Nerve Function & Communication PT 1

Question 1

T or F: The basic function of a neuron is to receive information, integrate signals to determine whether or not information should be passed along, and to communicate signals to target cells.

Answer 1

True

Question 2

Which of the following cations are found in higher concentrations outside of the cell? Select all that apply.

K+
Na+
Ca++
Cl-
OA-

Answer 2

Na+
Ca++

Explanation

Cations carry a positive charge. Na+ and Ca++ are cations that are found in higher concentrations outside of the cell. K+ is a cation, but it is found in higher concentration inside of the cell. Anions carry a negative charge. Cl- and OA- are anions. Cl- is found in higher concentration outside of the cell, and OA- are found in higher concentrations inside of the cell.

Question 3

During active transport a substance moves across the cell membrane due to “natural forces” requiring no energy expenditure from the cell.

True or False

Answer 3

False

Explanation

During active transport an ion is actively moved (forced) against its electrical and chemical driving forces. This process requires energy expenditure on the part of the cell. An example of active transport is the Na+/K+ pump which moves 2 K+ ions inside of the cell and 3 Na+ ions outside of the cell against their respective concentration gradients. During passive transport an ion is moved across the membrane by its electrical and chemical driving forces. This is a passive process and requires no energy expenditure on the part of the cell.

Question 4

Which of the following ion channels (transmembrane proteins) is important in establishing the resting membrane potential of neurons?

Leak channels
Voltage-gated ion channels
Ligand-gated ion channels
Signal-gated ion channels
Stress-gated ion channels

Answer 4

Leak channels

Explanation

Leak channels remain open all the time and are selective for certain ions. Leak channels that are selective for K+ are important for establishing the resting membrane potential of neurons. Voltage-gated ions channels open and close in response to changes in the membrane potential. These channels are important for the generation of an action potential. Ligand-gated ion channels open in response to the binding of a neurotransmitter. These channels are important for generating post-synaptic potentials (graded potentials). Signal-gated ion channels open in response to an intracellular metabolic event. These channels are important for generating graded potentials (post-synaptic and receptor). Stress gated ion channels open in response to deformation of the cell membrane. These channels are important for generating receptor potentials (graded potentials)

Question 5

Under resting conditions, which ion’s electrical force will cause the ion to move into the cell?

Na+
K+
Ca++
Cl-
OA-

Answer 5

Na+
K+
Ca++

Explanation

The principle of electrostatic pressure states that like charges will repel and unlike (opposite) charges will attract. Under resting conditions, the inside of the cell is negative with respect to the outside of the cell. Cations that carry a + charge will be attracted to the inside of the cell. Anions that carry a - charge will be attracted to the outside of the cell.

Question 6

Under resting conditions, which ion’s chemical force will cause it to want to move out of the cell? Select all that apply.

Na+
Ca++
K+
Cl-
OA-

Answer 6

K +
OA-

Explanation

The principle of diffusion states that an ion will move from an area of higher concentration to an area of lower concentration. Since K+ is in higher concentration inside the cell, it will diffuse out of the cell down its respective concentration gradient. *Note: OA- is also in higher concentration inside the cell so it will want to move out of the cell. However, the membrane is impermeable to OA- thus, it is essentially “trapped” inside the cell. Na+, Ca++, and Cl- are in higher concentrations outside the cell. These ions will want to move into the cell.

Question 7

Under resting conditions, which ion’s electrical and chemical driving forces are in the same direction?

Na+
K+
Ca++
Cl-
OA-

Answer 7

Na+, Ca++, OA-

Explanation

Na+, Ca++ and OA- have electrical and chemical driving forces that move the ions in the same directions. The electrical and chemical driving forces acting on Na+ and Ca++ will cause these ions to move into the cell. The electrical and chemical driving forces acting on OA- will cause it to want to move out of the cell. The electrical and chemical driving forces acting on K+ and Cl- are in opposite directions. The electrical force acting on K+ will cause it to want to move into the cell, while its chemical force will cause it to want to move out of the cell. The chemical force acting on K+ is greater than its electrical force. The electrical force acting on Cl- will cause it to want to move out of the cell, while its chemical force will cause it to want to move into the cell. The chemical force acting on Cl- is slightly greater than its electrical force.

Question 8

If membrane permeability increases (via the opening of ion channels) to Na+, it will move into the cell.

True or False

Answer 8

True

Question 9

When an ion reaches its equilibrium potential the electrical and chemical forces acting on the ion are equal and there is no net movement of the ion across the cell membrane.

True or False

Answer 9

True

Explanation

The electrical potential needed to keep an ion from diffusing down its concentration gradient is the ions equilibrium potential. When the electrical and chemical forces acting on an ion are equal there is no net movement of the ion across the cell membrane. The equilibrium potential is also known as the reversal potential because the direction of ion flow is in opposite directions on either side of this membrane potential.

Question 10

The resting membrane potential of a typical neuron approaches the equilibrium potential of Na+.

True or False

Answer 10

False

Explanation

The resting membrane potential of a typical neuron approaches the equilibrium potential of K+. This is because at rest the membrane is most permeable to K+.

