Neuro Final

What ionic mechanism (associated with voltage-gated sodium channels) is responsible for increased spiking after removal of inhibition ?

Removal of sodium channel inactivation

Why are temporal and spatial summation necessary for synaptic transmission in the CNS ?

Temporal and spatial summation are necessary for synaptic transmission in the CNS because ultimately, the rate of change along the membrane (which is represented by temporal and spatial summation) is responsible for determining if firing will occur or not. MOST IMPORTANTLY: Individual EPSPs are much smaller in the CNS than they are in the NMJ, therefore multiple signals are needed to reach the voltage threshold

What is Ohm's Law

(V/R) = I (Voltage/Resistance) = current

How can potassium channels prevent the entrance of Ca2+ into a cell ?

1) Potassium intake by ion channels decrease the membrane potential, restoring it to its rest state. Since many calcium channels are voltage-dependent, a reduction of the membrane potential would close them, effectively decreasing the calcium conductance. 2) Potassium channels may be coupled to different signaling pathways (i.e. G proteins), which may affect indirectly other calcium channels.

Be able to label diagram showing neurotransmitter being released, synaptic cleft, receptor in postsynaptic cell, and axon

Be able to label diagram

Be able to label diagram of NMJ, a synapse that could produce an EPSP, and a synapse that could produce an IPSP.

Be able to label diagram.

Presynaptic inhibition is due to a reduction in transmitter release. Which ion is most important for this process ?

Calcium (Ca2+)

Charging the lipid bilayer with a current pulse establishes a ..... across the membrane

Capacitor

EPSPs normally lead to DEPOLARIZATION or HYPERPOLARIZATION ?

Depolraization

_________ is said to occur when action potentials are evoked after a neuron is released from inhibition.

Disinhibition

Changing the permeability of a membrane to an ion changes the equilibrium potential of that ion.

False--look this up.

A more intense stimulus typically generates a larger action potential

False--no "size," only frequency

The primary inhibitory neurotransmitter int he CNS is:

GABA

The primary excitatory neurotransmitter in the CNS is:

Glutamate

The equation that describes the electrical potential across a membrane that is permeable to multiple ions is called the ..... equation.

Goldman-Hodgkin-Katz

How can graded potentials lead to an action potential ?

Graded potentials can lead to an action potential by spatial and temporal summation. With spatial summation, graded potentials along several parts of a neuronal membrane are summed, and, if there are enough graded potentials in a given region, then an action potential can occur. With temporal summation, graded potentials in close succession to each other can be summed, and if there are enough graded potentials close enough to each other time-wise, an action potential can occur.

Which two researchers developed this model of the action potential and won a Nobel Prize for their efforts ?

Hodgkin and Huxley

Under what condition could a GABA-A receptor linked to a chloride channel excite a postsynaptic neuron ?

If Vm is below Cl- equilibrium point

Some students wrote the word "strength" in a fill-in-the-blank question on a quiz earlier in this course. Correct the statement below to explain how stimuli are coded by action potentials: Information is coded by the strength of action potentials fired in response to an effective stimulus.

Information is coded by the frequency of action potentials fired in response to an effective stimulus. Action potentials fire in an all-or-none fashion. However, the strength of a stimulus is indicated by the frequency of action potentials over a period of time. The stronger the stimulus, then the higher the frequency of action potentials, while the weaker the stimulus, the lower the frequency of action potentials.

What key fact about the distribution of ACh receptors and the NMJ was established using iontophoresis ?

Iontophoresis was used to show that ACh receptors are found particularly at the NMJ. This indicated that ACh should also be factored into the Hodgkin and Huxley model.

What type of channel in this model limits the voltage level achieved by an applied current pulse ?

Leak channel

What potential can be estimated by the Goldman-Hodgkin-Katz equation

Membrane potential

Which type of receptor is linked to a G protein ? Ionotropic or Metabotropic ?

Metabotropic

The motor proteins kinesin and dynein mediate axonal transport of vesicles by traveling along what type of specialized protein located within axons ?

