After Midterm Flashcards
What is coincidence detection?
Temporal conjunction of neural activity leading to changes in synaptic strength.
What happens when an aversive stimulus to the tail (UCS) is paired with the activation of the siphon sensory neuron (CS)?
Increased gill withdrawal to a touch of the siphon in the absence of the aversive stimulus.
How is classical conditioning different from sensitization?
It required fewer repetitions to produce a big withdrawal and it showed specificity for siphon touch (the paired stimulus).
In classical conditioning of the Aplysia gill withdrawal reflex, what is the signal that temporally links activity of different neurons?
Calcium
What does calmodulin do?
Increases the activity of adenylyl cyclase
How does amplification occur in the Aplysia gill withdrawal reflex?
When the touch and the shock are close together
What do PKA catalytic subunits do?
Phosphorylate K channels leading to less hyperpolarization and broader action potentials due to increased calcium influx.
What causes short-term behavioral facilitation?
Post-translational changes (phosphorylation) of a protein (K channel) leading to increased release from the sensory nerve terminal.
What is the probability of vesicle release (p) very sensitive to?
Intracellular Ca
What are k, n and p?
k = size of quantum
n = number of vesicles that could potentially release
p = probability of any vesicle releasing
What is the overall likelihood of a vesicle being released equal to?
P* = n x p
What happens if the time between the shock and the touch is too long?
There will still be sensitization, but no amplification
How does the progression from short-term to long-term sensitization occur?
Sustained PKA activation from repeated shocks eventually phosphorylates CREB, which activated CREs that regulate DNA to increase transcription to make proteins.
How is ubiquitin hydroxylase made?
The result of CREB mediated gene expression/regulation
Why does specificity occur in classical conditioning?
Non-stimulated sensory neurons (ex. mantel) doesn’t have an increase in Ca concentration in its presynaptic terminal.
Why is the order of the US (shock) and CS (touch) important?
Ca needs to rise before 5HT is release so Ca-calmodulin can prime the AC so the the GP will have a greater effect
For conditioning, should the US (shock) or the CS (touch) be first?
The touch should come before the shock. If the shock comes first, there will be some sensitization, but no conditioning.
What is Hebbian plasticity?
Correlated presynaptic and postsynaptic activity produces long-term enhancement of connections (neurons that fire together wire together)
Where are long-lasting changes in synaptic efficacy often studied?
Hippocampus - CA3 to CA1 synapses
What is channel is required to induce LTP at CA3-CA1 synapses?
NMDA-R activation (voltage dependent)
Why does the siphon touch cause a bigger siphon withdrawal than the mantle touch?
There is amplification of adenylyl cyclase activity by Ca-calmodulin because it is paired with the shock.
Is the mantle touch or the siphon touch paired with the tail shock?
Siphon touch
What blocks LTP at the CA3-CA1 synapses?
Fast Ca chelators
What is long term depression?
Postsynaptic reduction in sensitivity not equal to “synaptic depression”
Why is it important that long-term plasticity is dual directional?
To avoid all synapses becoming super strong. LTP can erase LTD and LTD can erase LTD.
What is activated with lower levels of calcium?
phosphatases
How do NMDA receptors currents mediate LTP and LTD?
Large/fast Ca increase = LTP
Small/slow Ca increases = LTD
What are coincidence detectors?
Two “events” that occur close together in time cause persistent changes in behavioral responses at later times.
What cells synapse onto each other in the CA1/CA3 synapse of the hippocampus?
Cell from perforant path (entorhinal cortex) synapses onto a granule cell that synapses onto CA3 pyramidal cell that synapses onto CA1 pyramidal cell.
What would happen to the post synaptic potential if the presynaptic cell was stimulates with a train of stimuli?
Facilitation and temporal summation would occur until the there is a period of diminished response due to transmitter depletion.
What is the signal mechanism/pathway underlying LTP at the CA3 CA1 synapse?
Activation of the postsynaptic NMDA receptors allow the influx of Ca and Na, causing substrate phosphorylate and the insertion of additional AMPA receptors.
What two kinases are activated by NMDA receptor activation in the CA1 postsynaptic pyramidal cell?
Ca/Calmodulin Kinase II and PKC
What causes an increase in postsynaptic response to glutamate?
Depolarization of the postsynaptic cell while applying glutamate.
What is the difference between silent synapses and functional synapses?
Silent - NMDA receptors only
Functional - AMPA and NMDA receptors
What features cause the posttranslational changes in existing proteins and long lasting phases that require gene expression?
An early transient phase that relies on protein kinases.
Does tetanus have high or low levels of kinase activity?
high
What recruits AMPA receptors into the dendritic spines?
Depolarization and glutamate
Is CA3/CA1 Hebbian? Why?
CA3/CA1 is Hebbian because its activity needs to be both presynaptic and postsynaptic.
What happens to active zones in LTP?
They form a horseshoe shape, allowing for “two” active zones - doubling the probability of an event.
