Unit 2.2: Electrical Properties of Neurons

Question 1

How do neurons transmit electrical impulses?

Answer 1

Via energy stored as an electro-chemical gradient

Question 2

Which molecules can cross the cell membrane?

Answer 2

Hydrophobic molecules can slip past the phospholipid bilayer (steroid hormones)

Question 3

What is the equilibrium state?

Answer 3

If concentration gradient of ions balances, there’s no net movement (cell dies)

Question 4

What does the Nernst equation calculate?

Answer 4

The electrical potential of the cell needed to generate an equilibrium state (but you have to know the concentration gradient)

Question 5

What is the charge of a cell at rest?

Answer 5

-70 mV to -90 mV

Question 6

What can we predict about ions knowing there equilibrium potential?

Answer 6

Ions with positive equilibrium potential will tend to move into a resting cell
Ions with a very negative equilibrium potential will tend to move out of a resting cell

Question 7

What is the charge difference between the inside and the outside of a cell at rest called?

Answer 7

Resting membrane potential

Question 8

What sets the resting membrane potential?

Answer 8

Concentration of each ions and their relative permeability

Question 9

Which ions want to move in/out the cells?

Answer 9

• K+ wants to move out

- Na+, Ca2+, Cl- want to move in

Question 10

What is the equilibrium potential for K+?

Answer 10

-90 mV

Question 11

What is the equilibrium potential for Na+?

Answer 11

+60 mV

Question 12

Which molecules contribute the most to the resting membrane potential?

Answer 12

Those that are most permeable, the more easily it can cross the membrane, the more important it is for resting membrane potential

Question 13

How do we calculate membrane permeability?

Answer 13

Goldman-Hodgin-Katz (GHK) equation

Question 14

Which ion is the most important to resting membrane potential?

Answer 14

K+ ions

Question 15

Why doesn’t K+ keep leaking out of the cell (and Na+ into the cell) until they reach their equilibrium potentials?

Answer 15

They do leak out but Na+/K+ ATPase activity offsets the leak

Question 16

How are gates channels controlled?

Answer 16

1. mechanically gated
2. chemically gated
3. voltage-gated

Question 17

What are the 4 major types of selective ion channels in the neuron?

Answer 17

Na+, K+, Cl-, Ca2+ channels

Question 18

When do electrical signals in neurons occur?

Answer 18

When there are changes in membrane permeability to specific ions

Question 19

What is depolarization?

Answer 19

A decrease in the membrane potential difference

Cell membrane potential becomes less negative

Question 20

What is hyperpolarization?

Answer 20

A increase in the membrane potential difference

Cell membrane potential becomes more negative

Question 21

What is it called when the cell membrane returns to its resting membrane potential?

Answer 21

Repolarization

Question 22

How do cells change their membrane potential?

Answer 22

Change the membrane ion permeability

Question 23

How can cells change their permeability?

Answer 23

1. Change total number of protein channels
   This is slow, requires transcription, translation
2. Open or close existing protein channels
   This is fast, only needs a change in protein channel conformation

Question 24

Does Na+ contribute a lot to the resting membrane potential?

Answer 24

not really, due to low permeability

Question 25

How is Na+ critical to the cell?

Answer 25

It is critical in generating the changes in membrane potential that cause electrical signals

Question 26

What are the 2 types of signals generated by neurons?

Answer 26

Graded potentials (short distance)
Action potentials (long distance)