electrophysiology

Question 1

RMP

Answer 1

resting membrane potential

Question 2

charge of cytoplasm of typical cells

Answer 2

-70mV

Question 3

potassium leak

Answer 3

○ Membrane is 50-75x more permeable to K+ that to Na+

§ K+ leak

Question 4

Gibbs-donnan effect

Answer 4

§ Macromolecules assembled inside cells
§ Small building blocks diffuse in, and combine to produce larger molecules (proeteins, RNA) that can diffuse out
§ Most proteins ionise as anions (-ve) plus small ion H+ that can leave the cell
§ Traps negatively charged macromolecules in cytoplasm
§ Significant contribution to RMP

Question 5

leak channels

Answer 5

always open

Question 6

ligand-gated channels

Answer 6

open or shut when bound boy a specific ligand

Question 7

voltage gated channels

Answer 7

open at a specific membrane potential, close at a specific membrane potential

Question 8

influx of Na causes

Answer 8

depolarisation

makes the inside of the cell more positive

Question 9

efflux of K causes

Answer 9

hyperpolarisation

makes the inside of the cell less positive

Question 10

need for positive feedback

Answer 10

• Passive local potentials diminish over distance so are no good for transmitting messages
  
  • Depolarising stimuli wont transmit long distances without positive feedback

Question 11

action potential

Answer 11

□ 'all or nothing response'
				□ Always the same size (amplitude)
				□ Positive feedback after threshold value is exceeded 
				□ Des not diminish over distance 
				□ Open voltage gated sodium channels

Question 12

ligand gated Na channels

Answer 12

open when bound by specific ligands

provide initial stimulus

Question 13

voltage gated sodium channels

Answer 13

○ Open when membrane potential voltage exceeds threshold
○ Close a few ms later
○ Inactivated for a few ms afterwards (cant be activated again)

Question 14

• Voltage gated channels K+

Answer 14

○ Open due to membrane potential voltage exceeding threshold
○ Slower to open that Na channels (open later)
○ Close a few ms later
○ K channels don’t lock

Question 15

positive feedback in AP depolarisation

Answer 15

• Sub-threshold stimuli cause some Na+ channels to open, some Na+ enters the cell causing further depolarisation
  
  • Once the threshold membrane potential is exceeded all voltage gated Na channels open
  • Na floods into cell down its electrochemical gradient, causing rapid rise in membrane potential

Question 16

what causes initial stimulus of depolarisation

Answer 16

ligand gated sodium channel

Question 17

depolarisation

Answer 17

• At peak membrane potential, the cell is highly positively charges compared to ECF
  
  • Once the cell membrane potential peaks, voltage gates Na+ channels close and voltage gated K channels open
  • K+ floods out of the cell down electrochemical gradient causing repolarisation

Question 18

Hyperpolarisation

Answer 18

• After repolarisation, low K+ in cell and Na is being pumped out
  
  • K+ channels are slower to close so K+ leaks back out of the cell
  • Causes ICF to be more negative than at rest (until all the K+ channels close)

Question 19

Absolute refractory period

Answer 19

Neurone cannot be made to reach AP

Question 20

intraceullar calcium

Answer 20

maintained at low levels

Question 21

• Relative refractory period

Answer 21

○ Neurone can generate AP, but requires greater stimulus

○ Some Na+ cannels are reactivated

Question 22

After AP, neurones need to recover

Answer 22

○ Re-establish polarisation

○ Na+/K+ - ATPase pumps Na out of the cell and K in

Question 23

3 reasons to have a negative RMP

Answer 23

• Asymmetric ion distribution maintained by active transport
  
  • Membrane is 50-75x more permeable to K+ than Na+ causing K+ leak
  • Gibbs donnan effect

Question 24

a greater stimulus generates

Answer 24

• Greater stimulus does not generate more intense Aps, just more APs

Question 25

action potential propogation

Answer 25

- When an AP is achieved, it is only achieved in a small part of the membrane (not the whole cell) - Each AP generates electrical current, which generates a field, which changes the membrane potential next to the part that has generated an AP - The electrical field depolarises the neighbouring part of the membrane - Phenomenon spreads along the plasma membrane

Question 26

action potentials are spread along

Answer 26

membrane microdomains

Question 27

action potential starts at the

Answer 27

trigger zone - high density of voltage gated sodium channels

Question 28

why can't an action potential propagate backwards

Answer 28

the backward areas have locked channels due to refractory periods

Question 29

AP propagation velocity

Answer 29

2m/s

Question 30

schwaan cells secrete

Answer 30

myelin

Question 31

what does myelin do

Answer 31

fat that insulates and prevents action potentials from occurring

Question 32

myelin secreted by

Answer 32

glial cells schwaan cells in PNS oligodendrocytes in CNS

Question 33

gaps between myeline isolation

Answer 33

nodes of ranvier

Question 34

the process of jumping between nodes of ranvier is called

Answer 34

saltatory conduction