Synaptic Transmission, Neurotransmitter Release, and Neurotransmitter Systems

Comprehensive fill-in-the-blank practice flashcards covering quantal neurotransmitter release, vesicle fusion machinery, chemical and electrical synapse ultrastructure, and neurotransmitter metabolic systems.

Electron micrographs of the neuromuscular junction demonstrate that synaptic vesicles have a characteristic diameter of __________.

$$50\,\text{nm}$$

At low rates of activity, synaptic vesicles are made with the quick _______ style release

Kiss-and-run

Bernard Katz established that neurotransmitters are released in discrete, uniform packets known as __________.

quanta

Spontaneous, unprovoked depolarizations recorded at the muscle endplate have an average amplitude of __________.

$$0.4\,\text{mV}$$

When Fatt and Katz administered curare to block $10\%$ of nicotinic receptors, they observed a $10\%$ reduction in mEPP __________, rather than in frequency.

size

Application of the acetylcholinesterase inhibitor prostigmine causes an increase in mEPP __________ without changing mEPP frequency.

amplitude

In binomial modeling of synaptic release, the mean quantal content ($m$) is calculated as the product of the number of available quanta ($n$) and the probability of release ($p$), expressed as $m = \text{\_\_\_\_\_\_\_\_\_\_}$.

$$n \times p$$

In binomial modeling of synaptic release, the mean quantal content ($m$) is calculated as the fraction ______

mEPP/EPP

Using the Poisson distribution method under low-release conditions, mean quantal content is determined from failures by the formula $m = \text{\_\_\_\_\_\_\_\_\_\_}$, where $N$ is the number of trials and $n_0$ is the number of failures.

ln(N/n₀)

Current passing through a single nicotinic receptor channel at the muscle endplate produces a membrane depolarization of approximately __________.

0.1uV

Generating a single $0.4\,\text{mV}$ miniature endplate potential requires approximately __________ molecules of acetylcholine binding to postsynaptic receptors.

4,000

At central synapses such as the Calyx of Held, the mean quantal content ($m$) at each active zone during an action potential is approximately __________.

1

Synaptic vesicle neurotransmitter transporters act as __________ that harness the outward movement of protons down their electrochemical gradient to drive neurotransmitter uptake.

antiports

The small Ras-superfamily GTPase __________ cycles to its GTP-bound state to direct synaptic vesicles to dock near presynaptic voltage-gated $\text{Ca}^{2+}$ channels.

Rab3

The core neuronal SNARE complex forms a four-helix bundle consisting of synaptobrevin, syntaxin, and __________.

SNAP-25

The energetically favorable zippering of SNARE alpha helices enables vesicle priming by eliminating __________ between the opposing lipid bilayers.

water molecules

In priming stage II, the protein __________ clamps the partially assembled SNARE complex to prevent premature fusion until $\text{Ca}^{2+}$ influx occurs.

complexin

The primary $\text{Ca}^{2+}$ sensor triggering synchronous vesicle fusion is ________, which binds calcium via two carboxyl-terminal C2 domains.

synaptotagmin

In the illustrated SNARE dissociation reaction, disassembly of the stable complex after membrane fusion is catalyzed by the hexameric ATPase labeled __________.

NSF

At firing frequencies under $30\,\text{spikes/second}$, vesicles can release their contents through a transient fusion pore and recycle within 2 to 3 seconds via __________.

kiss-and-run

At a conventional chemical synapse, the fluid-filled synaptic cleft separating presynaptic and postsynaptic membranes spans a width of __________.

$$20\text{--}50\,\text{nm}$$

The proteinaceous postsynaptic density (PSD) directly underneath the postsynaptic membrane contains an estimated total mass of __________ of protein.

$$1\,\text{gigaDalton}$$

The specialized presynaptic cytoskeletal grid where docked and primed vesicles undergo exocytosis is designated the __________.

cytomatrix of the active zone

In the structural diagram shown, the excitatory asymmetric synapse characterized by a wide cleft, round vesicles, and an extensive postsynaptic density is classified as a __________ synapse.

Type I

E. G. Gray classified symmetric synapses with modest densities, flattened vesicles, and narrower clefts releasing GABA or glycine as __________ synapses.

