Midterm 2

Question 1

Neurons are electrically excitable, the membrane potential deviates from the resting membrane potential of _____________.

Answer 1

-70 mV

Question 2

Decreasing membrane potential is associated with depolarization, true or false?

Answer 2

False, Increasing

Question 3

Increasing membrane potential is associated with depolarization, true or false?

Answer 3

True

Question 4

Increasing membrane potential is associated with hyperpolarization, true or false?

Answer 4

False

Question 5

Neurons that are only capable of generating graded potentials are involved in what type of communication?

Answer 5

Local or short distance communication, as signal transmission distance is limited.

Question 6

Neurons that generate action potentials are capable of ______________ signalling.

Answer 6

Long-range

Question 7

The generation of action potentials depends on the generation of graded potentials, true or false?

Answer 7

True

Question 8

The generating of graded potentials depends on the generation of action potentials, true or false?

Answer 8

False, vice versa (action potentials depend on graded potentials)

Question 9

All neurons that can generate action potentials can also generate graded potentials, true or false?

Answer 9

True

Question 10

All neurons that can generate graded potentials can generate action potentials, true or false?

Answer 10

False

Question 11

How is the resting membrane potential generated?

Answer 11

An ion pump actively (requires energy, ATP) moves potassium ions (K+) from the outside (extracellular space) to the inside of the neurons. K+ concentration inside is elevated.

The pump also moves sodium (Na+) ions from the inside, keeping the concentration of sodium low relative to the outside.

Question 12

At rest, there are ion channels that allow some of the potassium to move from the inside to the outside, down the ________________________.

Answer 12

Concentration gradient

Question 13

If Na+ moves from the outside of the cell to the inside, down the concentration gradient, would the inside of the cell become more positive or more negative?

Answer 13

More positive

Question 14

The influence of K+ is much greater because the K+ channels are more ______________ than the Na+ channels.

Answer 14

Peremeable

Question 15

Action potentials depend on graded depolarization, what causes this depolarization in a simple sense?

Answer 15

The permeability of the Na+ channel increases, Na+ moves down the concentration gradient (from the outside of the cell to the inside), the membrane voltage than becomes more positive (depolarizes).

Question 16

Action potentials are produced by ion channels that are unlike those that produce graded potentials, what makes them different?

Answer 16

Action potentials are produced by ion channels that are voltage-gated. Graded potentials are produced by channels that are activated by a change in membrane potential.

Question 17

Voltage-gated Na+ channels are subject to intrinsic inactivation, meaning…

Answer 17

Soon after activation, voltage-gated Na+ channels inactivate (contributing to the falling phase after the peak).

Question 18

The falling of the action potential is due not only to the inactivation of voltage-gated Na+ channels but also due to…

Answer 18

A delayed activation of the voltage-gated K+ channels

Question 19

What is the absolute refractory period?

Answer 19

Voltage-gated Na+ channel inactivation imposes a refractory period on action potential generation. The absolute refractory period is the period during which, no matter how strong the stimulus, another action potential cannot be generated. It is due to the inactivation of the voltage-gated Na+ channels.

Question 20

What and when is the relative refractory period?

Answer 20

The relative refractory period is the time following Na+ channel reactivation, but when voltage-gated K+ channels are still sufficiently active to oppose the depolarization (increased hyperpolarization, moves in negative direction) to the threshold. A sufficiently strong stimulus could overcome such opposition.

Question 21

Voltage-gated K+ channels inactivate, true or false?

Answer 21

False, voltage-gated K+ channels do not inactivate, it takes a long time for voltage-gated K+ channels to return to resting levels, as membrane potential hyperpolarizes

Question 22

Explain what factors impose limits on the frequency that action potentials can be generated

Answer 22

Refractory periods

After hyperpolarization due to voltage-gated K+ channels (not inactivating)

Question 23

Name the two-mechanisms that allow for action potentials to travel further distances (active regeneration of the signal)

Answer 23

1. Voltage-gated channels expressed along the fiber so the action potential is constantly being boosted, this is the case in unmyelinated axons
2. Insulate the axon with myelin, to decrease the decay of the signal

Question 24

Does myelin cover the axon completely?

