Chapter 3
Approximately ___% of the known neurotransmitters and hormones activate ____________________ receptors
80, Metabotropic
_______________ _________________ _________: no action potentials can be produced.
Absolute refractory phase
____________________: changes in membrane potential after action potentials.
Afterpotentials
A drug classified as a(n) ____________ mimics the actions of a neurotransmitter; a drug classified as a(n) ____________________ prevents a neurotransmitter's action.
Agonist, antagonist
____________________ on presynaptic membrane bind transmitters; inform the cell about transmitter concentration in the cleft, which can be adjusted.
Autoreceptors
__________________ inform presynaptic cells about the net concentration of transmitter in the _____________ _______ and may regulate how much transmitter is released subsequently.
Autoreceptors, synaptic cleft
When an action potential arrives, the membrane of the axon terminal becomes more permeable to ____&_____2+;. The amount that then enters the cell determines the amount of ____________________released: A large influx of ___&_____2+; into the cell causes more vesicles to discharge their contents than does a small influx. The entrance of ___&_____2+; into the axon terminal and fusion of vesicles are the main cause of synaptic _________.
Ca, sup, neurotransmitter, Ca, sup, Ca, sup, delay
There is a delay between the arrival of the presynaptic action potential and the postsynaptic action potential at ______________ synapses; the presynaptic potential is first translated into _____________________release and then back into an electrical signal on the postsynaptic side.
Chemical, neurotransmitter
___________________ ____________: speed of propagation of action potentials—varies with diameter of the axon
Conduction velocity
___________________—rapid breakdown by an enzyme, e.g., acetylcholinesterase (AChE) breaks down ACh and recycles it - part of the ending synaptic transmission
Degradation
____________________: decrease in membrane potential—interior becomes less negative.
Depolarization
Two opposing forces drive ion movement: _____________: ions flow from areas of higher to lower concentration, along the _____________________ ________________. __________________ _____________: ions flow towards oppositely charged areas.
Diffusion, concentration gradient, electrostatic pressure
________________________ ___________—neurotransmitters and hormones produced by the body
Endogenous ligands
__________________ _________________ _______________ (EPSP): produces a small local depolarization, pushing the cell closer to threshold
Excitatory postsynaptic potential (EPSP)
Electrical synapses are found where conduction must occur very ________, such as in circuits involved in __________ behavior, and also in regions where a large number of fibers must be activated __________________, such as in the oculomotor system
rapidly, escape, simultaneously
The number of _______________ in cells can vary: • Daily in adulthood • During development • With drug use
receptors
____________—transmitter is taken up by presynaptic receptors called ___________________
reputake, transporters
There are two major mechanisms for clearing neurotransmitter from the synaptic cleft: _________________ degradation and neuronal ___________. In neuronal _______________, special receptors on the _______________ membrane called ____________________ remove molecules of neurotransmitter from the synapse. The prompt removal of neurotransmitter by these mechanisms contributes to the accuracy of neural messages.
reuptake, reuptake, enzymatic, presynaptic, transporters
Neuron membranes have_____________ __________________: some ion channels are open all the time and allow only _________________ _____ ( ___ +) to cross freely; other channels restrict flow of other ions.
selective permeability, potassium ions, K
The generation of an action potential is critically dependent on voltage-gated _________channels
sodium
The active membrane, while firing the action potential, is primarily a _____________ -dependent membrane. The Nernst equation predicts the membrane potential of this state to be +____mV, which corresponds to the _______ voltage of the action potential.
sodium, 40, peak
At threshold depolarization, these channels start to open, and the depolarization caused by the entry of _________into the axon causes still more voltage-gated channels to open, until _____________floods in and causes the membrane potential to suddenly become ____________.
sodium, sodium, positive
Neurons use a mechanism called the ___________ - _________________ ________ to maintain resting potential. It pumps three ___________ ________ ( _____+) out for every two K+ ions pumped in.
sodium-potassium pump, sodium ions, Na
Neurophysiology:
study of electrical and chemical processes in neurons.
