Membranes, Ions and Action potentials

Question 1

is intracellular K+ or extra. conc higher?

Answer 1

intracellular= higher

Question 2

is intracellular A- or extra. conc higher?

Answer 2

intracellular= higher

Question 3

what is A-?

Answer 3

fixed negative charges on macromolecules

Question 4

is intracellular Cl- or extra. conc higher?

Answer 4

extracellular= higher

Question 5

is intracellular Na+ extra. conc higher?

Answer 5

extracellular= higher

Question 6

is intracellular pH or extracellular higher?

Answer 6

extracellular = higher (7.4 compared with 7.0)

Question 7

what is resting memb potential?

Answer 7

between -20 to -95mV depending on cell type

Question 8

what causes ion gradients ro exist?

ie explain primary active transport

Answer 8

K+ accumulates where the impermeable anion A- locates. A- are fixed -ve charges on macromolecules
O there is a high conc of A- in inside the cell
O intracellular K+ conc is high
Na+ leaks into cell slowly and is pumped out against conc grad by Na pump
(req ATP)

Question 9

how is the low Na+ conc inside the cell used for glucose transport.
what is the transporter?

Answer 9

Na+ can diffuse into the cell through GLUT transporter WITH GLUCOSE
Na+ pumped out with ATP

the GLUT transporter is a SECONDARY ACTIVE TRANSPORTER

Question 10

what happens if extracellular K+ conc increases?

Answer 10

makes the membrane potential less negative than the resting membrane potential
- the membrane will be DEPOLARISED

Question 11

what is an action potential?

Answer 11

a transient depolarisation of the cell

Question 12

what are cells that generate aps called?

Answer 12

excitable cells

Question 13

where to aps transfer information to and from?

Answer 13

• from SENSORY CELL to CNS

eg brain to muscle

Question 14

what can aps initiate?

Answer 14

cellular events, eg muscular contraction

Question 15

what is all or nothing law?

Answer 15

once an ap has been initiated, varying the stimulus strength doesn’t change the configuration of the ap.

Question 16

what causes depolarisation?

Answer 16

transient inc of membrane Na+ permeability O Na+ rapidly diffuses in

Question 17

what causes repolarisation?

Answer 17

greater than normal inc of K+ permeability

O K+ leaves

Question 18

how do voltage gated channels work?

Answer 18

activated by change to membrane potential (eg electrical stimulus)

Question 19

how do ligand gated channels work?

what happens when a ligand binds to ligand gated channels?

Answer 19

extracellular chemical binds to receptor on membrane. The receptor is an ion channel

• when a lignd binds, the ion channel opens

Question 20

give an example of a voltage gated ion channel

Answer 20

eg Na+ channel

Question 21

what are the general functions of voltage gated channels?

Answer 21

support aps, eg in nerves and muscle

Question 22

where are ligand gated ion channels found?

Answer 22

muscle and nerve cells

secretory cells

Question 23

what are the two types of ligand gated channels?

what do each type cause to the cell?

Answer 23

1) cation selective (eg Na+ flows in)
causes DEPOLARISATION- cell becomes MORE EXCITABLE
2) anion selective (eg Cl- flows in)
causes HYPERPOLARISATION-cell becomes LESS EXCITABLE

Question 24

what is threshold potential?

Answer 24

-60mV

Question 25

what is resting memb potential?

Answer 25

-80mV

Question 26

give and explain the 4 ways an ap can be initiated?

Answer 26

1) artificial application of electrical current
2) synapses- NT bind to ligand gated channels on target cell
3) spontaneously in “pacemaker” cells eg in heart
4) sensory cells- convert a stimulus to change of memb pot of the associated nerve.
if stimulus= large enough then THRESHOLD IS REACHED

Question 27

what are local circuits?

Answer 27

• a local current PRECEDES the ap in cytoplasm of axon
• the ap is +vely charged, but regions around it are -vely charged (still under resting pot)
• Na+ ions at the point of ap are attracted to the -VE CHARGE
• O local circuit is set up and O Na+ channels in the local circuit open
• O ap continues and moves along axon

Question 28

what factors affect ap conduction velocity?

Answer 28

1) cell diameter (velocity inc as diameter inc)
2) temp (inc temp inc velocity)
3) myelination (myelin allows for saltatory conduction (jump from nodes of Ranvier))