Introduction to Sensory Processing Flashcards
Name the ‘type’ of sensory processing/coding that takes place in the olfactory system. (1)
Population coding
True or false? Explain your answer if necessary. (1)
In the olfactory system, and other brain systems, single neurones encode individual stimuli.
False - population coding occurs, where combinations of neurones encode a stimulus
What are the collections of neurones called in the olfactory bulb where primary olfactory neurones which detect similar stimuli synapse? (1)
Glomeruli
What is the missing word? (1)
………………… are the functional units of the olfactory bulb that process odours.
Glomeruli
Why are several glomeruli in the olfactory bulb activated when detecting a smell? (2)
Because smells are made up of different odour stimuli (chemicals)
which all activate different glomeruli.
What is meant by a ‘neuronal ensemble’? (2)
*Two slightly different definitions
The neuronal population that is activated by a specific stimulus.
A co-activated group of neurones which carry information on to the next synapse.
Fill the gaps regarding population coding in the olfactory system. (4)
Information is processed within groups of …………………..
For example, a stimulus will activate a range of different ……………….. which will synapse on …………………………
The neuronal population that is activated by a specific stimulus is called a ………………………..
neurones
neurones
a range of second order neurones
neuronal ensemble
Fill the gaps relating to population coding in the olfactory system. (9)
Olfactory sensory neurones lie within the ………………….
They express different ………………….., however each neurone expresses predominantly one type of ……………………. and responds to one particular type of …………………..
All neurones expressing the same receptor types will synapse on the same …………………………. in the ………………………..
However, smells are typically made up of different combinations of molecules and olfactory stimuli. Therefore, smells that humans see as distinct may show some ……………….. with the neurones that are activated.
It is the ……………….. of neurones, also known as the ………………………., which is activated which allows us to distinguish smells.
olfactory epithelium
olfactory receptors
receptor
stimulus
glomerulus
olfactory bulb
overlap
combination
neuronal population
True or false? Explain your answer if necessary. (1)
The number of smells that a human can distinguish well exceeds the number of individual sensory neurones.
True - this is because it is the combination of neurones activated which encode the stimulus
Fill the gaps relating to population coding in the olfactory system. (2)
Different smells activate different neurones at different …………………….. A certain population of neurones being activated at certain strengths give rise to a …………………..
strengths
smell
Name three types of interneurones found in the olfactory bulb. (3)
Periglomerular
Lateral projecting
Granule cells
Where in the olfactory bulb are periglomerular interneurones found? (1)
What neurotransmitter do they contain? (1)
Around the outside of the glomeruli
GABA
Where in the olfactory bulb are lateral projecting interneurones found? (1)
What neurotransmitter do they contain? (1)
connecting different glomeruli
GABA
The glomeruli in the olfactory bulb connect to second order neurones.
Name two types of second order neurone in the olfactory bulb. (2)
Tufted cells
Mitral cells
Second order neurones in the olfactory bulb project to which cortical area? (1)
Be specific. (1)
Olfactory cortex (piriform cortex)
Fill the gaps relating to population coding in the olfactory system. (3)
Granule cells are ……………….neurones in the ……………………, which modulate activity of ……………………….
inter
olfactory bulb
second order neurones
Describe why we get used to smells after a while. I.e. why do we get ‘nose blind’? (4)
The brain tries to predict the information going up to it
It sends top-down projections
in an attempt to silence the information coming in
because it doesn’t want too much information coming into the brain at a time
True or false? Explain your answer if necessary. (1)
Some neurones in the olfactory epithelium can respond to more than one smell.
True - they tend to express one receptor, but each smell is made up of different molecules so the neurones activated will overlap
What is the missing word? (1)
We only become aware of smells once neurones in the ……………………….. become activated.
olfactory cortex
True or false? Explain your answer if necessary. (1)
Some neurones overlap with how they are activated, however it is the population, not individual neurones, that help us to distinguish smells.
True
Describe how the olfactory system can differentiate between the concentrations of odours in the environment. (6)
An odour activates multiple neurones
they travel to the piriform cortex and activate different cortical neurones
they can also converge to weakly activate the same neurone
if the concentration of an odour is low the primary neurones may be activated at slightly different times so APs won’t converge/summate and activate the piriform cortex neurone
if the concentration of an odour is high the primary neurones will be activated very strongly and quickly so the EPSPs are summated on the cortical neurone and activate it
activity on the shared cortical neurone may help to encode odour strength
Describe how the brain is able to differentiate between different types of touch stimuli. (5)
- Different touch stimuli will preferentially activate different types of peripheral primary afferent fibre in different ways (strongly or weakly)
- So different populations of neurones in the spinal dorsal horn will be activated (both projection and interneurones)
- The brain (thalamus) then receives different patterns of activity from this neuronal population
- A population of neurones in the thalamus is activated
- And this population will project to the somatosensory cortex
Fill the gaps related to population coding in the dorsal horn. (4)
Sensory stimuli activate multiple ……………………. that will give rise to a sensory signal. This sensory signal activates numerous ………………. and ……………………. in the spinal cord.