Incoming information, in the form of EPSPs and IPSPs, is integrated in the postsynaptic neuron through the process of _______________ . There are two mechanisms by which this occurs: _________________ __________________ is the addition of two potentials that occur close together in time. __________ ___________________ is the addition of two potentials that occur close together physically on the cell membrane.
summation, Temporal summation Spatial summation
If the membrane potential reaches the ______________ (about -40 mV), an action potential is triggered. The membrane potential reverses and the inside of the cell becomes positive.
threshold
Specialized proteins mediate exocytosis. For example, __-_________are tethers attached to vesicles, and tethers attached to the presynaptic membrane are called __-___________. _______________ _________works by cutting up these proteins, disabling _______________.
v-SNAREs, t-SNAREs, Botulinum toxin, exocytosis
The membrane, synaptic, or action potential of a neuron may be experimentally measured and modified using ___________ _________________. In __________ ________________, a microelectrode tip pulls away a small portion of the membrane. Several variations are possible, such as a portion with a ___________ ion channel, a(n) "___________-out" membrane, or a(n)"____________-out" membrane.
voltage clamping, patch clamping, single, inside, outside
Information flows __________ a neuron via electrical signals; information passes _____________neurons through chemical signals.
within, between
Imagine a simplified neuron (lacking dendrites) with four synapses on the cell body—two inhibitory and two _____________. A pattern of firing that would provide the maximal likelihood of producing an action potential would be rapid, repeated firing at both excitatory synapses with no firing at _______________synapses, thus maximizing the likelihood of a threshold _____________________. This is because both temporal and spatial summation of the EPSPs would occur, with no IPSPs reducing the depolarization.
Excitatory, inhibitory, depolarization
__________________ : Influs of Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitter into the cleft.
Exocytosis
__________________ ____________—drugs and toxins from outside the body
Exogenous ligands
_______________ _______________: takes into account the intracellular and extracellular concentrations of several ions and the degree of membrane permeability to each
Goldman equation
The _____________ equation predicts voltage potentials by considering the ___________________ and ____________________concentrations of __________ ____ ions as well as the degree of membrane permeability to the ion(s).
Goldman, intracellular and extracellular, only Cl-
____________________________: increase in membrane potential—interior of the membrane becomes even more negative relative to the outside
Hyperpolarization
_______________ __________________ ________________ (IPSP): produces a small hyperpolarization; pushes cell further away from threshold. -result from chloride ions (Cl−) entering the cell, making the inside more negative.
Inhibitory postsynaptic potential
___________________ receptors open when bound by a transmitter (also called ligand-gated ion channel).
Ionotropic
____________ fit receptors exactly and activate or block them
Ligands
_________ ________________: potential that spreads passively across the membrane, diminishing as it moves away from the point of stimulation.
Local potential
__________________ receptors activate ___ ____________ when bound by a transmitter.
Metabotropic, G protein
____________ provides insulation around axons, forcing action potentials to jump between nodes of _____________. This process, termed _______________ conduction, promotes much __________ propagation of the action potential along the length of the axon.
Myelin, Ranvier, saltatory, faster
During the absolute refractory period, the membrane potential has collapsed (so there is no scope for further depolarization), and ___ &_____+; channels are inactivated. During the relative refractory phase, __&_____+; flows out of the cell, so the membrane potential is partially restored, and a ______ __________ stimulation may elicit a second action potential.
Na, sup, K,sup, very strong
_____________ _____________: predicts ________________ ______________—voltage needed to counterbalance the diffusion force. It predicts a potential of -____ mV but measured equilibrium potential is typically about -_____ mV.
Nernst equation, equilibrium potential, 80, 65
The value of a given neuron's resting membrane potential can be estimated by means of the ___________ equation. However, the measured value is generally slightly less negative than the predicted value, due to the slight permeability of the neuronal membrane to ___+ ions. The cell employs ____________- ________________ pumps to actively counter this movement; if it did not, the cell's resting potential would eventually be ___ mV.
Nernst, Na, sodium-potassium, 0
________ ____ _____________: Small gaps in the insulating myelin sheath.
Nodes of Ranvier
_______________________ ______________ are brief changes in the resting potential.
Postsynaptic potentials
__________________ __________ : only some stimuli can produce an action potential.
Refractory period:
_____________ ________________ ___________: only strong stimulation can produce an action potential
Relative refractory phase
Exocytosis is mediated by specialized proteins—___________ and ______________________
SNAREs, synaptotagmin
__________________ _________________: The axon potential travels inside the axon and jumps from node to node.
Saltatory conduction
____________ __________________ : summing of potentials that come from different parts of the cell.
Spatial summation
_________________ _________ : delay between action potential reaching the axon terminal and creating a postsynaptic potential.
