Lecture 10 + 9b

Question 1

Microdialysis

Answer 1

Use an artificial semipermeable membrane to either deliver molecules or measure them

Microdialysis probe is a small meatal tube that holds the membrane. Places in the animals brain

It takes time for the conc or molecules to equilibrate across the membrane so the fastest sampling rate possible is once a min. More common to see once every 10

Can then correlate the release of the detected neurotransmitter with the activity the animal was doing when it was detected

Question 2

Immunohistochemistry

Answer 2

Histological = label proteins and peptides
Make antibodies that are attracted to the receptor proteins of a specific target

Antibodies are florescent and when washed over a brain slice, bind to their targets making them labeled and easy to ID

Tells us which proteins the cell expresses and hence, what transmitters they released and what neurotransmitters they have receptors for

Cannot make an antibody for a neurotransmitter as too small but CABN target proteins associated with it

eg a protein that makes them like an enzyme is feasible

Question 3

Immunohistochemistry and expression of immediate early genes

Answer 3

Immediate Early Genes are expressed following periods of elevated spiking

c-Fos is one - rises in nucleus minutes after an increase in neural activity

Use immunohistochemistry to determine what neurons were highly active in the hour two before they died

Question 4

Sensation vs perception

Answer 4

Sensation - how cells of nervous system detect stimuli and how they transduce these signals

Perception - the conscious experience and interpretation of sensory information

Question 5

Sensory transduction

Answer 5

Transduction - sensory stimuli converted to receptor potentials

Question 6

Receptor potential

Answer 6

receptor potentials are graded change in the membrane potential of a sensory neuron caused by sensory stimuli

Question 7

Sensory neuron

Answer 7

Sensory neuron - specialized neuron that detects a particular category of physical event (eg photoreceptor cell)

Question 8

Do all sensory neurons make action potentials

Answer 8

NO

All release neurotransmitter

Some don’t make APs but release neurotransmitter in a graded fashion, depending on their membrane potential

The more depolarized, the more the release

Question 9

4 types of light detectors protein

Answer 9

Receptor proteins sensitive to light are called opsins

4 types of opsins

rhodopsin, and red, blue, green cone opsins
Each photoreceptor only has one

Question 10

Photoreceptors

Answer 10

Transduce EM energy of photons into receptor potential

There are 4 of these, one for each opsin

Question 11

Opsin

Answer 11

They are responsible for transduction. They are all INHIBITORY metabotropic, g-coupled receptors

Cone cells express one cone opsin
rods, rhodopsin

Question 12

Retinal

Answer 12

Small molecules (from vit A) the bind to opsin proteins

Retinal absorbs light

Type of light absorbed depends on protein it is bound to

Question 13

Two configurations of retinal

Answer 13

Is in opsin protein which is embedded in the cell membrane of photoreceptor cells

One electron absorbs energy from light

The high energy electron changes the shape of the retinal

This causes, the opsin to initiate intracellular g-protein signaling cascades cascades that change the membrane potential

An enzyme plus atp restore the original shape of retinal

Question 14

What the eye detects

Answer 14

Red = 580nm peak

Blue 530nm peak

Visible light 380-760nm

Each cone cell is sensitive to s spectrum. With the color the brain perceives coming from the average of all 3 and the intensity of the light in all three.
Hence, more than one rod type is needed for color vision

Question 15

Color perception & Trichromatic Coding

Answer 15

Is a function of the relative rates of activity in these three cell types codes for the color

Also these cells have different sensitivity for light and hence this sensitivity is also a factor

Green cells have the highest sensitivity for light

Question 16

Additive and Subtractive colour

Answer 16

Light, adds together

Paint adds together absorption therefore subtracts
Magenta - pure removal of green
Yellow - pure removal of blue
Cyan - pure removal of red

Question 17

Perceptual dimensions of Color and Light

Answer 17

Brightness - intensity (amount of light)

Saturation - purity (in terms of composite wavelengths)

Hue - dominant wavelength (color)

If saturation is 0%, there is equal contributions from all wavelengths which means you have a black and white image

