Chemical Senses

Question 1

Olfaction compared to other senses.

Answer 1

Can link to memories and emotions.

Dogs can smell tumours.

Multidimensional coding space and they are hard to categorise.
Vision can be categorised easily by colour and brightness. But smell cannot.

Question 2

Labelled line vs combinatorial code

Answer 2

Labelled line is where a single neuron responds to a specific molecule.

Combinatorial code is where sugar would be encoded across many channels and it’s not as simple as labelled line. And this is the case most of the time.

Question 3

Olfactory amplification

Answer 3

All of the secondary messenger signalling pathways are designed to amplify signals so even a very small amount of odour molecules can cause a response.

In mammals they are G protein
In insects they are ionitropic.

Question 4

Olfactory receptors in different animals

And when they mature

Answer 4

There are many types of olfactory receptor. Each type binds to a unique profile of odourants.

Flies have 50 types.
Humans have 300/400
Mice have 1000

Each neuron has only one type of receptor. As olfactory neurones mature they narrow down to express a single type of receptor. but at the start they can have many.

Question 5

Glomerulus and where it is

Answer 5

Means little ball of thread.

Sensory neurons with the same type of receptor all go to the same glomerulus.

In drosophila the sensory neurons send their axons to the antennal lobe (called olfactory bulb in humans)
Pictures can show the axons which come from sensory neurons expressing the same receptor and converge into one glomerulus.

Question 6

Sensory neurons vs receptor neurons

And where does the info go from here

Answer 6

In mammals it is called sensory neurons.

In drosophila is it called receptor neurons.

It goes to the second order neurons at the glomeruli.

Question 7

Second order neurons.

Answer 7

They are called mitral tufted cells in mammals.

They are called projections neurons in drosophila.

And each mitral cell receives input from one glomerulus.

Question 8

The first relay synapse

Answer 8

The synapse connecting the sensory neuron to the second order neuron.

Question 9

Sensory and second order neuron spiking.

Answer 9

Sensory neuron spikes evenly when the odour occurs.

Second order spikes a lot at the start and then less later on. This is due to adaptation.

The sensory neuron has vesicles saved up that it releases all at once to the second order neuron at the start of stimulation.

This allows the NS to respond to changes in the odour concentration.

Question 10

How do sensory neurons join to second order neurons.

Answer 10

Many sensory neurons converge into one second order neuron.

This reduces noise by having one neuron to average together the info from many sensory neurons.

It will strengthen weak responses because the second order neuron is listening to many sensory neurons at once.

Question 11

Lateral interglomerular cross talk

Answer 11

There are neurons that carry info between the different glomeruli.

Many of these are inhibitory.

They allow us to be sensitive to very weak and very strong odours.

They decorrelate population responses. They make responses to different odours as different as possible.

Question 12

Innate and learned odours.

Answer 12

Animals innately know that food smells good. Humans use the amygdala for this and insects use the lateral horn.

They can learn new odours.
In humans this is done by the piroform cortex
In insects it’s the mushroom body that contains Kenyon cells.

Silencing nice amygdala means they no longer avoid smells associated with danger.

Question 13

Innate neurons vs learned ones.

Answer 13

Innate neurons have a more dense activity because a neuron will respond to many smells if they are all in the same category.
They will have preferred odours and a more strereotyped activity.

Learning neurons have more sparse activity and are specific to a small number of odours.
They respond to arbitrary odours as they don’t know what possibilities are out there and they will have random connectivity.

Question 14

Bacteria movement

Answer 14

They can swim straight (runs) or turn (tumble) by spiralling their flagella.

They follow a simple rule to reach nutrients.
If nutrient conc increases then run more. If it decreases then tumble and swim another direction.

They have a nutrient receptor.

Question 15

C elegans rule

Answer 15

Their cillia detect an odour increasing and this causes suppression of the worm turning another direction.

When there is no odour then the suppression will not be there and they can turn away.

