Week 9 Flashcards
what is anatomical features of the rods
Rods • Outer segment (OS) and inner segment separated by the cilium. • Shape actually “guides” light to the discs. • OS contains discs with pigment. • IS contains cellular machinery
What is the major fuel requirement for the retina
Maintaining the electrical circuit requires within requires great deal of energy which is balanced by Na+/Ka+ ATpase
Rods have the highest energy requirement of all cells in the body and this happens in the dark when they are not doing anything!!
What is the difference between rods and cones
Overall structure (inner/ outer segment) is similar • Rods are thinner • Rods have rhodopsin in discrete discs • Cones have iodopsins (LMS or BGR) in discs which are continuous with the cell membrane.
How many types of cones are there?
There are three types of cones Long, Medium and Short wavelength (LMS; Red, Green, Blue) • Each has a slightly different pigment (iodopsin) that has a higher sensitivity to particular wavelengths of light • ~63% red, 31% green, 6% blue
What are bipolar cells and what is there function
Bipolars sit in the outer
nuclear layer with synapses
at the outer plexiform layer and inner
plexiform layers.
sit between photoreceptors and ganglion cells
They Begin the first level of post receptoral processing. By turning On and Off to light signals by weighing the probability to detect which cone the signal is coming from
The then send down the processed signal to ganglion cells
What are horizontal cells and what is there function
Located in the outer retina.
– Outer plexiform layer
Make contact with both
photoreceptors and bipolar
cells to change their firing
threshold. thus maintains light sensitivity
Responsible for
maximising contrast by modulating(controlling) brightness
What are amacrine cells and what is there function
Responsible for
modulation of brightness
and the beginning of
motion perception
What are ganglion cells and what is there function
All cell feed down to ganglion cell in one way or the other. Ganglion cell are the cells which then send signal off from the inner retina to the optic nerve and the brain
Located in the ganglion cell
layer (innermost layer of retina)
and synapse with bipolar cells in the inner plexiform layer
Cell bodies of the ganglion cells form
the ganglion cell layer of the retina
~ Axons form the retinal nerve fibre
layer
There may different types of ganglion cells and each having specific function and duty
Magno, Parvo, Konio
What are Muller cells and what is there function
V.imp Cell line all the way from the inner layers of the retina to REP
Spans the entire retina • Responsible for: – maintaining metabolic substrate delivery – Neurotransmitter recycling – removing and shunting Ions buffering – Act as Waveguides. like fibre optics
what is the simplest pathway of light travelling in the retina
hitting
photoreceptors –> bipolar cells –> ganglion cells
what forms the optic nerve and optic nerve head
Ganglion cell axons
converge to form the optic
nerve head
~ Continues outside the
globe as the optic nerve
•Ganglion cell axon entering at the edge of the optic nerve serve the retina furthest from the nerve
where does the optic nerve pass through?
The optic nerve passes through optic canal alongside ophthalmic artery
what provides insulation to the optic nerve fibres in the optic nerve and what is its purpose
• Nerve fibres insulated from their neighbours by neuroglia (a type of astrocyte cell)
why?
it prevents cross talk between optic nerve fibres so that there is no noise that is produced in our system
why is optic nerve myelinated?
Nerve fibres are myelinated from the retrolaminar portion of
the optic nerve head to the LGN
Role: Greatly increases speed and efficiency of action potential conduction (controls voltage drop)
Oligodendrites and myelin also prevent axon sprouting or
branching within the optic nerve
(so that ganglion cells can travel straight through the visual pathway without making wrong connections.
What happens to nerve fibres at the optic chiasm
Crossing of nerve fibres
-the nasal fibres cross whereas temporal fibres remain ipsilateral (same side)
The effect of this is that
Right visual field is represented in left visual cortex and left visual field represented in right cortex
Rotation of nerve fibres also occurs
