SYNAPTIC TRANSMISSION & PLASTICITY

Question 1

Synapse

Answer 1

– Connection between two neurons
(– Commonly, the axon of a pre-synaptic neuron contacts the dendrite of a post-synaptic neuron)

Question 2

Neurotransmitter

Answer 2

Chemical messenger sent across synapse, from pre-synaptic neuron to post-synaptic neuron

Question 3

Receptor

Answer 3

– Protein in cell membrane to which neurotransmitters bind
(– Commonly, a receptor is a ligand-gated ion channel, where the ligand is a neurotransmitter)

Question 4

Post-synaptic potential

Answer 4

– Subthreshold change in cell membrane potential due to movement of ions through channels
(– Post-synaptic potentials can be excitatory or inhibitory)

Question 5

Synaptic plasticity

Answer 5

– Change in how effectively information is transmitted across a synapse
(– Change in magnitude of the post-synaptic potential elicited by a pre-synaptic action potential)

Question 6

Axo-dendritic synapse

Answer 6

likely the most common type

Question 7

Axo-somatic synapse

Answer 7

can have relatively large influence on action potential generation from post-synaptic cell

Question 8

Axo-axonic synapse

Answer 8

can influence transmitter release from post-synaptic cell

Question 9

Synaptic cleft

Answer 9

space between pre-synaptic neuron and post-synaptic neuron
about 20nm wide (20 x 10-9m)

Question 10

Amino Acids

Answer 10

Main inhibitory transmitter in cerebral cortex

GABA, Glu (excitatory in cerebral cortex), Gly

Question 11

Amines

Answer 11

Commonly act as neuromodulators in brain, i.e., modulate influence of amino acid transmitters

Question 12

Neurotransmitter release

Answer 12

1) Synaptic vesicle docked at pre-synaptic “active zone”
2) Action potential leads to increased pre-synaptic calcium
3) Calcium triggers neurotransmitter release
4) Synaptic vesicle recycled

Question 13

Calcium triggers vesicle fusion with cell membrane

Answer 13

Proteins dock vesicle to cell membrane:
– SNARE proteins mediate fusion
– (SNARE = soluble NSF attachment receptor)
– Synaptotagmin activates fusion proteins
Calcium (Ca2+) binds to synaptotagmin
– Synaptotagmin acts as calcium sensor
– Synaptotagmin triggers fusion and transmitter release

Question 14

ligand-gated ion channel

Transmitter-gated ion channel

Answer 14

Transmitters bind to particular sites on channels:
– Transmitter-gated ion channels also called “receptors”
Transmitter-gated ion channel contains two functional domains:
– Extracellular domain contains neurotransmitter binding sites
– Membrane-spanning domain forms the ion channel
Transmitter binding leads to channel opening and membrane potential change:
– Positive ions (Na+, Ca2+) into cell causes depolarization (membrane potential more positive)
– Negative ions (Cl-) into cell causes hyperpolarization (membrane potential more negative)
Transmitter-gated ion channels produce rapid post-synaptic effects:

faster effects than G-protein-coupled receptors

Question 15

Receptor Subtypes

Answer 15

AMPA receptor = ionotropic
NMDA receptor = ionotropic (transmitter-gated and voltage-gated)
GABA A receptor = ionotropic
GABA B receptor = metabotropic

Question 16

Synaptic plasticity

change in synaptic strength

Answer 16

– Change in how effectively information is transmitted across a synapse
– Change in magnitude of post-synaptic potential (PSP) elicited by pre-synaptic action potential

Question 17

Synaptic strength can be increased or decreased

Answer 17

– Increased synaptic strength facilitates (potentiates) synaptic transmission (increased PSP)
– Decreased synaptic strength depresses synaptic transmission (decreased PSP)

Question 18

Short-term synaptic plasticity

Answer 18

– Short-term synaptic plasticity, lasting tens-to-thousands of milliseconds
– Short-term facilitation and short-term depression are temporary changes in synaptic strength
– Without continued pre-synaptic activity, synaptic strength will return to baseline level

Question 19

Long-term synaptic plasticity

Answer 19

– Long-term synaptic plasticity, lasting minutes-to-hours and more
– Long-term potentiation and long-term depression
– Considered to be important mechanism underlying learning and memory

Question 20

Long-term potentiation (LTP)

Answer 20

LTP is increased EPSP of post-synaptic neuron in response to pre-synaptic input
High-frequency activity (e.g., 100Hz for 1s) of pre-synaptic cell can induce LTP
LTP is input-specific – Increased EPSP only at synapses where pre-synaptic neuron was active

Large increase in Ca2+ inside post-synaptic cell induces LTP

Question 21

Mechanisms for long-term potentiation (LTP)

Answer 21

1) Increase effectiveness of AMPA receptor:
– i.e., phosphorylate AMPA receptor (add P043-):
2) Insert more AMPA receptors into synapse:
– Neurotransmitter can bind more receptors
3) Increase neurotransmitter release:
– Retrograde messenger (e.g., nitric oxide) sent from post-synaptic cell to pre-synaptic cell
– This increases pre-synaptic Ca2+ and transmitter release

Question 22

Long-term depression (LTD)

Answer 22

LTD is decreased EPSP of post-synaptic neuron in response to pre-synaptic input
Low-frequency activity (e.g., 1Hz for 10min) of pre-synaptic cell can induce LTD
LTD is input-specific – Decreased EPSP only at synapses where pre-synaptic neuron has low activity

Small increase in Ca2+ inside post-synaptic cell induces LTD

Question 23

Two types of post-synaptic potentials

Answer 23

– Excitatory post-synaptic potential (EPSP) produced by glutamate
– Inhibitory post-synaptic potential (IPSP) produced by GABA