Microtubules

What is the order of steps in synaptic vesicle cycling ?

Mobilization, docking, fusion, release, recycle

Based on your experiments in the Na Action Potential Tutorial in NIA and the last response paper, why is the "textbook" summary of the action potential (see figure below) an oversimplification.

Na+ and K+ channels do not close all at once but open and close throughout the following phase. As K+ tries to bring the membrane potential down, Na+ wants to keep it up, creating a tug of war between the two ions crossing the membrane before K+ finally comes out on top and brings the membrane potential down.

Nernst vs Goldman equation

Nernst = single ion; Goldman = multiple ions; Nernst describes equilibrium potential, whereas Goldman describes membrane potential

The standard equation for calculating the electrical potential across a membrane that is permeable to a single type of ion is called the

Nernst equation

If an ion is in equilibrium across the cell membrane, is there any net movement of the ion across the membrane ?

No

Does changing the potassium concentration also change the "strength" of the synapse ? Why or why not ?

No, because there is no change in the slope of the two lines in the diagram

What does patch clamp recording allow you to measure that cannot be measured with intracellular recording ?

Patch clamp recording allows you to measure voltage on either side of the membrane, whereas intracellular recording measures inside the membrane. MOST IMPORTANTLY: the main advantage is that patch clamp recording is used to study SINGLE CHANNELS

The duration of action potentials is on the order of

mili (m) -seconds

For the typical neuron, a hyperpolarization of the membrane drives the membrane to a more

negative potential (hyperpolarization = becomes more negative)

The cell's .... potential is established by adding the Na/K pump to the model.

resting

Proteins involved in synaptic transmission are returned to the cell body of a neuron by RETROGRADE or ANTEROGRADE axonal transport:

retrograde

If the concentration of sodium in the extracellular solution is reduced, the action potentials become

smaller (makes extracellular less positive, therefore inside is comparatively less negative)

Ion channels that generate action potentials in neurons are gated by:

voltage

Drug X bloks the (Na+-K+) pump. This results in a decrease in the amplitude of individual action potentials and a depolarization of the resting potential. Why ?

The Na+/K+ pump pumps three Na+ ions out of the cell for every two K+ ions it brings into the cell. This is AGAINST the Na+/K+ natural concentration gradient (Na+ naturally wants to come into the cell and K+ naturally wants to go out of the cell). Since Na+ is still going into the cell, the resting potential becomes depolarized as the positively-charged Na+ ions make the inside of the cell less negative in regards to the outside of the cell. As a result, because the resting potential is depolarized, it is already closer to threshold and does not need to depolarize as much from its resting potential to generate an action potential (hence the amplitude of the action potentials is smaller).

The number of ions that move through the membrane during the action potential does not significantly alter the overall distribution of ions across the membrane. What factor drives the dramatic shifts in membrane potential during the action potential ?

The dramatic shifts in membrane potential during an action potential are driven by ion permeability (determines ratio of ions) and conductance (driving force, how much the ions want to through the membrane)

Based on the simulations that we did on threshold, what factors determine if a neuron fires or note ?

The factors that determine if a neuron fires or not are the presence of ion channels, the presence of ions (Na+), and the depolarization of the membrane (the rate of change along the membrane)

Experiments like the one depicted in the figure to the right established that Ca2+ is crucial for synaptic transmission. Explain the figure. (see figure in exam)

The figure to the right shows that Ca2+ must be present BEFORE stimulation for a signal to be sent. In the total absence of Ca2+, there will be no firing of the motor neuron onto the postsynaptic cell when the presynaptic cell is stimulated. If Ca2+ is added after stimulation, there will again be no firing of the motor neuron onto the postsynaptic cell, but there will be a Ca2+ ejection (whereas when no Ca2+ was present, there was no Ca2+ to eject).

In a membrane with Hodgkin and Huxley channels, interactions between EPSPs can be highly non-linear. Based on the simulations that you ran in Neurons in Action, explain why the second EPSP, applied at a delay of 10 ms after the first EPSP, fails to trigger a spike in the plot to the right (see diagram on exam).

