Lec 4 Graded Potentials and Action Potentials

Question 1

What did Luigi Galvani claim?

Answer 1

Bioelectricity is an important factor in the nervous system.
While conducting his “dead frog” experiments he claimed the key to life is animal electric fluid

Question 2

What did Alessandro Volta invent, what else he do?

Answer 2

Invented the first electric battery
discredited Galvani’s work

Question 3

What is diffusion

Answer 3

the distribution of ions across a membrane in a medium

Question 4

What is osmosis

Answer 4

the diffusion of molecules from a high concentration gradient to a low concentration gradient

Question 5

Diffusion vs Osmosis

Answer 5

in osmosis movement of ions can be influenced using barriers

Question 6

What does a semi-permeable membrane do

Answer 6

semi-permeable membranes can create differences in diffusion in a medium

Question 7

What does electrochemical attraction do

Answer 7

electrochemical attraction can influence the movement of ions towards one another

Question 8

What does active transport do

Answer 8

carries molecules across a membrane from low concentration to high concentration

Question 9

What does a voltmeter measure

Answer 9

difference of charge between two points

Question 10

how long is a action potential

Answer 10

2ms

Question 11

where do action potentials take place and where in that structure are they generated

Answer 11

axons
initial axonal segment

Question 12

Describe Stage 1 of the action potential: sensory activity

Answer 12

• External stimuli is transformed to neural signal through sensory receptors
• potentials can be excitatory or inhibitory
• excitatory potentials produce small local depolarization as Na+ channels open and pushes cell closer to threshold
  -inhibitory potentials produce a small hyperpolarization moving the cell away from threshold

Question 13

Describe Stage 2 of the action potential: depolarization

Answer 13

-Energy from from step one goes through a voltage gated sodium channel which is a positive feedback loop which causes the rising phase

Question 14

Describe Stage 3 of the action potential: action potential peak

Answer 14

-action potential reaches its peak and the sodium channel closes
-potassium channels that were slowly opening, open and cause the falling phase which leads to the drop below resting potential.

Question 15

Describe Stage 4 of the action potential: returning to normal?

Answer 15

• potassium channels close
• Na/K+ pump restores resting potential

Question 16

Where is the absolute refractory period located, define what it is

Answer 16

phase 3
defined by when sodium gated channels are opened and cannot be opened anymore

Question 17

Where is the relative refractory period located, define what it is

Answer 17

phase 4
defined by potassium channels still being open and the neuron is hyperpolarized and sodium channels can only activate if they can overcome the additional negativity

Question 18

Describe temporal and spatial summation in single nerve cells

Answer 18

• spatial summation: summing of potentials that come from different parts of the cell
• temporal summation: summing of potentials that arrive at the integration zone at
  different time

Question 19

What are 3 problems with action potential speeds how have vertebrates and invertebrates solved these issues

Answer 19

• axon is leaky: low membrane resistance (Rm)
• axon is sticky: high membrane capacitance(Cm)
• axon is thin: high axoplasmic resistance (Ra)

Vertebrates have myelinated axons which fix the leaky and sticky issues
Invertebrates have bigger axons to fix thing issue