Tutorial Questions Flashcards
What is the excitation of GFP
Stimulated by blue light. Excitation wavelength of 395nm
Emission of GFP
Emits green light at 509nm wavelength. Microscope imaging tells us about the morphology and function of neurons
Describe channelrhodopsin
It’s a light gated non selective ion channel, which opens upon stimulation by blue light
What is the function of channelrhodopsin
Opening by blue light stimulation causes Na+ influx into cell = depolarisation. If threshold is met, an action potential will be generated
Describe Halorhodopsin
A chloride specific light-gated ion channel, which opens upon yellow light stimulation
What is the function of halorhodopsin
Upon opening by yellow light stimulation, Cl- influx into cell = hyperpolarisation. This moves membrane potential away from threshold, preventing the firing of an action potential
Describe the function of GCaMPs
GCaMPs are GTP-based calcium indicators - allows imaging and visualisation of neuronal responses to different stimuli
Describe the mechanism of GCaMPs
- 2 calcium binding proteins fuse to GFP
- Activity of neurons causes an increase in Ca+ inside the post-synaptic membrane
- In presence of calcium, the 2 binding proteins interact
- This interaction changes confirmation of the GFP
- GFP fluoresces much brighter
What are the benefits of using a confocal microscope
- High spacial resolution (pinhole in between lenses means only light from focal plane Is accepted)
- Can image live samples in situ
- Can produce 3D images
What are the main electrophysiological techniques
- Patch clamp
- Sharp electrode
- RNA tomography
- fMRI
What is the patch clamp technique used for
to study ionic voltage currents of single ion channels in individual isolated living cells, tissue sections, or patches of cell membrane. Opening of sodium channels causes drop in mV- brief downwards deflections in current
Describe how the patch clamp technique is done
- Touch cell with glass pipette filled with electrolyte
- Apply negative pressure to suction membrane
- This forms a tight junction with membrane for ion flow
- Record small electrical current of single channel via electronic amplifier
Patch clamp va sharp electrode
- Only patch clamp can record single channels
- The larger tip of the glass pipette in patch clamp allows for lower resistance = better electrical access to inside of cell
- Patch clamp experiences run-down or dialysis, where sharp electrode can record for longer periods
Describe sharp electrode recordings
uses a fine-tipped glass micropipette inserted into the neuron, allowing direct recording of electrical events generated by the neuron (membrane potential, resistance, time constant, synaptic potentials and action potentials. Records whole channels
Describe RNA tomography
This technique is used to understand neuronal diseases such as stroke. Thinly sliced tissue is profiled in all directions and then mathematically image reconstructed to determine genome wide 3D expression patterns
Describe the structure of the retina
3 layers of neurons and 2 layers of synapses
Layer 1: photoreceptors
Layer 2: outer plexiform layer
layer 3: bipolar cells
Layer 4: inner plexiform layer
Layer 5: ganglion cells
What are the feedforward neurons
- Photoreceptors (excitatory Glu)
- Bipolar cells (excitatory Glu)
- Ganglion cells (inhibitory GABA)
What are the feedback neurons
- Horizontal cells
- Amacrine cells (inhibit ganglion cells)
What are the function of Rods
• active in dim light
• black and white
• low resolution
What are the functions of cones
• active in bright light
• colour
• high resolution - in fovea
What area of the brain processes visual information
The lateral geniculate nucleus - located in the thalamus, it’s responsible for initial processing directly from ganglion cells via optic nerve
What are the 2 visual pathways
- Ventral Stream - identifies objects
- Dorsal Stream - spacial location & speed
Receive information from primary visual cortex
What happens when light intensity increases
• less glutamate release from photoreceptors - cones
• depolarisation of ON bipolar cells in the inner plexiform layer
• hyperpolarisation of OFF bipolar cells
What is the receptive field
An area of the retina which when illuminated activates visual neurons. Indirect activation by horizontal cells
What is centre surround organisation of the receptive fields
allows ganglion cells to transmit information about whether photoreceptor cells are exposed to light and about the differences in firing rates of cells in the center and surround. This is achieved by responding to differences in illumination. Illumination of centre & surround = responses in different polarities
Recall the different ganglion cells
- Parrocellular (80%)
• shape and colour
•Small receptive field - Magnocellular (10%)
• motion detection
•large receptive field
What features of a sound need encoding
- Frequency (pitch)
- Intensity (loudness)
- Onset
- Duration
Need to distinguish different sounds for communication, memory, survival
What are the important steps in transforming sound into a neuronal signal
SOUND WAVES enter the ear canal and cause the eardrum to vibrate. VIBRATIONS pass through 3 connected bones in the middle ear. This motion SETS FLUID MOVING in the inner ear. Moving fluid bends thousands of delicate hair-like cells which convert the vibrations into NERVE IMPULSES.
