Chapter 1: Nerve Cells and Nerve Impulses (Module 1.2)

Question 1

what is polarization?

Answer 1

a difference in electrical charge between the inside and outside of the cell

Question 2

what is the difference in voltage between the electrical charges called?

Answer 2

resting potential

Question 3

how do researchers measure the resting potential?

Answer 3

they insert a very thin microelectrode into the cell body

Question 4

what does it mean when the membrane has selective permeability

Answer 4

some chemicals pass through it more freely than others do

Question 5

this protein complex repeatedly transports three sodium ions out of the cell while
drawing two potassium ions into it

an active transport that requires energy

Answer 5

sodium-potassium pump

Question 6

what is the difference
in distribution of ions across the membrane called?

Answer 6

concentration gradient

Question 7

what is the proper analogy for the concentration gradient?

Answer 7

imagine a number of women inside a room. Men can enter the room or leave through a narrow door. They are attracted to the women, but when the men get too crowded, some of them leave. The concentration gradient counteracts the attraction

Question 8

When the membrane is at rest, are the sodium ions more concentrated inside the cell or outside?

Where are the
potassium ions more concentrated?

Answer 8

Sodium ions are more concentrated outside the cell and potassium is more concentrated inside

Question 9

When the membrane is at rest, what tends to drive the
potassium ions out of the cell?

What tends to draw them into the cell?

Answer 9

When the membrane is at rest, the concentration gradient tends
to drive potassium ions out of the cell, and the electrical
gradient draws them into the cell.

The sodium-potassium pump also draws them into the cell.

Question 10

the level that a depolarization must reach for an action potential to occur

Answer 10

threshold of excitation

Question 11

what are the messages sent by axons called?

Answer 11

action potentials

Question 12

what is hyperpolarization?

Answer 12

when the membrane potential becomes more negative at a particular spot on the neuron’s membrane

an exaggeration of the usual negative charge within a cell, a more negative level than usual

Question 13

What is the difference between a hyperpolarization and a depolarization?

Answer 13

a hyperpolarization is an exaggeration of the usual negative charge within a cell, a more negative level than usual

a depolarization is a decrease in the amount of negative charge within the cell

Question 14

What happens if the depolarization does or does not reach
the threshold?

Answer 14

If the depolarization reaches or passes the threshold, the cell produces an action potential.

If it is less than threshold, no action potential arises.

Question 15

what is depolarization?

Answer 15

a decrease in the amount of negative charge within the cell

Question 16

what does the all-or-none law state

Answer 16

it states 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.

Question 17

what are the three principles that make chemical events behind action potential look simpler?

Answer 17

1. At the start, sodium ions are mostly outside the neuron,
   and potassium ions are mostly inside.
2. When the membrane is depolarized, sodium and potassium channels in the membrane open.
3. At the peak of the action potential, the sodium channels
   close.

Question 18

what are the axon channels regulating sodium and potassium called?

Answer 18

voltage-gated channels

Question 19

State the all-or-none law

Answer 19

According to the all-or-none law, the size and shape of the action potential are independent of the intensity of the stimulus that initiated it. That is, every depolarization
beyond the threshold of excitation produces an action potential of about the same amplitude and velocity for a given axon.

Question 20

Does the all-or-none law apply to dendrites? Why or why not?

Answer 20

The all-or-none law does not apply to
dendrites, because they do not have action potentials.

Question 21

During the rise of the action potential, do sodium ions move
into the cell or out of it? Why?

Answer 21

During the action potential, sodium ions move into the cell. The voltage-dependent sodium gates have opened, so sodium can move freely.

Sodium is attracted
to the inside of the cell by both an electrical and a
concentration gradient

Question 22

As the membrane reaches the peak of the action potential, what brings the membrane down to the original resting potential?

Answer 22

After the peak of the action potential, potassium ions exit the cell, driving the membrane back to the resting potential.

Important note: The
sodium–potassium pump is NOT responsible for returning the membrane to its resting potential.

