Mastering the Neuron

Question 1

Which neural term is a synonym for action potential?

Answer 1

Nerve impulse

Question 2

Which glial cells form myelin in the central nervous system?

Answer 2

Oligodendrocytes

Question 3

Which is a difference between the synaptic cleft and the synapse?

Answer 3

A synaptic cleft is the space between a presynaptic axon terminal and a postsynaptic dendrite, and a synapse includes all three of these structures.

Question 4

In most cells, the concentration of ions contributing to the membrane potential is __________ in the intracellular fluid compared with the extracellular fluid, with the exception of __________ ions

Answer 4

lower; potassium

Question 5

Whether a neuron fires an action potential depends on __________.

Answer 5

a graded potential above threshold voltage reaching the trigger zone

Question 6

A neuron has a resting potential of -70 mV and a threshold voltage of -50 mV. There are currently three active synapses on the neuron’s dendrites, each located the same distance from the axon. The potential changes are + 40 mV at synapse 1, + 20 mV at synapse 2, and -10 mV at synapse 3. These synaptic potentials decrease by 50% by the time they reach the trigger zone. Will this neuron produce an action potential at this time? Explain. (Hint: Draw a graph of the voltage changes.)

Answer 6

Yes. At the trigger zone, all potentials have halved and will sum as follows: +20 mV (originated at synapse 1), + 10 mV (originated at synapse 2), -5 mV (originated at synapse 3) sum to produce a total potential change of +25 mV. The neuron required a minimum change of +20 mV (-70 mV + 20 mV = -50 mV), so it will fire an action potential.

Question 7

Which of the following would have the fastest action potentials?

Answer 7

A myelinated axon with a large diameter

Question 8

What would happen to the membrane potential if a resting cell suddenly became more permeable to Ca++?

Answer 8

It would depolarize.

Question 9

During an action potential, activation of voltage-gated sodium and potassium channels occurs at different rates. What is the effect of this difference on ion flow across an axon membrane?

Answer 9

Initially, Na+ flows into the cell and then K+ flows out of the cell.

Question 10

Which two properties determine how fast neurons conduct action potentials?

Answer 10

Axon diameter and the leak resistance of the membrane

Question 11

What triggers exocytosis of synaptic vesicle contents from an axon terminal?

Answer 11

The opening of voltage-gated Ca2+ channels

Question 12

Neurotransmitters are usually released into synapses by __________

Answer 12

exocytosis

Question 13

A ligand binds to a receptor-channel that stimulates a channel to open. This is a chloride channel. This will stimulate __________.

Answer 13

an inhibitory postsynaptic potential (IPSP)

Question 14

Which of the following statements best describes the concept of permeability?

Answer 14

the ability of a molecule to cross the cell membrane

Question 15

The two cells below are hypothetical cells with a concentration of 100 mOsm of K+ inside the cells and containing only leak channels for K+ within the membrane. Each cell is placed into a different solution containing different concentrations of K+ in the extracellular fluid. Which of the two cells below has a higher permeability to K+ and why?

Answer 15

B, because it has more ion leak channels for K+ than A.

Question 16

Which of the following statements best describes the resting membrane potential?

Answer 16

an electrical gradient that exists between the intracellular and extracellular fluids

Question 17

___ ions are more concentrated on the outside ___ to the cell.

Answer 17

Sodium (Na+), Outside

Question 18

___ ions are more concentrated on the ___ of the cell, this would result in diffusion of the ion out of the cell.

Answer 18

Potassium (K+), Inside

Question 19

Would result in a more positive membrane potential

Answer 19

Increasing the concentration of Na+ in the extracellular fluid, Increasing the concentration of K+ in the extracellular fluid

Question 20

Would result in a more negative membrane potential

Answer 20

Decreasing the concentration of K+ in the extracellular fluidDecreasing the number of leak channels for Na+ along the cellular membraneInserting more K+ leak channels into the cellular membrane

Question 21

Rising phase of Action Potential

Answer 21

Opening of voltage-gated Na+ channels; Sodium (Na+) ions move in to the axon; Membrane potential becomes positive

Question 22

Falling phase of Action Potential

Answer 22

Potassium (K+) ions move out of the axon; Voltage-gated Na+ channels close; Voltage-gated K+ channels open

Question 23

After-hyperpolarization of Action Potential

Answer 23

Potassium (K+) continues to move out of the axon; Some voltage-gated K+ channels still open