CsfVision again Flashcards
Normal CSF
Normal CSF is clear and colorless, contains little protein (15-45mg/dl), little immunoglobulins and only 1-5 cells/ml
Who would you see idiopathic intracranial hypertension/pseudotumour cerebri in?
Obese females of child bearing age
Management of idiopathic intracranial hypertension/pseudotumour cerebri
Weight loss, medication and potentially ventriculopertioneal shunt
Normal pressure hydrocephalus triad
Dementia
Incontinence
Gait disturbances
What does aqueous humour contain?
Oxygen, metabolites, bicarbonate
Ascorbate
Powerful antioxidant
Purpose of bicarbonate
Buffers the H+ produced in the cornea and lens by anaerobic gylcolysis
Direct (vertical) pathway for signal transmission
PBG
Photoreceptors
Bipolar cells
Ganglion cells
What do horizontal cells do?
Receive input rom photoreceptors and project to other photo receptors and bipolar cells
What do amacrine cells do?
Receive input from bipolar cells and project to ganglion cells, bipolar cells and other amacrine cells
What do photoreceptors do?
Convert electromagnetic radiation into neural signals (transduction)
4 main segments of photoreceptors?
Outer segment
Inner segment
Cell body
Synaptic terminal
Which current allows the brain to perceive objects in the visual field in light?
Na+ dark current
-cGMP channel open in the dark and closes in the light
Vm of photoreceptors
-20
Vm of photoreceptors
-20
Ciliary epithelium
Pigmented epithelium overlain by inner non pigmented epithelium
How is dorzolamide administered?
Eye drops
How is acetozolamide administered?
Oral administration –> targets kidneys
Most common type of glaucoma
Primary open angle
Pathogenesis of primary open angle glaucoma
Raised intra-ocular pressure
Obstruction to aqueous outflow across trabecular meshwork
Modulation of the dark channel
In the dark,
PNa –> PK (Na channels in the outer segment)
Vm therefore between ENa and EK
In response to light,
PNa is reduced (outer segment channels close), PK > PNa
therefore, Vm –> EK, hyperpolarizes
Change is local and graded
Rhodopsin
Primary pigment in rod receptors
Sensitive to light and allow light in low conditions
Molecular mechanism of phototransduction
all-trans-Retinal activates transducin
molecular cascade
decreases cGMP
This leads to closure of cGMP-gated Na+ channel
Lowered Na entry results in hyperpolarization
Dark channel and cGMP
Opened by cGMP
What is the purpose of the dark channel?
Keeps photoreceptors Vm more positive than most neurons
What does the dark channel transmit?
Steady release of neurotransmitter
What is visual acuity and how is it determined?
Visual acuity is the ability to distinguish two nearby points
Determined largely b photoreceptor spacing
(i.e. lots of photoreceptors together = better visual acuity)
Help you to see in dim light
Rods
Help you to see in normal daylight
Cones
More convergence in rods or cones?
More convergence in rod system, increasing sensitivity while decreasing acuity
Short wave cones
Blue
Middle wave cone
Green
Long wave cone
Red
Chromatic Central retina (fovea) Low convergence Low light sensitivity High visual acuity
Cones
Achromatic Peripheral retina High convergence High light sensitivty Low visual acuity
Rods
What is the receptive field
The part of the retina that needs to be stimulated to elicit actin potentials from a ganglion cell
What is the importance of the central surround organisation?
Emphasizes areas of contrast
Our visual system detects what differences in light?
LOCAL differences in light intesnsity not absolute differences in amount of light
Right visual field
Left cortex
Superior visual field
Lower cortex
