Electrophysiology Flashcards
What is an ion’s equilibrium potential?
Gradient across the membrane to maintain a concentration gradient.
If there is a higher concentration of Potassium ions inside the cell than outside what happens?
Potassium ions diffuse out the cell down the chemical gradient.
What is Chemical Potential governored by?
- Ion Concentration
2. Valency
Chemical Gradient
Difference in SOLUTE concentration across the membrane.
Electrical Gradient
Difference in charge across membrane.
Ionic Gradients
Chemical Gradient & Electrical Gradient
How influential the ionic gradients are on membrane potential depends on….
relative permeability of the membrane to each ion.
Why will most cells at rest have a membrane potential closer to potassium?
As the cell is most permeable to Potassium ions at rest.
Squid Axon- When lowering the external sodium in the solution what happens to the AP? Why?
Lowers to peak of the action potential because electrochemical driving force is lower.
What does a voltage clamp measure?
Measures the current.
Why are sodium/ potassium current active at different times?
Potassium/ Sodium channels are open at different times.
Lowering the intercellular concentration of potassium ions what does this cause? How?
Decreases peak of potassium ions of K+ current by lowering the value of Nearst Equation.
What is the magnitude of current dictated by?
- Number of channels the current can pass through.
2. The electrochemical gradient (different between both membrane potentials).
Absolute Refractory Period
Too few Sodium channels have recovered from inactivation so not possible to send another action potential.
Relative Refractory Period
Proportion of Sodium channels have recovered possible to send an action potential with a greater stimulus.
Why can cardiac action potentials not elect to summative contraction?
Refractive period too long.
Compare the length of a normal AP and a Cardiac AP:
Normal: 7 m/s
Cardiac: 225 m/s
What is the “ALL OR NOTHING PRINCIPAL”?
If an stimulus does not hit the threshold then the action potential will not fire. Action potentials are all the same size.
A single skeletal muscle action potential leads to what?
Release of Calcium ions in the sarcoplasmic reticulum which leads to a contraction.
How is a larger muscle contraction created?
Repeated stimulus at a neuromuscular junction.
Greater number of skeletal action potentials.
‘Summate’ larger contraction.
Voltage Gated Ion Channels?
Channel conductance is determined by changes in membrane potential.
Describe the structure of a potassium voltage gated ion channel.
6 Transmembrane Domains (S1-S6) = 1 Subunit.
4 Alpha Subunits= Channel
Channel is a TETRAMER of x4 alpha subunits
In a potassium voltage gated ion channel where is the pore region?
Between S5+S6.
Describe the structure of a sodium/ calcium voltage gated ion channel.
Similar to Potassium except 4 homologous domains form 1 protein.
Why is the S4 Helices in Voltage gated ion channels special? Why is it special?
Voltage Sensor.
Activation/ Deactivation of ion channel.
What type of current does positive ions entering the cell/ negative ions leaving the cell give?
Negative Current
Describe how the neuromuscular junction works?
- AP arrives at axon terminal of motor neurone.
- Voltage gated Calcium channels open so influx of Calcium ions down electrochemical gradient.
- Ca 2+ entry- Release of ACh by exocytosis.
- Ach diffuses across synaptic cleft and binds to receptors on sarcolemma.
- ACh binds to channels - Open Na+ channels- Influx of Na + into muscle fibre and K+ exit. More Na+ enters than K+ leaves.
- Local change in membrane potential called END PLATE POTENTIAL.
Acetylcholine broken down by Acetylcholinerases in synaptic Cleft.
Ligand- Gated ion channels.
Channels open (or close) in response to certain ligand.
What are Ligand- Gated ion channels also known as?
Ionic tropic Receptors.
What are Ligand- Gated ion channels also known as?
Ionic tropic Receptors.
What type of ion channels are Cys Loop Receptors? Why are they named Cys Loop Receptors?
Ligand- Gated ion channels.
Named after loop made by a disulphide bond between Cysteine residues in the N terminal of extracellular domain.
Examples of Cys Loop Receptors:
Cationic Channels:
Serotine (5- HT) Receptors
Nicotinic AcetylCholine Receptor
Zinc Activated Receptor
Anionic Channels:
GABA Receptor
Glycine Receptor.
Describe the structure in the Cys Loop Receptors receptor?
5 Protein Subunits.
What type of ion channels are Ionotrophic Glutamate Receptors? What neurotransmitter binds to them?
Ligand- Gated ion channels.
Glutamate.
Name examples of Ionotrophic Glutamate Receptors Cation Channel classifications:
GluA (AMPA)
GluK (Kainate)
GluN (NMDA)
GluD (‘Orphans’)
Describe the structure of Ionotrophic Glutamate Receptors.
4 subunits each have 4 domains:
- Amino- terminal domain.
- Extracellular ligand binding domain.
- Transmembrane domain.
- Intra- cellular carboxyl terminal domain.
What are P2X receptors activated by?
3x ATP molecules.
How many subtypes of P2X receptors are there?
7 (P2X1-7)
What type of ions do P2X receptors carry?
Cations- Mainly 1+ ions but sometimes carry Ca 2+ ions.
Where are P2X receptors expressed in?
- Vas Deferens
- Platelets
- Neurones
- Smooth Muscle
- Leukocyte.
