Synaptic Physiology I, II, and III

Question 1

Electrical synapses are mediated by _________ junctions.

Answer 1

gap

Question 2

Gap junctions are composed of __________.

Answer 2

six connexins

Question 3

Describe how electrical synapses work.

Answer 3

Depolarization of the presynaptic neuron passes through the cytoplasm – which is continuous with the postsynaptic neuron.

Question 4

List four advantages of electrical synapses.

Answer 4

1) They are faster than chemical synapses.
2) They are bidirectional.
3) They require fewer “moving pieces” – i.e., they are simpler.
4) It is easier (than in chemical synapses) to trigger synchronous activity.

Question 5

Charcot-Marie-Tooth X results from a defect in the gene coding for __________.

Answer 5

connexin

Question 6

List four disadvantages or limitations of electrical synapses.

Answer 6

1) They can only be excitatory.
2) It is difficult to integrate signals.
3) Signals cannot be amplified.
4) No learning or modulation of signals can take place.

Question 7

What triggers exocytosis of neurotransmitters in the presynaptic neurons of chemical synapses?

Answer 7

Calcium entry, which itself occurs upon depolarization of the axon terminus; calcium binds to synaptotagmin on the vesicle surface, which triggers exocytosis

Question 8

Describe the cellular pathology of myasthenic syndrome.

Answer 8

The body makes antibodies to the presynaptic calcium channels, preventing synaptic communication.

Question 9

What are the important protein interactions involved in vesicle exocytosis?

Answer 9

Synaptobrevin on the vesicle membrane interacts with syntaxin and SNAP25 on the presynaptic membrane.

Question 10

What vesicle-membrane protein senses intracellular calcium?

Answer 10

Synaptotagmin

Question 11

Botox is produced by which bacteria?

Answer 11

Clostridium botulinum

Question 12

Tetanus is produced by ______________.

Answer 12

Clostridium tetani

Question 13

Botox and tetanus toxin work by ____________.

Answer 13

clipping SNARE complexes, thus preventing synaptic communication

Question 14

What does the acronym mEPSP stand for?

Answer 14

Mini Excitatory Post-Synaptic Potential

Question 15

Mini release is independent of ____________.

Answer 15

action potentials and calcium entry

Question 16

Vesicles can only be released in ___________.

Answer 16

discrete quanta; that is, the presynaptic neuron cannot release 1.5 vesicles

Question 17

Minis are not related to __________.

Answer 17

signalling

Question 18

Describe the principle of the “driving force” in action potentials.

Answer 18

The driving force is the difference between reversal potential and actual potential; this force drives ions into or out of cells.

Question 19

Intracellular calcium is buffered by _________.

Answer 19

sodium-calcium antiporters and active transport

Question 20

___________ pinches off a new vesicle from the presynaptic membrane.

Answer 20

Dynamin

Question 21

Three chemical warfare drugs – ____________ – block acetylcholine esterase.

Answer 21

sarin, cyclosarin, and tabun

Question 22

__________ blocks the reuptake of dopamine.

Answer 22

Cocaine

Question 23

Endplates are _____________.

Answer 23

neuromuscular junctions

Question 24

Nicotinic acetylcholine receptors are found at ___________ and muscarinic acetylcholine receptors are found at ____________.

Answer 24

neuromuscular junctions (skeletal); autonomic nervous system (smooth muscle)

Question 25

What are the antagonists for nicotinic and muscarinic acetylcholine receptors?

Answer 25

Nicotinic: curare Muscarinic: atropine

Question 26

Because of acetylcholine esterase, about ________ of the acetylcholine is consumed on its way from the presynaptic neuron to the postsynaptic neuron.

Answer 26

half

Question 27

How many muscle fibers does one motor neuron innervate?

Answer 27

At least one, but can be many

Question 28

How many vesicles are released per action potential at the synaptic cleft?

Answer 28

30 - 100

Question 29

How many molecules of neurotransmitter are in each vesicle?

Answer 29

5,000 - 10,000

Question 30

How many molecules of acetylcholine are needed to activate one nicotinic acetylcholine receptor?

Answer 30

Two

Question 31

One vesicle depolarizes the membrane by about _______; how much depolarization is needed to excite an action potential in the postsynaptic neuron?

Answer 31

1 mV; 30 mV

Question 32

Curare was originally used by __________.

Answer 32

South American tribal people to paralyze prey

Question 33

What was the first medical use of curare?

Answer 33

Patient immobilization during surgery

Question 34

Modern medicines used to immobilize patients include the following: ____________.

Answer 34

rocuronium, vecuronium, pancuronium (all of which are non-depolarizing agents) and succinylcholine (which is a depolarizing agent)

Question 35

__________ blocks acetylcholine esterase and prolongs signals at neuromuscular junctions; it is used to treat myasthenic syndrome and myasthenia gravis.

