Changing Membrane Potential

Question 1

why are neurons electrically excitable?

Answer 1

because of the resting membrane potential!

Question 2

ligand gated channels

Answer 2

respond to chemical stimuli
(ligand binds to receptor)
- found in dendrites of some sensory neurons (pain) and dendrites and cell bodies of CNS and motor neurons

Question 3

mechanically gated channels

Answer 3

respond to mechanical vibration or pressure stimuli
- dendrites of some sensory neurons (touch, pressure and some pain)

Question 4

voltage gated ion channels

Answer 4

respond to direct changes in membrane potential
- ONLY the axons on all types of neurons

Question 5

leak channels

Answer 5

always open
found in nearly all cells, including dendrites, cell bodies and and axons of all types of neurons

Question 6

2 types of electrical signals in neurons

Answer 6

GRADED POTENTIALS
- short distances only
- ligand gated and mechanically gated
- occur in cell body

ACTION POTENTIALS
- short and long distances
- voltage gated

Question 7

out of electrical and chemical gradients, which will ions move with first?

Answer 7

chemical concentration gradient

Question 8

how can different ions cause hyper or depolarization?

Answer 8

Na+ in = depolarization
Ca2+in = depolarization
Cl- in = hyperpolarization
K+ out = hyperpolarization

Question 9

amplitude of a graded potential depends on the…

Answer 9

stimulus strength

Question 10

characteristics of graded potential strength

Answer 10

Amplitude of GP depends on stimulus strength
GPs can be added together to become larger in amplitude

Question 11

How is an action potential started?

Answer 11

enough graded potentials in cell body cause a strong electrical gradient that reaches TRIGGER ZONE, triggering voltage gated channels and an action potential

Question 12

describe the “all or none” principle

Answer 12

only if a large enough depolarizing graded potential occurs will an action potential be possible

Question 13

Describe process of an action potential

Answer 13

1. Resting state (-70mV)
2. Threshold
   - enough GP cause Na+ activation gates to open
3. Depolarizing phase
   - Na+ cells IN (+35mV)
   - Na+ in fast because it’s following electric and concentration gradient
   - K+ gates open more slowly
4. Repolarization phase
   - +35mV cause Na+ inactivation gates close
   - more K+ moves out of cell (via voltage channels AND sodium potassium pump)
5. End of repolarizing phase
   - @ threshold, activation gates close, inactivation gates open
   - K+ outflow returns membrane to -70mV
6. Afterpotential
   - if enough K+ leaves, causes hyperpolarization
7. Return to resting potential
   - via leak and sodium potassium pump

• voltage gated channels shut, repolarization occurs
• signal spreads over surface of axon without dying out

Question 14

what kind of GP do you need to trigger an action potential?

Answer 14

many DEPOLARIZING GPs

Question 15

Explain gate activity during resting membrane potential

Answer 15

• leak channels and sodium potassium pump maintain voltage
• K+ voltage gates closed
• Na+ activation gate closed, inactivation open

Question 16

difference between Na+ and K+ voltage gated channels

Answer 16

K+ have 1 gate
Na+ have 2 gates
- outside gate: ACTIVATION GATE
- inside gate: INACTIVATION GATE

Question 17

types of refractory periods and why its not possible to initiate action potentials

Answer 17

ABSOLUTE
- during depolarizing and repolarizing phase
- no action potential possible because Na+ gates not in resting position

RELATIVE
- during after potential
- suprathreshold stimulus (BIG) will start AP

Question 18

difference between GP and AP amplitudes

Answer 18

action potentials all have same amplitude
graded potentials have increasing amplitudes

Question 19

how does GP stimulus strength affect action potential strength?

Answer 19

as GP amplitudes increase, frequency of AP increase
*AP ALWAYS SAME AMPLITUDE, NEVER INCREASE IN STRENGTH ONLY FREQUENCY
*once MAXIMAL STIMULUS reached, any greater stimulus won’t make a difference in AP frequency

Question 20

suprathreshold stimulus

Answer 20

stimulus that can create an action potential from below threshold