Question 16

Drosophila smelling in the wind

Answer 16

Searching for smells in the air is a lot more complicated because of gusts of wind creating odour plumes.

If they smell something nice they go upwind.

If you lose the odour wait before turning around because plumes are turbulent.

Mechanoreceptors test wind direction.

Question 17

How we do active sensing.

Answer 17

Moving your head around lets you sample a larger space and helps to detect changes in odour conc best.

Mammals can coordinate the sniff cycle with how you move your head.

Question 18

Taste 4

Answer 18

Secondary messenger cascades work to amplify the signals.

Bitter sweet umami have G protein.
Salt and sour have ligand.

Taste buds send axons through the cranial nerves to the brain stem. Then to the ventral posterior medial nucleus of the thalamus and then to the cortex.

Question 19

Lateral inhibition in taste.

Answer 19

Helps with distinguishing tastes.

The sensory neurons are inhibited by bitter compounds.

A GABA interneuron will inhibit sweet neuron activation and stop feeding behaviour in response to bitter stimuli.
The GABA interneuron will stimulate the bitter neuron which cause avoidance behaviour.

Question 20

Mouse insula

Answer 20

There are hot spots in the mouse insula that are responsive to particular tastes.

Optogenetically expressed channel rhodopsin which activates neurons when illuminated. This can be used to activate sweet or bitter areas of the insula. Which made the mice approach or avoid the light which was activating their brain areas.

Question 21

what are some examples of how we do object localisation

Answer 21

the orienting reflex where we move the head and eyes to focus stimuli on the fovea, this can happen for auditory and visual stimuli.
smooth pursuit is where we follow a moving object.

we predict future motions during prey capture.
saccadic movements/ constant movement of eyes during object inspection, this is not random and the eyes are looked at most when we are studying a face.

Question 22

what leads to disappearance of the orienting reflex

Answer 22

ablation of the optic tectum (superior colliculus in mammals)

Question 23

how long does the phototransduction cascade take and why is this important

Answer 23

it takes 60ms so we are actually seeing the recent past, this is why we need motion prediction because some things move so fast we cannot follow them.

Question 24

g

Answer 24

g

Question 25

where does the superior colliculus receive information from and what does it do

what is its main function and what does a lesion cause

Answer 25

ganglion cells, auditory system, somatosensory system.
it integrates information from different sense to make a decision on where to move.

its main function is to regulate saccidic movements
lesion leads to disappearance of the orienting reflex.

Question 26

what is retinotopic map organisation

what is motor map organisation

how are they linked

Answer 26

neighboring cells in the retina feed info to neighboring places in their target structures (superior col, LGN etc)

the neruons in the superior colliculus are also organsied into maps, stimulation of a specific neuron will shift the eye to a specific angle, these are motor maps.

the retinotopic maps and the motor maps are aligned with eachother and when you see something in a particular visual field, a particular neuron is activated in the superior colliculus.
if this activation is too large it will lead to activation in the lower neurons which are responsible for moving the eye in a particular direction.

Question 27

which areas are involved in stimulus localisation and motion processing

Answer 27

the analysis of the info starts in the retina, there are direction orientation selective ganglion cells and neurons for motion anticipation.

the dorsal stream in the cortex

the superior and inferior colliculus.

Question 28

where does motion processing start to happen and where does the info go

what are the neurons like in the path

why do we need motion processing

Answer 28

it starts in the magnocellular ganglion cells and then down the dorsal stream.

the neurons are motion sensitive and retinotopically organised.

we need it to see coffee pour into a cup, if not everything would look static.

Question 29

what is the direction of movement that causes the biggest response in a neuron called

what is the direction giving no response called

where is this direction selectivity seen

Answer 29

preferred direction

null direction

in the ganglion cells in the retina
PIC OF CIRCLE GRAPH

Question 30

is the foveation hypothesis valid and what does it say

Answer 30

it is not valid

it says that interaction between the retinotopic maps initiates the orienting reflex

Question 31

what is the morphology like of direction selective cells

Answer 31

highly asymmetric, they only have dendrites in one particular direction and this helps with responding to motion in one particular direction.