The signals generated arrive at the spinal cord with a ………………….. pattern, which is an important component to the overall neural code.
fibre types
second order neurones
interneurones
temporal
Give three factors or qualities of the neural code that hold the key to population coding and deciphering a particular stimulus. (3)
Intensity of activation
Spatial pattern of activation
Timing of activation
Fill the gaps relating to information processing in the spinal cord. (7)
Each low threshold mechanoreceptor subtype displays unique …………………….. patterns and ………………… distributions.
Within sensory columns mapping to particular regions of skin, LTMR inputs converge onto ………………………
These units, also known as ………………….. represent the first sites of sensory information processing.
The ………………….. is the key initial locus of LTMR and nociceptor stimulus representation, integration, and processing of ensemble activity patterns.
The …………………… is then passed up the hierarchy to the next sensory processing centre (usually the …………………..).
central branching
collateral
iterative units
neural ensembles
dorsal horn
neural code
thalamus
Fill the gaps relating to information processing in the spinal cord. (8)
All distinct LTMR fibre types have unique ………………….. properties, …………………… thresholds, ……………………. velocities, …………………… patterns, and ……………………. kinetics. They all converge onto the ……………………..
This convergence of LTMR inputs occurs in a ……………topic, ……………….. manner, and these columns are likely to be key loci of LTMR integration and processing.
tuning
excitation
conduction
spike
adaptation
dorsal horn
somato
columnar
Low threshold mechanoreceptors principally use which fast neurotransmitter? (1)
Glutamate
Synaptic arrangements between LTMR subtypes, their postsynaptic targets, and interneurones, often form which complex structures in the spinal cord? (1)
Synaptic glomeruli
Give three types of fibre endings that are contained in synaptic glomeruli in the spinal cord. (3)
Primary afferent axonal boutons
Postsynaptic dendrites
Neighbouring interneurones
Fill the missing words relating to information processing in the spinal cord. (2)
Synaptic glomeruli feature lots of ………………, all coming in and synapsing onto …………………..
inputs
each other
Fill the gaps relating to information processing in the spinal cord. (2)
The presence of synaptic glomeruli allows for input …………………. at the very first synapse within the dorsal horn, and is thus thought to be the anatomical substrate for ……………………………
modulation
primary afferent presynaptic modulation
Are interneurones in the dorsal horn excitatory or inhibitory? (1)
Can be either
True or false? Explain your answer if necessary. (1)
Interneurones in the dorsal horn do not receive inputs from primary afferent fibres, and they are not known to modulate the neural code.
False - PAFs synapse on different interneurones and these interneurones WILL modulate the neural code
Give three possible ways that dorsal horn interneurones can be classified neurochemically. (3)
- By neurotransmitter
- By neuropeptide
- By calcium-binding protein expression
In which lamina/e of the dorsal horn are PKCy+ interneurones concentrated? (1)
Lamina II and III
Give four different firing patterns which can occur in dorsal horn interneurones. (4)
- Tonic
- Phasic
- Delayed-onset
- Single-spike
Spiking pattern variability in dorsal horn interneurones is significant in what way? What do spiking patterns represent? (1)
Reflect differences in the processing of tactile sensory information by these interneurones.
Which interneurones in the dorsal horn represent the spatial code of incoming information? (2)
Tonic
Delayed-onset
What are the proposed roles of tonic and delayed-onset interneurones in the dorsal horn? (2)
Integrators of sensory information
that detect which primary afferent fibres are actively releasing neurotransmitters.
Which interneurones in the dorsal horn represent the temporal code of incoming information? (2)
Phasic
Single-spike
What are the proposed roles of phasic and single-spike interneurones in the dorsal horn? (2)
Act as coincidence detectors
which recognise the co-occurrence of temporally close but spatially distributed input signals (interpret the timing of inputs)
Name two types of glial cells which may play a role in information processing in the spinal cord. (2)
Astrocytes
Microglia
Fill the gaps relating to information processing in the spinal cord. (3)
Surrounding every synapse are ……………………, which are able to regulate the ……………….. of neurones. ……………….. cells also play a role in this.
astrocytic end feet
excitability
microglial
Name two roles of glia that allow them to regulate the excitability of neurones. (2)
Glutamate buffering
Synaptic scaling
Describe how glia are involved in glutamate buffering when modulating the excitability of neurones. (4)
- Astrocytic end feet surround synapses
- Synaptic glutamate taken up by astrocytes
- Converted to glutamine
- Glutamine transferred to neurones to be recycled to glutamate again
Describe the process of how glial cells are involved in synaptic scaling. (4)
- Microglia and astrocytes release substances such as TNFa
- TNFa can activate intracellular signalling cascades
- Which can increase AMPA receptors
- And strengthen synapses
Describe what is meant by ‘synaptic scaling’. (2)
A homeostatic mechanism
for example synaptic strengthening if activity is too low.
