Electrophysiology

Question 1

What is an ion’s equilibrium potential?

Answer 1

Gradient across the membrane to maintain a concentration gradient.

Question 2

If there is a higher concentration of Potassium ions inside the cell than outside what happens?

Answer 2

Potassium ions diffuse out the cell down the chemical gradient.

Question 3

What is Chemical Potential governored by?

Answer 3

1. Ion Concentration

2. Valency

Question 4

Chemical Gradient

Answer 4

Difference in SOLUTE concentration across the membrane.

Question 5

Electrical Gradient

Answer 5

Difference in charge across membrane.

Question 6

Ionic Gradients

Answer 6

Chemical Gradient & Electrical Gradient

Question 7

How influential the ionic gradients are on membrane potential depends on….

Answer 7

relative permeability of the membrane to each ion.

Question 8

Why will most cells at rest have a membrane potential closer to potassium?

Answer 8

As the cell is most permeable to Potassium ions at rest.

Question 9

Squid Axon- When lowering the external sodium in the solution what happens to the AP? Why?

Answer 9

Lowers to peak of the action potential because electrochemical driving force is lower.

Question 10

What does a voltage clamp measure?

Answer 10

Measures the current.

Question 11

Why are sodium/ potassium current active at different times?

Answer 11

Potassium/ Sodium channels are open at different times.

Question 12

Lowering the intercellular concentration of potassium ions what does this cause? How?

Answer 12

Decreases peak of potassium ions of K+ current by lowering the value of Nearst Equation.

Question 13

What is the magnitude of current dictated by?

Answer 13

1. Number of channels the current can pass through.

2. The electrochemical gradient (different between both membrane potentials).

Question 14

Absolute Refractory Period

Answer 14

Too few Sodium channels have recovered from inactivation so not possible to send another action potential.

Question 15

Relative Refractory Period

Answer 15

Proportion of Sodium channels have recovered possible to send an action potential with a greater stimulus.

Question 16

Why can cardiac action potentials not elect to summative contraction?

Answer 16

Refractive period too long.

Question 17

Compare the length of a normal AP and a Cardiac AP:

Answer 17

Normal: 7 m/s
Cardiac: 225 m/s

Question 18

What is the “ALL OR NOTHING PRINCIPAL”?

Answer 18

If an stimulus does not hit the threshold then the action potential will not fire. Action potentials are all the same size.

Question 19

A single skeletal muscle action potential leads to what?

Answer 19

Release of Calcium ions in the sarcoplasmic reticulum which leads to a contraction.

Question 20

How is a larger muscle contraction created?

Answer 20

Repeated stimulus at a neuromuscular junction.
Greater number of skeletal action potentials.
‘Summate’ larger contraction.

Question 21

Voltage Gated Ion Channels?

Answer 21

Channel conductance is determined by changes in membrane potential.

Question 22

Describe the structure of a potassium voltage gated ion channel.

Answer 22

6 Transmembrane Domains (S1-S6) = 1 Subunit.
4 Alpha Subunits= Channel
Channel is a TETRAMER of x4 alpha subunits

Question 23

In a potassium voltage gated ion channel where is the pore region?

Answer 23

Between S5+S6.

Question 24

Describe the structure of a sodium/ calcium voltage gated ion channel.

Answer 24

Similar to Potassium except 4 homologous domains form 1 protein.

Question 25

Why is the S4 Helices in Voltage gated ion channels special? Why is it special?

Answer 25

Voltage Sensor.

Activation/ Deactivation of ion channel.

Question 26

What type of current does positive ions entering the cell/ negative ions leaving the cell give?

Answer 26

Negative Current

Question 27

Describe how the neuromuscular junction works?

Answer 27

1. AP arrives at axon terminal of motor neurone.
2. Voltage gated Calcium channels open so influx of Calcium ions down electrochemical gradient.
3. Ca 2+ entry- Release of ACh by exocytosis.
4. Ach diffuses across synaptic cleft and binds to receptors on sarcolemma.
5. ACh binds to channels - Open Na+ channels- Influx of Na + into muscle fibre and K+ exit. More Na+ enters than K+ leaves.
6. Local change in membrane potential called END PLATE POTENTIAL.
   Acetylcholine broken down by Acetylcholinerases in synaptic Cleft.

Question 28

Ligand- Gated ion channels.

Answer 28

Channels open (or close) in response to certain ligand.

Question 29

What are Ligand- Gated ion channels also known as?

Answer 29

Ionic tropic Receptors.

Question 30

What are Ligand- Gated ion channels also known as?

Answer 30

Ionic tropic Receptors.

Question 31

What type of ion channels are Cys Loop Receptors? Why are they named Cys Loop Receptors?

Answer 31

Ligand- Gated ion channels.

Named after loop made by a disulphide bond between Cysteine residues in the N terminal of extracellular domain.

Question 32

Examples of Cys Loop Receptors:

Answer 32

Cationic Channels:
Serotine (5- HT) Receptors
Nicotinic AcetylCholine Receptor
Zinc Activated Receptor

Anionic Channels:
GABA Receptor
Glycine Receptor.

Question 33

Describe the structure in the Cys Loop Receptors receptor?

Answer 33

5 Protein Subunits.

Question 34

What type of ion channels are Ionotrophic Glutamate Receptors? What neurotransmitter binds to them?

Answer 34

Ligand- Gated ion channels.

Glutamate.

Question 35

Name examples of Ionotrophic Glutamate Receptors Cation Channel classifications:

Answer 35

GluA (AMPA)
GluK (Kainate)
GluN (NMDA)
GluD (‘Orphans’)

Question 36

Describe the structure of Ionotrophic Glutamate Receptors.

Answer 36

4 subunits each have 4 domains:

1. Amino- terminal domain.
2. Extracellular ligand binding domain.
3. Transmembrane domain.
4. Intra- cellular carboxyl terminal domain.

Question 37

What are P2X receptors activated by?

Answer 37

3x ATP molecules.

Question 38

How many subtypes of P2X receptors are there?

Answer 38

7 (P2X1-7)

Question 39

What type of ions do P2X receptors carry?

Answer 39

Cations- Mainly 1+ ions but sometimes carry Ca 2+ ions.

Question 40

Where are P2X receptors expressed in?

Answer 40

1. Vas Deferens
2. Platelets
3. Neurones
4. Smooth Muscle
5. Leukocyte.