Synaptic delay
_______________ _________________: summing of potentials that arrive at the axon hillock at different times.
Temporal summation
Up-regulation is an increase in the number of receptors; down-regulation is a decrease.
Up-regulation, down-regulation
____________ - ______________ ___ ______________ open in response to depolarization, and Na+ ions enter; more channels open and more Na+ enters
Voltage-gated Na+ channels
Nicotine and muscarine function as ____________, whereas curare and bungarotoxin are __________________for receptors of the neurotransmitter acetylcholine.
agonists, antagonists, acetylcholine
An action potential is generated in its full form or not at all, called the ______-___-______property.
all- or- none
Action potentials are regenerated ________ _____ _______ — each adjacent section is depolarized and a new action potential occurs.
along the axon
Most synapses, from an axon to a dendrite, are called ____-_____________synapses, but other synapses exist. ____-__________synapses regulate how much neurotransmitter will be released from the targeted terminal; __________-____________synapses allow for coordination of neuronal activity; and in ________________synapses, postsynaptic neurons can communicate with presynaptic neurons by releasing a gas neurotransmitter, like carbon monoxide or nitric oxide.
axo-dendritic, axo-axonic, dendro-dentritic, retrograde
The action potential starts at the _____ ____________, which is studded with voltage-gated ____&_____+; channels, and it is recreated at successive positions down the length of the axon; in other words, the action potential _______________ itself.
axon hillock, Na, sup, regenerates
Positively charged ions are called _________, and negatively charged ions are called _________. Since the inside of a resting cell is negative relative to the outside, __________ on the outside of the cell will be attracted to the intracellular fluid and __________will be repelled by it.
cations, anions, cations, anions,
A(n) _____________________ is a medical condition in which the form and function of ion channels is altered as a result of a genetic ____________.
channelopathy, mutation
Loewi won the Nobel Prize for demonstrating that ____________ transmission is responsible for decreasing a frog's heart with stimulation of the __________ nerve. The substance Loewi called Vagusstoff was later identified as ____________________.
chemical, vague, acetycholine
As K+ ions build up inside the cell, they also diffuse out, along the ________________________ ___________.
concentration gradient
Ending synaptic transmission:
degradation and reuptake
When a metabotropic receptor is activated, parts of the G protein _______________, and the alpha subunit migrates away and affects any of a variety of cellular processes.
dissociate
A given neurotransmitter may have _________ an excitatory ___ inhibitory effect, depending on the _____ ______ ___ ____ ____________ ____ _____________. For instance, acetylcholine excites the postsynaptic cell by opening K+ and Na+ channels, inhibits the postsynaptic cell by opening Cl- channels.
either, or, the type of ion channel it activates
Like other bodily cells, the neuron under steady state conditions exhibits a slight ____________ difference between the inside of its cell membrane and the outside. This is known as the ____________ _______________. This potential is attributable to differential concentrations of _____ inside the cell relative to the outside and is about -50 to -80 ___________in magnitude.
electrical, resting membrane, ions, millivolts
At rest, K+ ions move into the negative interior because of __________________ _____________
electrostatic pressure.
K+ reaches ________________ when the movement out is balanced by the movement in, corresponding to the resting membrane potential of about -_____ mV.
equilibrium, 58
The stimulus is encoded in _____________ rather than _______________ of action potentials.
frequency, amplitude
Dendrites increase the amount of information a neuron can receive and integrate: ___________postsynaptic potentials spread passively along dendrites; they are _______________ in terms of their proximity the cell body. The farther out on the dendrite a ___________potential occurs, the less effect it can have at the axon ___________. Glia can ______________the overall strength of postsynaptic potentials by preventing ________________________ from leaking out of the synaptic cleft.
graded, weighted, graded, hillock, increase, neurotransmitter
A second force that helps determine the distribution of ions is the concentration ___________, which refers to the propensity of ions to move from regions of ______ concentration to areas of _____ concentration.