Question 18

Color blindness

2 types coded for by x chromosone

Answer 18

Genes on X chromosome

Protanopia
1% men
No red opsin. Get filled with green so normal acuity but green-red-yellow spectrum deficits
Mutation in the opsin instead produces milder symptoms (also 1% of males)

Deuteranopia
1% men
No green opsin. Get filled with red so normal acuity but green-red-yellow spectrum deficits
Opsin mutation SIX PERCENT OF MEN - most common color blindness
Less pronounced issue

Question 19

Blue blindness

Answer 19

Tritanopia
1% if population - not on X chromosome
Blue cells do not compensate but acuity preserved as blue cone opsin is not sensitive to light anyway

Question 20

Anatomy of eye

Answer 20

Cornea at front - focuses the incoming light a fixed amount
Iris is pigmented muscles
Lens consists of several transparent layers
Can change shape to focus - accommodation
Pupil regulates the amount of light entering the eye
Sclera is opaque and does not permit entry of light

At back, retina - contains photoreceptors
Central region - fovea, cones and high acuity vision
Blind spot/optic disk

Question 21

Fovea vs periphery

Answer 21

Fovea 1:1:1

receptor:bipolar:ganglia

Periphery 1:X:XY
Sensitive to dim light
Compression of info

Question 22

Cones vs rods

Answer 22

CONES
Prevalent in fovea
Sensitive to moderate/high levels of light
Provide info about hue
Excellent acuity

RODS
Peripheral retina, not found in fovea
Sensitive to low light
Monochromatic only
Poor acuity (cannot read with this)

Question 23

Saccadic movement

Answer 23

6 eye muscles
rapid, jerky movement
Scan scene by one of these to another
Hides blind spot

Pursuit movements allow us to maintain an image of a moving object

Question 24

Photoreceptor cells

Answer 24

Photoreceptor cells – neurons responsible for the transduction of light; they project to bipolar cells.
Bipolar cells – neurons that relay information from photoreceptor cells to ganglion cells.
Ganglion cells – the only neurons in the retina that sends axons out of the eye. They receive information from bipolar cells and project to the rest of the brain; their axons give rise to the optic nerve, which leaves the retina through the optic disc (i.e., the blind spot of the retina).
Horizontal cells – neurons that interconnect and regulate the excitability of adjacent photoreceptor and bipolar cells. They adjust the sensitivity of these neurons to light in general.
Amacrine cells – neurons that interconnect and regulate the excitability of adjacent bipolar and ganglion cells. There are many different types of amacrine cells, and each have different functions

Question 25

Transduction of light into receptor potentials

Answer 25

Photoreceptor cells do not have action potentials.

They release glutamate in a graded fashion dependent on their membrane potential: the more depolarized they are, the more glutamate-filled vesicles they release.

In addition to the regular leak potassium ion channels that all neurons have, photoreceptor cells express “leak” sodium ion channels which are open in the dark (when the cells are at rest).

In the dark, sodium continually enters through these ion channels, which depolarizes the photoreceptor cell membrane to -40 mV. At this depolarized membrane potential, photoreceptor cells continuously release glutamate.

When the retinal portion of the retinal-opsin complex absorbs light, it causes a conformational change (change in shape) in the opsin receptor protein. This launches a g-protein signaling cascade that closes the open sodium ion channels. The closing of these channels hyperbolizes the membrane to -70 mV, at which point the photoreceptor cell largely stops releasing glutamate.

So, photoreceptor cells are more depolarized and release more glutamate in the dark than in the light.

Question 26

Bipolar cells

Answer 26

Like photoreceptor cells, bipolar cells also do not have action potentials and release glutamate in a graded fashion dependent on their membrane potential.

There are two main types of bipolar cells: OFF bipolar cell and ON bipolar cellsOFF bipolar cells express ionotropic glutamate receptors, so they are depolarized by glutamate. Because photoreceptor cells constantly release glutamate in the dark, OFF bipolar cells are more active (more depolarized) in the dark than in the light.

ON bipolar cells (depicted to the right) only have inhibitory metabotropic glutamate receptors, so they are uncommonly inhibited by glutamate. Thus ON bipolar cells are more active (more depolarized) in the light vs the dark.

And finally, retinal ganglion cells (RGCs) are typical neurons. They have action potentials and are generally excited by glutamate.