Answer 35

Neostigmine

Question 36

How does fragile X affect dendritic spines?

Answer 36

It lengthens the dendritic spines and decreases their density.

Question 37

Review the cycle of glutamate/glutamine in central action potentials.

Answer 37

Glutamate passes across the synaptic cleft and activates a postsynaptic depolarization. It is then taken up by glial cells and converted to glutamine by glutamine synthetase. Glutamine is pumped out of the glial cells and taken up by presynaptic dendrites. Glutamine is then converted to glutamate by glutaminase.

Question 38

What ion do GABA receptors allow through?

Answer 38

Chloride

Question 39

Other than GABA, what molecules can activate GABA receptors?

Answer 39

Ethanol, barbiturates, benzodiazepines, and neurosteroids

Question 40

Integration occurs by _____________ summation.

Answer 40

temporal and spatial

Question 41

List the three types of central synapses.

Answer 41

1) Axo-dendritic 2) Axo-somatic 3) Axo-axonic

Question 42

What is synaptic facilitation?

Answer 42

The process in which repeated activation leads to accumulation of calcium in the presynaptic terminal; further action potentials will produce greater potentials by the release of more vesicles upon repeated depolarization.

Question 43

Why does synaptic depression occur?

Answer 43

Because presynaptic terminals use up vesicles, thereby leading to decreased strength of future action potentials

Question 44

Long-term potentiation and depression occur by the process of ______________.

Answer 44

calcium activating transcription factors for more receptors (in the case of potentiation) and lack of calcium leading to decreased presence of surface receptors

Question 45

Looking at a graph of time/amplitude, how can you identify summation and facilitation?

Answer 45

``` Summation = the cell does not repolarize completely between peaks Facilitation = the second peak has a higher amplitude (measured from the new baseline) than the first peak ```

Question 46

What are the three possible fates of neurotransmitters after they have bound to the postsynaptic cell?

Answer 46

1) Diffuse into the extracellular fluid/blood (most common in NMJ) 2) Be broken down by enzymes (such as cholinesterase) 3) Be pumped back into neurons or glial cells to be recycled

Question 47

NMJ (neuromuscular junction) synapses are always __________.

Answer 47

excitatory

Question 48

The ionotropic receptor on muscle cells allows _____________ through.

Answer 48

all cations (it is a non-selective cation channel)

Question 49

Describe the principle of the safety factor.

Answer 49

Presynaptic neurons secrete more neurotransmitter than is needed to ensure that a postsynaptic action potential occurs.

Question 50

Which comes first, synaptic facilitation or depression?

Answer 50

Facilitation

Question 51

What percent of prepared vesicles are released upon one depolarization?

Answer 51

About 10% (which can recover in five seconds)

Question 52

Patients with myasthenic syndrome will get stronger with exercise due to __________, while patients with myasthenia gravis will get weaker with exercise due to ____________.

Answer 52

synaptic facilitation; synaptic depression (because the acetylcholine receptors are partially blocked, more vesicles are needed to stimulate a response; thus vesicles are used up faster than unaffected people)

Question 53

Individual synaptic signals are much _________ in the CNS (as compared to the NMJ in the PNS).

Answer 53

weaker

Question 54

How do inhibitory synapses work?

Answer 54

They cause ion channels to open that hyperpolarize the cell membrane (often potassium channels).

Question 55

The main channel opened by glutamate in the CNS is _____________.

Answer 55

a non-selective cation channel

Question 56

The main channel opened by GABA in the CNS is ______________.

Answer 56

a chloride channel

Question 57

Importantly, inhibitory and excitatory signals don't neatly sum. Why?

Answer 57

Some ion channels may open for ions whose equilibrium potential is already at or near the resting potential. As such, those channels won't produce a big change in potential. However, if those ion channels are more permeable than others, they can prevent other ions from changing the potential as much as they otherwise would.

Question 58

Which signal is longer, ionotropic or metabotropic?

Answer 58

Metabotropic, because the second messengers persist in the cytoplasm longer than neurotransmitters persist in the synaptic cleft

Question 59

What two events do NMDA receptors need to be activated?

Answer 59

Presynaptic release of glutamate (which opens the channel gate) and a postsynaptic action potential (which causes the magnesium ion lodged in the channel to leave the cell)

Question 60

How do NMDA channels allow for conditioning?

Answer 60

Suppose a cell is receiving two signals – a strong, unconditioned stimulus (such as meat to a dog); and a weak, conditioned stimulus (Pavlov's bell). The weak stimulus can release glutamate to an NMDA channel, but the channel won't open because the signal is not strong enough to elicit an action potential. Coupled with the UCS, which does elicit an action potential, the NMDA channels associated with the bell open and then release more AMPA channels which can subsequently generate action potentials.

Question 61

What kind of channel is the glycine receptor?

Answer 61

Inhibitory chloride channel