Chapter 1.2: The Nerve Impulse

Question 1

electrical gradient or polarization p. 26

Answer 1

When at rest, the membrane maintains an electrical
difference in electrical charge between the inside and outside of the cell. The neuron inside the membrane has a slightly negative electrical potential with respect to the outside, mainly because of negatively charged proteins inside the cell.

Question 2

concentration gradient p. 27

Answer 2

The difference in distribution of ions across the membrane. It drives potassium outside of the cell. Sodium is more concentrated outside than inside, so just by the laws of probability, sodium is more likely to enter the cell than to leave it. However, he gates are closed during cell rest.

Question 3

resting potential p. 27

Answer 3

This difference in voltage at a resting neuron cell between interior and exterior electrical charge.

Question 4

selectively permeable p. 27

Answer 4

That is, some chemicals pass through it more freely than others do. Oxygen, carbon dioxide, urea, and water cross freely through channels that are always
open. Several biologically important ions, including sodium, potassium, calcium, and chloride, cross through membrane channels (or gates) that are sometimes open and sometimes closed.

Question 5

sodium–potassium pump p. 27

Answer 5

The sodium–potassium pump, a protein complex, repeatedly transports three sodium ions out of the cell while drawing two potassium ions into it. The sodium–potassium pump is an active transport that requires energy. Outside 10x> Inside

Question 6

action potentials p. 29

Answer 6

Messages sent by axons. which means increased polarization. When the stimulation ends, the charge returns to its original resting level.

Question 7

depolarize p. 29

Answer 7

Depolarize the neuron—that

is, reduce its polarization (negativity) toward zero.

Question 8

hyperpolarization p. 29

Answer 8

When a negative charge applies.The change is called hyperpolarization (more negative),

Question 9

threshold p. 29

Answer 9

Beyond the threshold of excitation produces a massive depolarization of the membrane. When the potential reaches the threshold, the membrane opens its sodium channels and permits sodium ions to flow into the cell.

Question 10

voltage-gated channels p. 30

Answer 10

protein that allows sodium to cross is called a sodium channel, one that allows potassium to cross is a
potassium channel, and so forth. The ones regulating sodium and potassium are voltage-gated channels.

Question 11

all-or-none law p. 31

Answer 11

More properly stated, the all-or-none law is that the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it, provided that the stimulus reaches the threshold. Thicker axons convey action potentials at greater velocities. Thicker axons can also convey more action potentials per second. An axon all it can change is the timing.

Question 12

local anesthetic p. 31

Answer 12

1

Question 13

refractory period p. 31

Answer 13

Immediately after an action potential, the cell is in a
refractory period during which it resists the production of further action potentials. In the first part of this period, the absolute refractory period, the membrane cannot produce an action potential, regardless of the stimulation. During the second part, the relative refractory period, a stronger-thanusual stimulus is necessary to initiate an action potential. The refractory period depends on two facts: The sodium channels
are closed, and potassium is flowing out of the cell at a fasterthan-usual rate.

Question 14

myelin p. 32

Answer 14

To increase the speed still more, vertebrate axons evolved a special mechanism: sheaths of myelin, an insulating material composed of fats and proteins.

Question 15

myelinated axons p. 32

Answer 15

Suppose an action potential occurs at the first myelin
segment. The action potential cannot regenerate along the membrane between nodes because sodium channels are virtually absent between nodes (. After an action potential occurs at a node, sodium ions enter the axon and diffuse, pushing a chain of positive charge along the axon to the next node, where they regenerate the action potential.

Question 16

propagation of the action

potential p. 32

Answer 16

The term propagation of the action potential describes the transmission of an action potential down an axon. In a sense, the action potential gives birth to a new action potential at each point along the axon.

Question 17

saltatory conduction p. 33

Answer 17

The jumping of action potentials from node to node is referred to as saltatory conduction. In addition to providing rapid conduction of impulses, saltatory conduction conserves energy: Instead of admitting sodium ions at every point along the axon and then having to pump them out via the sodium– potassium pump, a myelinated axon admits sodium only at its nodes.

Question 18

graded potential p. 34

Answer 18

When a local neuron receives information from other neurons, it has a graded potential, a membrane potential that varies in magnitude in proportion to the intensity of the stimulus. The change in membrane potential is conducted to adjacent areas of the cell, in all directions, gradually decaying as it travels. Those various areas of the cell contact other neurons, which
they excite or inhibit.

Question 19

local neurons p. 34

Answer 19

Neurons without an axon exchange information with only their closest neighbors. We therefore call them local neurons. Because they do not have an axon, they do not follow the all-or-none law.