Structure of the Visual System Flashcards
What is the stimulus for vision?
Light
Light can be characterised by two different measures. What are they?
Wavelength and intensity
What range of nanometres does the visible light spectrum fall into?
Between 400 to 700 nanometers
As the intensity of light increases, what happens?
The number of photons per seconds increases
The spatial distribution of light (optic array) is determined by which two factors?
Sources of light (The sun)
Reflectors of light (Visible objects)
What happens at the Optic Chiasm?
Decussation. This is where the optic nerves fibres split to make sure the left half of the world goes to the right side of the brain and the right side of the world goes to the left side of the brain.
Describe the base function of the visual system
It converts a structured pattern of light (imaged on the retina) to a perception of a solid three-dimensional world
What is pigment epithelium used for?
It is a black sticky substance at the back of the eye used to stop light bouncing around.
Name the two photoreceptors
Rods and Cones
Where does the electrical signal go after the Rods and Cones
To the Bipolar Cells
Where does the electrical signal go after the bipolar cells
To the Ganglion Cells
What do the axons of the ganglion cells form
The Optic Nerve
What are the Horizontal cells and Amacrine cells used for?
Horizontal cells help shape the ganglion cell receptive fields by modifying the synapse signal between photoreceptors and bipolar cells
Amacrine cells help shape the ganglion cell receptive field by modifying the synapse signal between bipolar cells and ganglion cells.
State the chief proprietor and define the receptive field
Chief proprieter - Goldstein
Definition - The region of retina that, when stimulated, influences the firing rate of the neurone
What is phototransduction and how does it work?
When photoreceptors (rods and cones) turn light into electricity
Photons of light are absorbed by visual pigment molecules
What is found within the Rhodopsin molecule?
Retinal
What happens within the protein Retinal?
A photon of light hits the retinal and isomerizes from an 11-CIS retinal to an ALL-TRANS retinal
This shape changes it to an active state which triggers an enzyme cascade
This biochemical chain reaction triggers an electrical signal within the photoreceptors
What unit of measurement are spikes(action potentials) recorded?
Spikes per second
How many axons are in the optic nerve?
Aroud 1 million
How many rods are there?
Around 120 million
How many cones are there?
Around 6 million
What do the retinal ganglions cells do?
They find intensity edges and contract between centre and surround which results it in it responding with a series of nerve impulses
The more stimulation provided, the faster the fire rate or spikes per second is recorded.
How many Lateral Geniculate Nucleus (LGN) does the brain have and what is it roughly the size of?
2
A peanut
Where is the Lateral Geniculate Nucleus (LGN) found in the brain?
They are located in the Thalamus which is found in the centre of the brain
Classically, how many layers of the Lateral Geniculate Nucleus (LGN) are there?
6
If the left eye was to send information to the right LGN, what term would define this?
Contralateral
If the right eye was to send information to the right LGN, what term would define this?
Ipsilateral
Starting from the bottom of the LGN, state each layer on whether it is contralateral or ipsilateral
1 - Contralateral 2 - Ipsilateral 3 - Ipsilateral 4 - Contralateral 5 - Ipsilateral 6 - Contralateral
What are the functions of the Lateral Geniculate Nucleous (LGN)?
It has a similar receptive field as the ganglion cells
May regulate information flow from the retina to the cortex
How many axons is the Striate Cortex (V1) innervated by through each LGN?
Around 1.5 million
How many layers does the Striate Cortex (V1) have?
6
How many neurones are contained in the Striate Cortex (V1)?
Over 250 million
