Chapter 3 Study Questions

Question 1

Like other body cells, the neuron under steady state conditions exhibits a slight _______ different b/t the inside of its cell membrane and the outside. This is known as the _______ potential. This potential is attributable to differential concentrations of _______ inside the cell relative to the outside, and is about -50 to -80 _______ in magnitude.

Answer 1

electrical; resting membrane; ions; millivolts

Question 2

Positively charges 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.

Answer 2

cations; anions; cations; anions

Question 3

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. Neuronal membranes exhibit selective _______, 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 re selectively permeable to _______.

Answer 3

gradient; high; low; PERMEABILITY; ION CHANNELS; POTASSIUM

Question 4

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 ______ tends to push potassium ions out of the cell. Eventually the 2 forces are exactly balanced, yielding the neuron’s _______ potential, which corresponds to the potassium _______ potential, in the range of -50mV to -80 mV.

Answer 4

negative; FIVE; CONCENTRATION GRADIENT; resting; EQUILIBRIUM

Question 5

The exact value of a given neuron’s resting membrane potential can be predicted by means of the _______ equation. However, the measured value is generally slightly less negative than the predicted value, due to they leakage of _______ ions into the neuron. The cell employs _______ pumps to actively counter this leakage; if it did not, the cell’s resting potential would eventually be at _______ mV.

Answer 5

Nernst; SODIUM (NA+); sodium-potassium; zero

Question 6

The generation of an action potential is critically dependent on _______ -gated _______ channels. At threshold depolarization, these channels start to open, and the depolarization caused by the entry of _______ into the axon causes still more _______ -gated channels to open, until _______ floods in and causes the membrane potential to suddenly become _______. The sodium channels are open for a little less than _______ ms. Positive charges inside the cell then push _______ ions out, and the resting potential is reap idly restored, although brief oscillations called _______ are observed.

Answer 6

voltage; sodium; voltage; sodium; POSITIVE; ONE (1); potassium; AFTERPOTENTIALS

Question 7

Increasingly strong depolarizing stimuli are also _______ mirrored by the neuronal membrane, up to the point at which the cell’s _______ depolarization is reached. At this point, a brief _______ potential is produced, consisting of a positive membrane potential that is propagated along the length of the _______.

Answer 7

PASSIVELY; threshold; action; axon

Question 8

An action potential is generated in its full form or not at all, called the _______ property. The stimulus is encoded in _______ rather than _______ of action potentials.

Answer 8

all-or-none; FREQUENCY; AMPLITUDE

Question 9

Axonal membrane as an action potential is generated
Membrane State State of gated K+ channels “ “Na+”
Resting
Depolarization
Threshold depolarization and action potential generated
Action potential collapses

Answer 9

closed;          closed
CLOSED;      some open
CLOSED;      many open
open;            closed
closed;          closed

Question 10

The active membrane, while firing the action potential, acts as a _______ membrane. The Nernst equation predicts the membrane potential of such a membrane to be _______ mV, which corresponds to the _______ voltage of the action potential.

Answer 10

sodium; +40; peak

Question 11

The action potential starts at the _______, which is studded with voltage-gated _______ channels, and its is recreated at successive positions down the length of the axon; in other words, the action potential _______ itself.

Answer 11

axon hillock, sodium, REGENERATES

Question 12

_______ 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.

Answer 12

myelin; Ranvier; saltatory; faster

Question 13

During the absolute refractory period, the membrane potential has collapsed (so there is no scope for further depolarization), and the _______ channels are inactivated. During the relative refractory phase, _______ flows out of the cell, so the membrane potential is partially restored and a very _______ stimulation may elicit a second action potential.

Answer 13

sodium; K+; strong

Question 14

A _______ is a medical condition in which the form and function of ion channels is altered as a result of genetic _______.

Answer 14

CHANNELOPATHY; mutation

Question 15

TTX is short for _______, and STX is short for _______; both TTX and STX selectively block the outer part of _______, preventing neurons from producing _______ potentials.

Answer 15

TETRODOTOXIN; SAXITOXIN; SODIUM; ACTION

Question 16

Invertebrate axons lack _______, and instead rely on large-_______ axons to carry action potentials quickly. Such _______ axons usually mediate important behaviors, such as _______ 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 _______ potential, is produced in the posynaptic cell. If the presynaptic cell is inhibitory, then an IPSP is produced on the postsynaptic cell instead, generally as a consequence of the opening of the _______ channels. A single neuron may be subject to hundreds of _______ potentials at any given time, each produced by the action of _______ substance at chemical synapses. The decision to produce an _______ generally depends on the effect of numerous EPSPs and IPSPs working together. Whether or not a synapse producers an IPSP or EPSP generally depends on the particular _______ used by that synapse.

Answer 16

myelination; DIAMETER; giant; ESCAPE; TERMINAL; depolarization; excitatory POSTSYNAPTIC; CL-; POSTSYNAPTIC; neurotransmitter; action potential; TRANSMITTER

Question 17

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.

Answer 17

rapidly; escape; SIMULTANEOUSLY

Question 18

Electrical synapses feature special _______ ion channels line dup 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 _______.

