Flashcards in 1.44 Visual Pathways Deck (46):
What colours do cones pick up?
Red, blue and green
What colours do rods pick up?
Just black and white
Which cells modify the signal from the rods and cones before its passed onto the retinal ganglion cells?
Horizontal and and amacrine cells - modulate activity - turn it up or down or alter activity
Which receptor protein is found in rods?
Which receptor protein is found in cones?
What is contained in the outer and inner segments of cones and rods?
Outer compartment - photopigment
Inner compartment - nucleus and mitochondria
what do rods and cones synapse with?
Bipolar and horizontal cells
What is phototransduction in simple terms?
The process of a cell absorbing light which results in a change of transmitter that is released.
What is released when light hits rhodopsin?
Opsin is released - it is a transmembrane protein
What is retinal?
A protein found in the photopigments, the one type of rod and three types of cones all have a different amount of this protein, this allows for different wavelengths to be absorbed.
What happens to retinal once light hits?
It changes from "cis" form to "trans" form, this triggers changes in the opsin
What is transducin?
It gets activated by the changes in rhodopsin after light hits, when its activated it exchanges its GDP for a GTP
What activates phosphodiesterase in the disc membranes?
The alpha subunit of the transducin after it was activated
What does phosphodiesterase do?
Hydrolyses cGMP, thus lowering its concentration
What does a lower concentration of cGMP result in?
Less ion channels open, because theres less cGMP to keep them open
In the dark, what is the membrane potential status of the outer segment?
It is depolarised due to a positive influx of calcium and sodium ions, however there is an outward flow potassium, causing hyperporalisation, however the the net outcome is depolarisation
What effect does the demoralised state of the membrane in the dark have on neurotransmitter release?
What happens to the membrane when light hits?
Less cGMP, less open channels, more K out than Na and Ca in, so the membrane becomes hyperporalised (negative)
What effect does hyperpolarisation of the membrane on the neurotransmitter?
Decreases amount of neurotransmitter released
What stops rhodopsin from continuing activating transducin?
Rhodopsin kinase phsophorylates then arresting binds to it
What is protonopia, tritanopia and deutaronopia?
Protanopia - red missing - brownie
Deutaronopia - Green missing - yellowie
Tritanopia - blue missing
Which gene is colour blindness carried in?
What are the two main types of ganglion cells?
On-centre - fires when light hits centre receptive field
Off-centre - fires when light hits surround receptive field
What happens when light hits the centre of the receptive field?
Hyperpolarisation - decreases neurotransmitter release
What does decreased neurotransmitter release result in?
Decreased inhibition of the on-centre bipolar cell so increased activity on the on-centre ganglion
Decreased excitation of the off-centre bipolar cell so decreased activity of the off-centre ganglion
Where do the axons from the retinal ganglion cells from both eyes meet?
How do axons cross over in the optic chiasm?
Axons from the right side of the visual field (from both eyes) project into the right optic tract and vice versa
Where do the majority of axons within the optic tracts synapse?
In the lateral geniculate nuclei of the thalamus and superior colliculus
How many layers of neuronal bodies are found in the LGN and what is their function?
6 layers - axons from there then project posteriorly through optic radiations to synapse in the occipital cortex
What type of input do layers 1,4 and 6 transfer?
What type of input do layers 2,3 and 5 transfer?
Which layers are the magnocellular layers and what are they involved in?
1 and 2, they are involved in detecting "where" an object is, so movement and contrast
Which layers are parvocellular and what are they involved in?
3,4,5 and 6, these are involved in deletion of colour and form
How many layers is there in the primary visual cortex?
Where is the calcarine sulcus?
Primary visual cortex
How many visual cortex parts are there?
4 - V1, V2, V3 , V4
Which parts of the visual cortex does the dorsal stream include and what is its function?
Magnocellular - V1, V2, V3 - Visuospatial - where things are
Which parts of the visual cortex does the ventral stream include and what is its function?
Parvocellular - (lower) - V1, V2, V3, V4 - Features - colours - what things are
If there is a lesion in the optic nerve in the right eye, what visual damage will that result in?
Loss of vision in the right eye
If there is a lesion in the optic chasm, what visual damage would that result in?
Bitemporal (lateral) heteronomous hemianopia
What causes right homonymous hemianopia?
A lesion in the left visual tract
A patient present with loss of vision in the left temporal visual field and right nasal visual field, where is the lesion present?
A lesion in the right optic tract, producing a homonymous hemianopsia
If a patient had a lesion in the right nucleus of Edinger Westphal, then a light shone in the right pupil would result in...
no direct effect on the pupil size, but a consensual effect on the left pupil size
If a patient had a lesion in the left occipital cortex, they would present with...
Intact pupillary reflexes (loss of accommodation reflexes) in the right eye, but a loss of vision from the right visual field
Glaucoma can be due to an increase in aqueous humour production from the ....