Lecture 3: Action Potentials

Question 1

In most cells Vm (membrane potential) stays constant for long period of time at a value called resting membrane potential. Explain

Answer 1

Resting membrane potential is when the overall voltage across the cell membrane when the cell is not transmitting an electrical signal.
RMP is an example of steady state ie no movement of charge across the membrane because influx and efflux of various ions due to electrochemical gradient and active transport balance each other out.
-all cells excitable or not have a RMP
-RMP usually negative inside relative to outside because at rest membrane is more permeable to K+ ions (they leak out)

Question 2

K+ ions dominate the RMP in most cells. Ecokain

Answer 2

Concentration gradient for K+ is slightly bigger than for Na+
-at rest the number open ion channels for K+ is 25x higher than open channels for Na+

Question 3

Electrochemical gradients acting at RMP.

Ie describe what is happening with K+ and Na+ ions when the cell is at resting membrane potential.

Answer 3

• large K+ efflux down chemical gradient leaves a net negative charge on inside.
• this creates an electrical gradient for both Na+ and K+ influx
• K+ continues to leave the cell down its chemical gradient, creating an increasingly string electrical gradient for Na+ and K+ to move into the cell.
• at a particular value of membrane potential, K+ efflux (chemical gradient) will be roughly opposite and equal to Na+ influx (chemical and electrical gradient) and K+ chemical gradient.
• the membrane will be quite stable at this point, called the resting membrane potential

Question 4

Why doesn’t this efflux of K and influx of Na eventually change the composition of the ICF and ECF?

Answer 4

Need pumps, which used energy to move ions against their electrochemical gradient. Adding more channels wont work coz ions just move with their electrochemical gradient.
What kind of a pump is used? Na/K ATPase pump

Question 5

The Na+/K+ ATPase Pump

Answer 5

Uses energy from ATP to move Na and k against their electrochemical gradients.
Each cycle pumps 3na+ ions out of the cell and 2K+ into the cell

Question 6

Electrical signalling in excitable cells

Answer 6

Excitable cells use electricity to transmit signals

Excitable cells transmit electrical signals by changing their membrane potential.

Question 7

What is the terminology for cells changing their membrane potential

Answer 7

Depolarisation: Vm more positive than RMP
Hyperpolarisation: Vm more negative than RMP
Repolarisation: Vm returning towards RMP following depolarisation/ hyperpolarisation
View slide 18 for image

Question 8

Neurons propagate two main types of electrical signals. What are they?

Answer 8

1) graded potentials (input signals)
2) action potentials (output signals)
Both types of signals involve the opening or closing of gates ion channels.
View slide 21 for image of it -good

Question 9

Learn the difference between graded potential and action potentials on slide 44

Answer 9

Better do it or ill smash you

Question 10

Read through the lecture summary printed out and understand….ya bitch

Answer 10

Yeah