Resting Membrane and Action/Graded Potentials

Question 1

what is resting membrane potential determined primarily by?

Answer 1

• K+ concentration gradient
• cell’s resting permeability to K+, Na+, and Cl-

Question 2

changes in a membrane’s permeability result in ion movement

Answer 2

• Movement creates an electrical signal
• Very few ions move to create large changes in
  membrane potentials

Question 3

what two things should you associate with resting membrane?

Answer 3

• membrane permeability
• electrochemical gradient

Question 4

depolarization

Answer 4

• associate with Na+ movement
• all based on passive transport

Question 5

hyperpolarization

Answer 5

• associate with K+ movement

Question 6

resting membrane potential value

Answer 6

-70 mv

Question 7

what are ion channels named for?

Answer 7

• the primary ion that passes thru them

Question 8

gated channels control ion permeability

Answer 8

– Mechanically gated, chemically gated, voltage-gated ion channels

Question 9

threshold voltage varies from old channel type to another

Answer 9

– Activation rates vary (always open)
– Inactivation rates vary (always closed)
- keeps it moving in a one way fashion
- both look at Na

Question 10

two basic types of electrical signals

Answer 10

• Graded Potentials (think calcium)
  – Variable strength
  – Used for short distance communication (not a lot of resistance)
  
  • heart uses this
• Action Potentials
  – Very brief, large depolarizations
  – Rapid signaling over long distances

Question 11

graded potentials reflect stimulus strength

Answer 11

• Local current flow is a wave of depolarization that moves through the cell
• Graded potentials lose strength as they move through the cell due to
  – current leak
  – cytoplasmic resistance
• If strong enough, graded potentials reach the trigger zone in the axon hillock and initial segment
• Excitatory versus inhibitory
• Cell’s excitability is the ability to fire an action potential.

Question 12

action potentials travel long distances

Answer 12

• Conduction is the high-speed movement of a action potential along an axon.
• All-or-none (happens or it doesn’t)
• Wave of electrical signal at constant amplitude

Question 13

what are graded potentials based on?

Answer 13

• strength and calcium usage

Question 14

when does action potential begin?

Answer 14

when graded potential reaching trigger zone depolarizes to threshold

Question 15

rising phase of action potential

Answer 15

voltage-gated Na channels open and Na entry depolarizes cell

Question 16

falling phase of the action potential

Answer 16

• at peak, Na channels close, slower voltage-gated K+ channels open
• K+ exit repolarizes then hyperpolarizes cell
• voltage-gated K+ channels close, less K+ leaks out of the cell
• cell retruns to resting membrane potential of -70 mV
• one action potential does not alter ion concentration gradients

Question 17

axonal Na+ channels have two gates

Answer 17

• Activation vs. inactivation gates
• Action potentials will not fire during the absolute refractory period
• The refractory period prevents backward conduction
  
  • Potential delay of 1-2 msec between action potentials independent of
    intensity of trigger
• Absolute refractory period is due to voltage-gated Na+ channels resetting
• Relative refractory period follows an absolute refractory period
• Limits the rate at which signals can be transmitted

Question 18

depolarization

Answer 18

• Positive charge spreads along adjacent sections of axon by local current flow
• Dependent on voltage-gated Na+ channels
• passive – how far Na+ is going into the cell

Question 19

local current flow causes what?

Answer 19

• new section of the membrane to depolarize
  
  • Backward flow can’t occur because the Na+ channels are inactivated

Question 20

local current flow

Answer 20

• when a section of axon depolarizes, positive charges move by local current flow into adjacent sections of the cytoplasm
• on the extracellular surface, current flows toward the depolarized region
• one way system
• depolarizing nerve = want it to go in a one way

Question 21

larger neurons conduct what?

Answer 21

• action potentials faster

Question 22

is conduction faster in myelinated or unmyelinated neurons?

Answer 22

• myelinated neurons
  – Resistance of axon membrane to ion leakage out of the cell
  ▪ Saltatory conduction between nodes of Ranvier
  – Demyelinating diseases cause loss of myelin
  ▪ Multiple sclerosis vs. Guillain-Barre syndrome
• Schwann cells = myelination of CNS
• oligodendrocytes = myelination of PNS

Question 23

chemical factors alter electrical activity

Answer 23

• Variety of chemicals alter the conduction of action potentials by binding to the channel
• Alterations in ECF concentration of ions also affects effects electrical activity
• Ca2+ and K+
• Hyperkalemia brings neuron closer to threshold
• Hypokalemia moves neuron further from threshold

Question 24

a delta

Answer 24

faster pain fiber

Question 25

c fiber

Answer 25

slow pain fiber