous Superior Quadrantanopsia
- Only one optic radiation taken out
What could cause this?
- Damage to the Left Optic Radiation
- Only one optic radiation taken out
Explain what possible visual impairments could be seen at different letters
Interpretation to Perception of visual information
- The first step is visual signal processing in the Visual Cortex (Area 17)
- Perception involves Primary Visual Association Cortex (Areas 18 & 19)
- The Retina can be mapped roughly to the Association Cortex, with a lot of overlap. (This overlap likely explains the “cover up” of the physiological blind spot. (Brain fills things in))
Perception: What? or Where?
-
Where – Medial Part of Cortex (Dorsal stream) interprets location of features in the environment, also called “vision for action” – parietal, motor and frontal lobes
– 3D space and action
– Motor control stuff -
What – Lateral Part of the Cortex (Ventral stream) interprets the identity of things within the visual field – temporal lobe
– What objects are, object recognition, facial recognition
– Description, identification
Posterior Parietal Cortex and Vision
- Adds contextual meaning to vision
- Plays a role in coordination of 3-D visual perception (again, think utility for action)
Coordination and Vision
- Motor Association Cortex
- Basis for visually guided motions
What and Where Pathway - Interactions
These streams work together but we simplify it to be able to understand. Very complex.