What are the different chambers of the cochlea
- Scala vestibular
- Scala tympani
- Scala media
What chambers are filled with perilymph
Scala vestibular and Scala tympani
Contains low K+, normal Ca2+ and high Na+
What chambers are filled with endolymph
Scala media
Filled with high K+, low Ca2+ and low Na+
What is the function of the chambers of the cochlea
The ST and SV sense pressure changes caused my sound waves. The SM contains the organ of Corti and basilar membrane where the vibrations move the stereocillia to transduce sound into a a neuronal impulse
What is cochlear tonotopy
In the auditory system their is a gradient of high and low frequency. The apex of the cochlea receives low frequency sounds and the base high frequency sounds
Why is tonotopic organisation important
Sounds travel along cochlea and activate specific hair cells. It is the position of the active IHC along the cochlea that encodes sound frequency, this allows for interpretation of a specific sound frequency. PLACE-FREQUENCY CODE
Describe the organ of Coti
Located within the Scala media. Transduction of sound waves - It contains rows of Inner and outer Hair cells which bend with sound waves to produce neuronal activity
Describe the function of inner hair cells
Located on basilar membrane of the Organ of Coti. convert, or transduce, mechanical stimuli evoked by sound and head movements into electrical signals which are transmitted to the brain via auditory nerve.
How is tonotopy established
It’s created by the basilar membrane and preserved along the entire auditory pathway
Describe the function of outer hair cells
Combined movement of 3 rows of OHCs:
1. Acts as positive feedback in cochlea
2. Increases movement of Basilar Membrane
3. Increases stimulation of IHCs in hair bundles
AMPLIFIES STIMULATION OF IHCs
How to OHCs act as a cochlear amplifier
Their stimulation results in electromotility of the CF region, amplifying movement of basilar membrane - increasing stimulation of the IHCs. Damage or loss of OHCs can cause hearing loss
Areas of the ventral stream involved in stimulus recognition
- V1 (detection of edges)
- V2 (orientation)
- V4 (colour)
- IT (faces)
-> temporal pathway
OBJECT INDENTIFICATION
Simple cell receptive fields
E.g V1 neurons
• found in layer 4 & 6 of Cortex
• elongated receptive fields
• centre of receptive field is position linearly (in a line)
Complex cell receptive fields
E.g V2 neurons
• found in layers 2, 3 & 5 of cortex
• can respond to objects in a certain orientation anywhere in receptive field
• collect information from many simple cells with similar RF orientation
Principle behind hierarchal model of object recognition
Increase complexity of response and receptive field size of neurons as you go along the ventral stream
- involves the integration of information from multiple levels of processing.
