Neuroscience-Chapter 3

Question 1

What does depolarizing the membrane potential to the threshold potential cause?

Answer 1

A rapid increase in Na permeability that produces an action potential followed by a slower increase in K permeability that restores the membrane potential to its usual resting level.

Question 2

What is the Voltage Clamp Method?

Answer 2

A method discovered Kenneth Cole and utilized by Alan Hodgkin and Andrew Huxley which provides the information needed to define the ionic permeability of the membrane at any level of membrane potential.

Question 3

What happens during an action potential?

Answer 3

An early influx of Na produces a transient inward current whereas the delayed efflux of K produces a sustained outward current

Question 4

What do some poisons do?

Answer 4

Tetrodotoxin blocks the Na current without affecting the K current while Tetraethylammonium blocks the K current without affecting the Na current.

Question 5

What is Ohm’s Law?

Answer 5

V=IR, voltage=(current)(resistance)

Question 6

What is membrane conductance?

Answer 6

The reciprocal of membrane resistance

Question 7

What is the ionic current that flows during an increase in membrane conductance?

Answer 7

I=g(V-E) where I=current, V=membrane potential, E=equilibrium potential, and g=conductance

Question 8

What is the refractory period?

Answer 8

When the axon is unable to produce an action potential for a short amount of time

Question 9

Why is there an undershoot?

Answer 9

Because K conductance (permeability) is temporarily higher than it is at resting potential, which yields an undershoot.

Question 10

What causes a refractory period?

Answer 10

The long amount of time it takes to turn off the K conductance and the persistence of Na inactivation

Question 11

How does long-distance signaling occur?

Answer 11

The local current generated by an action potential will flow passively down an axon and depolarizes the the membrane potential in the adjacent region of the membrane which triggers another action potential, which will happen until the action potential reaches the end of the axon.

Question 12

Why can action potential not propagate backwards?

Answer 12

The refractoriness of the membrane region where an action potential has been generated prevents subsequent re-excitation of this membrane as action potentials are generated in adjacent regions of the membrane

Question 13

What is conduction velocity?

Answer 13

The measurable rate of transmission of an action potential from one end of the neuron to the other

Question 14

Why does increasing the diameter of the of an axon improve passive current flow?

Answer 14

It decreases the internal resistance to passive current flow.

Question 15

What does myelination do?

Answer 15

Speeds up the rate of conductance because it reduces the ability of current to leak out of the axon

Question 16

How does myelination occur?

Answer 16

Oligodendrocytes in the CNS wrap nerve cells while Schwann cells in the PNS wrap nerve cells

Question 17

Where does action potential generation occur?

Answer 17

At the nodes of Ranvier, which are gaps in myelin wrapping.

Question 18

Why are there gaps in the myelin sheath?

Answer 18

Because if the whole axon was wrapped, current could not flow out of the axon and action potentials could not be generated

Question 19

Where are voltage-gated Na channels found?

Answer 19

Only at the nodes of Ranvier

Question 20

What does saltatory mean?

Answer 20

That the action potential jumps from node to node.

Question 21

What can loss of myelin cause?

Answer 21

Serious neurological problems such as multiple sclerosis