Question 1

Under which of the following conditions would you expect NMDA receptors to contribute to postsynaptic currents in the hippocampus?

Accepted Answer

NMDA receptors require a depolarization of the postsynaptic membrane to relieve the Mg2+ block and allow current flow. A train of presynaptic action potentials at high frequency is more likely to sufficiently depolarize the postsynaptic neuron, allowing NMDA receptors to contribute to postsynaptic currents.

Question 2

What is a competitive antagonist?

Accepted Answer

A competitive antagonist is a type of inhibitor that binds to the same site on a receptor as the natural activating ligand, thereby preventing the natural ligand from binding and activating the receptor.

Question 3

How does the technique called ionophoresis work?

Accepted Answer

Ionophoresis works by using an electrical charge to move molecules across a barrier, such as the skin or the membrane of a glass pipet. This technique relies on the principle that charged molecules will move towards an electrode with an opposite charge, allowing for controlled delivery or extraction of molecules.

Question 4

How are acetylcholine receptors distributed along the muscle membrane?

Accepted Answer

Acetylcholine receptors are highly concentrated directly under the presynaptic terminal at the neuromuscular junction (NMJ), facilitating efficient synaptic transmission and muscle activation.

Question 5

How does acetylcholine binding to nicotinic receptors alter the permeability of the muscle membrane?

Accepted Answer

When acetylcholine binds to nicotinic receptors on the muscle membrane, it causes the postsynaptic membrane to become more permeable to sodium, potassium, and calcium ions, but not to chloride ions. This change in permeability leads to depolarization and muscle contraction.

Question 6

What is responsible for the time course of decay of the endplate current recorded at the neuromuscular junction?

Accepted Answer

The decay of the endplate current is primarily determined by the mean open time of the acetylcholine receptor channel, as this dictates how long the channel remains open and allows ions to flow, influencing the duration of the current.

Question 7

Why do single channel measurements of acetylcholine receptor currents show that all channel openings reach the same amplitude?

Accepted Answer

When the acetylcholine receptor channel is in the open state, the pore conducts the same amount of current due to the permeation properties of that channel. This means that the physical and chemical properties of the open channel determine the amplitude of the current passing through it, leading to uniformity in the amplitude of channel openings.

Question 8

How many acetylcholine molecules have to bind to the muscle nicotinic acetylcholine receptor to maximally activate this ionotropic receptor channel?

Accepted Answer

Two acetylcholine molecules must bind to the muscle nicotinic acetylcholine receptor to maximally activate this ionotropic receptor channel.

Question 9

Which technique can be used to determine the specific conductance changes in the muscle membrane, and their voltage dependence, after acetylcholine binds to nicotinic receptors?

Accepted Answer

Voltage clamp experiments are specifically designed to measure the conductance changes in the membrane and their voltage dependence, which is crucial for understanding how acetylcholine binding to nicotinic receptors affects muscle membranes. This technique allows researchers to control the membrane potential and measure the ionic currents that pass through the channels, providing insights into the function of these receptors and their role in muscle activation.

Question 10

What is the reversal potential for a channel?

Accepted Answer

The reversal potential for a channel is the membrane potential at which the net current flux through the channel is zero. At this potential, the driving forces for ions moving in and out of the cell through the channel are balanced, resulting in no net movement of ions across the membrane through that channel.

Question 11

What would happen to the synaptic potential amplitude caused by an ionotropic receptor in a postsynaptic neuron (e.g. glutamate-mediated EPSP) if the input resistance of the postsynaptic membrane was decreased?

Accepted Answer

When the input resistance of the postsynaptic membrane decreases, less current is required to change the membrane potential, leading to a smaller synaptic potential amplitude.

Question 12

At the frog neuromuscular junction, when you block voltage-gated sodium channels selectively in muscle (but not nerve), and then record EPPs (using the microelectrode technique) in response to repeated low frequency nerve stimulation, you see EPPs that are very large (each depolarizes muscle membrane above resting potential to about -30 mV), but these EPPS do not fluctuate significantly when you compare the size of each EPP. Why do these EPPs not vary significantly in amplitude?

Accepted Answer

The large EPP depolarizes the muscle membrane close to the reversal potential for the acetylcholine receptor channel, which minimizes fluctuations in amplitude.

Question 13

The reversal potential for the nicotinic acetylcholine receptor is about -15 mV because it is determined by its selective permeability for

Accepted Answer

The answer of The reversal potential for the nicotinic acetylcholine...

Question 14

Which two synaptic specializations are present at neuromuscular synapses, but not at CNS synapses?

Accepted Answer

Postjunctional folds increase the surface area of the postsynaptic membrane, which allows for more acetylcholine receptors to be present. Schwann cells are glial cells that wrap around the axon of the motor neuron and help to insulate it. These two specializations are not present at CNS synapses because they are not necessary for the efficient transmission of signals at these synapses.

Question 15

What is the principal excitatory transmitter in the CNS?

Accepted Answer

Glutamate is the principal excitatory neurotransmitter in the central nervous system, playing a key role in neural activation and synaptic plasticity.

Question 16

What happens to the reversal potential for IPSPs when chloride is injected into an adult neuron to increase the cytoplasmic concentration of chloride?

Accepted Answer

The reversal potential for inhibitory postsynaptic potentials (IPSPs), which are primarily mediated by chloride ions (Cl-), becomes more positive when the cytoplasmic concentration of chloride is increased. This is because the increased internal chloride concentration reduces the electrochemical gradient for chloride ions to move into the cell, thus requiring a more positive membrane potential to balance the inward and outward movements of chloride ions, which in turn shifts the reversal potential in a more positive direction.

Question 17

What is the reversal potential for an IPSP in an adult neuron?

Accepted Answer

The reversal potential for an inhibitory postsynaptic potential (IPSP) in an adult neuron is near the neuron's resting potential, typically around -70 mV, because IPSPs are primarily mediated by the flow of chloride ions (Cl-) into the neuron or potassium ions (K+) out of the neuron, which stabilizes the membrane potential near its resting level, making the neuron less likely to fire an action potential.

Question 18

In embryonic neurons, activation of ionotropic GABA or glycine receptors results in

Accepted Answer

In embryonic neurons, the intracellular chloride concentration is higher than in mature neurons, so activation of ionotropic GABA or glycine receptors leads to an outward movement of chloride ions, causing depolarization.

Question 19

If one impales a neuron with two different intracellular microelectrodes, one to measure membrane potential and a second to pass brief hyperpolarizing current pulses into the cell, why does the size of the measured changes in membrane potential caused by the current pulses decrease when transmitter binds to an ionotropic receptor?

Accepted Answer

When ionotropic receptors open, they allow ions to flow across the membrane, increasing the membrane's conductance. This leads to a decrease in the input resistance of the cell, which means that for a given amount of current injected, the change in membrane potential will be smaller.

Question 20

In adult neurons, activation of ionotropic GABA or glycine receptors results in

Accepted Answer

In adult neurons, activation of ionotropic GABA or glycine receptors typically causes an inward movement of chloride ions. This influx of negatively charged chloride ions leads to hyperpolarization of the neuron, making it less likely to fire an action potential.

Quiz 11: Mechanisms of Direct Synaptic Transmission