Question 11

A graded potential is a very large fluctuation of the membrane potential that typically brings a neuron to its threshold potential.

True or False

Answer 11

False

Explanation

A graded potential is a small fluctuation in the membrane potential caused by excitatory or inhibitory input coming into a neuron. They decay with distance and time. It is the summation and integration of these inputs that will determine whether a neuron reaches its threshold potential.

Question 12

A change in the membrane potential from -70 mV to - 50 mV means the membrane is hyperpolarizing.

True or False

Answer 12

False

Explanation

When the membrane becomes more positive (or less negative), we call that depolarization. When the membrane becomes more negative (or less positive), we call that hyperpolarization. Since in the above example the membrane went from a negative value to a less negative value, we would say the membrane depolarized.

Question 13

A post-synaptic potential is generated by the binding of a neurotransmitter to a receptor.

True or False

Answer 13

True

Explanation

There are two kinds of graded potentials: receptor potentials and post-synaptic potentials. A receptor potential is generated by a sensory receptor. A post-synaptic potential is generated when a pre-synaptic neuron releases a neurotransmitter (ligand) and that neurotransmitter binds to a receptor (ligand-gated ion channel or signal-gated ion channel) located on the post-synaptic neuron.

Question 14

An inhibitory post-synaptic potential causes depolarization of the cell membrane.

True or False

Answer 14

False

Explanation

An inhibitory post-synaptic potential causes membrane hyperpolarization, while an excitatory post-synaptic potential causes membrane depolarization.

Question 15

The opening of which of the following ligand-gated ion channels will result in the generation of an IPSP. Select all that apply.

Na+ channel
K+ channel
Ca++ channel
Cl- channel

Answer 15

K+ channel, Cl- channel

Explanation

The opening of either a K+ or Cl- channel will produce an IPSP. The chemical forces acting on K+ and Cl- are greater than their respective electrical forces. Thus, if a K+ channel is opened K+ will diffuse out of the cell taking its + charge. If a Cl- channel is opened, Cl- will diffuse into the cell bringing its negative charge with it. In either case, the membrane will hyperpolarize. Both the chemical and electrical forces acting on Na+ and Ca++ will cause these ions to move into the cell. Thus, if channels open that are selective for these ions, they will diffuse into the cell bringing their positive charges with them. In either case, the membrane will depolarize (EPSP is generated).

Question 16

The additive effect of high frequency input of one pre-synaptic neuron on a post-synaptic neuron is called_________________________.

Spatial summation
Temporal summation
Integration

Answer 16

Temporal summation

Explanation

Temporal summation is the additive effect of high frequency input of one pre-synaptic neuron on a post-synaptic neuron. Spatial summation is additive effect of simultaneous stimulation from multiple presynaptic neurons on a post synaptic neuron. Integration involves the combining of excitatory and inhibitory inputs.

Question 17

The threshold potential is the membrane potential at which an action potential will be triggered.

True or False

Answer 17

True

Question 18

Depolarization of the initial segment of the axon causes the opening of which of the following ion channels?

Leak channels
Voltage-gated Na+ channels
Ligand-gated Na+ channels
Signal-gated Ca++ channels

Answer 18

Voltage-gated Na+ channels

Explanation

Depolarization of the initial segment of the axon will result in the opening of voltage-gated Na+ channels. It is the change in the voltage of the membrane that causes these channels that are usually closed to open. Leak channels are transmembrane proteins that are always opened. Ligand-gated channels open in response to the binding of a neurotransmitter (ligand). Signal-gated ion channels open in response to an intracellular metabolic event.

Question 19

What causes the rising phase of the action potential?

Influx of K+
Influx of Na+
Efflux of K+
Efflux of Na+

Answer 19

Influx of Na+

Explanation

The influx of Na+ is what causes the rising phase of the AP. The efflux of K+ is what causes the falling phase of the AP.

Question 20

The absolute refractory period is due to the inactivation of voltage-gated K+ channels.

True or False

Answer 20

False

Explanation

The absolute refractory period is the period of time when another action potential cannot be triggered. This is due to the inactivation of the voltage-gated Na+ channels.

Question 21

As the magnitude of a stimulus increases, the amplitude of the action potential increases.

True or False

Answer 21

Fasle

Explanation

An action potential is an all or none response. Its amplitude will remain the same regardless of the amount of stimulation coming into the neuron. The magnitude of the stimulus will be reflected in the frequency of firing of the APs. Greater stimulation coming into the neuron will cause an increase in the number of APs that are fired.

Question 22

Saltatory conduction is produced in myelinated axons.

True or False

Answer 22

True

Explanation

In myelinated axons active current only needs to be generated at the nodes of Ranvier (unmyelinated segments of the axon). This gives the appearance of the AP jumping from node to node - called saltatory conduction(saltatory comes from the Latin saltare, which meand to hop or leap)

Question 23

Which of the following axons will conduct action potentials with the greatest speed?

small, myelinated axons
large, myelinated axons
small, unmyelinated axons

Answer 23

large, myelinated axons

Explanation

Speed of conduction is dependent on the axon’s diameter and whether or not the axon is myelinated. The fastest conducting axons are those that have the largest diameters and are heavily myelinated.