Lecture 5: Graded Potentials

Question 1

neurons signal using changes in Em, there are 2 categories of changes:

Answer 1

Graded Potentials and Action Potentials

Question 2

Graded Potentials are…

Answer 2

Changes of Em observed in the cell body and dendrites

-received signals of sensory stimuli or chemical messengers are converted to this change in membrane potential

Question 3

How incoming signal generates a graded potential

Answer 3

• incoming stimuli either open gated ion channels to increase permeability to the ion or close gated ion channels to decrease membrane permeability
• either way there is a change in membrane potential

Question 4

Examples of changes of Vm

Answer 4

• cone cells in retina

- changes in muscle spindle

Question 5

Larger and longer stimulus occurs:

Answer 5

-the more ion channels are open and for longer time
-the greater the change in membrane permeability over a longer duration
Both make for greater magnitude and duration of GP

Question 6

Why do graded potentials only occur at dendrites and cell body?

Answer 6

• they travel short distances only, cannot carry info long distances like AP
• the short distance is due to GP decaying back to rest Vm very quickly

Question 7

Propagation of Graded Potential

Answer 7

1. incoming stimulus at dendrite or cell body causes sodium gated ion channels to open at the site of stimulation
2. permeability for Na+ increases
3. Influx of Na+ creates a change in electrical potential outside and inside the membrane, which is the generated GP that depolarizes the MP
4. Site of stimulation becomes more +ve than surrounding region inside and more -ve than surrounding region outside
5. This differences generates an electrotonic current of positive charges that propagate along hte membrane and change the Vm, though the GP decreases in mag. the further it travels from the site of stim.

Question 8

Creation of electrotonic current

Answer 8

• difference in potential between site of stim. and surrounding regions creates the current
• as it spreads it changes the MP and the +ve charges move towards the -ves along the membrane, while those outside are repelled from the +ve charges outside and move towards the ion channel

Question 9

Why electrotonic current decays

Answer 9

• as the current spreads it leaks back out through leak channels back out of the axon, completing the circuit
• current weakens as it leaks, thus the changes in Vm get weaker and the GP decays over distance

Question 10

Which ion is the primary carrier of electrical charges that leak through leak channels?

Answer 10

Potassium (K+)