The sodium–
potassium pump is too slow for this purpose.

Question 23

this term describes
the transmission of an action potential down an axon

Answer 23

propagation of the action potential

in a sense, the action potential gives birth to a new
action potential at each point along the axon.

Question 24

what is the process of the action potential?

Answer 24

1. When an area of the axon membrane reaches its threshold of
   excitation, sodium channels and potassium channels open
2. At first, the opening of potassium channels produces
   little effect.
3. Opening sodium channels lets sodium ions rush into
   the axon.
4. Positive charge flows down the axon and opens voltage-gated sodium channels at the next point.
5. At the peak of the action potential, the sodium gates snap
   shut. They remain closed for the next millisecond or so,
   despite the depolarization of the membrane.
6. Because voltage-gated potassium channels remain open,
   potassium ions flow out of the axon, returning the membrane toward its original depolarization.
7. A few milliseconds later, the voltage-dependent potassium channels close.

Question 25

what are sheaths of myelin and what do they do

Answer 25

sheaths of myelin are an insulating material composed of fats and proteins and they increase the speed of travel for action potentials

Question 26

where are myelinated axons found?

Answer 26

they are only found in vertebrates.

Question 27

what is saltatory conduction?

Answer 27

it is the jumping of action potentials from node to node

Question 28

what happens in multiple sclerosis regarding myelin sheaths?

Answer 28

In multiple sclerosis, the immune system attacks myelin
sheaths.

An axon that never had a myelin sheath conducts impulses slowly but steadily, but an axon that has lost its myelin
is not the same, because it lacks sodium channels where the
myelin used to be

AND BECAUSE OF THIS MOST ACTION POTENTIALS DIE OUT BETWEEN ONE NODE AND THE NEXT

Question 29

In multiple sclerosis, the immune system attacks myelin
sheaths. An axon that never had a myelin sheath conducts impulses slowly but steadily, but an axon that has lost its myelin
is not the same, because it lacks sodium channels where the myelin used to be

Answer 29

If the nodes were closer, the action potential would
travel more slowly.

If they were much farther apart, the
it could success- if action potential would travel faster
fully jump from one node to the next.

When the distance
becomes too great, the current cannot diffuse from one
node to the next and still remain above threshold, so the action potentials would stop.

Question 30

Suppose researchers find that axon A can produce up to
1,000 action potentials per second (at least briefly, with maximum stimulation),

but axon B can never produce more
than 100 per second (regardless of the strength of the stimulus). What could we conclude about the refractory periods
of the two axons?

Answer 30

Axon A must have a shorter absolute refractory period, about 1 ms, whereas B has a longer absolute
refractory period, about 10 ms.

Question 31

what happens in the refractory period?

Answer 31

the sodium gates snap shut and the cell resists the production of
further action potentials

Question 32

what happens in the absolute refractory period?

Answer 32

the membrane cannot produce
another action potential, regardless of the stimulation

Question 33

what happens in the relative refractory period?

Answer 33

a stronger than-usual stimulus is necessary to initiate an action potential

Question 34

what two facts do the refractory period depend on?

Answer 34

the sodium channels are closed
and
potassium is flowing out of the cell at a faster-than-usual rate.

Question 35

what is another name for neurons without an axon?

Answer 35

local neurons since they only exchange information with only their closest neighbors

Question 36

what is a graded potential?

Answer 36

a membrane potential that varies in magnitude in proportion to
the intensity of the stimulus

Question 37

what happens during the event known

Answer 37

When the membrane is sufficiently depolarized to reach the cell’s threshold, sodium and potassium channels open.

Sodium ions enter rapidly, reducing and reversing the charge across the membrane

Question 38

what happens after the peak of action potential?

Answer 38

the membrane
returns toward its original level of polarization because of the outflow of potassium ions

Question 39

are transmissions in myelinated axons faster than unmyelinated axons?

Answer 39

yes

Question 40

what does the membrane do after an action potential

Answer 40

it enters a refractory period where it is resistant to starting another action potential