6- synap phys 2

Question 1

What is mechanism that determines whether synapse is direct (fast) or indirect (slow)

examples of each

Answer 1

Fast = ionotropic (NT act directly on ion channel)

Slow = metabotropic (NT acts on GPCR and requires activ of 2nd messenger)

Question 2

What is example of ionotropic and metabotropic mechanisms

Answer 2

ex = muscle fiber depol –> ACh bind nicotinic AChR –> open NSC channel –> Na+ enter –> muscle depol

ex = opening of K+ channel in heart
ACh bind muscarinic AChR –> activ GPCR –> gammaBeta released and diffuse to K+ channel –> open and K+ exits

Question 3

What channel is opened in fast excitation? What is major NT involved?
What ions is permeable

Answer 3

major excitatory NT =glutamate and opens non-selective cation channel
permeable to Na and K

Na enter cell and depol

Question 4

Define elctrical driving force

What is it the difference btwn

Answer 4

force to move ion across membrane (difference btwn voltage ion wants to be at (equilibrium) and actual membrane potential (Em))

Question 5

Define reversal potential

Answer 5

Reversal potential = due to many NSC channels open –> membrane potential settle btwn ENa and Ek (~10 mV)

since greater than threshold –> therefore, excitatory and membrane depol

Question 6

what kind of channel is opened during fast inhibition
main NT involved?

Which direction is the ion moving?

Answer 6

GABA
opens Cl channels in postsynap membrane

Cl- equilibrium potential more negative than threshold potential so Cl- movement does NOT CAUSE ACTION POTENTIAL

Question 7

Why is inhibition more powerful than one might predict from size of an IPSP

Answer 7

b/c depends on relative permeabilities of ions

Small IPSP can reflect huge permeability change if ion’s equilibrium potential is close to resting membrane potential

Question 8

Distinguish btwn temporal and spatial summation of postsynap potentials

Answer 8

When two diff presynap inputs synapse on a single neuron, potentails added to form larger potential since large amt of NT released

IF single input stim twice in succession, 2nd rise can start rising before previous AP has ended

Question 9

Mechanism of synpatic transmission

Answer 9

1) AP arrives
2) open VG Ca2+ channel
3) Ca2+ bind synaptotagmin causing fusion of lipids of vesicles and surface membrane
4) open fusion pore to release NT (exocytosis)
5) NT bind receptors

Question 10

Postsynaptic response depends on

Answer 10

nature of postsyn receptor

Question 11

3 ways of removing NT

Answer 11

1) diffuse out of cleft
2) recycle by pump back to presyn terminal using Na coupled carrier molec
3) NT destroyed using extracellular degradative enzymes (ex = Ach)

Question 12

How do you recycle the vesicle

Answer 12

1) vesicle membrane reinternalized (endocytosis) and filled with NT
2) NT synth locally and pump via Na coupled transporters into vesicle

Question 13

Speed 
Effect 
Strength 
Transmitter 
Termination 

of NMJ vs CNS synapses

Answer 13

fast vs. (fast or slow)

excitatory vs (excit or inhib)

strong vs weak

Ach vs many others (Ach, glu, GABA, 5-HT, DA, Asp…)

diffusion/degradation by esterase (reuptake) vs. reuptake or diffusion (degradation)

Question 14

difference btwn postsyn membrane in skeletal vs. neuron

Answer 14

skeletal = many folds to incr density of NT receptors

Question 15

Motor unit define

NT in motor synapses with muscle

Answer 15

motor unit = axon + muscle fibers

NT = ACh

Question 16

Ach receptor is what type of channel

Answer 16

ligand gated ion channel (binding of Ach stim open gate and influx of Na to depol)

Question 17

what type of channel is ACh

Answer 17

NSC (permeable to all cations)

Question 18

components of ACh receptor

Answer 18

4 subunits (2A, B, C, D) around pore 
each A binds one ACh and must bind simult

Question 19

how to clear Ca from synapse

Answer 19

2 channels

1) ATP driven
2) Na/Ca exchanger

Question 20

What happens if ECl is equal to resting membrane potential

Answer 20

IPSP amplitude = 0 but would still be inhibitory on EPSP

Question 21

What happens when the NT causes a decr in K+ ion permeability

Answer 21

depolarized bc excitatory synapse

Question 22

Describe presynaptic inhibiton

Answer 22

inhib nerve terminal synape on excitatory presynap terminals

–> inhib release GABA –> open Cl in presynap cell –> decr Ca2+ ch, less excitatory NT release

shuts off input to cell without affect cell’s resting membrane potential or synaptic effect of other input

Question 23

Suppose a single excitatory input was stimulated twice in succession. The first EPSP was 10 mV in amplitude, and lasted 20 msec. The second stimulus was given 50 msec after the first, and the EPSP was 15 mV. Was the larger size due to facilitation or summation or both?

Answer 23

facilitation, of course, because the first EPSP had completely decayed before the second stimulus was given

Question 24

suppose the second stimulus in the example above was given only 10 msec after the first, and the peak of the EPSP was 15 mV.

Answer 24

temporal summation - it arises when the same input stimulated in succession.

Question 25

benefit of indirect over direct synaptic transmission

Answer 25

NT in cleft longer –> extended action after NT action finished (ex= emotion)

2nd messengers transmit chemical signals to nucleus –> change gene expression

Question 26

example of first messenger doing double duty turning on fast and slow (direct/indirect)

Answer 26

autonomci ganglion receive cholinergic input from CNS –> ACh release –> ionotropic in NMJ –> NSC that depol

ACh activ metabotropic receptor in postsyn –> slower depol by closing K+ channels

Question 27

2 types of ACh receptors

agonist and antagonist

Answer 27

nictoinic ACh receptor
agonist = nicotine
antagonist = curare

muscarinic ACh receptor (GPCR)
agonist = muscarine
antagonist = atropine

Question 28

Define
Neostigmine
Curare (d-tubocurarine)

Answer 28

blocks ach esterase and prolongs current at NMJ (used for myasthenia gravis/syndrome)

Curare = block ACh receptor and induces paralysis; relaxant in anesthesia