Chapter 2 module 2.2

Question 0

Polarization

Answer 0

A difference of electrical charge between two locations

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

Question 1

Electrical gradient

Answer 1

A difference of electrical charge between the inside and the outside of the cell

Question 2

Resting potential

Answer 2

The difference in voltage in a resting neuron

The resting potential is mainly the result of negatively charged proteins inside the cell

Question 3

The membrane is selectively permeable

Answer 3

That means that some chemicals can pass through it more freely than others can

More large or electrically charged ions and molecules cannot cross the membrane at all

Chemicals that can cross are: water, Origen, carbon dioxide, and urea. They cross through Channels that are always open.

Question 4

What are the major ions that cross through the selective channels?

Answer 4

Sodium, potassium, calcium, and chloride

Question 5

When the membrane is at rest…

Answer 5

Sodium channels are closed.

Question 6

Sodium-potassium pump

Answer 6

A protein complex that repeatedly ran sport three sodium ions out of the cell while drawing two potassium ions into it

This requires energy

Question 7

Concentration gradient

Answer 7

The difference in distribution of ions across the membrane

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

Question 8

Potassium

Answer 8

Potassium is positively charged and the inside of the cell is negatively charged, so the electrical gradient tend to pull potassium in. However, potassium is more concentrated inside the cell the outside, so the CONCENTRATION GRADIENT tends to drive it out.

For potassium, the electrical gradient and concentration gradient are almost in balance

Question 9

Chloride

Answer 9

Negatively charged
Not actively pump in and out
And it’s channels are not voltage dependent
Therefore chloride ions are not the key to action potential

Question 10

Why resting potential?

Answer 10

The advantage is that the resting potential prepares the neuron to respond rapidly to a stimulus

-70mV

Question 11

When an axon membrane is at rest…

Answer 11

The recordings show a steady negative potential inside the axon

Question 12

Hyperpolarization

Answer 12

Means increase polarization

Question 13

Depolarization

Answer 13

Reduction of the polarization in the neuron

Question 14

Threshold of excitation

Answer 14

Any stimulation beyond the threshold of excitation produces a sudden, massive depolarization of the membrane

When the potential reaches the threshold, the membrane suddenly opens it’s sodium channels and permit a rapid, massive flow of ions across the membrane

Question 15

Action potential or neural firing

Answer 15

A rapid depolarization and slight reversal of the usual polarization

+30 mV

Question 16

Voltage-activated channels

Answer 16

Membrane channels whose permeability depends on the voltage difference across the membrane

At the resting potential, the channels are closed.

Question 17

When the potential across the membrane reaches threshold…

Answer 17

the sodium channels open wide. Sodium ions rush into the neuron explosively until the electrical potential across the membrane passes beyond zero to a reversed polarity.

From -70mV To +30mV

Question 18

What happens at the pick of the action potential?

Answer 18

The sodium gates quickly close and resist reopening for about the next millisecond

Question 19

What brings the membrane to its original state of polarization?

Answer 19

Not the sodium-potassium pump which transports three sodium ions outside of the cell while drawing two potassium ions inside it, this would prove to slow. Instead, after the action potential is underway, the potassium channels open. Potassium ions flow out of the cell simply because they are much more concentrated inside than outside and they are no longer held inside by the negative charge.

As they flow out of the axon they carry with them a positive charge.

Question 20

What is the all-or-non law?

Answer 20

The amplitude an intensity of an action potential are independent of the intensity of the stimulus that initiated it

Question 21

What does an axon do in order to signal the difference between a weak stimulus and a strong stimulus?

Answer 21

The axon can’t send bigger or faster action potentials, all it can change is the timing

Question 22

Researchers have long known that a greater frequency of action potentiall per second indicates ‘‘stronger’’ stimulus. In some cases, a different rhythm of response also carries information .. Page, 44

Answer 22

.

Question 23

Refractory period

There are two: absolute and relative

Answer 23

The membrane resists the production of further action potentials

Question 24

Absolute refractory period

Answer 24

The membrane cannot produce another action potential regardless of the stimulation

Question 25

Relative refractory period

Answer 25

A stronger that usual stimulus is necessary to initiate an action potential

Question 26

Absolute, about 1ms

Relative, about 2-3

Answer 26

.

Question 27

Axon hillock

Answer 27

A swelling whrere the axon exits the soma

Question 28

Propagation of the action potential

Answer 28

It describes the transmission of an action potential down the axon

Question 29

Electrical conduction in a copper wire with free electrons travels at a rate approaching the speed of light, 300 million meters per second.

Answer 29

In an axon, transition relies on the flow of charged ions through a water medium. In thin axons, action potentials travel at a velocity of less than 1m/s. Thicker axons and those covered with an insulating shield of myelin conduct with greater velocities . Though greater diameters only give axons the capacity to transmit the action potential at a speed of 10 m/s

Question 30

Myelin

Answer 30

It’s an insulating material composed of fats and proteins that help increase the speed up to about 100 m/s

Made of glial cells ( Greek, ‘‘glue’’ )

Question 31

Saltatory conduction

Answer 31

The jumping of action potentials from node to node

A flow of ions

The diffuse within the axon pushing a chain of positive ions along the axon to then next node where they regenerate the action potential

Question: what is there in the myelin shield that facilitates the movement of ions across the axon

Question 32

Local neurons

Answer 32

Neuron with short axons that share information only with adjacent neurons

They do not produce action potentials but graded potentials