Physiology Flashcards
what is papiloedema?
optic disk swelling due to increased cranial nerve pressure on the subarachnoid space around the optic nerve
What is the function of aqueous humor?
to provide O2 and metabolites to the structures of the anterior eye
Contains bicarbonate to buffer H+ produced in cornea and lens
contains ascorbate= antioxidant
what is the circulatory system of aqueous humour?
produced from epithelia of the ciliary body
released into posterior chamber of the eye
flows into anterior chamber
drains to scleral sinus through a trabecular network and the canal of Schlemm (angle between iris and cornea (iridocorneal) ange)
small amount diffuses through vitreous to be absorbed across retinal pigment epithelium
What are the two cellular layers of the ciliary epithelium?
outer pigmented epithelium (PE)
inner non-pigmented eithelium (NPE)
which ciliary epithelial layer is responsible for secreting aqueous humour?
non-pigmented epithelial cells
what channels allow ion exchange between the two layers of ciliary epithelia?
gap junctions
what does carbonic anhydrase do in the ciliary epithelia?
aids sodium and chloride influx into the cells from the stroma by causing the efflux of H+ and bicarbonate ions
this allows the influx of water as it follows sodium and chloride
what prevents the production of aqueous humour?
carbonic anhydrase inhibitors
why is it important to have a steady volume of aqueous humour?
to maintain a healthy intraocuar pressure
what can increased intraocular pressure lead to?
glaucoma
what is the order of the cells involved in signaling in the retina?
Photoreceptors-> bipolar cells -> ganglion cells
yet these are aranged the other way around (with ganglion cells most internal and photoreceptors most external
what is the function of photoreceptors?
to transduce light signals into electrical current
what are the lateral connections in the retina signaling pathway?
horizontal cells (recieve input from photoreceptors and project to other photoreceptors and bipolar cells) Amacrine cells (recieve imput from bipolar cells and project to ganglio cells, biopolar cells and other amacrine cells)
what makes up the structure of a photo receptor?
outer segment
inner segment
cell body
synaptic terminal
what are the different types of photoreceptors?
rods (one type)
cones (short, medium, long wave)
are photoreceptors polarised or depolaroised?
depolarised
(more positibe resting Vm)
Vm= voltage of membrane
what happends when photoreceptors are exposed to light?
Vm hyperpolarizes
what is the signal for Vm to hyperpolarise?
less glutamate release
closure of cGMP gated sodium channels
is there more glutamate release in the dark or in the light?
the dark
do photoreceptors work independently or dependently?
independently
what are the visual pigment molecules called?
rhodopsin
what is photopigment comprised of?
a retinal molecule and an opsin (GPCR)
what happens to rhodopsin in the presence of light?
changes the protein shape (from 11-cis-Retinal to all-trans-Retinal)
this initates a cascade
how does the rhodopsin changes affect the membrane potential of the photoreceptors?
the molecular cascade induced results in dreased cGMP –> closure of cGMP gated sodium channels –> hyperpolarisation due to low sodium levels
is there more glutamate in the light or dark?
dark
what does a high acuity mean on a cellular level?
there are more photoreceptors
also influenced by refraction
which photoreceptor type is designed for seeing in dim light?
rods
which photoreceptor is designed for seeing in normal daylight?
cones
which photoreceptor type has more photoreceptors to a ganglion
rods
which photoreceptor type produces a more focused image?
cones
do you need more rods or more cones to generate an action potential?
more rods
how do we see colours?
different wavelengths of light detected by the different types of cones
what colour do the different cone types percieve?
short wave= blue
middle wave= green
long wave= red
what happens if you shut off one eye while it’s still developing?
the other eye will become predominant-the terminals on the visual cortex only supplied by the open eye.
