Vision Flashcards
Cornea
Transparent region of sclera
Sclera?
Outer fibrous layer
Connected to extra ocular muscles
Iris
Pigmented region
Pupil
Opening in iris
Aperture size determined by muscles of the iris
Innervated by ANS
Aqueous humour?
Fluid between cornea and lens
Suspensory ligament
Attaches lens to ciliary body
Capillary body
Smooth muscle
Contraction alters shape of eye
Vitreous humour
Fluid behind lens
Retina
Contains photoreceptors
Optic disc
Axons of retinal neurons enter the optic nerve
Fovea
Concentration of cones
Choroid
Vascularised layer
How is the position of the eye controlled?
6 extra ocular muscles innervated by 3rd,4th and 6th cranial nerves
Stimuli include visual and vestibular info
Types of eye movement?
SACCADES- jerky, rapid eye movements which centre images on the fovea
PURSUIT MOVEMENTS- slow movement of the eye, tracking an object
VERGENCE MOVEMENTS- mirror image movements of the eye, so images remain in focus on both retinas
Describe the visual pathways
Axons of ganglion cell gather at the optic disc and pass into the optic nerve
2 optic nerves converge to form the optic chiasm at the base of the brain
Axons from the nasal retina decussate, those for temporal retina remain ipsilateral
Optic tracts this formed terminate in LGN
some collateral fibres from the optic tract terminate in the brainstem
Fibres from LGN terminate in primary visual cortex
3 phases of CP
Preceitical- visual circuitry preformed without visual experience
Critical- modification of existing circuitry
Post critical- similar experience to above, has no effect (?)
What are NDMA receptors ?
Subset of ionotropic glutamate receptors
Mediate a slower epsp and produce a greater Ca permeability
Readily blocked by Mg2+ overcome by sustained depolarisation
What is LTP?
Long term potentation
Long lasting enhancement of synaptic transmission occurring at CNS synapses
Opposite is ltd
What is inhibitory activity?
In the cortex
Important in determining developmental processes
What do neurotrophins do?
Regulate neuronal survival and differentiation
NGF BDNF NT-3
What role do neurotrophins play in the critical period?
Control duration
Block endogenous BDNF,
Mechanism of actions of neurotrophins
Production and release dependent on visual activity
Modulate both pre and post synaptic function- fast, altering transmitter release
Slow- modulation of gene expression
Production and electrical activity are linked might be a means by which connections are strengthened
Each NT has a specific target
What other factors affect visual plasticity?
Factors in extra cellular environment
tPA- extracellular protease induced by electrical activity
Glycoproteins in extracellular compartments of CNS may influence plasticity
