BNS 305 Chapter 5: Synaptic Transmission

motor

ACh (acetylcholine) is highly concentrated in the synaptic vesicles of ____ neurons

synapsin

CaMKII frees synaptic vesicles from the reserve pool by phosphorylating ______

metabotropic

G-protein-coupled receptors are also called ______ receptors

quanta

Katz discovered that a presynaptic action potential causes a postsynaptic EPP because it synchronizes the release of many transmitter _____

neuromuscular junction, MEPPs

Katz found that when the _____ _____ is bathed in a solution that has a low concentration of Ca2+, stimulating the motor neuron evokes EPPs whose amplitudes are reduced to about the size of ______

clathrin, dynamin, actin, Hsc70, auxilin

Steps of membrane budding during endocytosis: 1) adaptor proteins connect _____ to the vesicular membrane which assembles into a coat and curves the membrane to form a coated pit. 2) this cage constricts the lipid stalk connecting the two membranes 3) a _____ ring coil forms and pinches off the lipid stalk 4) the coated vesicle is translocated by _____ filaments 5)______ and ______ uncoat the vesicle

end plates

The complex postsynaptic specialization at the site of nerve contact on skeletal muscle fibers.

terminal, calcium, vesicles, neurotransmitters, receptor, excitability, glial, degradation

The main sequence of events involved in chemical synapse transmission: An action potential invades the presynaptic ____. Depolarization causes opening of voltage gated ______ channels and these ions flow into the cell. This causes _____ to fuse with the presynaptic membrane. Then, _______ are released into the synaptic cleft via exocytosis. They bind to ______ molecules in the postsynaptic membrane which causes opening or closing of postsynaptic channels. This changes the _____ of the postsynaptic cell. The neurotransmitters are removed by _____ uptake or by enzymatic ______.

G-proteins

___-_____ can be though of as transducers that couple neurotransmitter binding to a receptor with regulation of postsynaptic ion channels.

end plate

_____ ______ potentials evoked by stimulation of a motor neuron are normally above threshold and therefore produce an action potential in the postsynaptic muscle cell

dynamin

_____ forms ringlike coils around the lipid stalks of budding membranes; these rings disconnect vesicle membrane from plasma membrane during endocytosis.

gap

_____ junctions contain a unique type of channel called a connexon

small-molecule

_____-_____ neurotransmitters are packaged in small clear-core vesicles.

connexins

______ are integral membrane proteins that form the subunits of connexons

dynamin

______ causes the final pinching off of a coated vesicle in endocytosis

metabotropic

______ receptors don't have ion channels as part of their structure. They have an intracellular domain that indirectly affects channels through the activation of intermediate molecules called G-proteins

synaptotagmin

_______ binds to the SNARE complex and entering Ca2+ binds to ______, leading to curvature of the plasma membrane, which brings the membranes together. Fusion of the membranes leads to exocytotic release of neurotransmitter. (______)

acetylcholine

_______ is a neurotransmitter that acts in the heart and a variety of postsynaptic targets in the central and peripheral nervous systems, preeminently at the neuromuscular junction of striated muscles and in the visceral motor system

ionotropic, acetylcholine

_______ neurotransmitter receptors generally mediate rapid postsynaptic effects. Examples are the EPP produced at neuromuscular synapses by _______.

calcium, coated, endosomes

_______-regulated fusion of vesicles with the presynaptic membrane is followed by endocytotic retrieval of vesicular membrane via ______ vesicles and _____, and subsequent re-formation of new synaptic vesicles.

lowering

________ calcium concentration decreases the number of vesicles that fuse with the plasma membrane of the terminal

small-molecule, neuropeptides

________-_____ neurotransmitters mediate rapid synaptic connections, whereas _______ tend to modulate slower, ongoing neuronal functions.

EPP

_____s represent the simultaneous release of many MEPP-like units

synaptic vesicle

a quantum of transmitter release is due to fusion of a single _____ ______ with the presynaptic membrane

synaptic vesicles

a rise in calcium concentration causes ____ ___ to fuse with the presynaptic plasma membrane and release their contents into the space between the pre and post synaptic cells

Hsc70, auxilin

after coated vesicles are transported away from the plasma membrane by actin (during endocytosis), the clathrin coats are removed by an ATPase, ______, and another protein, _____.

