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RESEARCH TECHNIQUES IN NEUROBIOLOGY Introduction Electric charge • Electrically charged objects experience mutual force when “close” to each other • Repulsive forces exist between objects with the same sign of charge • Attractive forces exist between opposite charged objects Electric potential • The electrical potential of a location is the energy that a “basic” charge has there • The potential difference between two points is called Voltage • Voltage has influence on charged objects 5V 5V 10V • We consider the voltage to be between two points Movement of objects • A charged object pushes or pulls nearby charged objects • A pushed object might push the next object and a chain movement will occur • A conductor (mediator) is a matter containing movable charged objects Electric Conductor • The potential in a group of (perfect) attached conductors is one • Therefore, a (perfect) conductor is an extension to a point with potential • This way, the potential can be felt from far 10V 10V Electric current • A chain movement of charges is called Current • The current moves faster than the objects • Current can exist only in conductors • Current can influence Electric circuit • An electric circuit is a “continues” chain of conductors where one end of the chain is connected to the other • Circuit + voltage will generate current • Non perfect conductors resist the current and slow it – those are resistors Driving force • Voltage can be a driving force for current • Other things can generate current Electrons current • The current in artificial systems depends on electrons – basic negative particles of atoms • The conductor is metal in which electrons can move from one atom to another Ionic current • The current in neural systems depends on ions – electrically charged molecules • The conductor is a solution with ions • Voltage is created due to differences of ionic concentrations What is the voltage between the inside and outside of the cell? Use the electrons or ions? • The voltage in the preparation is the potential to move ions • The computer measures potential to move electrons • The medium is different A combined circuit • An electric circuit can be combined • The intersection should be suitable • A chemical reaction is needed to convert A solution with ions • In our case (negative) Chloride ions Voltage in the solution • What happens when inserting two metal wires connected to a battery? The negatively charged Chloride ions will be drawn to the positive pole and a chemical compound might be created Closing the circuit • Switching between the poles and adding an electronic device • Ions are released from the negative pole and push towards the positive pole • A chemical reaction enables current to continue in the metal Out of ions • When the negative pole is out of ions the current stops Switching the poles again • Switching between the poles again reactivates the current The voltage is very small and can be affected by the measurement itself or changed on the way to the computer The Voltage Follower is close to the preparation and can measure accurately without affecting the voltage The amplifier can also inject current to stimulate The computer begins to record a bit before there is stimulation Noise • The voltages and currents are tiny • Parts of the set might become antennas and insert “noise” to our recording • To overcome this problem – Voltage follower close to the preparation – Isolation of the system – Connecting everything to the “ground” and thus direct noise to there instead into our measuring devices