Answer 24

No, there are small gaps (Nodes of Ranvier)

Question 25

On a myelinated axon, voltage-gated Na+ and K+ channels are found only at which part?

Answer 25

The nodes. Myelin reduces the decay of the electrical signal so that the voltage is above threshold when it reaches the node, at the node the signal is regenerated.

Question 26

Conduction velocity is affected by axon diameter, what does this mean?

Answer 26

Larger axons have less longitudinal resistance and thicker myelin

Question 27

What are the two basic types of synapses?

Answer 27

1) Electrical synapses (gap junctions) 2) Chemical synapses (release neurotransmitter)

Question 28

What is an electrical synapse (gap junction)?

Answer 28

Transmembrane channels that connect the interior of one cell with the interior of another cell

Question 29

Which type of synapse is bidirectional and essentially has no synaptic delay?

Answer 29

Electrical synapse (gap junction)

Question 30

What is a chemical synapse?

Answer 30

A neurotransmitter is released at axon terminals, crosses the synaptic cleft, and then acts on receptors on a postsynaptic membrane.

Question 31

What type of synapse is unidirectional?

Answer 31

Chemical synapse

Question 32

Chemical synapses are bidirectional, true or false?

Answer 32

False, chemical synapses are unidirectional (presynaptic to postsynaptic)

Question 33

Neurotransmitters are contained within __________________________, which fuse with the presynaptic membrane and release contents into the synaptic cleft

Answer 33

Synaptic vesicles

Question 34

There is partial fusing of vesicles, true or false?

Answer 34

False, there is NO partial fusing of vesicles, if a vesicle fused, all of the neurotransmitter in the vesicle is released.

Question 35

The amount of neurotransmitter released by a single vesicle is called a __________________.

Answer 35

quantum (quanta if more than one vesicle fuses)

Question 36

The total amount of neurotransmitter released by a single action potential corresponds to the number of quanta, the number of vesicles released depends on?

Answer 36

How much Calcium enters the terminal, which is related to ... the extent of voltage-gated calcium channel activation, which is related to ... the number and frequency of action potentials that reach the terminal

Question 37

How is synaptic transmission halted?

Answer 37

In most cases, transporters on the pre-synaptic membrane can remove neurotransmitter from the synaptic cleft and recycle it. In some cases, the neurotransmitter is broken down by an enzyme and used to synthesize more of the neurotransmitter.

Question 38

The neurotransmitter released from synaptic vesicles produces graded potentials that can either transiently depolarize (producing a(n) ___________) or transiently hyperpolarize (producing a(n) ______________) the postsynaptic membrane.

Answer 38

Depolarize = excitatory post-synaptic potential Hyperpolarize = inhibitory post-synaptic potential

Question 39

Glutamate is the most common excitatory neurotransmitter in the central nervous system. Glutamate is synthesized from the amino acid glutamine, and vesicles are loaded with glutamate by a _________________________.

Answer 39

Vesicular glutamate transporter (vGlut)

Question 40

To remove glutamate from the synaptic cleft, it is transported by _____________________ into ______________________.

Answer 40

Excitatory amino acid transporters into astrocytes

Question 41

Astrocytes covert glutamate into __________________.

Answer 41

Glutamine

Question 42

After astrocytes convert glutamate into glutamine, the glutamine is then transported (by other transporters) back to the _____________________ where it is converted into glutamate (by the enzyme glutaminase) and loaded into vesicles.

Answer 42

presynaptic neuron

Question 43

For excitatory neurotransmission, glutamate acts primarily at post-synaptic __________________. When glutamate binds to ______________________ a channel allows _____ to enter the postsynaptic neuron, leading to depolarization.

Answer 43

AMPA receptors Na+

Question 44

A type of glutamate receptor that is permeable to Na+ and Ca2+. The influx of these cations (especially Na+) can contribute to excitatory post-synaptic potential.