Type II

In the schematic comparison of receptor signaling, panel B illustrates indirect gating where neurotransmitter binding triggers a G protein to activate the enzyme __________.

adenylyl cyclase

Spatial summation of synaptic inputs across dendritic sites is determined primarily by the membrane's __________, whereas temporal summation depends on the time constant.

space constant

Axo-axonic presynaptic inhibition reduces transmitter output by opening presynaptic $\text{K}^+$ channels prematurely and directly closing presynaptic voltage-gated __________ channels.

$$\text{Ca}^{2+}$$

As illustrated in the gap junction diagram, six connexin subunits assemble in the plasma membrane to form a hemichannel termed a __________.

connexon

The central aqueous pore formed across the extracellular gap by two joined connexons has an internal diameter of __________.

$$1.5\,\text{nm}$$

At an electrical synapse, the physical intercellular gap separating opposing neuronal membranes narrows to __________.

$$3.5\,\text{nm}$$

Because of junctional resistance and postsynaptic capacitance, electrical synapses filter spike trains exceeding $10\,\text{spikes/second}$ into a continuous, __________ potential.

direct current

The neurotransmitter verification criterion of __________ dictates that exogenous application of a chemical must evoke the exact same postsynaptic response as electrical nerve stimulation.

mimicry

Presynaptic release-regulating autoreceptors diminish vesicle release probability during repetitive firing to expand a terminal's __________.

dynamic range

The cytoplasmic enzyme responsible for synthesizing acetylcholine from acetyl-CoA and choline is __________.

choline acetyltransferase

All somatic motor neurons and preganglionic autonomic motor neurons release acetylcholine onto postsynaptic cells expressing __________ acetylcholine receptors.

nicotinic

In volume neurotransmission, a single human cholinergic or monoaminergic axon can establish a cumulative arborization length of __________.

$$10^7\,\text{meters}$$

The initial rate-limiting enzyme in catecholamine biosynthesis that converts tyrosine into L-DOPA is __________.

tyrosine hydroxylase

Unlike cytoplasmic catecholamine enzymes, the enzyme __________ is localized entirely within the lumen of synaptic vesicles.

dopamine B-hydroxylase

The resting tremor and poverty of movement in Parkinson's disease result from degeneration of dopaminergic neurons projecting from the __________ to the striatum.

substantia nigra

Serotonin biosynthesis is initiated by the conversion of tryptophan to 5-HTP catalyzed by the enzyme __________.

tryptophan hydroxylase

The majority of serotonin-synthesizing neuronal somata within the mammalian brain are located in the pontine and midbrain __________ nuclei.

raphe

In glutamatergic terminals, astrocyte-derived glutamine is converted into glutamate by the mitochondrial enzyme __________.

phosphate-activated glutaminase

GABA is synthesized from glutamate in a single enzymatic step catalyzed by __________.

glutamic acid decarboxylase

Glycine is enzymatically synthesized from the precursor amino acid __________ by serine hydroxymethyltransferase.

serine

Unlike small-molecule transmitters that can be locally replenished in the terminal, neuropeptides must be transcribed and translated in the __________.

cell body

Large, dense-core vesicles undergo exocytotic fusion away from the active zone only when the axon terminal experiences __________ $\text{Ca}^{2+}$ influx.

repeated

As shown in the sympathetic co-transmission diagram, small granular vesicles (SGV) release ATP and noradrenaline, while large granular vesicles (LGV) co-release __________.

NPY

Nitric oxide diffuses across neuronal membranes to stimulate cytosolic __________ to produce cGMP, thereby enhancing presynaptic glutamate release.

guanylate cyclase

Endocannabinoids act as retrograde messengers by binding to presynaptic GPCRs designated as __________ receptors, inhibiting further transmitter release.

CB1

Rab3 is active and promotes synaptic vesicle docking only when bound to _________

GTP

Rab3-GTP mediates synaptic vesicle docking by binding to a presynaptic plasma membrane effector protein called _________

Rab3 Effector

Rab3 Effector is bound to ____ on the presynaptic membrane

voltage gated Ca²⁺ channels

in the SNARE complex are two T-SNAREs and a V-SNARE called

synaptobrevin

According to the ionic concentration table, the extracellular concentration of $\text{K}^+$ ($[\text{K}^+]_{\text{out}}$) is _________.

5 mM

According to the ionic concentration table, the intracellular concentration of $\text{K}^+$ ($[\text{K}^+]_{\text{in}}$) is _________.

100 mM

According to the ionic concentration table, the extracellular concentration of $\text{Na}^+$ ($[\text{Na}^+]_{\text{out}}$) is _________.

150 mM

According to the ionic concentration table, the intracellular concentration of $\text{Na}^+$ ($[\text{Na}^+]_{\text{in}}$) is _________.

15 mM

According to the ionic concentration table, the extracellular concentration of $\text{Ca}^{2+}$ ($[\text{Ca}^{2+}]_{\text{out}}$) is _________.

2 mM

According to the ionic concentration table, the intracellular concentration of $\text{Ca}^{2+}$ ($[\text{Ca}^{2+}]_{\text{in}}$) is _________.

0.0002 mM

According to the ionic concentration table, the extracellular concentration of $\text{Cl}^-$ ($[\text{Cl}^-]_{\text{out}}$ ) is _________.

150 mM

According to the ionic concentration table, the intracellular concentration of $\text{Cl}^-$ ($[\text{Cl}^-]_{\text{in}}$) is _________.

13 mM