Nervous System IV

Question 1

What is current flow?

Answer 1

Flow of electrical charge carried by an ion

Question 2

What is Ohm’s Law?

Answer 2

Current flow is directly proportional to electrical potential different between two point and inversely proportional to the resistance

Question 3

What are 2 sources of resistance in a cell?

Answer 3

• membrane resistance
• internal resistance of the cytoplasm
  Resistance will determine how far current will flow before energy is dissipated

Question 4

What are the two types of electrical signals?

Answer 4

Graded potentials and action potentials

Question 5

What are graded potentials?

Answer 5

Variable strength signals that travel short distances and lose strength as they travel
Can be depolarizing (influx of Na+) or hyperpolarizing (influx of Cl- or eflux of K+)
If large enough depolarization it can induce an action potential

Question 6

What are action potentials?

Answer 6

Very brief, large depolarizations that travel for long distances through a neuron without losing strength

Rapid signals over long distances
All or none

Question 7

Where are graded potentials and APs created in CNS and efferent neurons?

Answer 7

Created in dendrites or soma

Created in axon to axon terminal

Question 8

Where are graded potentials and APs created in sensory neurons?

Answer 8

Graded (generator potentials) in peripheral portion by dendrites
Action in axon

Question 9

What are properties of graded potentials?

Answer 9

• graded because amplitude (size) is directly proportional to strength of the stimulus and can vary
• decrease in strength as spread out from origin
• generated by chemically gated (ligand) ion channels or closure of leak channels (CNS and efferent)
  -chemical, mechanical, thermal gated (sensory)

Question 10

What is local current flow?

Answer 10

Wave of depolarization or hyperpolarization that moves through the cell
Depends on gated or leak channel

Question 11

Why do graded potentials lose strength as they move through cell?

Answer 11

• current leak: open channels allow ions to leak out
• cytoplasmic resistance

Question 12

What happens with excitatory postsynaptic potential?

Answer 12

Depolarization

Question 13

What happens with inhibitory postsynaptic potential?

Answer 13

Hyperpolarization

Question 14

What is the axon hillock?

Answer 14

The trigger zone where if graded potential is strong enough will reach and fire an AP
High concentration of voltage gated Na+ channels

Question 15

What is membrane potential for AP to be generated?

Answer 15

Depolarization of ~ -55 mV or more positive for gate to open

Question 16

What is sub threshold graded potential?

Answer 16

Graded potential below threshold

Question 17

Suprathreshold graded potential?

Answer 17

Graded potential above threshold creating an AP

Question 18

What is an action potential?

Answer 18

• electrical signals of uniform strength (all-or-none) that travel from the trigger zone to the axon terminals

Question 19

What is conduction of AP?

Answer 19

Movement of AP along axon

Question 20

Why is AP like dominoes?

Answer 20

Sequential opening of voltage gated ion channels in the axon membrane as electrical current moves down
Regenerating signal: AP un each adjacent segment of axon
A new AP generated in each adjacent area