NERVOUS SYSTEM: EXPERIMENTAL TECHNIQUES IN NEUROPHYSIOLOGY Flashcards
Define: electrophysiology
Electrophysiology: the branch of physiology that pertains to movement of ions in biological tissues and their flow across cellular membranes, as well as the electrical recording techniques that enable the measurement of these ionic movements
Define: in vitro
In vitro: in glass; studying cells in a petri dish
Define: in vivo
In vivo: tests, experiments, and procedures that researchers perform in or on a whole living organism
Describe what the voltage clamp technique is and when would it be useful
In voltage clamp, the experimenter specifies the voltage and measures the resulting current.
Useful if you want to:
- Study single channels or one specific type of channel
- Investigate which ions the channel is permeable to or the speed of opening and closing
- Test if a particular chemical or substance alters any of the biophysical properties of the channel
Describe the current clamp technique and when would it be useful
In current clamp, the set up is the same, but the experimenter injects current, and measures the resulting changes in membrane potential (usually action potentials).
Useful if you want to:
- Study excitable cells like neurons
- Find out which ions are important for action potentials
- Test if a particular drug blocks action potentials
Define: patch clamp electrophysiology
Patch clamp electrophysiology: Involves forming a tight (high resistance) seal between a glass micropipette containing an electrode and the plasma membrane of a cell.
What is patch clamp electrophysiology useful for
Useful for: Allows experimenters to record movement of ions or changes through single channels or a population of channels. Allows experimenter to control the extracellular and intracellular composition.
Who invented the patch clamp electrophysiology method? What are they also known for
Developed by Dr. Erwin Neher and Dr. Bert Sakmann in 1978.
They were the first to record currents from single channels and shared the 1991 Nobel Prize.
differentiate between
- cell-attached recording
- inside-out recording
- whole-cell recording
- outside-out recording
Cell-attached recording: using a glass pipette you make tight contact between pipette and membrane
Inside-out recording: using glass pipette create suction on cell membrane to remove a piece of the cell membrane
Whole-cell recording: remove a section of the cell membrane and with a glass pipette create strong suction so the glass pipette becomes joints the cell membrane. Now the cytoplasm is continuous with the interior of the pipette allowing for whole cell recording
Outside out recording: using a glass pipette take a piece of the cell membrane have the ends anneal and record this pice
What are the advantages and disadvantages of in vivo recordings
advantages:
- Real-time recordings in live animals
- High physiological relevance
Disadvantages:
- Technically difficult
- Little to no control of intracellular or extracellular fluids
What are the advantages and disadvantages of in vitro recordings
advantages:
- Isolated tissues or cells are easier to work with
- Control over solutions
Disadvantages:
- May be less physiologically relevant
- Molecular techniques required
Define: heterologous expression
Heterologous expression: Take a cell type (ex cancer cells), insert a gene into it (ex: gene for sodium expression), and study how the channel responds to being in that cell type
What are the advantages and disadvantages of heterologous expression
Advantages:
- Higher expression levels result in larger currents
- Control over solution composition
- Ability to modify channel structure using molecular biology techniques
Disadvantages:
- Endogenous channels may interfere with recordings
- Less physiological relevance
- Channel may require accessory component not expressed in system
- Cloning, subcloning, transfection, RNA purification, etc. often required
