PPP - excitable cells

Question 1

How would you measure the potential of a single ion channel?

Answer 1

patch clamping

Question 2

What are the ranges in a waveform for intracellular, extracellular and patch clamp electrode recording?

Answer 2

intracellular = -70 - +40 (110mV)
extracellular = 0.1mV
patch clamp = 1pA

Question 3

What establishes electrochemical gradient?

Answer 3

sodium-potassium pump

Question 4

How does the cell membrane act like a capacitor?

Answer 4

stores ionic charges on it’s surface

Question 5

What is capacitance of a membrane?

Answer 5

ability of a membrane to hold charge

Question 6

What is the membrane potential?

Answer 6

the work required to separate charges on the inner and outer surfaces

Question 7

What is the equilibrium potential?

Answer 7

when the concentration gradient is balanced by electrical gradient in the opposite direction (no net ion movement)

Question 8

How can you determine the equilibrium potential?

Answer 8

using the Nernst equation:

E = 58 x log([C]out/[C]in)

Question 9

What is the average resting membrane potential?

Answer 9

-70mV

Question 10

What is the equilibrium potential of potassium and sodium?

Answer 10

Ek = -90mV
Ena = + 50

Question 11

Why is the resting membrane potential closer to Ek than Ena?

Answer 11

the membrane is 50x more permeable to K+ than Na+

Question 12

What determines the driving force of an ion?

Answer 12

Vm-Eeq

Question 13

What determines permeability of a membrane to an ion?

Answer 13

number of open channels for that ion

Question 14

What is a problem with the Nernst equation, and how can this be overcome?

Answer 14

• doesn’t account for relative permeabilities of ions

- can use the Goldman Hodgkin Katz equation

Question 15

Why is a threshold required for an action potential?

Answer 15

as Pk is much greater than Pna at rest, so the flow of K+ can counteract the flow of Na+

Question 16

What is resistive current?

Answer 16

when current comes from ions moving through a channel

Question 17

What is capacitive current?

Answer 17

when current comes from ions approaching 1 side of the membrane and another being expelled from the other side

Question 18

What effect does thin axons have on speed of conduction?

Answer 18

decreases the speed

Question 19

How do action potentials spread in cardiac cells?

Answer 19

through intercalated discs

Question 20

What happens at neuromuscular junctions?

Answer 20

• VGCC in pre-synpatic cleft open when cell depolaries
• calcium causes vesicles to release neurotrasmitter into synapse
• Ach binds channels on skeletal muscle causing Na+ to enter and K+ to leave the cell

Question 21

What is the end plate potential?

Answer 21

The voltage which causes depolarisation of skeletal muscle fibres

Question 22

Name some drug agonists for neurotransmitter (NT) release?

Answer 22

L-DOPAa - acts as precursor
black widow venom - stimulates NT release
nicotine - stimulates post synaptic receptors
clondine - increases NT synthesis and release
cocaine - blocks Ach reuptake
physostigmine - inactivates acetylcholinesterase

Question 23

Name some drug antagonists for neurotransmitter (NT) release?

Answer 23

reserprine - prevents vesicles storing NT
botox - inhibits release from vesicles
curane/atropin - blocks postsynaptic receptors
PCPA - inhibits NT synthesis
apomorphine - inhibits synthesis and release of NT

Question 24

What are miniature end plate potentials (MEPP)?

Answer 24

small depolarisations at the neuromuscular junction which summate to form the end plate potential

Question 25

What is the excitatory neurotransmitter in the knee jerk reflex?

Answer 25

glutamate

Question 26

What is the inhibitory neurotransmitter in the knee jerk reflex?

Answer 26

glycine

Question 27

What is conductance (g)?

Answer 27

the ease with which ions flow

Question 28

What is capacitance measured in?

Answer 28

farads