Electrical signalling

Question 1

why are ion channels or transporters required?

Answer 1

biological membrane is impermeable to the ions therefore ion channels/transporters for ion movements - allows selective permeability

Question 2

what does the membrane usually allow and not allow?

Answer 2

allows 
1. hydrophobic molecules: O2, CO2, N2
2. small uncharged polar molecules 
Does not allow 
1. large uncharged polar molecules: glucose, sucrose 
2. ions: na+,K+, H+

Question 3

what is the significance of ion flow?

Answer 3

• to establish concentration gradient
• generates membrane potential
• utilised for electrical signalling

Question 4

what is an action potential?

Answer 4

transient alterations in membrane potential that propagate along the axons

Question 5

give few examples of excitable and non-excitable cells

Answer 5

• excitable cells
  1. neurones - synaptic vesicle release
  2. endocrine cell - hormone release
  3. muscle cells - contraction
• non-excitable cells - epithelial, adipose

Question 6

how is resting membrane potential established?

Answer 6

• selective membrane permeability of K+ ions
• K+ - primary determinant of RMP
• varying Na+ minimal effect

Question 7

what are the various phases of action potential and how do the Na+/K+ channels mediate those?

Answer 7

• depolarisation: opening of VG Na+ channels
• repolarisation: closure of Na+ and opening of VG K+ channels
• hyperpolarisation: VG K+ channels remain open after the potential reaches resting level

Question 8

what is the difference b/w excitatory and inhibitory?

Answer 8

EPSP - Na+ influx (via GluR)

IPSP - Cl- influx (via GABAR/GlyR)

Question 9

what is the refractory period and what is its advantage?

Answer 9

• absolute RP and RP
• absolute RP - stimulus fails to initiate AP
• relative RP - bigger stimulus - AP fired thus, longer hyperpolarisation period
• because activation and inactivation involve VGSC conformation changes which needs time to reset

Question 10

what is the advantage of refractory period?

Answer 10

favours unidirectional prorogation