Electrophysiology

Question 1

Describe equilibrium potentials

Answer 1

Only K+ can leave the cell and diffuse out down the chemical gradient as the inside of the cell becomes more negative [K+] = 150mM

Question 2

What is the chemical potential governed by?

Answer 2

ion concentration and valency

Question 3

Describe the Nernst equation

Answer 3

If a cell is only permeable to one ion and you know the temperature you can work out the equilibrium potential

Question 4

What is the equilibrium potential?

Answer 4

potential gradient across the membrane to maintain concentrations gradient

Question 5

What does the influence of ionic gradients depend on membrane potentials?

Answer 5

The relative permeability of the membrane

Question 6

What is the membrane potential of cells at rest closer too?

Answer 6

Closer to the potential of potassium because its permeable to potassium and impermeable to sodium and calcium

Question 7

What does a current clamp record?

Answer 7

Records action potentials

Question 8

What is the magnitude of a current determined by?

Answer 8

• the number of channels that will pass current

- the electrochemical gradient

Question 9

Describe potassium voltage gated ion channels

Answer 9

• 4 alpha subunits to form channel, each unit with 6 transmembrane domains
• Pore forming region between s5-s6
• Tetramer

Question 10

Describe the pore opening mechanism

Answer 10

Charged amino acids change in voltage causes a change in protein structure which opens pores - activation

Question 11

Describe cys loop receptors

Answer 11

Disulfide bond between two cysteine residues in the N terminal extracellular domain 
Cationic
-serotonin receptors 
-nicotinic 
zinc activated 

Anionic

• GABAa Receptors
• Glycine Receptors

Question 12

Describe ionotropic Glutamate receptors

Answer 12

Glutamate receptors bind to the neurotransmitters
Composed of 4 subunits each with 4 discrete domains
Cation channels classified as:
-AMPA
-kainite
-NMDA
-Orphan

Question 13

What are the domains of the 4 ionotropic Glutamate receptors?

Answer 13

• and amino terminal domain
• an extracellular ligand binding domain
• the transmembrane domain
• an intracellular carboxyl-terminal domain

Question 14

Describe ATP gated channels (P2X)

Answer 14

Activated by 3x ATP molecules 
7 different subtypes 
cation channels expressed in a variety of tissues including:
vas deferens 
platelets 
neutrons
leukocytes 
smooth muscle

Question 15

Describe the relative refractory period

Answer 15

• a proportion of Na+ channels have recovered

- possible to elect an action potential with increased stimulus

Question 16

Describe the absolute refractory period

Answer 16

• too few Na+ channels have recovered from inactivation

- not possible to elect an action potential

Question 17

Describe myasthenia gravis

Answer 17

immune system makes antibodies that attack the ACh receptor cites at the neuromuscular junction

Question 18

What is the duration of cardiac action potentials?

Answer 18

300ms