4, 6

all connexins have ____ transmembrane domains, and all connexons consist of ___ connexins that come together to form a hemi-channel in both the pre and postsynaptic neurons.

fast, bidirectional

although they are a minority, electrical synapses have several advantages. One is that transmission is extraordinarily ____ and another unique advantage is that transmission can be ______ (current can flow in either direction)

electrical

at ____ synapses, current flows through connexons, which are specialized membrane channels that connect two cells at gap junctions

electrical

at _____ synapses, gap junctions occur between pre and postsynaptic membranes

ion channels, receptor

at chemical synapses, there is no intercellular continuity and therefore no direct flow of current from pre to postsynaptic cell. Synaptic current flows across the postsynaptic membrane only in response to the secretion of neurotransmitters, which open or close postsynaptic ____ _____ after binding to _____ molecules on the postsynaptic membrane.

connexons, gap

at electrical synapses, current flows through _____, which are specialized membrane channels that connect two cells at ____ junctions

action potential

binding of neurotransmitter to receptors causes channels in the postsynaptic membrane to open or close. This alters the conductance and usually the membrane potential of the postsynaptic neuron, increasing or decreasing the probability that the neuron will fire an _____ ______

acetylcholine

both EPPs and miniature EPPs are sensitive to pharmacological agents that block postsynaptic _______ receptors

connexins

connexons are composed of a unique family of ion channel proteins, the ______, which serve as subunits to form connexon channels

gap junction

current flow at electrical synapses arises at an intercellular specialization called a ____ ____, where membranes of the two communicating neurons come extremely close to one another and are linked together

yes

do spontaneous miniature EPPs (MEPPs) occur in the absence of presynaptic stimulation?

SNARE

during docking of the synaptic vesicle, _____ proteins on the vesicle and plasma membranes form a complex that brings together the two membranes

actin

during endocytosis, coated vesicles are transported away from the plasma membrane by the cytoskeletal protein _____

SNARE proteins, synaptotagmin

during exocytosis, _____ _____ bring the plasma and vesicular membranes close together, while calcium induced changes in _______ then produce the final curvature that enables rapid fusion of these membranes

miniature end plate

end plate potentials (EPPs) are made up of individual units, each equivalent to a _____ _____ _____ potential

receptors

following exocytosis, transmitters diffuse across the synaptic cleft and bind to specific ______ on the membrane of the postsynaptic neuron

connexon

gap junctions contain a unique type of channel, called a _____, which provides the path for electrical current to flow from one neuron to another

ions

gap junctions contain connexon channels that permit ____ to flow passively from the presynaptic cell to the postsynaptic cell

co-transmitters

in some cases, neurons synthesize and release two or more different neurotransmitters; in this case, the molecules are called ___-_____

presynaptic

in the _______ terminal, dense projections are associated with the active zone where synaptic vesicles discharge their neurotransmitters into the cleft

active zone

in the presynaptic terminal, dense projections are associated with the ____ ____, the place where synaptic vesicles discharge their neurotransmitters into the synaptic cleft

clathrin

individual ______ triskelia assemble together to form membrane coats involved in membrane budding during endocytosis

ligand-gated ion channels

ionotropic receptors are also called _____-_____ ____ _____

ionotropic

ligand-gated ion channels are also called ______ receptors

faster

membrane fusion during exocytosis is much _____ than budding during endocytosis

G

metabotropic receptors are also called __-protein-coupled receptors

slower

metabotropic receptors typically produce much _______ responses than ionotropic receptors

depolarization

microinjection of Ca2+ into a squid giant presynaptic terminal triggers transmitter release, measured as a ______ of the postsynaptic membrane potential

CaMKII

mobilization of reserve pool vesicles is caused by phosphorylation of synapsin by protein kinases, most notably ____, which allows synapsin to dissociate from the vesicles

small clear-core

most small-molecule neurotransmitters are packaged in vesicles 40-60 nm in diameter, the centers of which appear clear in electron micrographs. These vesicles are called ______ ______-_____ vesicles.

large dense-core

neuropeptides are packaged into synaptic vesicles that range from 90 to 250 nm in diameter. Because the centers of these vesicles appear electron-dense in electron micrographs, they are referred to as _____ _____-____ vesicles

soma

neuropeptides are synthesized in the ____ of a neuron

axonal transport

neuropeptides are synthesized in the soma of a neuron, and peptide-filled vesicles are transported along an axon and down to the synaptic terminal via ____ _____.

receptors

neurotransmitter ______ are proteins that are embedded in the plasma membrane of postsynaptic cells and have an extracellular neurotransmitter binding site that detects the presence of neurotransmitters in the synaptic cleft

postsynaptic

neurotransmitter receptors are embedded in the plasma membrane of _______ cells

exocytosis

neurotransmitters are released into the synaptic cleft in a process called _______

SNARE

once vesicles are free from the reserve pool (thanks CaMKII), they make their way to the plasma membrane and are then attached to this membrane by docking reactions that involve _____ proteins

metabotropic, G

one family of neurotransmitter receptor is _______ receptors, called that because the eventual movement of ions through a channel depends on intervening metabolic steps. These receptors don't have ion channels as part of their structure- instead they have an intracellular domain that indirectly affects channels through the activation of intermediate molecules called ___-proteins