gradient, high, low
Imagine that a single vesicle discharges its transmitter into the cleft, followed a short time later (after the transmitter has been cleared from the synapse) by the release of transmitter from a second vesicle. Compared to the size of the effect that the first vesicle has on the postsynaptic potential, the size of the second vesicle's effect is ________________because each vesicle contains _________ _____ ________ number(s) of molecules of transmitter.
identical, about the same
Ions are dissolved in ________________fluid, separated from the _________________fluid by the _____ membrane
intracellular, extracellular, cell membrane
Neurons regulate _______________ levels of calcium by _____________ Ca2+ ______ of the cell and ___________ Ca2+ ___________ the cell.
intracellular, pumping, out, storing, inside
Neuronal membranes exhibit selective permeability, which means that the types of ____ ____________ present in the membrane determine the types of ions that can be moved by these forces through the cell membrane. Neurons at rest are selectively permeable to ______________.
ion channels, potassium
Receptors control ion channels in two ways:
ionotropic receptors and metabotropic receptors
A receptor that directly opens a channel when bound is called a(n) ________________ receptor. This type of receptor is therefore also known as a __________-gated ion channel
ionotropic, ligand
Electrical synapses feature special ________ ion channels lined up on both sides of the synapses, which allow ______ to flow directly from the presynaptic cell into the postsynaptic cell across a very _______ cleft. Transmission at these synapses resembles the conduction along a cell's axon.
large, ions, small
The nicotinic ACh receptor is a(n) __________-gated ion channel consisting of __ protein subunits, of which __ are identical and contain Ach-binding sites; __ such sites must be bound in order for the channel to open.
ligand, 5, 2, 2
The cell membrane is a _________ ____________; _____ _____________ are proteins that span the membrane and allow ions to pass.
lipid bilayer; ion channels
A neuron at rest has a membrane potential of -50 to -80 millivolts (mV); the cell's interior has negative polarity.
membrane, millivolts, negative polarity
In contrast, a receptor belonging to the _______________family uses an intermediary called a _____________ __________________, activated via a G protein, to produce its cellular effects. Use of such a ____________ ______________________may allow for ___________________ of the effect of the transmitter (e.g., many channels may open, or long-lasting biochemical changes in the neuron may occur).
metabotropic, second messenger, second messenger, amplification
Action potentials are produced by ________________ ____ _____ ions into the cell
movement of Na+
Increasingly strong depolarizing stimuli are ___________ spread by the neuronal membrane, up to the point at which the cell's threshold depolarization is reached. At this point, a brief _________ _____________ is produced, consisting of a positive membrane potential that is propagated along the length of the axon.
passively, action potential
The sodium channels are open for a little less than 1 ms. Positive charges inside the cell then push _____________ ions out, and the resting potential is rapidly restored, although brief oscillations called after potentials _____ _____________.
potassium, are observed.
Invertebrate axons lack _______________ and instead rely on large-____________ axons to carry action potentials quickly. Such ________ axons usually mediate important behaviors, such as escape movements, but even so, they are only as fast as ________ myelinated fibers in vertebrates. When an action potential arrives at the axon _______________ of an excitatory presynaptic neuron, a local, graded _____________________, known as an excitatory postsynaptic potential, is produced in the postsynaptic cell. If the presynaptic cell is inhibitory, then an _____ is produced on the postsynaptic cell instead, generally as a consequence of the opening of ___- channels. A single neuron may be subject to hundreds of ________________ potentials at any given time, each produced by the action of neurotransmitter at chemical synapses. Whether a(n) action potential is produced generally depends on the sum of numerous EPSPs and IPSPs. Whether a potential is an IPSP or an EPSP generally depends on the particular _________________ acting on the synapse.
myelination, diameter, giant, small, terminal, depolarization, IPSP, Cl, postynaptic, transmitter
All living cells have an electrical charge—more ______________ on the inside than on the outside.
negative
Proteins are large anions within a neuron that create a ____________charge that tends to pull potassium ions into the cell. However, there are already about _______ times as many potassium ions inside the neuron as there are outside, so the concentration gradient tends to push ______________ ions out of the cell. Eventually the two forces are exactly balanced, yielding the neuron's ____________ potential, which corresponds to the potassium equilibrium potential, in the range of -50 mV to -80 mV.
negative, five, potassium, resting
Action potentials travel in ______ _____________ because of the refractory state of the membrane after a depolarization.
one direction