Visual Pathway Lab Briefing Flashcards
what is the role of the visual pathway
involved in the relay of light from the visual field of both eyes, to the primary visual cortex in the occipital lobe of the brain.
How do rays of light travel to the retina
Rays of light from the visual field are refracted by the cornea so that they pass through to the retina, which is located at the back of the eye.
Describe the structure of the retina and how it helps in the visual processing pathway
The retina is a multi-layered structure and the deepest layer consists of photoreceptor cells called rods and cones, which convert light energy into a neural impulse.
How is the neural signal produced by photoreceptor cells travel to the optic nerve
The neural signal is transmitted through intermediate layers of bipolar and horizontal cells, to the retinal ganglion cells (RGC) which reside within the innermost surface of the retina.
The cell bodies of retinal ganglion cells are close to the vitreous humour of the eye. Axons of the retinal ganglion cells (RGCs) exit the eye at the optic disc, where the axons then form the optic nerve.
Briefly name the components of the visual pathway
*goes downwards* Optic nerve Optic chiasm Optic Tract Lateral Geniculate Nucleus Optic Radiation Visual Cortex
Describe Optic nerve
2nd CN
Outgrowth of the brain
Paired nerve
Each optic nerve contains sensory afferent nerve fibres from the left or right eye
Axons of the retinal ganglion cells form the optic nerve
Describe optic chiasm
50-60% (partial) decussation of the nerve fibres contained within the optic nerve (50-60% of the nerve fibres from each eye cross over)
–> This allows the visual cortex of both the left and right cerebral hemispheres to receive visual information from BOTH eyes and permits binocular and stereoscopic vision- perception of depth and 3-dimensional structure is obtained.
Describe Optic Tract
Nerve fibres now travel as the optic tracts and are no longer part of the optic nerve.
This is because the optic nerves carry nerve fibres from one eye only, whereas the optic tract contains nerve fibres from both the left and right eyes.
Describe Lateral Geniculate Nucleus
Relay centre of thalamus
6 layers of alternating grey and white matter
Nerve fibres from optic tract project to LGN
Nerves of the optic tract terminate within the LGN and synapse with neurons located within the LGN.
Describe Optic Radiations
The neurons of the LGN then project to the visual cortex via the optic radiations, so called because the nerve fibres fan out to form a distinctive anatomical feature
what is the visual cortex also known as?
The primary visual cortex can also be called V1 (vision 1 – since it is the primary visual processing area) or the ‘striate cortex’, because of its striped appearance, which is due to a prominent band of myelinated nerves fibres
Not all nerve fibres within the visual pathway project to the lateral geniculate nucleus. some project somewhere else. what is this place and what are their functions
Midbrain area:
- Superior colliculus: eye movements
- pretectal area: pupillary light reflex
The left eye receives both right and left visual fields, but they are transmitted to different parts of the left eye. Name these
LEFT EYE:
- LEFT visual field transmitted to NASAL retina of left eye
- RIGHT visual field transmitted to TEMPORAL retina of left eye
What is the fate of the right visual field which transmits to the temporal retina of the left eye.
- Axons from the retinal ganglion cells (RGC) of the TEMPORAL RETINA exit the left eye via the LEFT optic nerve and then STAY on the LEFT HAND SIDE of the pathway
- Axons travel through optic tract and into the LEFT LGN
- Neurons of the left LGN project to the LEFT visual cortex through optic radiations
Stimuli from the right visual field projects to the ______ visual cortex
left
