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?