The first EPSP fails because the K+ channels of the first one are still active. This hyperpolarizes the cell and makes it much more difficult for Na+ to raise the voltage to cause an AP.

What are the consequences for synaptic integration (temporal and/or spatial) of having the processes that generate trace C in the membranes of all neurons ?

The processes that generate trace C cause each initial input current to have an effect for a long time (it stays depolarized for longer and then must go back to threshold from its dip below threshold in order to fire again). Therefore, temporal synaptic integration is longer (ie. the process is slower) due to the processes that generate trace C.

How is reversal potential measured in the plot from the 1960 paper by the Takeuchis ?

The reversal potential was measured by determining the change in the x-intercept (K+ concentration was changed at the endplate)

Why does the sodium/potassium pump cost a molecule of ATP to transport sodium and potassium ions across the membrane ?

The sodium/potassium pump costs a molecule of ATP to transport sodium and potassium ions across the membrane because they are being moved against their concentration gradients.

What does the voltage near -75 mV represent for this ion channel ? What does the relationship between current and voltage shown in the plot tell us about how ionic currents are sensitive to voltage ? See image on test.

The voltage near -75 mV represents the reversal potential, as it is where the curve crosses the y-axis. The relationship between current and voltage shown in the plot tells us that ionic currents' sensitivity to voltage is a non-linear potential.

What is the term for the voltage level that must be exceeded for a neuron to fire an action potential ?

Threshold

True or false: Electrical transmission is mediated by gap junctions and is faster and less temporally variable compared to chemical transmission.

True

What measurements are enabled by using the voltage-clamp method ?

Voltage clamp holds the voltage at a particular value and allows for studying purely ionic current; because of this, you can determine the reversal potential and the current-voltage relationship

What is the primary determinant of the direction of flow down an axon ?

Voltage-gated K+ channels are the primary determinant of the direction of flow down an axon.

If sodium is in equilibrium across an artificial membrane and sodium is the only ion in the solution, what will be the potential across the membrane ?

Zero (0)

To calculate potentials with these equations, one needs to measure the concentration of the ions on the inner and outer sides of the membrane. Which is larger, [K+]o or [K+]i

[K+]i (o is outward, i is inward; sodium moves out, potassium moves in)

The ...... refractory period is the time after the initiation of one action potential when it is impossible to initiate a second action potential no matter how much the cell is depolarized.

absolute

A neuron is ...-polarized immediately before firing an action potential

de

What processes in the model of the subthreshold EPP in the NMJ tutorial from Neurons in Action are depicted by the lines labeled A, B, and C in the plot on the right (Membrane Voltage vs Time plot)

A is the initial current, B is the passive membrane current, and C shows the process of added Na+ channels keeping the cell depolarized (by bringing more Na+ into the cell) for a longer period of time until K+ channels open in order to take K+ out of the cell (to make up for the influx of Na+), WHICH EVENTUALLY CAUSES....

The neurotransmitter mediating the end-plate potential (EPP) is:

Acetylcholine (Ach)

An isolated nerve muscle preparation treated with a moderate dose of curare would exhibit a decrease in the _______________ of mini EPPs: frequency but not amplitude, amplitude but not frequency, frequency and amplitude

Amplitude but not frequency...curare blocks acetylcholine

An isolated nerve muscle preparation exposed to a low concentration of extracellular Ca2+ would exhibit a: increase, decrease, or no change in transmitter release

An isolated nerve muscle preparation exposed to a low concentration of extracellular Ca2+ would exhibit a decrease in transmitter release

What does the figure to the right (from the simulations that you ran in the Synaptic Integration tutorial in Neurons in Action) reveal about EPSP integration in a passive membrane ? (see diagram on exam)

EPSPs temporally summate in a passive membrane where the closer the first and second EPSPs are to each other, the larger the change in voltage, but this subsides the larger the time difference is between the two.

What potential is the Nernst equation used to calculate ? Equilibrium potential, membrane potential, or resting potential ?

Equilibrium potential for the ion in question