Which two neurotransmitters are largely released by descending pathways into the spinal cord? (2)
Noradrenaline
Serotonin
Describe the actions of NA and 5HT, released by descending pathways, in the spinal cord. (3)
Act on GABAergic and enkephalin-containing interneurones
to indirectly modulate primary afferent and secondary projection neuronal excitability
and thus alter the neural code projected up to higher centres of the pain processing pathway.
Descending modulatory systems release neurotransmitters onto interneurones in the spinal cord.
What two neurotransmitters are these interneurones likely to contain? (2)
GABA
Enkephalin
Name three elements of the CNS that can alter the neural code produced in dorsal horn projection neurones (not peripheral input). (3)
Interneurones
Glial cells
Descending pathways
Give two examples of drug types which can target descending pathways projecting to the dorsal horn. (2)
Describe the effects of these drugs. (4)
Serotonin reuptake inhibitors
Noradrenaline reuptake inhibitors
- Potentiate effects of 5HT and NA in spinal cord
- Therefore, more activation of GABA and enkephalin-containing interneurones
- So less activation of second order projection neurones
- And alteration of neural code projecting to brain
Describe how population coding can result in allodynia during inflammation. (4)
- Inflammation changes properties of primary afferent fibres (peripheral sensitisation)
- So a touch stimulus results in a different activation pattern in primary afferent fibres
- The PAFs then activate a slightly different population of cells in the dorsal horn
- So there is a different neural code in spinal cord (which may signal pain)
Fill in the gaps relating to neural coding of sensory stimuli. (4)
The first neural code produced in PAFs is transformed in the ………………………. via ……………….. synapses.
The code is then further transformed in the …………………… At each step, neuronal activity has to be changed into a ………………., then back into neuronal activity.
spinal cord dorsal horn
chemical
thalamus
chemical signal
Describe how neural coding of noxious and innocuous stimuli differs. (3)
- Different pattern of primary afferent fibres activated
- Different neural codes produced in spinal cord
- Different neural codes transferred to brain
Describe how maladaptive plasticity, or central sensitisation in the spinal cord may result in an innocuous stimulus being misinterpreted as pain (allodynia). (5)
Misrepresentation of neural code as it is being transformed
due to altered connections and synaptic strengths in the spinal cord
eg. neurones may become more excitable
which disrupts and changes the normal neural code for that stimulus
and the new neural code may resemble a ‘painful’ stimulus, so is misinterpreted as noxious
Name three theories of neural coding. (3)
- Intensity theory
- Specificity theory
- Combinatorial theory
What is the intensity theory of neural coding? (2)
Pain is caused by sufficiently strong activation of unspecialised neurones.
This could be any primary afferent fibre as this theory states that they do not have specific roles.
What is the specificity theory of neural coding? (2)
What is another name for this theory? (1)
- Specialised high threshold neurones respond to noxious stimuli
- It is these neurones’ activation that causes pain
Also called the labelled line principle.
Give one drawback of the specificity (labelled lines) theory of neural coding. (1)
It is too simple to fully explain what is occurring at the level of the spinal cord.
Describe the combinatorial theory of neural coding. (4)
- Noxious stimuli activate high threshold nociceptors, and their activation is involved in evoking pain
- however the stimulus can also activate other primary afferent fibres such as low threshold neurones
- because the central pathways carrying these signals interact
- pain will depend jointly on high threshold neurone and low threshold neurone activation levels
Give an example of a type of combinatorial neural coding. (1)
How does this type of processing work? (3)
Opponent processing
The HThN synapses onto a second order neurone
The LThN synapses onto its own second order neurone and also a GABAergic interneurone
This interneurone stimulates GABA release onto the HThN’s second order interneurone to inhibit it
Describe the thermal grill illusion. (5)
Alternating warm and cool stimuli very close to one another
So cool and warm neurones are activated very close together on the skin
And they project to the same neuronal ensemble in the spinal cord and partake in opponency processing (cancel each other out)
However cold neurones are also weakly activated in other areas
and these are not cancelled out so cause a burning pain sensation
True or false? Explain your answer if necessary. (1)
In the context of the thermal grill illusion, a warm stimulus will only activate hot nerve fibres, however cold and cool stimuli separately will activate both cold and cool nerve fibres.
True
