Open Neuroscience Initiative: Chapter 4, Electrical Properties of Neurons

electroactive

sensitive to electrical charge; characteristic of neuronal cell membranes (2)

selectively permeable

some molecules are able to travel across the membrane easily, other molecules have an intermediate ability to cross, and other molecules are completely incapable of passing (2)

pore

the tunnel of a transmembrane protein that allows molecules and ions to pass across the cell membrane (2)

transmembrane protein

huge protein complexes that span the entirety of the membrane and allow certain molecules (ex: ions, glucose) to pass (2)

ion channel

A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient (2)

hydration shell

the sphere of water molecules around each dissolved ion, which vary in size; provides one way for ion channels to be selective (4)

leak channels

ion channels that are always open (ex: K+ and Cl- channels) (4)

voltage-gated ion channels

ion channels that's ability to open and close depends on the electrical charge of the membrane (ex: Na+ channel) (4)

ligand-gated ion channels

ion channels that open in response to binding certain molecules, such as neurotransmitters; aka ionotropic receptors (4)

ligands

A molecule that binds specifically to a receptor site of another molecule

electrical gradient

the electrical forces acting on charged molecules, "pulling" opposite charges together while also "pushing" like charges away from one another (5)

~70 mV

What is the interior of the cell at rest? (5)

Vm

What is the symbol for the voltage of a neuron? (5)

chemical gradient

the natural process by which a high concentration of a substance, given enough time, will eventually diffuse to a lower concentration and settle evenly over the space (5)

electrochemical gradient

the electrical and chemical gradient (6)

dynamic equilibrium

Result of net 0 electrochemical gradient where there is continuous movement of particles but no overall change in concentration (7)

equilibrium potential Ex

the value of Vm, determined by the electrochemical gradient; aka reversal potential (7)

Nernst equation

mathematical equation that calculates the equilibrium potential of a neuron (8)

RT/(zF)ln([x]0/[x]1)

The Nernst equation, where [x]0 is outside the cell and [x]+ is inside the cell, Ex = (8)

electrical charge of the ion

What does z stand for in the Nernst equation? (8)

Goldman-Hodgkin-Katz equation (GHK equation)

formula that combines the Nernst potentials of three relevant ions (Na+, K+, and Cl-) into a single equation that, when evaluated, gives us the value of the membrane potential Vm (10)

permeability

the ability for an ion to cross the membrane through ion channels (10)

action potential

a short-lasting (1 or 2 milliseconds), temporary change in membrane potential that can travel down the length of the axon (11)

graded potentials

Sub-threshold changes in Vm (11)

depolarization

When Vm goes from negative to a more positive potential (11)

hyperpolarization

when Vm changes to a value that is more negative (11)

action potential threshold

To trigger an action potential, the sum of the inputs must be sufficiently depolarizing to bring the Vm to a value that is more positive than the ___________________ (11)

postsynaptic potentials PSPs

small deviations in membrane voltage (12)

spatial summation

happens when two small EPSPs from two adjacent inputs are triggered (12)

temporal summation

occurs when multiple EPSPs from the same input occur close together in time (12)

allodynia

dysregulation in an individual's somatosensory systems that cause them to experience pain even in the absence of injurious stimuli (14)

nociception

a complex sensation from a noxious stimulus that the nervous system detects rapidly (14)

noxious stimulus

A stimulus that is damaging or threatens damage to normal tissues

repolarization

The rapid downwards deflection (+40 mV to -70 mV), lasting for about half a millisecond (15)

Afterhyperpolarization

The slow return back to the resting membrane potential (-70 mV to -80 mV and back to -70 mV) that can last for a few milliseconds, due to the gradual deactivation of voltage-gated potassium channels (15)

absolute refractory period

In the moments following the beginning of an action potential, there is a time window where a second action potential cannot be fired (16)

relative refractory period

During this phase, it is more difficult to fire an action potential compared to the resting condition, due to receptors state (Na+ channels haven't reset and K+ channels are still open); lasts as long as afterhyperpolarization (17)

tetrodotoxin TTX

toxin that is produced by a bacterium that live symbiotically in pufferfish organs; when ingested, prevents efferent signaling, possibly leading to death (19)

phrenic nerve

innervates the diaphragm

conduction velocity

the speed at which an action potential travels down the length of the axon; increased by myelin (19)

saltatory conduction

the changes in electrical charge are detected at intervals down actions (intervals defined by nodes of Ranvier) (20)

Na+

main chemical responsible for depolarization

nodes of Ranvier

some sodium ion influx occurs at these location along myelinated axons; unmyelinated sections (20)