Generation and Propagation of Action Potentials Study Guide

Question 1

In terms of resting membrane potential, what is unique about neurons?

Answer 1

Neurons can rapidly change their membrane potential

Question 2

Opposite charges _____; same charges _______.

Answer 2

• attract
• repel

Question 3

It requires energy to keep opposite charges separated. So, when opposite charges are separated by a membrane, the system has ____________.

Answer 3

potential energy

Question 4

voltage

Answer 4

the measure of potential energy generated by separated charges – the charge difference across a plasma membrane

Question 5

current

Answer 5

flow of electrical charge (ions) from 1 points to another

Question 6

What is used to measure voltage?

Answer 6

• Always measured between 2 points – called the potential or potential difference
• Measured in volts (V) or millivolts (mV)
• The greater charge difference between the 2 points, the higher the voltage

Question 6

resistance

Answer 6

hindrance to charge flow

Question 7

current equation

Answer 7

• current (I) = voltage (V) / resistance (R)
  
  • Greater voltage = greater current, current is directly proportional to voltage
  • Greater resistance = smaller current, current is inversely proportional to resistance

Question 7

In terms of resistance, define conductor and insulator.

Answer 7

insulator: substance with high electrical resistance
Conductor: substance with low electrical resistance

Question 8

In the human body, what TWO things generate the resting membrane potential?

Answer 8

The slight difference in the amount of positive and negative ions on either side of a cellular plasma membrane creates potential
Plasma membranes provides resistance to current flow

Question 9

What are the two types of ion channels? Functionally, what is different about leakage vs gated channels?

Answer 9

Leakage (nongated) channels: always open
Gated channels: requires a change in protein shape to open/close the channel

Question 10

What are the 3 types of gated channels? How does each open/close? Give examples of chemically gated and voltage gated channels from the muscle portion of this unit.

Answer 10

• Chemically gated: open only with binding of a specific chemical (ex - neurotransmitter_
  
  • ACH, sodium potassium pump
• Voltage gated: open/close in response to changes in the membrane potential
  
  • t-tubules
• Mechanically gated: open/close in response to physical deformation of receptors
  
  • Sensory receptors for touch/pressure

Question 11

What are the two components of an electrochemical gradient?

Answer 11

Chemical concentration gradient
Electrical gradient

Question 12

Based on chemical concentration, ions will move from _______ to _______ concentration.

Answer 12

• higher
• lower

Question 13

Based on electrical charge, ions will move towards _________________ .

Answer 13

the opposite electrical charge

Question 14

What are the differences in ionic composition across a plasma membrane? Of these differences, which ion plays the most important role? T

Answer 14

• ECF has higher concentration of Na+ than ICF
  
  • Balanced by chloride ions Cl-
• ICF has higher concentration of K+ than ECF
  
  • Balanced by various negatively charged proteins
• K+ plays the most important role in membrane potential - tangerine story of high potassium

Question 15

How permeable are plasma membranes to the following:
- Large anionic proteins
- Cl-
- Na+
- K+

Answer 15

• Large anionic proteins impermeable
• Cl- quite permeable
• Na+ slightly permeable (leakage channels)
• K+ 25x more permeable to K+ than Na+ (more leakage channels)
  - K+ diffuses out of a cell – down its concentration gradient

Question 16

Through the leakage channels, which direction does Na+ move? How about K+?

Answer 16

More K+ diffuses out than NA+ diffuses in

Question 17

Based on movement of Na+ and K+, how is the negative resting membrane potential established?

Answer 17

• Membrane is highly permeable to K+, so K+ flows down its concentration gradient
• As positive K+ leaks out, a negative voltage (electrical gradient) develops on the membrane interior. The electrical gradient pulls K+ back in

Question 18

Which direction are Na+ and K+ moved through Na+/K+ pumps? How does this help to maintain resting membrane potential? Recall why this process requires energy.

Answer 18

Sodium-potassium pumps stabilize resting membrane potentials by maintaining concentration gradients for Na+ and K+
- 3Na+ are pumped out of the cell while 2K+ are pumped into the cell

Question 19

What are the TWO things that can change a resting membrane potential?

Answer 19

1. Changes in the concentrations of ions across the membrane
2. Changes in membrane permeability to ions

Question 20

Changes in resting membrane potential can produce 2 different types of signals. Name and define the 2 types. Be sure to note what is different about the 2 types in terms of their strength.

Answer 20

• Graded potentials: incoming signals with variable strength operating over short distances
• Action potentials: long-distance signals of axons with consistent strength

Question 21

Define depolarization

Answer 21

decrease in membrane potential (moves toward zero and above)
- inside of the membrane becomes less negative than resting membrane potential
Ex. -70mV → -55mV
- Probability of producing impulse increases

Question 22

Define hyperpolarization.

Answer 22

Increase in membrane potential (away from zero)
- Inside of the membrane becomes more negative than resting membrane potential
Ex. -70mV → -75mV

Question 23

Why are graded potentials “graded”?

Answer 23

Their magnitude varies directly with stimulus strength
- Stronger stimulus → more voltage change → farther current flow

Question 24

The associated current flows __________________________ with distance.

Answer 24

decay or decrease in magnitude

Question 25

When is a postsynaptic potential produced?

Answer 25

When the stimulus is a neurotransmitter released by another neuron

Question 26

__________ are the principal way neurons send signals over long distances.

Answer 26

action potentials

Question 27

_______ potentials are often initially activated by _______ potentials. where does this transition take place?

Answer 27

• action
• graded
  the initial segment of the axon

Question 28

What is the average change in membrane potential for an action potential?

Answer 28

~100mV

Question 29

Do action potentials decay over distance?

Answer 29

they do not decay over distance

Question 30

Define an activation gate and an inactivation gate.

Answer 30

• Activation gate: closed at rest, opens with depolarization to allow Na+ to enter
• Inactivation gates: opens at rest, blocks the channel when it is open to prevent more Na+ from entering the cell

Question 31

What defines “threshold”? What kind of feedback loop is triggered by reaching a threshold?

Answer 31

• Membrane is depolarized to 15 to 20 mV from resting value
• Na+ permeability increases and Na+ influx far exceeds K+ efflux – positive feedback cycle

Question 32

How does an action potential propagate - i.e. how are adjacent areas depolarized?

Answer 32

Influx of Na+ through the voltage gates in one area of the membrane causes local currents that will depolarize adjacent areas of the membrane in the forward direction (away from the point of origin)

Question 32

Why are action potentials only propagated in one direction?

Answer 32

The refractory period of repolarization

Question 32

What is meant by the all-or-none phenomenon?

Answer 32

Action potential either happens completely or does not happen at all - like igniting a fire

Question 33

Why is propagation a better term to describe what is happening in an axon than conduction?

Answer 33

AP is regenerated anew at each membrane patch; every subsequent AP is identical to the one that generated initially