Synaptic Transmission

Question 1

dendrites

Answer 1

highly receptive area with large surface area

• receptors for transmitters
• voltage-gated ion channels amplify graded synaptic signal
• primary areas for receiving and integrating complex info from thousands of synapses

Question 2

cell soma of neurons

Answer 2

surrounds nucleus and contains organelles for house-keeping functions
-membrane contains receptors for chemical transmitters

Question 3

axon of neurons

Answer 3

single thin process arising from cell body at axon hillock (loaded with voltage gated Na+ channels)

• transmits all-or-none APs to terminals after integrating changes
• can be a meter+ in length with axoplasm-like cytoplasm (cell body)
• usually surrounded with myelin sheath

Question 4

presynaptic terminals

Answer 4

specialized structures that convert electrical signals propagated down axon (APs) into chemical signals (nt) released from presynaptic vesicles and trasmitted to target at the synapse

Question 5

difference between postsynaptic potentials and action potetions

Answer 5

postsynaptic potentials are small graded changes

Question 6

axoplasm

Answer 6

contains parallel arrays of microtubules and neurofilaments

• kinesin: anterograde from soma to terminal
• dynein: retrograde from terminal to soma

Question 7

electrical synapses background info

Answer 7

electrical response in one cell is transmitted to another

• extremely fast (little/no delay) and bidirectional passive flow between gap junctions
• less common than chemical synapses in nervous system

Question 8

criteria for chemical neurotransmitters

Answer 8

1. present in presynaptic terminal
2. released in voltage- and Ca+ dependent manner
3. specific receptors present in postsynaptic target cell
4. means to inactivate the transmitter (enzymatic breakdown, re-uptake, GABA inhibitors, etc.)

Question 9

steps in a chemical synaptic transmission

Answer 9

1. transmitter molecules are made and packaged in vesicles
2. AP arrives at presynaptic terminal
3. depolarization of terminal opens voltage-gated Ca+ channels
4. increased Ca++ in terminals trigger vesicle fusion
5. transmitter diffuses across cleft and binds to postsynaptic receptors
6. postsynaptic response occurs
7. transmitter molecules are cleared/inactivated by enzymatic degradation, uptake, or diffusion

Question 10

what happens if neurotransmitters are not cleared in synapse?

Answer 10

initially a “high” but then will be desensitized after a long period of time
-receptors are internalized, etc.

Question 11

active zones of presynaptic terminals

Answer 11

docking site for transmitter-containing vesicles

-preferentially released in response to AP, Ca+ influx

Question 12

postsynaptic density

Answer 12

electron dense area with many neurotransmitter receptors in postsynaptic cells
-aligned with presynaptic active zones to promote efficiency

Question 13

functional magnetic resonance imaging for synapses

Answer 13

measures changes in regional blood flow associated with changes in local cerebral glucose metabolism

Question 14

exocytosis and vesicle fusion

Answer 14

regulated by Ca++ (binds to V-SNARES) and endocytosis (to prevent enlargement of presynaptic membrane)

Question 15

are synaptobrevin, synaptotagmin, and syntaxin V-SNAREs or T-SNAREs?

Answer 15

synaptobrevin and synaptotagmin are v-SNAREs

syntaxin is a t-SNARE

Question 16

two classifications for postsynaptic receptors

Answer 16

ionotropic - have ligand-gated ion channel (usually Na/K)
-nicotinic (nicotine can selectively activate it)
metabotropic - linked to G-PRO that transduce slower biochemical signal
-muscarinic (muscarin can selectively activate it)

Question 17

how are postsynaptic potentials produced?

Answer 17

conductance changes due to ion channel openings/closings lead to ionic current flow thru channels that lead to changes in membrane potential

Question 18

what is the major excitatory neurotransmitter for EPSPs? and relation to AMPA and NMDA

Answer 18

glutamate - binds to both ionotropic and metabropic receptors for depolarization

• AMPA receptor channels - mediate fast EPSP via flow of Na/K down gradients
• NMDA receptor channels - mediate slower EPSP via flow of Na/K/Ca
• -typically don’t open unless sufficiently depolarized b/c blocked in voltage-dependent manner by Mg

Question 19

what is the major inhibatory neurotransmitter FOR IPSPs? and difference between GABA-A, GABA-B

Answer 19

GABA - binds to both ionotropic and metabotropic receptors for hyperpolarization

• A: mediate fast IPSP via flow of Cl- down gradient
• B: slower IPSP b/c G-PRO linked receptors

Question 20

pentobarbital

Answer 20

drug that elicits larger IPSP when GABA is present b/c increases channel open time/singl channel current

Question 21

synaptic bouton

Answer 21

branches of terminal regions of axons
-myelination lost if in close contact with dendrite or cell body of another neuron, and when they fuse neurotransmitters are released

Question 22

cable theory

Answer 22

temporal and spatial effects of summation

-potential can be lost via decremental conduction

Question 23

which conditions allow summation? long or short time constants or space constants?

Answer 23

longer time and space constants allow for summation

-shorter constants usually terminate before they can summate