midterm 2

Question 1

forms of short term synaptic plasticity resulting from repeated neuron stimulation

Answer 1

synaptic facilitation- residual calcium causes extra NT release.
synaptic depression- depletion of NT vesicles so they cant be used as fast
post tetanic potentiation- increase in efficacy due to repeated synaptic activity
augmentation- like potentiation, but much shorter and faster.

Question 2

habituation

Answer 2

decreased response with repeated or prolonged exposure to the same stimulus.

Question 3

sensitization

Answer 3

increased response to noxious stimulus

Question 4

How does pairing siphon touch with tail shock modify the presynaptic neuron?

Answer 4

A facilitator neuron releases serotonin, which activates a G-protein-coupled receptor (GPCR) in the presynaptic neuron.

Question 5

What is the role of serotonin in sensitization?

Answer 5

Serotonin activates GPCR, which stimulates adenylyl cyclase to produce cAMP, leading to activation of PKA. PKA phosphorylates a K⁺ channel, reducing its probability of opening, which prolongs depolarization in the presynaptic neuron.

Question 6

Why does prolonged depolarization lead to increased neurotransmitter release?

Answer 6

More Ca²⁺ influx occurs due to the extended depolarization, increasing neurotransmitter release.

Question 7

Why is short-term sensitization temporary?

Answer 7

The potassium channels eventually become dephosphorylated, and the increased neurotransmitter release returns to normal.

Question 8

What molecular change converts short-term sensitization into long-term sensitization?

Answer 8

Persistent PKA phosphorylates CREB, a transcription factor that promotes gene expression.

Question 9

What role does ubiquitin hydrolase play in long-term sensitization?

Answer 9

It degrades regulatory subunits of PKA, keeping PKA persistently active and sustaining phosphorylation effects.

Question 10

REVIEW NMDA receptor

Answer 10

• Permeable to Na+, K+ and Ca2+
• Mg2+ block at resting membrane potential
• postsynaptic depolarization relieves Mg2+ block
• Requires a co-agonist glycine
• Requirement of glutamate plus depolarization
• Some Glutamatergic synapses have only AMPA/Kainate or NMDA receptors
• Most have both AMPA and NMDA

Question 11

what is a silent synapse

Answer 11

In utero there are synapses in the brain that have only NMDA receptors and no AMPA receptors. This means the synapse could not be activated as there would be no depolarization from the AMPA receptor. The silent synapses are turned on by the addition of AMPA receptors.

Question 12

What is Long-Term Potentiation (LTP)?

Answer 12

LTP is a long-lasting increase in synaptic strength following high-frequency stimulation of synapses.

Question 13

What hippocampal pathway is involved in LTP?

Answer 13

The trisynaptic circuit, including CA1 pyramidal neurons and Schaffer collaterals.

Question 14

How is LTP induced experimentally

Answer 14

A brief high-frequency train of stimuli (tetanus) results in increased EPSP amplitude.

Question 15

What happens when a tetanic stimulus is applied to one pathway?

Answer 15

Only that pathway shows increased synaptic response; unstimulated pathways remain unchanged.

Question 16

schaffer collateral and presynaptic and postsynaptic dependency

Answer 16

Presynaptic stimulation alone is insufficient—LTP occurs when postsynaptic depolarization coincides with presynaptic activity.

Question 17

What does it mean that LTP is synapse/input specific

Answer 17

When LTP is induced by activating one synapse, it does not occur in another. Therefore, each of the thousands of synapses of a neuron can store information

Question 18

What is Associativity in LTP?

Answer 18

A weak stimulus alone does not induce LTP, but if a nearby synapse is strongly stimulated simultaneously, the weakly stimulated synapse is strengthened (slug)

Question 19

What receptor is required for LTP induction?

Answer 19

NMDA receptors for Ca influx

Question 20

How does AMPA receptor trafficking contribute to LTP

Answer 20

1.AMPA receptors are stored in recycling endosomes.
2.Synaptotagmin, activated by Ca²⁺, inserts AMPA receptors into the synapse.
3.More AMPA receptors = Stronger postsynaptic response to glutamate.

Question 21

How do kinases contribute to LTP

Answer 21

calcium activates CaMKII and PKC phosphorylate AMPA receptors, increasing their conductance and insertion into the synapse.

Question 22

What retrograde signal strengthens the presynaptic response in LTP?

Answer 22

NO enhances presynaptic glutamate release

Question 23

How does LTP lead to long-term structural changes?

Answer 23

Persistent PKA activation leads to CREB-mediated gene expression, forming new synapses.

Question 24

What is the key difference between LTP and LTD regarding Ca²⁺ signaling?

Answer 24

LTP: Large, fast Ca²⁺ influx activates kinases.
LTD: Small, slow Ca²⁺ increase activates phosphatases, leading to AMPA receptor internalization.

Question 25

How does LTD occur in the cerebellum

Answer 25

When climbing and parallel fibers are stimulated together, LTD occurs at the parallel fiber-Purkinje cell synapse.