Answer 44

NDMA receptors

Question 45

Explain the mechanism of the NDMA receptor.

Answer 45

Under resting conditions, the NDMA receptor channel is blocked by Mg2+. To remove the Mg2+ block requires that the receptor is depolarized (e.g., by AMPA receptors). Activation of NDMA receptors also requires the presence of co-transmitter glycine.

Question 46

The AMPA and NDMA receptors are both involved in excitatory post-synaptic potentials, what is the main (broad) difference between the two?

Answer 46

The AMPA receptor is less "complicated" than the NDMA. NMDA receptor requires voltage-dependent removal of the Mg2+ block, and require partnership from AMPA and co-transmitter glycine. Excitatory postsynaptic potentials produced by AMPA alone can be brief, those produced by NDMA (+AMPA) receptors can be of longer duration.

Question 47

How are inhibitory post-synaptic potentials generated?

Answer 47

Inhibitory post-synaptic potentials are generated by inhibitory neurotransmitters, the most common inhibitory transmitter is GABA.

Question 48

GABA is synthesized from _______________ and loaded into synaptic vesicles by the vesicular GABA transporter.

Answer 48

Glutamate

Question 49

Once released GABA is cleared from the synapse by __________________ either on the presynaptic membrane (where it can be loaded again into vesicles) or on ________________ where it is converted to glutamine and can be returned for synthesis of GABA.

Answer 49

GABA transporters Astrocytes

Question 50

GABA can act exert an inhibitory influence by acting either at GABA(A) receptors, increasing the influx of ________, or at GABA(B) receptors that increases the efflux of ________ through channels.

Answer 50

Cl- K+

Question 51

GABA(A) receptors (as well as AMPA and NDMA receptors) are ________________ receptors

Answer 51

Ionotropic (directly control permeability of the membrane)

Question 52

GABA(B) receptors are _______________ receptors.

Answer 52

Metabotropic receptors (indirectly control permeability of the membrane, binds to receptor through G-protein second messenger)

Question 53

What are the two types of neurotransmitter receptors discussed in class?

Answer 53

Ionotropic receptors Metabotropic receptors

Question 54

What are the characteristics of ionotropic receptors?

Answer 54

Ions move rapidly across the membrane through ligand-gated ion channels (channels are selective to certain ions). Effect requires transmitter to be bound to the receptor (many desensitize even in the continued presence of neurotransmitter, so ion flow is brief)

Question 55

What are the characteristics of metabotropic receptors?

Answer 55

Typically involves G-protein activation that either directly, or indirectly (second messenger system) influences ion channel permeability or other intracellular processes. Slower than ionotropic Second messengers may persist after removal of transmitter.

Question 56

Ionotropic receptors work faster than metabotropic receptors, true or false?

Answer 56

True

Question 57

Ionotropic receptors work slower than metabotropic receptors, true or false?

Answer 57

False, ionotropic receptors work faster than metabotropic receptors.

Question 58

The amplitude of an excitatory post-synaptic potential depends on the strength of the signal arriving at the synaptic terminal which affects...

Answer 58

The amount of neurotransmitter (glutamate) release.

Question 59

The neuron that receives the signal is called the presynaptic neuron, true or false?

Answer 59

False, the neuron that receives the signal is called the postsynaptic neuron.

Question 60

An excitatory postsynaptic potential may not be sufficient to depolarize the postsynaptic neuron to the threshold required for action potential generation, true or false?

Answer 60

True

Question 61

Excitatory postsynaptic potentials can summate if sequenced quickly enough (__________________ summation) or through multiple inputs (_________________ summation).

Answer 61

Temporal summation = sequenced quickly Spatial summation = multiple inputs

Question 62

The summation of excitatory postsynaptic potentials allows for...

Answer 62

The postsynaptic membrane potential to reach threshold

Question 63

Inhibitory postsynaptic potentials can prevent excitatory postsynaptic potentials from reaching threshold, true or false?

Answer 63

True, postsynaptic inhibition