Question 32

what types of input do the retinal ganglion cells receive

what happens when there is motion in the preferred direction compared to the null

Answer 32

they get excitatory input from bipolar cells and inhibitory input from amacrine cells.

when there is motion in the preferred direction the cell depolarises and fires an AP. the excitation input is larger than the delayed inhibitory input.
when the motion is null the cell depolarises but doesnt fire an AP. the excitation is smaller and delayed and the inhibition is larger.

PICTURE OF SMALL BAD WAVES

Question 33

what is the difference between how static and moving objects are processed

Answer 33

the retina predicts the location of moving objects, they start spiking before the object approaches the receptive field, 80ms before.
for static objects spiking will occur 60ms after it has entered the receptive field.

Question 34

what is the difference between declaritive and non declaritive memory

long term vs short term memory

Answer 34

declaritive is memories of facts and events.
non declaritive is accessed without conscious thought like walking or biking.

long term memory lasts longer than short term.

Question 35

synaptotagmin

Answer 35

triggers ntm release when ca binds

Question 36

what are the types of synaptic vesicle

Answer 36

readily releasable vesicles are attached to the active zone and are released as soon as the Ca conc rises

proximal pool vesicles are not in the active zone yet and are not ready to be released

reserve/resting pool of vesicles which is where most of the vesicles are, far from the active zone.

Question 37

what are the types of glutamate receptor

which ones are permeable to Ca

Answer 37

there are two ionotropic types-
NMDA and non NMDA.

there is one type of metabotropic-
mGlut.

NMDA receptor is permeable to Ca but the non NMDA receptor is not.

Question 38

why is it good to use invertebrates for study

Answer 38

they have larger neurons sizes than mammals so electrophysiology is easier.
they have simpler circuits but we cannot directly correlate it to humans.
most of them are temperature dependant so you dont have to worry about what temperature to keep the animals at.
they have characteristic neurons so you can make neuron maps and each neuron can be defined.

Question 39

what are some simple forms of memory in invertebrates

Answer 39

habituation- a form of adaptation where a repeated stimulus will result in the response decreasing, but only if the stimulus is not harmful. after a while you will become desensitized to the stimulus.

sensitisation- repeated presentation of a stimulus results in increased behavioral response.

Question 40

aplysia- what do they look like and what reflexes do they have.

how do the reflexes change with repeated stimulation

Answer 40

they have a gill for breathing and a siphon for locomotion.
they have a gill withdrawal reflex when poked on siphon, a sensory neuron on the siphon detects something and sends info to the gill by motor neuron to withdraw.
when you touch the siphon many times the reflex is reduced.
they are happy being cold

Question 41

why does habituation occur

Answer 41

there is a reduction in synaptic strength.
there is reduced transmitter release, the readily releasable group of vesicles is much fewer, a 50% lower quantal release.

Question 42

example of sensitisation in the aplysia

what are the different neurons involved and how do they cause a bigger response

Answer 42

pairing an electric shock with poking the siphon causes an increase in the response.
after a while, poking with no shock will still give a large response.
the L29 neuron will detect the electric shock and synapse with the presynaptic side of the sensory neuron.
the L29 neuron releases seratonin from its pre synapse onto the sensory neuron axon. This will activate the G protein and then adenylyl cyclase and then pka.
pka inactivates K channels and means there will be more depolarisation for longer and more vesicle release.
PICTURE

Question 43

discuss the siphon touch and shock pairing in terms of pavlovs dogs

Answer 43

the siphon touch is the conditioned stimulus
the shock is the unconditioned stimulus

the L29 neuron and the sensory neuron are activated at the same time.

Question 44

associative learning vs sensitisation

Answer 44

associative learning gives a bigger response than sensitistion because in associative learning both L29 and the sensory neuron are active together.