What happens if the Schaffer collaterals are only stimulated two or three times per minute?
The size of the evoked EPSP in CA1 remains constant
What happens if the Schaffer collaterals are given a brief, high-frequency train of stimuli?
LTP - long lasting increases in EPSP amplitude
What causes an increase in the EPSP in CA1?
Pairing of a stimulus with depolarization of CA1 and close timing between paired pre/postsynaptic activity.
How is LTP input specific?
It is restricted to ACTIVATED synapses rather than to all the synapses on a given cell.
What leads to short-term sensitization vs long-term sensitization?
Short - post translational changes
Long - change in gene expression
Why can the synthesis of new proteins occur in the dendrites?
Ribosomes are present
If new synapses or new active zones are increased by LTP, is k, n or p increased?
How can LTP be increased/decreased?
Increased - faster, close together stimuli
Decreased - slower, spaced out stimuli
Why do small, slow NMDA-mediated Ca current increases lead to LTD?
Low concentrations of Ca can only activate phosphatases, not kinases.
What is spike timing dependent plasticity (STDP)?
The order and precise temporal interval between presynaptic and postsynaptic spikes determine the sign and magnitude of LTP or LTD.
How does spike timing dependent plasticity lead to LTP and LTD?
LTP - presynaptic spike, then postsynaptic spike (pairing enhances)
LTD - postsynaptic spike, then presynaptic spike (antiparallel depresses)
How does long-term synaptic depression occur in the cerebellum?
Climbing fiber and parallel fibers of granule cell axons excite the inhibitory Purkinje fibers
Is LTD in the cerebellum Hebbian or non-Hebbian?
Hebbian - presynaptic and postsynaptic activity (coincident detection)
What is the role of the climbing fiber in LTD in the cerebellum?
Depolarizes the dendritic spine of the Purkinje cell through a voltage-gated Ca channel.
What does it mean for a receptor to be polymodal?
Naturally sensitive to more than one stimulus modality.
What is the threshold detection of a stimulus?
The weakest stimulus that produces a response in a receptor 50% of the time.
How does the size of dynamic range influence sensory discrimination?
Large dynamic range means poor sensory discrimination and small dynamic range means high sensory discrimination.
What is range fractionation?
Groups of receptors can work together to increase dynamic range without decreasing sensory discrimination.
What is the dynamic range of a receptor?
The range of stimulus intensities over which a receptor neuron can encode changes in intensity as changes in neuronal activity (between threshold intensity and receptor saturation)
What is dynamic range dependent on?
Firing rate and depolarization - can’t encode when saturated or if the stimulus isn’t strong enough.
How do sensory neurons code stimulus intensities?
Through changes in action potential frequency or through graded membrane potential change (depolarization).
Stevens’s Power Law
Measures the relationship between physical stimulus intensity and the perceived intensity of the physical sensory stimulus.
What is phasic firing rate?
Produce APs only at the beginning or end of the stimulus
How is tonic non-adapting firing different from tonic slowly adapting firing?
Non-adapting - produce APs without much slowing down as long as the stimulus continues
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Slowly adapting - AP frequency decreases if stimulus intensity is maintains at the same level
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Why are action potentials produced at the end of a stimulus?
Release of suppression
What causes shifts in dynamic range?
Adaptation - depolarization changes
Which afferent fibers project to the medulla ipsilaterally/contralaterally?
Ipsilaterally - Mechanoreceptors (touch) - (then crosses at medulla)
Contralateral - Nociceptors (pain/temperature)
Which cells are slowly adapting and which are rapidly adapting?
Slowly - Merkel and Ruffini
Rapidly - Pacinian and Meissner
What is Piezo 2?
A mechanotransducer for touch, proprioception and interception
What is unique about Pacinian Corpuscle afferent fiber endings?
Can be free or encapsulated as part of an organ
What two things does sensory adaptation depend on?
Properties of ion channels in the sensory neuron or the physical properties of the sensory “organ” in which the receptor is found.
What are the four mechanoreceptors and their functions?
Merkel - form/texture/edges
Meissner - motion and grip
Pacinian - vibration and pressure
Ruffini - stretch and proprioception
Which mechanoreceptor encodes the position of Braille most accurately?
Merkel
Which mechanoreceptor response take a while to turn on and off?
Pacinian
What is the importance of spatial resolution?
Important for the cortex to distinguish two points in space
What are dermatomes?
Body surface mapped to segments of spinal cord
What are the two somatosensory tracts synapse at the caudal medulla and what are their functions?
Gracile - lower body
Cuneate - upper body
What sensory stimuli is not relayed to the thalamus?
Olfaction
Where does mechanoreceptor inputs decussate?
Medulla
In what layer of the cortex does the majority of thalamic input terminate?
Layer 4
What is the function of the medial lemniscus pathway?
Transport sensory spinothalamic information from the caudal medulla to the ventral posterior lateral nucleus of the thalamus.
What is the pathway for mechanoreceptors coming from the face?