Answer 18

LARGE; IONS; SMALL; axon

Question 19

Incoming information, in the for of EPSPs and_______, is integrated in the postsynaptic neuron through the process of _______ There are two mechanisms by which thos occurs:

1. _______ summation is the addition of two potentials that occur close together in _______.
2. _______ summation is the addition of two potentials that occur close together physically on the cell membrane.

Answer 19

IPSPs; SUMMATION; TEMPORAL; TIME; SPATIAL

Question 20

Imagine a simplified neuron (lacking dendrites) with 4 synapses on the cell body–2 inhibitory and 2 excitatory. Pick the correct net (i.e. postsummation) effect on the cell’s membrane of each of the following situations.

1. When 1 excitatory synapse fires (extent…effect)
2. When 1 inhibitory synapse fires
3. When both excitatory synapses fire simultaneously
4. When both inhibitory synapses fire simultaneously
5. When one excitatory synapse and one inhibitory synapse fire simultaneously
6. When all four synapses fire simultaneously
7. When one excitatory synapse fires several times in rapid succession
8. First an inhibitory synapse fires, then a few moments later an excitatory synapse fires (think carefully before answering this one!)

Answer 20

1. MODERATE depolarization
2. MODERATE hyperpolarization
3. larger depolarization
4. larger hyperpolarization
5. no change
6. no change
7. LARGER depolarization
8. SLIGHT DEPOLARIZATION

Question 21

Imagine a simplified neuron (lacking dendrites) with four synapses on the cell body—two inhibitory and two excitatory. A pattern of firing that would provide the maximal likelihood of producing an action potential would be rapid repeated firing at both _______ synapses with no firing at _______ synapses, thus maximizing the likelihood of a threshold _______. This is because both _______ and spatial summation of the EPSPs would occur, with no _______.

Answer 21

excitatory; inhibitory; depolarization; temporal; IPSP’S

Question 22

The presence of dendrites adds additional information processing to the neuron because the _______ postsynaptic potentials must spread passively along dendrites; consequently, they tend to be _______ in terms of their proximity to the cell body. The farther out on the dendrite a _______ potential occurs, the less overall effect it can have at the axon _______. Glia can _______ the overall strength of the postsynaptic potentials, perhaps by preventing _______ leakage from synapses.

Answer 22

graded; WEIGHTED; graded; hillock; increase; neurotransmitter

Question 23

There is a delay between the arrival of the presynaptic action potential and the postsynaptic action potential because most synapses are _______ ; the presynaptic potential is first translated into _______release and then back into an _______ signal on the postsynaptic side.

Answer 23

CHEMICAL; NEUROTRANSMITTER; ELECTRICAL

Question 24

Put events in order.
A _______ potential (EPSP or IPSP) spreads toward the axon hillock.
Postsynaptic _______ respond by opening ion channels.
Synaptic transmitter is rapidly_______.
Presynaptic action potential propagates to the _______.
Neurotransmitters are removed rapidly from the synaptic cleft by transporters.
Calcium influx induces synaptic vesicles to fuse to the _______ membrane and release neurotransmitter.
Volatage-gated _______ channels open.

Answer 24

(GOT ALL STEP #S WRONG)
5. GRADED
4. RECEPTORS
6. INACTIVATED
1. AXON TERMINAL
7.
3. presynaptic 
2. calcium 

(my guess: 1,5,3,2,4,7,6) (chemical, membrane, fired, axon hillock)

Question 25

When an action potential arrives, the membrane of the axon terminal becomes more permeable to _______ . The amount of _______ that then enters the cell determines the amount of _______ released: A large influx of _______ into the cell causes more vesicles to discharge their contents than does a small influx. Processes associated with the entrance of _______ into the axon terminal are the main cause of synaptic _______.

Answer 25

calcium; calcium; neurotransmitter; calcium; calcium; DELAY

Question 26

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 about the same number of _______ of transmitter.

Answer 26

IDENTICAL; MOLECULES

Question 27

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 _______ removal of neurotransmitter by these mechanisms contributes to the accuracy of neural messages.

Answer 27

ENZYMATIC; REUPTAKE; REUPTAKE; PRESYNAPTIC; TRANSPORTERS; PROMPT

Question 28

A given neurotransmitter may have _______ an excitatory _______ inhibitory effect, depending on _______. For instance, acetylcholine
1. inhibits the postsynaptic cell by closing K+ and Na+ channels. _______
2. excites the postsynaptic cell by opening Ca2+ channels. _______
3. excites the postsynaptic cell by opening K+ and Na+ channels. _______
4. excites the postsynaptic cell by opening Cl– channels.
_______
5.inhibits the postsynaptic cell by opening Cl– channels.
_______

Answer 28

either; OR; the type of ion channel it activates. false; false; true; false; true

Question 29

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.

Answer 29

ligand; TWO; 2

Question 30

A drug classified as a(n) _______ mimics the actions of a neurotransmitter; a drug classified as a(n) _______ prevents a neurotransmitter’s action. Nicotine and muscarine function as _______ , whereas curare and bungarotoxin are _______ for receptors of the neurotransmitter_______

Answer 30

agonist; antagonist; agonists; antagonists; acetylcholine

Question 31

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 _______.

Answer 31

chemical; vagus; acetylcholine