CaMKII

phosphorylation of synapsin by ______ allows synapsin to dissociate from the vesicles in the reserve pool

chelators

presynaptic microinjection of calcium _______ (proteins that bind Ca2+ and keep its concentration buffered at low levels) prevents presynaptic action potentials from causing transmitter secretion

synaptotagmins

proteins present in wall of synaptic vesicle that bind calcium and help stimulate the process of exocytosis

chelators

proteins that bind ions and prevent them from being used

MEPP

release of acetylcholine does indeed occur in discrete packets, each equivalent to a _____.

synapsin

several lines of evidence indicate that the protein _____, which reversibly binds to synaptic vesicles, may keep these vesicles tethered within the reserve pool by cross-linking vesicles to each other

synaptic vesicles

synapsin tethers _____ _____ in a reserve pool

vesicles

synaptic _____ loaded with transmitter are the source of the quanta Katz discovered

action potential

synaptic transmission is initiated when an _______ ________ invades the terminal of the presynaptic neuron.

terminal

synaptic transmission is initiated when an action potential invades the _____ of the presynaptic neuron

presynaptic, postsynaptic

synaptic vesicles are filled with one or more neurotransmitters, chemical signals that are secreted from the ______ neuron and detected by specialized receptors on the _____ neuron

Na+

tetrodoxin blocks ____ channels

voltage clamp

the ____ ____ method detects currents flowing across the presynaptic membrane when the membrane potential is depolarized

active

the _____ zone of the presynaptic terminal is the site of synaptic vesicle exocytosis

calcium

the amount of neurotransmitter released is very sensitive to the exact amount of ____ that enters

postsynaptic

the binding of neurotransmitter to receptors causes channels in the _____ membrane to open (or sometimes close), thus changing the ability of ions to flow across the postsynaptic membrane

calcium, presynaptic

the change in membrane potential caused by the arrival of the action potential at the presynaptic terminal leads to the opening of voltage-gated ______ channels in the presynaptic membrane. The rapid rise in this ion allows synaptic vesicles to fuse with the plasma membrane of the ______ neuron.

calcium

the first indication of presynaptic _____ channels occurred when Katz observed that presynaptic terminals treated with tetrodoxin (which blocks Na channels) could still produce a peculiarly prolonged type of action potential

endocytosis

the fused vesicle membrane is actually retrieved and taken back into the cytoplasm of the nerve terminal (a process called _____)

pore

the hemi-channels of connexons are precisely aligned to form a ____ that connects the two cells and permits electrical current to flow

calcium

the influx of ____ through voltage gated channels triggers the secretion of neurotransmitters

clathrin, dynamin

the most important protein involved in endocytotic budding of vesicles from the plasma membrane is _____. This protein forms a cagelike coating around the vesicle membrane and curves the membrane until it forms a coated vesicle-like structure that remains connected to the plasma membrane via a narrow lipid stalk. ______ forms a ringlike coil that surrounds the lipid stalk and pinches it off to complete the production of a coated vesicle

synaptic vesicles

the most important structural feature of chemical synapses is the presence of small, membrane-bound organelles called _____ _____ within the presynaptic terminal. These contain neurotransmitters

ionotropic

the receptors in one family contain a membrane-spanning domain that forms an ion channel. These receptors combine transmitter-binding and channel functions into a single molecular entity and thus are called ______ receptors, aka ligand-gated ion channels

synaptic cleft

the space between the pre and postsynaptic neurons is substantially greater at chemical synapses than at electrical synapses and is called the ______ _____

end plates

the synapses between spinal motor neurons and skeletal muscle cells occur at specializations called ______ _____ because of the saucerlike appearance of the site on the muscle fiber where the presynaptic axon elaborates its terminals.

small-molecule

the synthesis of ____-____ neurotransmitters occurs locally within presynaptic terminals

cytoplasm

the synthesis of small-molecule neurotransmitters occurs in the _______ of presynaptic terminals. So, locally.

presynaptic, postsynaptic

the upstream neuron is called the _____ neuron and the downstream neuron is termed ______

calcium, acetylcholine

the usual means of eliminating muscle contractions is either to lower _____ concentration in the extracellular medium or to partially block the postsynaptic ______ receptors with the drug curare

small-molecule, neuropeptides

there are over 100 types of neurotransmitter and they can be classified into two broad categories: ______-______ neurotransmitters and _____

ionotropic, metabotropic

there are two broad families of neurotransmitter receptor proteins: _______ and _______ receptors

large dense-core

what type of vesicles are neuropeptides packaged in?

small clear-core

what type of vesicles are small-molecule neurotransmitters packaged in?

action potential

when Katz blocked Na+ channels in presynaptic membranes with tetrodoxin, he found that the terminals could still produce a peculiarly long type of ____ ____. The explanation for this was that current was still flowing through Ca2+ channels. This is how presynaptic Ca2+ channels were discovered

yes

will microinjecting Ca2+ into a presynaptic terminal trigger transmitter release without a presynaptic action potential?