What are the types of columns in the cortex
- Ocular dominance column
- Orientation column
Each column receives information from either eye - Left or Right column - Blobs (colour)
- shown together as a hypercolumn
Describe retinotopic maps
These are an organisation where neighbouring cells in retina feed information to neighbouring places in their target structures. Created mapping of visual information from retina to neurons in brain
Describe the function of the dorsal stream in stimulus localisation
MOTION DETECTION
1. V1 cortex ( edges)
2. V2 cortex (orientation)
3. V3 cortex (motion)
4. Medial temple cortex (movement)
-> parietal pathway (where)
Circuit of direction selectivity (motion anticipation)
- Orientation selective photoreceptors send information to ganglion cells
- Information is sent via the dorsal stream to process motion
- The superior and inferior colliculus orientates body towards stimulus - saccades
What is sound localisation
the ability to tell the direction of a sound source in a 3-D space - needed in survival and perception
What are the different strategies used to localise sounds in the horizontal space
- Interlaural level differences
- differences in loudness In each ear - Interlaural timing differences
- differences in arrival time in each ear
Describe the sound localisation mechanism using ILDs
• detected in the LSO
• excitatory in near ear, inhibitory in far ear
• neurons in LSO encode the summation of the excitatory and inhibitory inputs from both ears
• brain recognises position of sound from balanced & opposite outputs of both LSO channels
• closer the sound the larger the input
Describe the sound localisation mechanism using ITDs
• detected by the MSO
• 2 excitatory inputs converge in MSO
• encoded by neurons that compare the coincident arrival of excitatory inputs from both ears
• brain is able to recognise position of a sound from balanced & opposite outputs of the 2 MSO channels
Compare the 2 mechanisms used for sound localisation
• both based on 2 broadly tuned channels
• recognition is based on the balanced and opposite outputs of the channels
• LSO tuned to sounds from the same side of head (e.g left LSO - left side head)
Where the MSO is tuned to the opposite side of the head (e.g left MSO - right side of head)
• LSO encodes excitatory and inhibitory inputs, where the MSO only detects excitatory inputs
Interaction between visual and auditory senses
The visual map is dominant for space perception & used to realign any differences between sensory and auditory map. Visual system rapidly adapts but the auditory map takes longer
3 types of memories in aplysia
- Habituation - decrease gill withdrawal reflex
- Sensitisation - increase gill withdrawal reflex
- Associative learning
Describe the mechanism of habituation
Repeated stimulation decreases amplitude of motor response.
Reduced synaptic strength = reduced glutamate release
Depletion of RRP
Describe the mechanisms of sensitisation
Seratonin released at presynaptic L29 sensory neurons - action at G protein coupled receptors
G protein binding with adenyl cyclase -> cAMP -> pKA -> phosphorylation of K+ channels = longer depolarisation time and therefore more neurotransmitter released
Describe the mechanism of associative learning
Conditioning:
Weak siphon touch paired with strong shock - bigger withdrawal response
Early stage: G protein + adenyl cyclase -> cAMP -> pKA = phosphorylation of K+ channels -> longer depolarisation and increased sensitisation
Late stage: MAP kinases activate gene transcription = increased sensitisation
Mechanism of LTP
- Synaptic changes due to glutamate cause LTP
- When LTP occurs NMDA receptors open
- Ca2+ influx into post synapse
- Increase calcium concentration activates protein kinases
- Phosphorylation of certain proteins
- Leads to increase in amplitude of EPSPs
Cerebellar Mechanism of LTD
- Cerebellar mechanism
• needs co incident activation from both signally pathways
• occurs at excitatory synapses of Cerebellar cortex
Involves 3 receptors: - Metabotrophic glu-R
- AMPA-R
- Voltage-gated Ca2+ channels
• reduces currents by endocytosis
• reduced responsiveness to glutamate
Hippocampal mechanism of LTD
• requires activation of NMDA receptor
• calcium dependent
• synapses weaken when they are active when shouldn’t be
• reduced responsiveness to glutamate
Describe how to trigger LTP
Prolonged high frequency stimulation of post synaptic neurons = increased amplitude of EPSPs
Depolarisation of 2 neurons at same time increases synaptic strength and EPSP rate = LTP phenomenon
Role of NMDA receptors
They have a voltage dependent Mg2+ block - must be indirectly pre activated by GLUTAMATE
Then they can depolarise to cause calcium influx
What is the role of calcium in LTP and LTD
