2.2 The Nerve Impulse

Question 1

Concentration gradient

Answer 1

The difference in distribution for various ions between the inside and outside of the membrane

Question 2

Selective permeability

Answer 2

The ability of some molecules to pass much more freely through the membrane than others do

Question 3

Sodium-potassium pump

Answer 3

A protein complex which transports three sodium ions out of the cell while simultaneous drawing two potassium ions into the cell

Question 4

Electrical gradient

Answer 4

The difference in positive and negative charges across the membrane

Question 5

Hyperpolarization

Answer 5

Increased polarization

Question 6

Depolarization

Answer 6

Reduction of its polarization

Question 7

Threshold of excitation

Answer 7

Any stimulation beyond a certain level; produces a sudden, massive depolarization of the membrane

Question 8

Action potential

Answer 8

A rapid depolarization and slight reversal of the usual polarization

Question 9

Voltage-activated channels

Answer 9

Membrane channels whose permeability to sodium or some other ion depends on the voltage difference across the membrane

Question 10

Local anesthetic drugs

Answer 10

Attached to the sodium channels of the membrane, preventing sodium ions from entering; i.e. Novocain and Xylocaine

Question 11

General anesthetics

Answer 11

Decrease brain activity by opening stern potassium channels wider than usual; i.e. ether and chloroform

Question 12

All-or-none law

Answer 12

The size, amplitude, and velocity of an action potential are independent of the intensity of the stimulus that initiated it

Question 13

Refractory period

Answer 13

During which the cell resist the production of further action potentials

Question 14

Absolutely refractory period

Answer 14

The sodium gates are firmly closed and the membrane cannot produce an action potential, regardless of the stimulation; ~1 ms

Question 15

Relative refractory period

Answer 15

The sodium gates are reverting to the usual state, but potassium gates remain open. Because of the free flow of potassium, a stronger than usual stimulus is necessary to initiate an action potential. ~2-4 ms

Question 16

Where does an action potential begin?

Answer 16

On the axon hillock

Question 17

Axon hillock

Answer 17

A swelling where the axon exits the soma

Question 18

The propagation of the action potential

Answer 18

Describe does the transmission of an action potential down an axon

Question 19

Myelinated axon

Answer 19

Found only in vertebrates; covered with myelin sheath, a coating composed mostly of facts

Question 20

Nodes of Ranvier

Answer 20

Short unmyelinated sections of axon; each node is only about one micrometer wide

Question 21

Saltatory conduction

Answer 21

The jumping of action potentials from node to node

Question 22

Plural of soma

Answer 22

Somata

Question 23

Graded potentials

Answer 23

Membrane potential is that vary in magnitude and do not follow the all-or-none law

Question 24

Polarization

Answer 24

The neuron inside the membrane has a slightly negative electrical potential with respect to the outside