Trigeminal complex - trigeminal ganglion enters into the brainstem so the pathway crosses over immediately
What is pathway for proprioception?
Spinocerebellar tract - travels ipsilaterally to the cerebellum and synapses in the cerebellum/dorsal column nuclei
What proprioceptors provide information on muscle length/tension?
Length - muscle spindles
Tension - Golgi tendon organ
What causes the stretch/no stretch in the intrafusal and extrafusal muscle fibers?
Whether the muscle is contracted or relaxed
What are the largest and fastest conducting somatosensory axons for?
Proprioception
What are the different afferent axon types for the different somatosensory receptor types?
Muscle spindles - Ia/II
Touch - Aβ
Nociception/Temp - Aδ
Nociception/Temp/Itch - C
How is the somatosensory cortex organized?
Lateral to medial = up and down the body
Rostral to caudal = homunculus
What are the functions of the 4 Brodmann’s areas of the somatosensory cortex?
1 - cutaneous (texture)
2 - tactile and proprioceptors (size and shape)
3a - proprioceptors
3b - cutaneous (tactile)
What area of the thalamus is important in the somatosensory pathways?
ventral posterior complex
What are the two functions of the anterior lateral system?
two questions
- Where is the stimulus coming from? (ventral posterior nucleus to S1 and S2)
- Is the stimulus unpleasant/painful? (midline thalamic nuclei to anterior cingulate/insula)
Where does nociceptive and mechanoreceptive projections cross over?
Nociceptive - spinal cord
Mechanoreceptive - medulla
What happens to touch and pain perception with a lesion in the spinal cord?
Lose ipsilateral touch and contralateral pain
What is the difference between visceral pain and neuropathic pain?
Visceral - mechanical or chemical activation of nociceptors by compression/obstruction in an internal organ that manifests as pain on the body surface
Neuropathic - damage to afferent fibers or central nervous system pathways
What are vanilloid receptor VR-1 activated by?
Heat > 45 degrees or tissue injury (capsaicin - from chiles)
What do endovanilloids activate?
Transient receptor potential (TRP) channels
What is special about TRPM VR1 in birds?
Not sensitive to capsaicin (chile)
How does the raphe nuclei inhibit pain?
Serotonin binds to enkephalin neurons (opioid receptors) inhibiting calcium influx in the terminal of the nociceptors
How do descending inputs from the locus coeruleus inhibit pain?
Inhibits dorsal horn projection neuron directly or inhibits calcium influx from C fiber (nociceptor)
Where does processing of painful stimuli occur?
In the dorsal horn of the spinal cord
What happens to pain perception when a mechanoreceptor and a nociceptor are activated at the same time?
Inhibitory local circuit neurons are activated, decrease the effectiveness of the C fiber (nociceptor), inhibiting the dorsal projection neuron, reducing pain stimulus
What happens with stimulation of the midbrain periaqueductal gray (PAG)?
Analgesic effects - lessens pain reception
What blocks PAG analgesic effects?
CB1 blockers
What is released from the locus coeruleus?
Norepinephrine
What system does the dorsal horn of the spinal cord project to?
Anterolateral system
Which somatosensory receptors are unmyelinated?
C fibers (nociceptor)
What is hyperalgesia?
A form of peripheral sensitization with increased sensitivity to pain (ex. with sunburn)
What is allodynia?
When pain is induced by a normally not harmful stimulus (ex. with sunburn)
What substances cause inflammation in response to tissue damage?
Prostaglandins, bradykinins, serotonin and histamine (and ATP and H)
Other than the ventral posterior nucleus and the midline thalamic nuclei, where does the anterolateral system project to?
Amygdala, hypothalamus, periaqueductal grey, superior colliculus and reticular formation
Why does neuropathic pain often arise following amputation of an extremity?
Due to rewiring of circuits in the absence of sensory input from the amputated limb
How does the conduction speed of sound differ in water compared to air?
5 times faster in water than air (air = 340m/s and water = 1500m/s)
What part of the ear increases the amount of pressure delivered to the oval window?
ossicles - malleus, incus and stapes (after pressure wave is concentrated on the tympanic membrane)
Where in the ear are pressure waves concentrated?
TYMPANIC membrane (“ear drum”)
What muscles regulates the transmission of sound to the inner ear?
small muscles - tensor tympani and stapedius - that control the tension of the bone joints
What is special about a cricket’s hearing?
Have a membrane in their foreleg that picks up pressure waves - has a blocking system so the it’s auditory system is shut off when it plays its song
What are the functions of inner hair cells vs outer hair cells?
Inner - communicate sound information to the brain
Outer - amplify sound vibration, increasing sensitivity to sound
What is the Scala media?
The cavity in the cochlea that divides the Scala TYMPANI and the Scala vestibuli
What is the function of the TECTORIAL membrane?
Sits on top of the hair cells and move them back a forth
What is the difference between the oval window and the round window?
Sound vibrations go in through the oval window and out through the round window