Topic 3: Nervous System 1 - Neuronal Physiology

Question 1

What is resting membrane potential (RMP)?

Answer 1

• At rest (not stimulated), a charge difference (potential difference) exists just across a cell membrane
• this is called membrane potential

Question 2

What does RMP equal?

Answer 2

around -70 mV (inside cell is more negative)

Question 3

What are the 3 factors that establish RMP?

Answer 3

1. Na+/K+ - ATPase (pump) - NOT A CHANNEL
2. org- inside cell
3. More non-gated K+ channels than non-gated Na+ channel

Question 4

What occurs in the sodium potassium - ATPase? (2)

Answer 4

• breaks down 1 ATP and uses energy to pump 3 Na+ out and 2 K+ in
• both ions are pumped against CG = active transport

Question 5

What are two effects of the sodium potassium pump?

Answer 5

1. maintains CG of sodium and potassium
2. contributes a little (a few mV) to RMP bc pumping more positive ions out than in

Question 6

Why does org- establish RMP?

Answer 6

cannot cross membrane

Question 7

why is RMP established by the fact that there are more non-gated potassium channels than sodium channels? (2)

Answer 7

• membrane is more permeable to potassium than sodium at rest
• therefore potassium is the major determinant of RMP

Question 8

What occurs due to there being more potassium channels than sodium?

Answer 8

1. K+ diffuses out of cell down CG
2. Cell loses positive charge, inside more negative
3. Unlike charges attract and K+ diffusion slows as inside becomes increasingly negative
4. Na+ diffusion into cell increases due to increasing attraction to negative cell interior

Question 9

What happens before and after -70 mV is reached? (5)

Answer 9

5. until -70 mV reached, positive out (K+) > positive in (Na+), bc greater K+ permeability
6. once at -70 mV, the amount of positive (K+) moving out equals the amount of positive (Na+) moving in
   - force of Na+ much higher than on K+
7. therefore the net movement of charge (ions) is 0 (equal in both directions)
   - RMP of -70 mV

Question 10

What are considered electrically excitable cells?

Answer 10

ONLY muscle and nerve cells

Question 11

What are electrically excitable cells capable of producing?

Answer 11

• capable of producing departures from RMP in response to stimuli (changes in external or internal environment)

Question 12

In electrically excitable cells, what happens when a neuron is stimulated?

Answer 12

1. GATED ion channels open
2. MP changes, producing a graded potential
3. If threshold potential is reached, it triggers an action potential

Question 13

What are graded potentials (GPs)? (2)

Answer 13

• stimulus causes a small change in RMP, usually on dendrite or cell body (NO LONGER AT REST) by opening gated channels
• this changes membrane permeability

Question 14

What are two possible results for graded potentials?

Answer 14

1. more positive than RMP = depolarization
   ex. -70 mV to -65 mV (closer to 0)
2. More negative than RMP = hyperpolarization
   - ex. -70 mV to -75 mV

Question 15

How do ions move in GPs? (2)

Answer 15

• ions move passively (unlike charges attract)
• called current flow, causing depolarization or hyperpolarization on adjacent membrane

Question 16

How long are GP signals? (2)

Answer 16

• short distance signals
• die away quickly (short lived)

Question 17

How is magnitude and distance of GP determined?

Answer 17

• varies directly with strength of the stimulus
  ex. the larger the stimulus, the larger GP that travels further

Question 18

What is meant by “graded potentials can summate?” (2)

Answer 18

• first GP is present when 2nd stimulus occurs
• these add together to create the resulting GP

Question 19

What occurs after a graded potential? (2)

Answer 19

• repolarization
• return to RMP after depolarization or hyperpolarization

Question 20

Why are graded potentials important?

Answer 20

• essential in initiating a nerve impulse (action potential)

Question 21

What occurs if a graded potential causes depolarization?

Answer 21

• if it causes depol. and is large enough (ie. caused by critical stimulus or multiple GPs summate), it leads to an action potential

Question 22

What are the steps in creating an action potential? (3)

Answer 22

1. critical stimulus (or summating stimuli)
2. GP reaches threshold
3. Action potential

Question 23

Pathway explained so far

Answer 23