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Electrical potential
Uni of Notts, fundamentals of neuroscience, first year
| Term | Definition |
|---|---|
| Membrane potential | Difference in voltage between the inside of a neurone and the outside, typically using an electrode inside & outside the cell |
| Reasons why membrane potential is controlled (5) | Maintains osmolarity Action, receptor, & post-synaptic potentials Energy source for transmembrane transports Affects proliferation & migration Changes associated with disease (e.g., migraine & epilepsy) |
| Reversal potential | Electrochemical point at which the cell voltage directly opposes the concentration of ions flowing across the membrane causing equilibrium. Represented as x in the Nernst equation |
| Nernst equation | Ex = RT/ZF.log10([x]o/[x]i) Ex = reversal potential of ion R = gas constant T = temperature Z = valence state of ion F = Faraday's constant [x]o = extracellular ion concentration [x]i = intracellular ion concentration |
| Faraday's constant | Electrical charge per mole of electrons, this is approximately 96,500 coulombs per mole (Cmol^-1) or just 96,500C |
| Non-Nernstian cells | Cells whose electrode potentials differ from what was predicted by the Nernst equation due to factors such as only being permeable to one type of ion. In this case the membrane potential (Em) would equal the reversal potential of that ion (Ex) |
| Goldman-Hodgkin-Katz (GHK) equation | Vm = RT/F.ln((Px[x+]o + Py[y+]o + Pz[z-]i)/(Px[x+]i + Py[y+]i + Pz[z-]o)) Vm = resting membrane potential P = membrane permeability of each ion |
| Orthodromic | Under physiological conditions, an action potential will only travel one way from axon hillock to terminal |
| Compound Action Potential (CAP) | Sum of action potentials from all temporally linked axons simultaneously contributing to a signal: population response |
| Extracellular electrophysiology | Measuring CAP of a nerve by stimulating & recording outside the cell membrane using electrodes. Voltage can be maintained at a specific level using a voltage clamp |
| Post-synaptic potentials (PSPs) | Graded potentials caused by binding of neurotransmitters which are decremental & aren't self-propagating making them weaker as they travel along the axon. Can be excitatory (EPSP) or inhibitory (IPSP) |
| Ionic basis for action potentials | When threshold is reached, membrane potential moves more towards the reversal potential of sodium & away from potassium due to changes in permeability of sodium ions in the membrane. Vice versa for repolarisation |
| Structure of voltage gated sodium ion channels at resting potential | 2 parts: activation gate & inactivation gate, activation is shut & inactivation is open at resting potential but sodium ions cause a conformational shape change to open it |
| Structure of voltage gated sodium ion channels at depolarisation & refractory period | Once +30mV is reached the inactivation gate slowly closes, decreasing membrane permeability to sodium despite depolarisation. The time taken for inactivation to close is the refractory period |
| Encoding potentials | The stronger a stimulus the higher frequency of action potentials is given while the refractory period maintains precise encoding. Different firing patterns depend of different neurones & cause an appropriate response |
| Voltage clamp | A 'command' voltage is set but if electrodes detect a potential difference between the reference & monitoring electrodes the clamp will administer a voltage to keep the cell at the desired voltage |
| Patch clamp: Neher & Sakman (1970) | Measuring flow of ions through a particular membrane channel by suctioning it with a small pipette to record whether the channel is open or closed & its responses to ligands or drugs |
| How brain polarisation is measured | Voltage sensitive fluorescent dyes are incubated in brain tissue to visualise polarisation, calcium sensitive dyes detect calcium influx from an action potential as well calcium waves in glial syncitium |
| Optogenetics | Neuromodulation method which modifies neural cells to contain opsin channels that can excite or inhibit cells when exposed to light. This comes from infecting tissue with modified viruses |
Created by:
Beech47
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