Question 26

What is the signaling pathway for cerebellar LTD

Answer 26

-Glutamate released from Climbing and Parallel fibers -Activates AMPA and mGlu receptors on postsynaptic Purkinje neuron dendrites. -mGlu receptors activate PLC. IP3 and DAG generated -Spreading depolarization from Climbing fiber opens voltage-gated Ca2+ channels leads to Ca2+ influx -Voltage-gated calcium channel together with IP3 activate IP3 receptors on ER – Ca2+ potentiates IP3 mediated Ca2+ release from the endoplasmic reticulum -PKC activated by Ca2+ from 2 sources and DAG -PKC phosphorylates protein targets, triggering internalization of AMPA receptors -Fewer AMPA receptors at synapse - Parallel fiber synapse weakened: LTD

Question 27

What is Spike Timing-Dependent Plasticity (STDP)?

Answer 27

STDP is a form of synaptic plasticity where the timing of presynaptic and postsynaptic spikes determines whether a synapse is strengthened (LTP) or weakened (LTD).

Question 28

How does the timing of spikes determine whether LTP or LTD occurs?

Answer 28

Presynaptic spike → Postsynaptic spike (within ~20 ms): LTP occurs (synaptic strengthening). Postsynaptic spike → Presynaptic spike: LTD occurs (synaptic weakening). follows the rules: If the presynaptic neuron fires first, it likely contributed to the postsynaptic firing → Strengthen the synapse (LTP). If the postsynaptic neuron fires first, it suggests the presynaptic neuron was less important → Weaken the synapse (LTD).

Question 29

5 classes of cells in the retina

Answer 29

photoreceptors bipolar cells ganglion cells horizontal cells amacrine cells

Question 30

What happens to rods and cones when they are activated by light?

Answer 30

Light hyperpolarizes rods and cones, reducing neurotransmitter release. In darkness, they remain depolarized due to open cGMP-gated channels, which close upon light activation.

Question 31

What is the first molecular event that occurs when light hits the photoreceptor

Answer 31

Retinal (inside opsin) undergoes photoisomerization, changing from cis to trans, activating rhodopsin.

Question 32

What is the phototransduction cascade

Answer 32

Photon absorption → cis-retinal → trans-retinal Activates rhodopsin Rhodopsin activates transducin Transducin activates phosphodiesterase (PDE) PDE breaks down cGMP Less cGMP = cGMP-gated channels close Hyperpolarization = Less NT release

Question 33

How is the phototransduction signal turned off?

Answer 33

Rhodopsin kinase phosphorylates rhodopsin which allows arrestin binding Arrestin binds to rhodopsin, preventing further activation of transducin Trans-retinal is converted back to cis-retinal in the epithelial cells for reuse

Question 34

How does the retina adapt to excessive light? (Photoadaptation)

Answer 34

Increased guanylate cyclase activity → More cGMP produced Increased rhodopsin kinase activity → More arrestin binding Increased cGMP-gated channel affinity for cGMP Reduced intracellular Ca²⁺, reducing sensitivity

Question 35

How does phototransduction differ in invertebrates?

Answer 35

Unlike vertebrates, invertebrate photoreceptors depolarize in response to light. Some invertebrates, like octopi, have photoreceptors on their arms.

Question 36

how does trans retinal get transformed back to cis retinal

Answer 36

Trans retinal gets turned back to cis retinal by a chaperone protein that moves it into the epithelial cell to get turned back.

Question 37

on center ganglion cell

Answer 37

increases firing of action potentials as light is increased in the receptive field

Question 38

off center ganglion cell

Answer 38

decreases firing of action potentials as light is decreased

Question 39

on vs off bipolar cells

Answer 39

on bipolar cell has mglu receptors, off has ampa kainate receptors.

Question 40

why is glutamate received differently in on and off bipolar cells

Answer 40

on bipolar cells have mglu receptors which give an inhibitory response in the bipolar cell whereas off bipolar cells have AMPA receptors which give an excitatory response in the bipolar cell.

Question 41

neurons visual receptive field

Answer 41

For a photoreceptor, the receptive field is a point of light in the visual field that falls on the outer segment on the photoreceptors

Question 42

foveation

Answer 42

shifting your gaze so that any new object of interest in the visual field is on the fovea.

Question 43

saccades

Answer 43

quick ballistic eye movements used to align the fovea with a particular part of a scene

Question 44

otolith organs: utricle and saccule

Answer 44

detect translational accelerations of the head and head position related to gravity. utricle is horizontal saccule is vertical

Question 45

semicircular canals

Answer 45

detect rotational accelerations of the head

Question 46

otolith organs structure

Answer 46

sensory epithelium (macula) consisting of hair cells and supporting cells, gel layer over hair cells, calcium carbonate crystals (otoconia) for weight.

Question 47

what happens in the semicircular canal when you tilt your head

Answer 47

there is a viscous liquid that lags behind as you bend your head which causes hair cells to bend and cause changes in polarization.

Question 48

3 major classes of reflexes vestibular system participates in

Answer 48

1. maintain gaze during movement 2. maintain/adjust body posture 3. maintain muscle tone

Question 49

vestibulor-ocular reflex (VOR)

Answer 49

helps maintain steady image on retina during body movements. driven by vestibular input. for example, right rotation of the head causes compensatory eye movements to the left.

Question 50

optokinetic reflex

Answer 50

holds image stable on retina during sustained head movements/rotations, is driven by visual stimuli “retinal slip”, and results in eye stabalization on the visual scene.