NCS Exam 1

Question 1

Initial Segment

Answer 1

integrates synaptic potentials into action potentials

Question 2

Membrane potential

Answer 2

voltage difference across the neuronal membrane

Question 3

Depolarization

Answer 3

opening Na+ channels at synapse causes post synaptic neuron to become less negative (outward current)

Question 4

Hyperpolarization

Answer 4

opening Cl- channels at other synapses cause the post synaptic neuron to become more negative (inward current)

Question 5

synaptic potentials

Answer 5

analog signals (tells neuron about strength of its input)

Question 6

dynamic polarization

Answer 6

describes how the receptive surfaces of a neuron gather input to generate AP, how the initial segment achieves the goal of AP generation, how axon propagates an AP, how current drives release of chemical messengers

Question 7

Dendritic spines

Answer 7

site of most excitatory synapses

Question 8

receptive surfaces

Answer 8

1. the cell body: major site for synapses that hyperpolarize and site for synapses that depolarize if neuron doesn’t have spines
2. shafts of dendrites major site for synapses that hyperpolarize and site for synapses that depolarize if neuron doesn’t have spines
3. dendritic spines: target of only depolarizing synapses of al depolarizing synapse on the neurons that have spines

Question 9

Axon terminals

Answer 9

specialized regions that contain machinery necessary for communication between neurons

Question 10

cells that form myelin

Answer 10

1. oligodendrocytes
2. Schwann cell

Question 11

Saltatory Conduction

Question 12

Nodes of ranvier

Question 13

Velocity of conduction (dependent on?)

Answer 13

1. diameter of axon
2. thickness of myelin sheath

Question 14

Action potential

Answer 14

AP that invade axon terminals lead them to
release neurotransmitter
molecules —->
Those molecules bind to
receptor proteins in the plasma membranes of other neurons.
In many cases the binding of
neurotransmitter to receptor
leads to the opening of ion
channels to produce a synaptic
potential

Question 15

2 factors that determine membrane potential

Answer 15

1. ion concentration gradient
2. selective permeability of membrane

Question 16

Nernst equation(works for only one kind of ion)

Answer 16

Ex = RT/zF ln [x0]/[xi]
at room temp (20 degrees):
Ex = 58/z log [x0]/[xi]

at body temp (37 degrees):
Ex = 61.5/z log [x0]/[xi]

Question 17

Ion permeability

Answer 17

the ability of ions to cross the membrane and is directly proportional to the total number of open channels for a given ion in the membrane. The membrane is permeable to K+ at rest because many channels are open

Question 18

What two forces are driving ions across the membrane?

Answer 18

1. thermodynamic (chemical) force : concentration gradient
2. electrical force: difference in electrical potentials (voltage)

Question 19

Equilibrium Potential

Question 20

Goldman-Hodgkin Katz equation

Answer 20

steady-state membrane potential for multispecies of ions

Vm = RT/F = Erev

Question 21

Erev

Answer 21

The reversal potential for the membrane permeability – this is
the membrane potential at which total current goes from being
inward to being outward or vise versa. At Erev, the net current across the membrane is 0

Question 22

K+ selective leak channels

Answer 22

In general, resting potential is determined largely by K+ ions, because the
resting membrane is primarily permeable to K+ through K+-selective leak
channels

Question 23

Na+/K+ pump

Answer 23

proteins that hydrolyze ATP to pump the two ions against their concentration gradients - it pumps K+ back into the neuron and Na+ back out of it
1. Consumes ATP
2. 3:2 Na+/K+ Exchange
3. Electrogenic:
net outward INa  hyperpolarization but contributes
less than 10% of Vrest.
Na+/K+ Pump consume up to 70% of ATPs in neurons (30% in other
cells) due to synaptic activities and action potentials.

Question 24

Driving force

Answer 24

how strongly
an ion is driven electrochemically across a membrane
DF = Vm - Ex
- = inward flow
+ = outward flow

Question 25

Ohm’s Law

Answer 25

V = I * R
I = current
V = voltage
R = resistance

Question 26

Conductance

Answer 26

how easily ions move across the membrane/ how many channels/how long do they stay open
More channels = lower resistance, higher conductance

g = conductance
g = 1/R
V = I/g

Question 27

changes in Vm

Answer 27

ions inside and outside the cell do not vary from moment to moment, so change in resting potential arises from change in ion permeability (conductance due to opening and closing channels)

Question 28

Passive properties

Answer 28

1. equivalent circuits of the cell membrane
2. distance (lamda)
3. time(T1 and T2)
4. propagation of AP along myelination

Question 29

lamda (length constant)

Question 30

T1 (membrane (input) time constant

Answer 30

delay in moving current into the cell

Question 31

T2 conduction time constant

Answer 31

how long is the delay from synapse to initial segment (how quickly current will move down the axon)
small T2 = small delay

Question 32

Myelination Facilitates Propagation of Signals

Answer 32

increase in rm —> increase in lamda
decrease in cm —> T2

Question 33

Why Myelination Facilitates Propagation of Signals

Answer 33

Both factors improve the spread of the
action current, such that the action
potential jumps from node to node in high
speed, giving a high velocity of action
potential propagation. (ri is not affected
by myelination.

Question 34

myelin affects on T2 and lamda

Answer 34

One key is to get the
nodes of Ranvier as far apart as they can be
without causing the action potential to fail
along the myelinated segment. This is
dictated by . The reduction in 2 is also
critically important in myelin’s ability to
increase conduction velocity from less than 1
m/sec in tiny

Question 35

membrane capacitance

Answer 35

proportional to surface area
cm = Cm * 2pi a

Question 36

Capacitor

Answer 36

When two conducting surfaces are separated by a non-conductor, they become a capacitor

Question 37

Regenerative propagation

Answer 37

An action potential generated at one site
triggers the generation of a new action
potential at its nearby site. The new action
potential then triggers the generation of
another action potential at its downstream
site. This process goes on and on, so the
original action potential is propagated all
the way to the axon terminals.

Action potentials propagate at constant
amplitude and shape without losing its
strength (compare the amplitude of the
depolarization in E1 and E2) due to the
regenerative nature of the propagation

Question 38

Saltatory Conduction

Answer 38

n a myelinated axon an
action potential appears to
jump from one node of
Ranvier to the next. That’s
because the myelinated
segment has little voltage-
gated Na+ channels; and so
current entering at a previous
node during an action
potential flows passively
along the myelinated
segment until it reaches the
next node to triger a new
action potential

Question 39

Voltage Clamp

Answer 39

technique is an
experimental technique to manipulate
membrane potential (Vm) as such Vm is
kept (clamped) at a constant value.
It allows measuring membrane current
(Im) needed to maintain Vm to a constant
value during the clamping period
By measuring Im(t) at a “constant” Vm, one can calculate
the change of membrane conductance over time, gm(t), at this Vm.

Question 40

Positive feedback

Answer 40

Action potentials are all-or-none and do
not vary in amplitude because they are
produced by a positive feedback loop. An
initial depolarization leads to opening of a
small number of voltage-gated Na+
channels (i.e., increasing gNa), which leads
to inflow Na+ and then further
depolarization, which in turn leads to
opening of more voltage-gated Na+
channels and then additional
depolarization. That cycle continues until
no additional depolarization can occur and
Na+ channels inactivate