Week 2 - H - Pharmacology 6 - Physiology of Vision

Question 1

Label the coloured boxes on the diagram - start with the black and work way around to the purple

Answer 1

Black - cornea Blue - iris Green - pupil White - anterior chamber Red - suspensory ligaments of the lens (zonule fibres) Yellow - ciliary body Purple - fovea

Question 2

For the light to reach the photoreceptors it has to pass by the bipolar and ganglion cells in the retina Once reached the photoreceptors in then travels back on these cells to reach the otpic nerve WHat are the types of photoreceptors?

Answer 2

The two types of photoreceptor are rods and cones

Question 3

What cells recieve the signal information from the photoreceptors? What do they project the signal on to before it reaches the amacrine cells?

Answer 3

Horizontal cells recieve the information from the photoreceptors They project information onto bipolar cells which then project onto the amacrine cells

Question 4

Once the amacrine cells receive the signal, what do they project onto before the optic nerve recieves the signal?

Answer 4

They project onto the ganglion cells which come together to form the optic nerve : Photoreceptors horizontal cells bipolar cells amacrine cells ganglion cells optic nerve

Question 5

Which cell in the pathway for visual signals is it where transduction for light to a neuronal signal takes place?

Answer 5

This happens in the photo-receptors

Question 6

There are two types of photoreceptors in the human retina, rods and cones. Is it rods or cones that are responsible for vision at low light levels?

Answer 6

It is the rods that are responsible for vision at low light levels Cones are responsible for vision at normal light levels and colour vision

Question 7

Do rods or cones provide sharp visual acuity?

Answer 7

It is the cones that provide sharp visual acuity Rods provide a low visual acuity

Question 8

Glutamte is the neurotransmitter released by the photoreceptors in the signal pathway for vision Is more glutatamte released in the light or in the dark?

Answer 8

In the dark more glutamate is released and less is released in the light resulting in hyperpolarization of the cell

Question 9

What facilitates high acuity?Photoreceptor Spacing Visual Acuity Ability to distinguish two nearby points. Determined largely by photoreceptor spacing and refractive power What is the receptive field?

Answer 9

This is the part of the retina that needs to be stimulated to elicit action potentials from a ganglion cell in the cell’s receptive field (basically if light hits a certain aspect of the retina, the receptive field will show the image that correlates to the photoreceptors of a specific ganglion cell in the area hit)

Question 10

Rods – seeing in dim light Cones – seeing in normal daylight The rods need to be spaced apart to increase their sensitivity, what does this mean for the acuity?

Answer 10

This results in a decreased visual acuity in dim light

Question 11

Rods or cones Peripheral retina Colour vision (chromatic) Night time? High sensitivity? High visual acuity?

Answer 11

Peripheral retina - rods Colour vision (chromatic) - cones Night time - rods High sensitivity - rods - hence why they are better fr night vision High visual acuity - cones

Question 12

Which cells produce the action potentials in the retina? What are the retinal neuronal cells again?

Answer 12

The ganlion cells are the only cells in the retina that can produce an action potential The rest can only produce graded potenitals Photoreceptor- horizontal cell - bipolar cell - amacrine cell - ganglion cell - optic nerve

Question 13

Do nerve fibres from the nasal or temporal halfs of the retina cross over?

Answer 13

Nerve fibres from the nasal half of the retina cross over

Question 14

What is the nuclei of the optic nerve?

Answer 14

These are the lateral geniculate nuclei found in the thalamus

Question 15

What is the striate cortex and where is it roughly located?

Answer 15

The striate cortex is the primary visual cortex located mainly around the calcacrine sulcus Upper half of calcarcine sulcus represents the lower half of visual field Lower half of calcacrine sulcus represents the upper half of visual field

Question 16

State the location of the lesion and the visual defect

Answer 16

A - right optic nerve - right monocular blindness B - optic chiasm - bitemporal hemianopia C - right optic tract - left homonymous hemianopia D - right temporal inferior optic radiation - left superior homonymous quadrantanopia E - right occipital cortex - left homonymos hemainopia with macular (central) sparing

Question 17

Why does the optic radiation split into temporal and parietal? What is the loop known as?

Answer 17

They split due to the temporal radiation having to loop around the inferior horn of the lateral ventricle The loop is known as Meyer’s loop Nb PITS- Parietal inferior (visual field), temporal superior (visual field)