Calcium plays a role in long term plasticity by triggering post-synaptic signaling pathways for both the strengthening (LTP) and weakening (LTD) of synapses
Discuss the phosphate- kinase balance
• small increases in Ca2+ from NMDA-receptors trigger more phosphatase action and reduce AMPA-R efficacy = INCREASES LTD
• large increases activate more protein kinases and increase AMPA-R efficacy = INCREASES LTP
Discuss AMPA receptor trafficking
AMPIFICATION - ready-prepared AMPA receptors delivered to synapse. - increases in AMPAR function at synapses result in the long-term potentiation (LTP) of synaptic strength, whereas removal of synaptic AMPARs leads to long-term depression (LTD)
Describe cerebellum LTD circulatory
• inputs +ve mossy and climbing fibres
• outputs -ve purkinje fibres
• paired purkinje fibre and climbing fibre input to single purkinje cell evokes LTD
Explain the drift diffusion model
• start at initial Z level
• as you proceed with evidence moving either way - draw a marker
• then with confidence of evidence you reach a decision
What is the speed accuracy trade off
Cut trail short there isn’t enough time to accumulate noisy - sensory input = can’t reach correct decision bound
- evidence accumulation traces on wrong side of DD model
How to neurons adapt to increasing motion strength
Neurons in the LIP increase activity with increased coherence in stimuli and therefore will decrease their reaction time
Evidence accumulated by Kenyon cells - decrease K+ channel expression to spike membrane potential towards threshold
Describe classical conditioning
The conditioned stimulus should coincide with or proceed the unconditioned stimulus
US - food
UR - drooling to food
CS - bell
CR - drooling with bell
Pavlov’s dogs
What is the neural circuitry underlying olfactory learning in flies
Odour -> olfactory receptor neurons -> projection neurons -> kenyon cells
• within the mushroom body
• kenyon cell axons subdivided into categories by innervation of MBONs and DANs
• -> approach / avoid memory
How does learning happen in drosophila
•DANs are paired with MBONs of the opposite valence -
Dopamine signalling weakens synapses between KCs and MBONs = wrong actions
Experimental data for olfactory learning in flies
Pairing electric shocks and odour stimulus
Stimulating electrode to brain
Similarities between insect mushroom body and cerebellum-like structures
•training of circuit reduces wrong behaviour
• stimulus is detected by receptors which are projected to neurons in brain where they are processed and analysed for learning (e.g granule cells vs kenyon cells)
How do odours differ from other senses
They can’t be classified dimensionally
Don’t enter thalamus for processing, sent straight to cortex
Principles of odour transduction
- Odourants bind to receptors on cilia surface - causing a G- protein cascade
- G protein + adenyl cyclase = cAMP
- cAMP activation causes opening of cation channels
- Depolarisation of olfactory neuron by Na+ influx -> firing of an AP
* amplification by 2nd messengers
* signalling cascade of events
Key brain areas involved in olfactory behaviour
- Olfactory bulb - processing
- Piriform cortex (mammals) & mushroom body (insects) - LEARNED BEHAVIOUR (discriminate)
- Amygdala (mammal) & lateral horn (insects) - INNATE BEHAVIOUR (categorise)
Which neurons are involved in odour transfer to 2nd order neurons at the glomeruli
(Mammals) Olfactory sensory neurons -> granule cells -> mitral & tufted cells
(Flies) olfactory receptor neurons -> local neurons -> projection neurons
How is odour specificity carried through
receptor- specific matching of sensory neurons to second order neurons at glomeruli
Here the odour code is transformed
How do we distinguish this odour codes with background noise
Lateral cross-talk:
1. Gain control - become sensitive to very weak and very strong odours
2. De-correlation - make neuronal population responses to every odour as different as possible
- cancel out weaker responses and distinguish odour
Discuss olfactory search behaviour: biased random walk
• bacteria and C.Elegans can swim straight “run” or turn “tumble”
-> if things are getting better bacteria will run more and tumble less
Discuss olfactory search behaviour: head casting
• mice, dogs
• move head around = sample a larger space & detect odour concentrations
- faster detection of smell
How do IHCs transduce sounds
- Vibrations from sound wave cause shorter hair cells to bend towards longer hair cells
- This action causes stretching of tip-links = mechanical transducer channels open
- K+ influx causes depolarisation
- Leads to Ca2+ influx -> exocytosis of glutamate
- Activation of synapses cause AP down afférent neuron
• slackening of hair cells closes channels
